Interventions/Procedures Flashcards
AAA (EVAR)
Pre-operative
* careful pre-operative assessment for elective repair - multiple co-morbidities
* ?refused for open repair due to increased risk
* ECG, U+Es, dynamic assessment of heart
Intra-operative
* in radiology/angio suite
* GA/RA/LA
* invasive monitoring
* simple analgesia + local infiltration to insertion site
Post-operative
* ICU not usually needed
* ?HDU or vascular ward
* long term monitoring needed for Endoleak
AAA (Open Repair)
Pre-operative
* careful pre-operative assessment for elective repair - often multiple co-morbidities
* ECG, U+Es, dynamic cardiac assessment
* continue cardiac medications (MI risk)
Intra-operative
* thoracic epidural
* art line (awake) + 2x big drips + CVC +/- vascath +/- CO monitor
* full invasive monitoring +/- CO monitor
* warm upper body only
* opiate heavy induction
* may need vasoconstrictors pre-clamp/post unclamp
* may need vasodilatation post-clamp - wean prior to release (aim BP >110)
* aim for warm, pain free, non acidotic, non coagulopathic, well oxygenated + well filled patient
* cell salvage, TXA, calcium etc
Post-operative
* early extubation
* ICU/HDU
* continue epidural + multimodal analgesia
* monitor fluid balance, U+Es, may need RRT
Anaesthesia after Chemotherapy
Pre-operative assessment
* focused history of cancer management - detailed drug history including precise chemo regimen, and toxic effects suffered by the patient
* systems review
– respiratory - infection, metastatic disease, PE, drug induced pulmonary toxicity (e.g. pneumonitis, progressive pulmonary fibrosis)
– cardiovascular - hypotension, hypertension, arrhythmias (Torsades), MI, CCF, cardiomyopathy, myocarditis, pericarditis, pericardial effusion, tamponade, radiotherapy may cause damage to cardiac valves, vessels and pericardium
– renal - acute or chronic renal failure
– nervous system - peripheral neuropathy, muscle pain, cranial neuropathy, orthostatic hypotension (ANS), vocal cord palsy, seizures
– GI - common after most chemotherapy drugs - nausea, vomiting, mucositis, diarrhoea +/- dehydration
– hepatic - abnormal LFTs (metastases, infections, liver disease, hepatotoxic medications), chemotherapy related liver damage (parenchymal damage with fatty change, cholestasis, hepatocellular necrosis), many chemotherapy drugs are metabolised by the liver
– haematopoietic - myelosuppression with risk for lifethreatening sepsis in absence of typical signs/symptoms
* thorough examination including full neurological examination
* routine investigations - FBC, U+Es, coagulation, ECG
* additional investigations e.g. CXR, ABG, PFTs, echo may be required depending on the treatment regimen used
* minimise fasting/dehydration time
* fluid resuscitate + corrent U+Es prior to surgery if possible
* consider RSI if N+V
Pulmonary toxicity - cytotoxic antibiotics, nitrosureas, alkylating agents, anti-metabolites, plant alkaloids, biological response modifiers, taxol
Cardiotoxicity - cytotoxic antibiotics, plant alkaloids, alkylating agents, 5FU, cisplatin, interferon, IL2, taxol
Hepatotoxicity - nitrosureas, anti-metabolites, cytotoxic antibiotics, 5FU, vincristine, cisplatin
Nephrotoxicity - nitrosureas, bleomycin, cisplatin, cyclophosphamide, MTX, mitomycin C, vincristine
Neurotoxicity - vincristine, high dose MTX, cisplatin, paclitaxel, osaliplatin, ifosfamie
Intra-operative
* caution with laryngoscopy causing severe bleeding in presence of mucositis
* aim for SpO2 of 88-92% for bleomycin due to lifelong risk of lung injury, high O2 only with extreme caution for immediate life-saving indications
* caution with myocardial depressants - consider invasive arterial pressure and CO monitoring
* careful fluid optimisation
* multimodal analgesia (avoid NSAIDs if renal issues)
* maintain normothermia
* regional relatively contraindicated if patients has neurological side effects after chemotherapy - careful documentation of deficit if it is to be used
* drug dosing in renal/hepatic impairment
Post-operative
* respiratory - chest physio, good analgesic regimes, early mobilisation
* consider HDU
Emergency Ocular Surgery
Goals
* Provide a stationary globe
* Provide profound analgesia
* Monitoring and attenuation of the oculocardiac reflex
* Prevent harmful increases in IOP - limit coughing, retching, vomiting, forceful blinking, crying etc during emergence (risk of extrusion of globe contents with elevated IOP
Pre-operative
* may have full stomach even hours post injury
* common injury in paeds - need to avoid eye rubbing, crying, breath holding, screaming due to raised IOP
* analgesia pre-op (antiemetics if opioids)
Intra-operative
* LA technique can be used in some cases
* GA with armoured LMA/ETT (may need RSI)
* can use sux (raised IOP balanced by decreased with induction agent) or use roc + sugammadex
* avoid hypertensive response to laryngoscopy
* avoid coughing on emergence
Post-operative
* simple analgesics usually adequate + codeine/diclofenac
* consider regular anti-emetic
Anaesthetic Gas Monitoring
- IR absorption spectrophotometry
– light source passed through filter (of specific wavelength e.g. Co2 4.28micrometers) and then sample of gas, amount of light measured using a photo detector and converted to voltage and then to a visual display
– change wavelength of filter to detect different agents - separate filters/detectors or rotating
– sample analyser lined in sapphire, as this does not absorb IR
– absorption of light is proportional to the amount of molecules present in the sample
– blockage of sample lines, water vapour absorbs infrared across a wide spectrum, N2O cdan cause problems with CO2 measurement (collision broadening effect) - Photoacoustic spectrophotometry
– sample gas irradiated with pulsatile IR, of a suitable wavelength
– periodic expansion and contraction of the gas produces a pressure fluctuation of audible frequency that can be detected by a microphone
– extremely stable
– fast rise and fall times give a much truer representation of any change in CO2 - Raman scattering
– light passed through a gas sample causing reflective process
– incident light loses energy to the molecules of gas and is reflected at lower frequency
– magnitude of light frequency shift is specific to the gas and analysis of the reflected light allows identification of the gas
– rapid, with breath to breath analysis but bulky and heavy - Refractometry
– shining monochromatic light source through gaseous medium and focussing them on a screen
– pattern of light and dark bands appear, dependent on the medium’s refractive index and concentration
– difficult to use for breath-by-breath analysis
– used to calibrate vaporizer output and theatre and environmental exposure - Mass spectrometry
– sample gas drawn or injected into a low-pressure sample chamber that is attached to another chamber, at a pressure nearing that of a vacuum
– molecular leak pathway constructed between the chambers
– molecules ionised in second chamber and accelerated by a cathode plate
– fixed magnets or electro,agnets influence the ions and allow separation by the ion’s mass and charge
– ions are narrow-band filtered and detected by photo-voltatic receptors
– signal amplified and processes
– require powerful vacuum pumps and cannot return sample to patient
– response and delay times
– very accurate
Awake Craniotomy
Pre-operative
* appropriate patient selection
* anticonvulsant prophylaxis +/- dex (tumour surgery)
* well prepared patient + experienced staff
* as far craniotomy
Intra-operative
* LA + sedation or asleep-awake-asleep (LMA)
* routine monitoring as for craniotomy (BIS)
* ensure adequate sedation, analgesia, cardio-respiratory stability
* avoid hypercarbia, nausea and vomiting
* ensure awake, co-operative patient when required (TCI)
Post-operative
* as for craniotomy
* morphine at the end
Awake Tracheal Intubation
Indications
* suspected or known difficulty airway - reduced mouth opening, limited neck extension, OSA, morbid obesity, progressive airway compromise
* aspiration risk
* C-spine instability
Options
* FOI
* VL
* DL
* Blind nasal
Contraindications
* absolute - refusal despite careful discussion, lack of compliance
* relative - airway bleeding (+/- severe coagulopathy for nasal), operator inexperience, true LA intolerance, high risk for aspiration
Procedure
* Consent
* Preparation
– consider antisialogogue
– monitoring
– checklist
– ideally second anaesthetist for sedation
* Oxygenation
– apply HFNO early
– titrate HFNO from 30-70l/min
– continue HFNO throughout the procedure
* Topicalisation
– lidocaine 10% spray to oropharynx, tonsillar pillars, base of tongue (20-30 sprays during inspiration, over 5 minutes)
– co-phenelcaine to nose if nasal route
– test topicalisation atraumatically
– 2% lidocaine 2ml above, at and below vocal cords via MAD or epidural catheter
– max 9mg/kg lidocaine (lean body weight) for topicalisation
* Sedation
– remifentanil TCI Ce 1-3ng/ml
– midazolam 0.5-1mg
* Performance
– appropriate tracheal tube
– patient sitting up
– ensure operator can readily see patient monitor, infusion pumps and video screen
– clear secretions
– face patient for fibreoptic, behind patient for VL
– maximum 3+1 attempts
– two point check to confirm position of tracheal tube - visualisation of the tracheal lumen or tube through vocal cords + capnography
– timing of cuff inflation guided by relative risks of aspiration, patient movement, coughing and tracheal tube displacement
– induce anaesthesia
* Post intubation plan
– DAS guidelines for extubation
– NBM for at least 2hrs following airway topicalisation
– documentation
Blood Gas Analysis
- pH - pH electrode
– Ag/AgCl measuring electrode in KCl with H+ sensitive glass
– Ag/AgCl reference electrode
– blood sample passed by both electrodes
– difference in H+ concentration between blood sample and buffer solution generates an electromotive potential across the glass which is amplified and displayed - pCO2 - Severinghaus electrode
– CO2 diffuses across a CO2 permeable membrane in a bicarbonate solution
– dissociates to form H+ ions
– Ag/AgCl measuring electrode in buffer solution with H+ sensitive glass
– Ag/AgCl reference electrode in KCl
– difference in H+ concentration between the samples generates an electromotive potential across the glass which is amplified and displayed - pO2 - Clarke polarographic electrode
– Ag/AgCl anode
– platinum cathode
– KCl electrolyte solution
– oxygen diffuses into KCl through a semi-permeable membrane
– oxygen reacts with electrons in solution, generating voltage bewteen anode and cathode - HCO3 is calculated from the Henderson-Hasselbalch equation
- BE and O2 saturation derived
- Hb - absorption spectroscopy
Blood Pressure Measurement
Non Invasive + Intermittent
* Palpation
* Auscultation
* Oscillotonometric - von Recklinghausen
* Oscillometric - DINAMAP
– computer controlled inflation and deflation of cuff, looking for pulsations from the artery
– first oscillations = systolic BP
– cessation of oscillations = diastolic BP
– maximum oscillation amplitude = MAP
* Manual sphygmomanometer
– cuff (bladder ~80% of the circumference of the arm)
– compression of bronchial artery
– auscultation over brachial artery - Korotkoff sounds caused by turbulent flow
– sharp tapping (phase 1) = systolic pressure
– change from softer thump to softer, blowing, muffled sound (phase 3–>4) = diastolic pressure
Non Invasive + Continuous
* Finapres - Penaz technique
– small cuff partially occluding arterial supply to a finger with a LED and photodiode
– cuff changes in pressure to the keep the volume in the artery the same - this pressure change is proportional to the blood pressure
* Radial accelerometry
* Doppler USS
Invasive
* Arterial line
– cannula (short, wide) in artery connected to a transducer with a tube of fluid between them (short, wide, stiff tubing)
– saline keeps the cannula patent and flushes the line at ~3ml/hr
– transducer at the level of the patients heart creates an electrical signal from arterial pulsations
– monitor displays arterial trace
Overdamped signal - take a long time to respond to a step change –> squashed arterial trace
Underdamped signal - hyper resonant and overreads any changes in pressure
Optimal damping - rapid return to zero with a minimal (but present) overshoot
Brainstem Dead Organ Donor
- I+V, critical care area, confirmed dead by neurological criteria
Process
* Early recognition and referral
* Assessment of suitability
* Collaborative approach to family (explain 24-48hrs likely minimum time frame)
* Formal consent process + medical, social, travel history, discuss special requests
* Further patient assessment
* Blood testing - blood group, HLA typing, birology
* Liaise with coroner/ME if needed
* Register donor with ODT hub - matching process (ABO compatibility, HLA compatibility, waiting time, locations, matchability)
* Activate NORS team
* Organ retrieval and thorough documentation
* Post donation family support
Physiological Optimisation
* Assess fluid status and correct hypovolaemia with fluid boluses
* Introduce vasopressin infusion where required, wean noradrenaline/adrenaline
* Perform lung recruitment maneouvres to correct atelectasis
* Identify, arrest and reverse effects of DI
* Administer methylprednisolone
Use donor optimisation care bundle
* Airway - ensure cuff of ETT is appropriately inflated
* Breathing - lung protective ventilatory strategy, chest physio + suctioning, 30-45 degrees elevation, patient positioning, bronch +/- BAL?
* Circulation - monitor CO, vasopressin +/- dopamine rather than noradrenaline/adrenaline, correct hypovolaemia
* Fluids and metabolic - methylpred 15mg/kg, maintain Na <150mmol/L (IV crystalloid/NG water)
* Maintain UO 0.2-5ml/kg/hr (may need DDAVP)
* Insulin to maintain BM 4-10
* Continue NG feeding
* VTE prophylaxis - TEDS/Flowtrons/LMWH
* Lines and monitoring - left arterial, RIJ CVC, hrly obs, normothermia, 12-lead ECG, CVR +/- echo
* Review and stop all unnecessary meds
Capnography
IR absorption spectrophotometry
– light source passed through filter (of specific wavelength e.g. Co2 4.28micrometers) and then sample of gas, amount of light measured using a photo detector and converted to voltage and then to a visual display
– sample analyser lined in sapphire, as this does not absorb IR
– absorption of light is proportional to the amount of molecules present in the sample
– blockage of sample lines, water vapour absorbs infrared across a wide spectrum, N2O cdan cause problems with CO2 measurement (collision broadening effect)
Sidestream vs Mainstream
* Sidestream - 150-250ml/min of gas from patient end of circuit, added back in after analysis
– monitoring equipemnt on machine rather than patient
– larger analysers, able to measure more agents
– length of tube proportional to the delay between breath and capnograph response
* Mainstream - attached directly to the breathing circuit
– clips around a clear plastic window in the breathing circuit
– minimal delay in response
– typically only measure CO2 due to size and battery dependence
– usually small and portable
– can get hot
– can be unreliable due to water vapour problems
What can capnography tell us?
* presence of venous return (CO2 from tissues to heart)
* presence of pulmonary blood flow (CO2 from heart to lungs)
* presence of ventilation (effective movement of gas in and out of the lungs)
* confirmation of tracheal tube placement
* rate of ventilation
* quality of chest compressions (ETCO2 >2kPa with consistent waveform)
* ROSC during CPR
* guide to prognostication
* shape of trace
Normal Capnogram
* Phase 1 (inspiratory baseline) - inspired gas, normally devoid of CO2
* Phase 2 (expiratory upstroke) - transition between dead space and alveolar gas from respiratory bronchioles and alveoli
* Phase III (alveolar plateau) - end tidal at point just prior to inspiration
* Phase O (inspiratory downstroke) - the beginning of the next inspiration
* ETCO2 only represents alveolar CO2 when a relatively horizontal plateau phase is seen
CO2 Traces
* Low ETCO2
– decreased CO2 production - hypothermia
– pulmonary perfusion - reduced CO, hypotension, hypovolaemia, cardiac arrest, PE
– alveolar ventilation - hyperventilation, apnoea, total airway obstruction, extubation
– apparatus malfunctioning - circuit disconnection, leak sampling tube, ventilator malfunction, gas monitor zero
* High ETCO2
– increased CO2 production - sepsis, MH, endocrine causes, exogenous CO2, tourniquet release, sodium bicarbonate
– pulmonary perfusion - increased CO, increased BP
– alveolar ventilation - hypoventilation, bronchial intubation, partial airway obstruction, rebreathing
– apparatus malfunction - exhausted CO2 absorber, inadequate fresh gas flows, ventilator malfunction, leaks in ventilator tubing
* Sudden drop in ETCO2 to zero - kinked ET tube, defective analyser, total disconnection, ventilator defective
* Flat ETCO2 trace - ventilator disconnection, airway misplaced, capnograph not connected, respiratory/cardiac arrest, apnoea test, capnography obstruction
* Sudden change in baseline (not to zero) - calibration error, water drops/condensation, saturated CO2 absorber
* Sudden increase in ETCO2 - ROSC, correction of ETT obstruction
* Elevated inspiratory baseline - CO2 rebreathing, contamination, inspiratory valve malfunction
* Slanting and prolonged phase 2, increased slope of phase 3 - obstruction/COPD/bronchospasm
Cardiac Surgery (Off Pump)
Management is as for CABG but without bypass and using a “stabiliser” to keep the heart as still as possible e.g. Octopus
- keep well filled with crystalloid
- keep warm
- may need vasoconstrictor
- consider TOE/oesophageal Doppler
- may still required full/half dose heparin - aim ACT 250-300
- 1-10% may need bypass
- use depth of anaesthesia monitoring to avoid over-anaesthetising
- pace if bradycardic but void tachycardia
- maintain contractility
- correct U+E disturbance
Cardiac Surgery (On Pump)
Pre-operative
* careful pre-op assessment
* bloods, ECG, radiology
* cardiac investigations - TTE/TOE, catheter studies, cardiac MRI, digital subtraction angiography, angio
* euroscore risk calculation
* pre-med —> aim for relaxed, non tachy patient - benzo/morphine/hyoscine/O2
Intra-operative
* large bore IV and arterial access
* consider haemodynamic goals
* ensure lack of awareness
* benzo/opiate heavy induction + long acting NMBA
* CVC +/- PA sheath +/- TOE +/- NIRS +/- BIS
* phenylephrine
* TIVA/fent + isoflurane
* TXA 30mg/kg
* heparinisation + CPB —> propofol maintenance (ACT aim 4x baseline >480s)
* support CVS/RS, reverse coagulation post CPB
Post-operative
* cardiac ITU management
* extubate once warm, awake, weaned and not bleeding
Cardioplegia
Used for myocardial protection and facilitation of surgery requiring a still heart.
Features:
- Potassium 20mmol/L
inactivates fast inward Na channels
prevents upstroke of the myocyte action potential
diastolic arrest with an unexcitable myocardium - Mannitol - to make solution slightly hyperosmolar to limit tissue oedema
- Bicarbonate or histidine to offset acidosis from tissue ischaemia
- Calcium (at a lower than normal plasma level) to maintain cell membrane integrity while avoiding myocardial activity
- Magnesium to prevent loss of magnesium from cells and stabilise the myocardial membrane
- Procaine to decrease excitability at reperfusion
- Glutamate/aspartate to promote oxidative metabolism in energy-depleted hearts
Carotid Endarterectomy
Pre-operative
* usually high risk patients
* check normal blood pressure (to target intra-op)
* assess and document neurology
* continue anti-hypertensives (not ACEI/ARB), beta blockers + statins, anti-platelets can continue
Intra-operative
* GA vs regional (superficial/intermediate/deep cervical plexus blocks)
* consider invasive haemodynamic monitoring
* augment arterial pressure as required within 20% of baseline
* consider pre-med if GA
* 2x IV access + ETT
* consider cerebral monitoring techniques
Post-operative
* monitor neurology
* airway oedema is common
* control BP (risk of hyperperfusion)
Cataract Surgery
Pre-operative
* often elderly
* co-morbidities and anti-coagulants
Intra-operative
* positioning - head horizontal
* monitoring
* cannula?
* topical, blocks, GA (LD, kids, dementia)
Post-operative
* typically day case
Categorising Mechanical Ventilation
Primary ventilator target during inspiration
* pressure (pressure generator)
* flow/volume (flow generator) - constant flow, decelerating profile
* dual mode - tidal volume guarantee with advantages of pressure control
What starts inspiration?
* time cycled - RR, I:E ratio, insp/exp time
* patient triggered - pressure trigger or flow trigger
* mixture
What ends inspiration?
* time
* drop in flow (pressure control)
Cerebral Monitoring
- Monitoring ICP
— intraventricular - catheter inserted into lateral ventricle via a burr hole (also allows drainage), risk of haemorrhage and infection, insertion may be challenging
— intraparenchymal - most commonly used - micro-miniature silicone strain gauge monitor inserted into the brain parenchyma, accurate and relatively easy to insert
— subdural/subarachnoid - Monitoring cerebral oxygenation
— jugular venous oxygen saturation
— NIRS
— direct brain tissue oxygenation - Monitoring CBF
— transcranial Doppler/colour coded duplex
— radiological imaging e.g. CT perfusion, xenon enhanced CT, perfusion weighted MRI, nuclear medicine methods (PET/SPECT) - Monitoring cerebral metabolism
— microdialysis
ICP waveforms - 4 kinds
* Normal - systolic upstroke, diastolic downstroke with a dichrotic notch
* A waves - plateau waves - steep increases in ICP lasting 5-10 minutes, always pathological, indicative of early brain herniation
* B waves - oscillations of ICP 0.5-2 waves per minute - associated with unstable ICP, possible due to cerebral vasospasm
* C waves - oscillations that occur 4-8 waves per minute - likely reflection of cardiac and respiratory cycles
Circle system
Benefits
* preserves anaesthetic gases making volatile anaesthesia cost-effective
* preserves medical gases (oxygen) which is useful in reousrce-limited settings
* preserves heat and moisture
* reduces fire risk
Closed-circuit system
* requires re-breathing of expired gases
* CO2 is actively removed
* only gases which must be replaced are those consumed by the patient or lost via leak
Components
* Y piece connecting the circuit to the patient
* Expiratory and inspiratory valves - ensuring unidirectional flow
* A means of generating pressure - ventilator and reservoir bag with APL valve (typically placed on expiratory limb)
* Soda lime to absorb CO2 (NaOH + Ca(OH)2 + H2O)
* Fresh gas flow
* Separate high pressure high flow oxygen flush which bypasses the vapouriser
Complications of Epidurals
- 1:8 inadequate
- 1:20 GA required for section
- 1:50 hypotension
- 1:100 PDPH (1:500 for spinal)
- 1:1000 nerve damage
- 1:13000 nerve damage lasting more than 12 months
- 1:50000 epidural abscess
- 1:100000 epidural haematoma
- 1:100000 meningitis
- 1:250000 severe injury including paralysis
Consent for Regional Anaesthesia
Contraindications:
Absolute
* patient refusal
* sepsis at injection site
* allergy to LA agents
Relative
* coagulopathy
* pre-existing neuropathy
* systemic infection
* altered anatomy
Specific blocks
* SCB - severe respiratory disease
* ICB - contralateral phrenic/recurrent laryngeal nerve palsy, pneumothorax or pneumonectomy, severe respiratory disease, bilateral blocks
Benefits:
* Reduction in acute pain, PONV, delirium, CPSP, stress response, cost, post-operative morbidity
* Possible reduction in cancer recurrence
* Avoidance of GA and it’s associated risks
* Improved sleep, surgical function (e.g. AV fistula), patient satisfaction
Risks/Complications:
* Failure of block
* LA toxicity
* Infection
* Haematoma
* Temporary nerve damage <1:10
* Permanent nerve damage 1:2-5000
* Effects of block
* - risk of injury while anaesthetised
* - block specific effects
* – arterial puncture
* – pneumothorax
* – Horner’s Syndrome
* – Phrenic nerve palsy
* – Recurrent laryngeal nerve palsy
* – Autonomic blockade
Depth of Anaesthesia Monitoring
Non specific
- clinical signs
- CVS parameters
- agent monitoring (end tidal volatile)
Specific
- HR/ECG variability
- lower oesophageal sphincter contractility
- isolated forearm technique
- BIS/entropy/processed EEG
- Auditory evoked potentials
- Skin conductance
Detecting Venous Air Embolism
- ETCO2 - causes sudden drop
- Precordial Doppler - most sensitive non invasive monitor but limited by positioning, interference from diathermy and not quantitative
- TOE - more sensitive but invasive, placement and interpretation difficult
- PA catheter - invasive but sensitive, not specific for air, not routinely used
- Precordial/oesophageal stethoscope - least sensitive - “Mill Wheel Murmur” only apparent after massive venous air embolism
ECT
Induction of a generalised, tonic-clonic seizure
Indications
* severe medication-resistant depression
* mania
* catatonia
Contraindications
* raised ICP
* recent CVA
* untreated cerebral aneurysm
* MI or uncontrolled cardiac failure
* unstable major fracture
* severe osteoporosis
* DVT until anticoagulated
* phaeochromocytoma
* retinal detachment or glaucoma
* cochlear impants
Challenges
* remote site - must have appropraite resuscitation equipment and drugs, and meet standards for monitoring, trained assestance and recovery facilities
* elderly patients
* significant co-morbidities - discussion about whether anaesthesia should take place somewhere else
* patients can be poor historians
* consent
* seizure threshold with anaesthetic agents
Involves:
* Electrical current applied transcutaneously to the brain, via two electrodes positioned bilasterally or unilaterally.
* Bilateral ECT more common
* Unilateral ECT over the non-dominant hemisphere minimises cognitive adverse effects
* Overall aim is to induce a generalised seizure with characteristic EEG changes (>10s, <120s)
* Typically performed twice weekly until there is a lack of further improvement
Pre-operative
* Full pre-op assessment
* Check for reflux or and contraindication
* Clarify current medications
* Physical examination for evidence of cardiac failure, severe valvular disease, dysrhythmia, uncontrolled hypertension, poor dentition or dehydration requiring fluid therapy
* Blood tests, ECG + other investigations as indicated
* Time to optimize balanced against urgency of ECT
Intra-operative
* Consent
* Fasting
* Continue regular medications
* Avoid pre-medication
* Empty bladder prior to anaesthesia
* Pre-oxygenation
* Induction - methohexital 0.5-1.5mg/kg (gold standard - minimal anticonvulsant properties), propofol, etomidate
* NMBA - decrease the risk of severe injury - sux most commonly used
* Airway management - FM, bite block
* Gentle hand ventilation until breathing resumes
Post-operative
* Standard monitoring and oxygen supplementation
* Risk of emergence agitation - secluded, calm recovery environment, small doses of midazolam
Elective Craniotomy
Pre-operative
* pathophysiology of underlying condition
— symptoms of raised ICP, consider hydration status
— symptoms of SOL - headache, poor balance, seizures, CN defects, on dex/PPI?
— pituitary function - ACTH, Cushings, DI, SIADH, GH + acromegaly, hypo/hyperglycaemia
— implications on renal function/electrolytes
— posterior cranial fossa symptoms - e.g. cough/gag
— neurological examination including ask regarding changes in vision/hearing
* other health issues
* consent for positioning complications, haemorrhage + transfusion, cardiovascular instability, post-op HDU/ITU
* discuss positioning with surgeon
Intra-operative
* maintain adequate CPP (MAP)
* avoid rise in ICP (maintain ETCO2 4.5)
* full monitoring + temp, invasive BP, UO, depth of anaesthesia, PNS
* 1-2 large bore peripheral IV access +/- CVC (consider position) - long extensions, foot cannulas
* positioning - supine/prone/lateral/park bench
* armoured ETT - secure with tapes
* thio/prop + remi (gentle induction) + NMBA (monitor TOF)- may need sugammadex if using MEPs
* maintenance - TIVA or volatile/remi
* dexamethasone + anti-emetics
* deep extubation - avoid coughing
* multimodal analgesia - start giving morphine once starting to close/after extubation
Post-operative
* manage pain and vomiting
* monitor GCS, signs of raised ICP, massive haemorrhage
* pneumatic boots
* avoid NSAIDs
* watch for hyperglycaemia and other metabolic derangements
Endoscopic Thoracoscopic Sympathectomy
Pre-operative
* usually young with few co-morbidities - hyperhidrosis, blushing, long QT, CRPS, angina
* cardiovascular evaluation if for angina/long QT
* G&S, warn about possibility of open procedure
Intra-operative
* routine standard monitoring +/- art line
* GA usually (thoracic epidural/intercostal block)
* standard ETT +/- BB/DLT/Proseal LMA with controlled ventilation (CO2 insufflation)
* usually bilateral procedure (10-15 min per side)
* intrathoracic LA under direct vision by surgeons
* paracetamol + NSAID
* big drip due to risk of catastrophic bleeding
Post-operative
* simple analgesia + opioids PRN
* CXR in recovery
* often day case if straightforward
Enhanced Recovery
Pre-operative
* optimise glycaemic control/BP
* smoking cessation + ETOH advice
* weight loss
* measure albumin + correct nutritional deficiency
* patient education and counselling
* pre-habilitation
* optimise PMH and risk stratification
* assessment and correction of anaemia
* pre-op carb loading + “sip til send”
* avoid bowel prep + sedating pre-med
Intra-operative
* minimally invasive
* avoid NGT/drains
* short acting agents, regional
* temp control
* PONV prevention
* VTE prophylaxis
* restrictive fluid
Post-operative
* early PO intake and IV discontinuation
* multimodal analgesia + adjuncts
* drains out early
* early mobilisation
* criteria based discharge
Enteral Nutrition
Daily nutritional requirements in critical care:
Water 30ml/kg, Energy 25cal/kg, Protein 0.8-1.5g/kg, Fat 1g/kg, Carbohydrates 2g/kg, Nitrogen 0.2g/kg, Na 1-2mmol/kg, K 0.8-1.2mmol/kg, Cl 1-2mmol/kg, PO4 0.5mmol/kg, Ca 0.1mmol/kg, Mg 0.1mmol/kg
When to start enteral nutrition on ITU?
* as soon as feasible
* ideally once fully resuscitated and off vasopressors
* within 48hrs with cautious monitoring
How?
* no evidence that post-pyloric feeding is superior to NG
* post-pyloric feeding is more complex and requires input from radiology or GI teams
* early parenteral nutrition has not been found to affect outcomes
* exhaust all EN strategies before considering PN (suggests after 3-7 days if not tolerating EN)
Benefits of EN
* Reduce stress related catabolism
* Minimise bacterial translocation
* Maintain intestinal mucosal integrity
* Stimulates intestinal blood flow
* Prevent or reverse malnutrition
* Cheaper and simpler with fewer complications than PN
* Improves healing, weaning and recovery
Risks of EN
* Aspiration (decreased with post-pyloric feeding)
* Sinusitis
* GI complications - perforation of organs, intolerance
* Bowel ischaemia
* Tube malpositioning/dislodgement
* Metabolic complications e.g. refeeding syndrome, hyperglycaemia
Benefits of PN
* Can be started early
* Does not rely on gastric/intestinal function
* Less need for interruptions
Risks of PN
* CVC associated infection
* Metabolic complications - hyperglycaemia, electrolyte abnormalities, Wernicke’s, nutrient excess or deficiency, liver dysfunction, refeeding syndrome
Eye Anaesthesia
Topical LA for eyes
* Gel - 2% lidocaine gel applies topically to the cornea
* Intracameral LA - <0.5ml 1% preservative free lidocaine instilled into the anterior chamber of the eye
* Eye drops - fast onset 15-20s, 20 minute duration
– amethocaine 0.5% or 1% - stinging on application, relatively high degree of corneal toxicity, better analgesia
– oxybuprocaine 0.4% - less toxic than amethocaine
– proxymetacaine 0.5% - doesn’t sting, lowest toxicity, preferred for kids
* Regional blocks
– Sub-Tenon’s
– Retrobulbar
– Peribulbar
Sub-Tenon’s Block
* Tenon’s capsule - connective tissue layer that encapsulates the sclera, fused posteriorly with the dural layer of the optic nerve head, attached to the bulbar conjunctiva anteriorly
* Gives almost instantaneous sensory blockade then spreads posteriorly along the contour of the globe, through the capsule opening into the intraconal space leading to motor block
* IV access + monitoring
* LA drops + clean
* Inferomedial quadrant with patient looking up and out
* Non toothed forceps to lift conjunctiva, blunt ended scissors to dissect
* Blunt, curved cannula following the curvature of the globe to the equator
* 3-5ml of LA injected slowly
– 2% lidocaine (lasts ~40 mins)
– 0.75% levobupivicaine (slower onset, longer duration)
– hyaluronidase improves speed of onset and quality of block (7.5-15IU/ml) by hydrolysing bonds between glucosamine and glucuronic acid in hyaluronic acid, breaking down the extracellular matrix
* Gentle pressure to eyelid
* Advantages - wide range of procedures, lower risk of life/sight threatening complications, safe in anticoagulated or antiplatelet agents, can be topped up, doesn’t increase IOP
* Disadvantages - chemosis + subconjunctival haemorrhage can affect some procedures, risk of difficulties if scarring from previous procedures, potential damage to optic nerve or short posterior ciliary arteries if too posterior, eye may still be mobile if small volume LA used
Retrobulbar block
* Sharp needle technique
* Injecting directly into the intraconal space - acts directly on sensory and motor nerves
* IV access + monitoring
* LA drops + clean
* Gaze straight ahead, 31mm 23G needle inserted transconjunctivally just lateral to limbus
* Directed posteriorly until tip just past the equator, then redirect upwards and medial towards the apex
* 1-3ml injected slowly
* Advantages - small volume injection, rapid onset of anaesthesia and akinesia
* Disadvantages - tip of sharp needle close to optic nerve, dural sheath and ophthalmic artery, orbicularis oculi may not be paralysed
Peribulbar block
* Sharp needle technique
* Injecting into extraconal space - spreads into intraconal space leading to action on sensory and motor nerves as well as lid akinesia
* 2x injections - 1x medial, 1x inferolateral
* IV access + monitoring
* LA drops + clean
* Gaze straight ahead, 25mm 25G needle medial to caruncle, directed back and medial then redirected posteriorly
* 3-5ml slow injection
* Gaze straight ahead, injection through conjunctiva just lateral to limbus, down towards bone, then redirected posteriorly and medially
* 4-6ml slow injection
* Advantages - suitable for a wide range of procedures, excellent akinesia or globa and lids
* Disadvantages - sharp needle technique, increased risk of globe performation if longer axial length, difficult/hazardous if scleral buckle present
Complications
* Life-threatening - brainstem anaesthesia, anaphylaxis, intravascular injection of LA, LAST, CNS toxicity
* Sight-threatening - globe perforation/penetration, prolonged dysfunction of extraocular muscles, orbital haemorrhage, optic nerve damage
* Minor - pain, chemosis, proptosis, subconjunctival haemorrhage
Intraoperative neurophysiological monitoring
Aim - to reduce risk of injury to neural structures during surgery. Usually carried out by dedicated neurophysiologists.
Cause of Injury
* direct mechanical disruption from surgical manoeuvres
* thermal injury from surgical coagulation
* pressure injury from patient positioning
* ischaemia due to local or global hypoperfusion
Types of Surgery
* Vascular surgery involving carotids - SSEPs, MEPs
* Resection of intracranial tumours/AVMs - SSEPs, MEPs
* Posterior fossa/brainstem surgery - BAEPs
* Surgery with risk of direct injury to spinal cord/roots or risk of compromising their blood supply e.g. scoliosis, thoracoabdominal aneurysm repair - SSEPs, MEPs, EMG
* Surgery close to cranial nerves or peripheral nerves e.g. facial nerve in parotid preocedures, RLN in thyroid surgery - EMG
Options
* detection of spontaneous activity e.g. EEG, EMG
* measurement of evoked electrical response of a specific neural pathway after an active stimulation e.g. SSEP, MEP, BAEP
* wake up test
EMG - electromyography
* electrodes used to initiate an action potential in a peripheral nerve
* action potential arrives at the NMJ, depolarises nerve terminal releasing ACh
* ACh binds to the alpha subunit on the post junction all receptors, allowing influx of sodium
* depolarisation of the end plate, activating further sodium channels allowing depolarisation away from the end-plates to both ends of muscle fibre at 3-5m/sec (7-7ms to spread through 5cm muscle)
* muscle action potential via T-tubule system depolarises the membrane, releasing calcium, leading to excitation-contraction coupling
* EMG is the sum of the action potentials of the adjacent fibres in a muscle
* one electrode over the mid part of the muscle and the other at the end of the muscle
* action potential is recorded as it travels down the muscle
* repetitive stimulation gives normal response if there is no defect in neuromuscular transmission
BAEPs - Brainstem Auditoy Evoked Potential
* acoustic stimulus delivered at the ear canal
* electrical signals, generated by the cochlear, travel along the vestibulocochlear nerve into the nucleus and brainstem
* response recorded by an electrode at the mastoid or ear lobe
SSEPs - Somatosensory Evoked Potential
* monitors ascending sensory pathways through transcutaneous electrical stimulation of a peripheral nerve
* ascends cord via dorsal columns
* decussates at medulla, asends to thalamus and sensory cortex
* median or ulnar nerve stimulation
* posterior tibial nerve stimulation
MEPs- Motor Evoked Potential
* monitors integrity of descending corticospinal and corticobulbar tracts
* stimulation at motor cortex
* electrical activity descends along the motor tracts, travelling along the nerve, across the NMJ to produce muscle contraction
* can be transcranial through the scalp or direct electrical stimulation on the brain
* measures compound muscle actions potentionals - composite electrical activities within the effector muscles e.g. thenar muscles, tibialis anterior, abductor hallucis
Anaesthetic considerations with IOM
* anaesthetic agents produce dose-dependent suppression of evoked potentials - TIVA technique optimal, short acting NMBAs or reverse
* need to provide stable physiology to facilitate meaningful interpretation of signal changes and accurate surgical guidance - maintain MAP, avoid hyperventilation, avoid hypothermia, avoid anaemia and hypoxaemia, maintain normoglycaemia
* potential for nonsurgical causes of neural injury - need to act promptly to manage and prevent secondary injurys
* risks of IOM e.g. bite injury, patient movement during stimulation, use of sharps
Fetal Surgery
Fetal conditions amenable to fetal interventions
* twin reversed arterial perfusion
* twin-twin transfusion syndrome
* catheter-based balloon aortic valvuloplasty or septoplasty for cardiac anomalies
* CDG - fetal endoscopic tracheal occlusion
* myelomeningocele - open or fetoscopic repair
* sacrococcygeal teratoma - open resection
* fetal cystoscopy/vesicoamniotic shunt for urinary tract obstruction
* EXIT open airway management
* intrauterine transfusion of RBCs
Classes of intervension
* Minimally invasive and fetoscopic - maternal laparotomy or percutaneous insertion of trocars into uterus, uterus remains intact, instrucments inserted into closed uterus under direct vision
* Open fetal surgery - maternal laparotomy and hysterotomy with aim to close hysterotomy at the end of the case
* Open fetal surgery with delivery at the end - maternal laparotomy and hysterotomy
Risks of open fetal surgery
* preterm birth
* chorion-amnion separation
* spontaneous membrane rupture
* oligohydramnios
* placental abruption
* maternal pulmonary oedema
* increased incidence of uterine thinning/dehiscence of the uterine scar at deliveru - will need C-sections
Pre-operative
* comprehensive history
* physical examination
* cross match
* fetal studies - USS, MRI, echo, genetic testing
* psychosoial evaluation and extensive counselling
Intra-operative
* from LA +/- sedation to deep GA depending on case
* minimise risk of pulmonary aspiration - prophylaxis, position
* left uterine displacement
* low thoracic epidural + GA for open fetal surgery
* RSI
* invasive BP monitoring for optimal uterine perfusion pressure - phenylephrine infusion
* restricted crystalloid due to risk of pulmonary oedema
* high MAC (1.5-2)
* magnesium sulphate bolus and infusion to prevent preterm labour
Free Flap Surgery
Pre-operative
* full anaesthetic assessment - especially cardio, respiratory, nutrition
* airway strategy (if head and neck) - MDT approach
* investigation - FBC, U+Es, coag, G+S (LFTs, glucose)
Intra-operative
* hyper dynamic circulation - increased CO, decreased SVR, Hct 30%
* invasive monitoring + catheter
* minimise stress response (remi)
* avoid barotrauma/atelectasis
* controlled hypotension during dissection
* increased MAP once anastomosing
* caution with fluid (flap oedema)
* ?NGT
* smooth emergence (avoid surge in BP/flow to flap)
Post-operative
* HDU/flap monitoring
* normothermia, normotension, Hct 30%
* sats >94% (LRTI prevention - physio, mobilise)
* analgesia
* LMWH
* avoid additional stress e.g. withdrawal
Glaucoma Surgery
Pre-operative
* paeds
* often multiple previous procedures
Intra-operative
* adrenaline drops
* ketamine GAs for kids
* laser therapy
* LA (? Lower volume) or GA acceptable
Post-operative
* most done as day case
Humidification Methods
Passive
* cold water bath - sterile water reservoir through which gas is bubbled at room temperature (< 50% relative humidity unless either very low gas flow or large water surface area)
* soda lime - energy produced by reactions of Ca(OH)2 and NaOH with CO2
* HMEF - conserves patients own heat and water without the need for an external power or water source, compact cheap and effective though efficiency reduces over time (60-70% relative humidity)
Active
* hot water bath - sterile water reservoir that is electrically heated through which gas is bubbled, risks of scalding and infection (100% relative humidity)
* nebulisers - supplies water in droplet form, greatest relative humidity but risk of water intoxication (>100% relative humidity)
Hypotensive Anaesthesia
Controlled, induced or deliberate hypotension
* 30% reduction in baseline MAP
* effective at reducing blood loss
* improves quality of the surgical field
* extreme caution if impaired autoregulation or high risk of organ dysfunction
* limit duration and extent even in fit and well individuals
Elements
* head up/elevation of surgical site for positioning
* reduce SVR - calcium channel blockers, inhalational anaesthetic agents
* reduce contractility - inhalational agents, beta blockers
* reduce SV - beta blockers, remifentanil
* selective alpha-2 adrenergic agonists
* TIVA
* use of histamine releasing agents - morphine, atracurium
Insertion of VP shunt
CSF drainage for hydrocephalus
Pre-operative
* as for craniotomy
* often paediatric patients
* often have raised ICP
* consider RSI if emergent
Intra-operative
* routine monitoring
* art line/CVC not usually required
* antibiotics + strict antisepsis
* advancing trocar to allow tunnelling of shunt is particularly stimulating —> additional analgesia +/- relaxation
Post-operative
* monitor GCS
* risk of intracranial haemorrhage if CSF drained too fast
* risk of shunt blocking/infection
* watch for pneumothorax
LASER (Light Amplification by Stimulated Emission of Radiation)
Physics
* Lasing medium
* Energy source - energizes particles in the gain medium - when the temporary excited state decays, a photon is emitted of a specific wavelength
* Optical resonator - a cavity containing the lasing medium with 2 parallel mirrors on either side - one highly reflective, the other partially reflective allowing the ouput beam
Safety
* Burns - retina, optic nerve, skin
* Fire - use air + low FiO2, avoid N2O, non flammable ETT, non reflective instruments and equipment, wet swabs, non combustible drapes
* Theatre - laser operator, fire extinguisher, eye protection, doors locked with warning signs, windows covered
Types
* solid state eg. Ruby for hair removal and tattoo removal, Holmium:YAG for lithotripsy, Nd:YAG for cutting and coagulating
* gas e.g. CO2 (far IR) for cutting, coagulating, resurfacing; argon for retinal surgery and AV malformations
* dye e.g. pulsed yellow dye for birthmark removal or vascular skin lesions
* semiconductor diode (red/IR) e.g laser pointer, hair removal, bar code scanners
Intra-operative
* designated laser safety officer
* matt surfaces
* locked doors and signs
* eye protection
* cover exposed skin
* wet swabs to adjacent tissues
* avoid flammable skin prep
* LASER specific ETT - metallic tube with double cuff filled with saline/methylene blue (high volume, low pressure cuff)
* avoid nitrous oxide
* low flow, low FiO2
Liver Resection
Pre-operative
* As far any major abdominal surgery
* Screening of liver function and coagulation
Intra-operative
* Large bore IV access +/- art line +/- CVC
* Thoracic epidural
* GA + ETT + IPPV
* Aim for relatively hypotensive + low CVP to minimise blood loss
* Minimise fluid input prior to resection
* Active warming
* POC coagulation if needed
* Pringle manoeuvre for control of bleeding
* Fluid load following resection
Post-operative
* HDU/PACU
* Risk of coagulopathy and encephalopathy
* Use short acting drugs
* Avoid drugs that rely on hepatic metabolism or may cause encephalopathy
* Consideration re: timing & removal of epidural if coagulopathy (may need FFP cover)
Lung Surgery
Pre-op Lung Function Tests
* FEV1 >2L for pneumonectomy and >1.5L for lobectomy
* ppoFEV1 and ppoDLCO >40% + oxygen says >90% = average risk
* if either/both ppoFEV1 and ppoDLCO <40% –> CPET
Exercise Tests
* shuttle walk (25x10) - high risk if not completed
* 6mwt - high risk if <70% of predicted distance achieved or <250m
* stair climbing test - high risk if <22m
* CPET
— relatively good function if VO2 max >15ml/kg/min (BTS 2010)
— high risk if VO2 max <10ml/kg/min or <35% of predicted (ACCP 2013)
— moderate risk if 10-20ml/kg/min or 35-75% predicted
— low risk if >20ml/kg/min or >75%
Measurement of Flow
- Rotameters - variable orifice, constant pressure - needle valve controls the flow of gas through the flow meter and a tube which grdually increases in diameter with an internal bobbin, as the gas flow increases, the bubbin rises (calibrated for gas density)
- Pheumotachograph - constant orifice - small wide tube with a mesh in it to reduce the volocity of the flow of gas, pressure drop is measured by a differential pressure transducer across the resistance - as the flow increases, the pressure drop across the resistance increases
- Inferential flowmeter - Wright’s respirometer - set of very low resistance vanes, flow of gas causing them to spin - amount of spinning proprtional to flow rate
- Wright Peak Flow Meter - variable orifice, as the internal diaphragm moves with the air blown it, it opens a larger orifice for air to escape
- Hot wire anemometer - measures heat loss of an electrically heated wire placed in the air stream
- Ultrasonic flowmeter - use sound waves to determine the velocity of a fluid flowing in a pipe
Measuring Humidity
- Wet and dry bulb hygrometer - one bulb open to air, one wrapped in a wet rag - at 100% humidity, the wet and dry temperatures should be identical. As humidity decreases, evaporation occurs from the wet bulb, decreasing the temperature on the thermometer due to latent heat of evaporation
- Regnault’s dew point - air blown through a silver tube containing ether - at dew point, condensation occurs on the outer surface of the tube
- Hair hygrometer - increasing humidity increases length of hair
- Mass of hygroscopic crystals - absorb moisture and weight vs dry weight can be used to measure humidity
- Electrical methods
— resistance sensors - measure the resistance change in a moisture absorbing material - impedence change usually has an inverse exponential relationship to humidity
— capacitance sensors - hygroscopic dielectric material placed between a pair of electrodes that forms a small capacitor - capacitance increases with higher humidity - Mass spectrometry - principle of reduction in the UV light transmitted through the medium containing water vapour
Methods of CO Measurement
Non Invasive
- clinical signs - core-peripheral temperature
- ballistography, bioimpedance
- suprasternal Doppler
- NICO - indirect Fick partial rebreathing
Minimally invasive
- oesophageal Doppler
- pulse contour analysis (PICCO)
Invasive (PAFC)
- dye dilution
- thermodilution
- continuous CO, SVO2
Methods of Disinfection
Used for “SEMI-CRITICAL” items that touch mucous membranes or skin that is not intact
- thermal washer disinfector - initial clean at <35 then 71 for 3 mins or 80 for 1 min or 90 for 1 sec
- pasteurisation (low temp steam) - more than 70 for 30 minutes
- boiling water for 5 minutes
- chemical - 70% ETOH, iodine, glutaraldehyde, chlorine, hydrogen peroxide etc
Methods of Neuromuscular Monitoring
- visual, tactile - ability to sustain head lift for 5s
- electromyography - recording of a compound action potential that occurs during muscular contraction
- mechanomyography - measurement of evoked muscle tension using a strain gauge transducer and recorder (arm and hand must be fixed with movement of the thumb along the length of the transducer for accuracy)
- acceleromyography - measures acceleration of the contracting muscle to calculate force (f=ma), acceleration being measured by a piezoelectric ceramic wafer strapped to the thumb, producing a voltage proportional to its acceleration
Qualitative:
* Single twitch 70-80mA, 0.1ms
* Train of four 70-80mA, 0.1ms at 4Hz - 4 equal twitches seen from about 70% receptor occupancy
* Double burst stimulation - 2 sets of 3 twitches (70-80mA, 0.2ms, 50Hz separated by 750ms)
* Post tetanic count 70-80mA, 0.1ms twitches at 1Hz after a tetanic stimulus of 50Hz for 5s - number of twitches present is inversely related to the length of time until recovery from block (9 = return of first twitch in TOF)
Methods of Oxygen Analysis
Electrochemical
* polarographic (Clarke) electrode
– oxygen molecules diffuse across a teflon membrane
– current flows between a silver cathode and a platinum anode
– current is proportional to the partial pressure of oxygen in the inspiratory gas
– battery powered
– life expectancy ~3yrs due to deterioration of the teflon membrane
* galvanic fuel cell
– on the inspiratory limb of the breathing system
– oxygen molecules diffuse across a membrane and an electrolyte solution to a gold (or silver) cathode, which is connected through the electrolyte solution to a lead anode
– electrical current generated which is proportional to the partial pressure of oxygen in the inspired gas
– response time of approx 20s, accurate to within 3%
– depleted by continuous exposure to oxygen, life span ~1yr
Physical
* paramagnetic
– presence of 2 electrons in unpaired orbits means it is weakly attracted into a magnetic field
– sample gas delivered to anaylser via sampling tube
– two chamber analyser separated by sensitive pressure transducer
– sample gas to one chamber, room air to reference chamber
– electromagnet rapidly switched on and off causing o2 molecules to be attracted and agitated
– results in changes in pressure on either side of the pressure transducer
– pressure difference is proportional to the oxygen partial pressure difference between the sample gas and the reference gas
– very accurate and highly sensitive
– affected by water vapour, have a water trap incorporated
* mass spectrometry
– sample gas drawn or injected into a low-pressure sample chamber that is attached to another chamber, at a pressure nearing that of a vacuum
– molecular leak pathway constructed between the chambers
– molecules ionised in second chamber and accelerated by a cathode plate
– fixed magnets or electro,agnets influence the ions and allow separation by the ion’s mass and charge
– ions are narrow-band filtered and detected by photo-voltatic receptors
– signal amplified and processes
– require powerful vacuum pumps and cannot return sample to patient
– response and delay times
– very accurate
Methods of Sterilisation
Used for “critical” items that enter normally sterile tissue or the vascular system
- steam - 121 for 30 mins or 132 for 4 mins
- ethylene oxide
- hydrogen peroxide (28-52 mins)
- ozone
- dry hot air - 160 for 2hr
- ionising radiation e.g. cobalt-60, gamma
Pulse Oximetry
- Based on absorption of light shone through a sample
- Absorption of deoxy-Hb and oxy-Hb is the same at 805nm - isobestic point
- Deoxy-Hb has a high absorption at 660nm (red) and low at 940nm (IR)
- Oxy-Hb has a high absorption at 940nm and low at 660nm
- Absorbance of light through different substances - bones/flesh/tissue/venous blood are all static features and can be filtered out
- Arterial blood is pulsatile so varying absorption
- 2x LEDS shone from one side - 1 at 660nm, 1 at 940mm, flashing alternately
- Photocell/detector on the other side of the finger then sees how much light is absorbed –> microprocessor calculate relative concentrations of Oxy and deoxy-Hb and hence, convert to oxygen saturations to display on a monitor
- Most modern devices also include “off” within the cycle to compensate for stray ambient room light
Errors
* Pulsatiles venous blood flow e.g. AV fistulas, heart failure, placement of probe substantially lower than heart - will cause a lower reading due to pulsatile deoxygenated blood
* Presence of carboxyhaemoglobin will cause over-estimation of saturations (CO-Hb has similar absorption spectra to Oxy-Hb)
* Presence of light leaks
* Presence of high bilirubin levels
* Presence of intravascular dyes (methylene blue, indocyanine green) - cause artifactually lower readings
* Surgical diathermy
* Poor peripheral perfusion
* Body movements
* Inaccurate below 70%, completely unreliable below 50%
MRI
Physics
* Patient placed in a strong magnetic field
* Atoms with odd numbers of protons have an asymmetrical spin which allows them to align in the presence of an external magnetic field
* Application of pulses of radio frequency energy causes protons to “flip” between energy levels
* When the pulse is switched off, the protons “flip” back and release energy which can be detected
* Energy detected can be processed and converted to visual images dependent on differences in the hydrogen nuclei density between tissues
* Physical and chemical differences in the tissues produces 2 distinct relaxation patterns with time constants T1 and T2
* T1 - fat is bright and water dark. Good for grey-white matter contrast.
* T2 - water is bright, fat is dark. Good for tissue oedema.
* Addition of gadolinium contrast alters the relaxation rates of hydrogen nuclei
Practicalities
* MRI safety checks for patient and staff
* MRI safe equipment incl. non ferrous trolley, MR compatible ventilator/anaesthetic machine or long tubing, long extensions to infusions or MR safe infusion pumps, MR safe monitoring leads (high impedance, braided, short ECG leads), fibreoptic probe connections for oximetry secure pilot balloon away from site of scan if ferromagnetic material —> monitoring transmitted to control room
* Long tubing - risk of disconnections or delays in response
* Risk of magnetic field heating tissues, avoid closed loops, coiled wires, any metal in clothing
* Noise level - earplugs for patient
* Remote site anaesthesia
* Difficulty observing and monitoring patient while in scanner
* Superconducting magnet needs to be kept cool - if there is sudden shutdown or spontaneous leak, helium will vapourise
Neuroprotective Measures
- Optimise venous drainage from head - tapes not ties, 30 degree head up positioning, maintain TV 6-8ml predicted body weight, keep driving pressure <15
- Avoid increased ICP - control seizures, adequate analgesia, sedation
- Optimise oxygen delivery to brain - PaO2 >11, maintain CPP (MAP >80mmHg), Hb >7g/dL
- Maintain physiological normality - normothermia, normovolaemia, normoglycaemia, normonatraemia
Oculoplastic Surgery
Pre-operative
* range of surgeries - lid, orbital decompression, nasolacrimal duct problems, eviscerations etc
* may need to check TFTs
Intra-operative
* Rubens pillow
* drops both eyes (for prep)
* lots of cases have sedation for location
* GA
* throat pack/relative hypotension for dacrocystorhinostomy (? Art line)
Post-operative
* may be painful
Oesophageal Doppler
Measurement based on the Doppler Principle: a doppler shift in frequency occurs when the ultrasound wave is reflected back from moving RBCs - the shift in frequency is proportional to the velocity of the blood flow
- Small ultrasound transducer mounted on the top of a flexible probe
- Inserted orally or nasally into the oesophagus
- Lubricate with aqueous gel to prevent signal disturbance
- Tip to lie around T5/6 (35-40cm oral length, 40-45cm nasal length)
- Rotate bevel so it faces posteriorly
- Tip adjusted to lie alongside descending thoracid aorta with beam at 45 degree angle to blood flow
- Manipulate probe to achieve best signal
Measures
* Contractility - PV - peak blood velocity - peak of curve. Mormal range is age related
* Preload - the “flow time” corrected for HR (low flow time corresponding to hypovolaemia or increased afterload) - width of the base of the curve
* Stroke volume - the “stroke distance” is the area under the curve
Numbers
* CO - calculated from SV x HR
* CI - CO corrected for BSA (based on input data on height/weight)
* SV - stroke distance multipled by aortic diameter (usually averaged over several beats, based on nomograms from patient height and weight data correlated to aortic dimensions from CT)
* SVI - stroke volume normalised for BSA
* FTc - flow time is the duration of forward flow of blood in the aorta, corrected to heart rate of 60. Normal = 330-360m/s
* MA - maximum acceleration - index of contractility (peak acceleration of blood flow in the aorta)
* PV - peak velocity. Normal = 90-120cm/s at 20yrs, 70-100cm/s at 45yrs, 50-80cm/s at 70yrs
Response
* low SV or FTC –> give fluid
* low PV –> give inotrope
* low PV + low FTc –> decrease afterload
Advantages
* Minimally invasive
* Provides real time measurements
Disadvantages
* May be inaccurate even if probe positioned appropriately e.g. coarctation, aneurysm, neuraxial anaesthetic (lower limb vasodilatation)
* Cannot be used in patients with IABP
* Should not be used in patients with known pharyngo-oesophageal pathology or injury
* Learning curve - significant inter and intraobserver variability
* Probe displacement requiring repositioning
* Difficult to use in awake patient
* Complications related to insertion of probe
One Lung Ventilation
Absolute Indications
* prevent damage or contamination of health lung e.g. abscess
* control distribution of ventilation e.g. bronchopleural fistula
* facilitate single lung lavage e.g. in CF
Relative Indications
* to improve surgical access
* lung surgery, minimally invasive cardiac surgery, thoracic aneurysms, VATS, oesophagectomy, diaphragmatic surgery, scoliosis surgery
Indications for right sided DLT
* surgery involving the left main bronchus - left pneumonectomy, left lung transplant left tracheobronchial disruption, left sided thoracoscopic surgery
* distorted anatomy of left main bronchus - aneurysm of descending thoracic aorta, tumour compression of left main bronchus
Lung isolation techniques
* Double lumen tube - right or left?, 35/37/39/41Fr
– 39 for average male, 37 for average female (1 size up or down for larger and smaller patients)
– risk of malposition, airway trauma, tension PTX
– may be difficult to place in abnormal/distorted airways
– not ideal for postoperative ventilation
– allows suction and bronchoscopy of isolated lung
– can provided CPAP to operated lung, can alternate OLV to either lung
– can insert even if FOB not available
* Bronchial blockers - coaxial or independent
– require use of FOB to confirm position and more time consuming for insertion and accurate positioning
– easier placement in difficult airways
– can allow selective lobar lung isolation and possibility for postoperative dual lung ventilation
– slow and incomplete collapse, suction not possible, bronchoscopy of isolated lung impossible, difficult to alternate OLV
* Single lumen tube advanced into right or left main-stem bronchus
– easier placement in emergencies and difficult airways
– bronchoscopy, suction and CPAP impossible to isolated lung
Confirmation fo DLT Placement
* Sequential clamping and auscultation
* Step 1 - inflate tracheal cuff to seal leak - PPV and auscultate to confirm bilateral air entry, obtain ETCO2 trace
* Step 2 - clamp tracheal limb and disconnect, inflate bronchial cuff and ventilate, auscultate to confirm unilateral ventilation and no audible air leak
* Step 3 - release tracheal lumen clamp and close port, auscultate to confirm resumption of bilateral air entry
* Can also use fibreoptic bronchoscope, especially for right sided DLT (to ensure sustained RUL ventilation)
Orthognathic Surgery e.g. bimaxillary osteotomy
Pre-operative
* most are young and fit
* occasionally OSA or syndromic
* airway plan - nasal tube with nasal prep
Intra-operative
* nasal tube with careful fixation + throat pack
* minimise bleeding - induced hypotension, head-up, ETCO2 low-normal, normothermia
* remifentanil, paracetamol + morphine
* surgical nerve blocks
* steroids
* haemostasis challenge
* suction under direct vision
* deep/SGA exchange/awake extubation - avoid pressure to jaw/face
Post-operative
* airway risk +/- nasal bleeding —> soft tissue oedema/haematoma
* PONV risk due to swallowing blood
* multimodal analgesia
* ?intermaxillary fixation
Park bench and Sitting positions
Park bench position - modified lateral position. Head flexed until the chin is almost at sternum, rotated contra-laterally to the lesion, and flexed 30 degrees laterally torward the contralateral shoulder (increases the angle between the atlas and foramen magnum).
Risks
* VQ mismatch (atelectasis of dependent lung)
* Brachial plexus injury
* Ear and eye injury
* Suprascapular nerve injury of the dependent shoulder
* Stretch injuries (axillary trauma) and decreased perfusion to the dependent arm
Sitting position aka Beach Chair position - improves surgical access to the posterior fossa by facilitating gravity assisted drainage of blood and CSF and decreasing ICP. Improves surgical orientation, access to the midline structures and decreases the amount of surgical retraction needed to gain access to deeper structures. Also used for some shoulder surgery.
Contraindications
* Absolute - V-A shunt, R–>L shunt
* Relative - PFO, uncontrolled hypertension, extremes of age, autonomic neuropathy
Risks
* Patients must be returned to supine position rapidly for resuscitative measures in case of an acute cardiovascular collapse
* Cardiovascular instability - venous pooling in legs, surgical stimulation near vital structures may result in variable cardiovascular responses
* VAE (site of surgery above the level of heart increases risk of air entrainment)
* Pneumocephalus
* Macroglossia - obstruction to venous and lymphatic drainage of the tongue because of flexed neck –> post operative respiratory obstruction
* Quadriplegia - prolonged focal pressure on the spinal cord secondary to the acute flexion of the head, compromise to the cord during episodes of significant hypotension
Ingested Food Bolus/Foreign Body
Concerns
* Patient - often paediatric so have parents to deal with as well, co-morbidities, aspiration risk? what is the FB? what urgency of removal
* Surgical - type of FB, location, plan - local trauma to GI tract, impaction/obstruction, systemic toxicity?
* Anaesthetic - induction method, maintenance, shared airway?
Management
* A-E approach - resuscitation and supportive care
* Investigations guided by presentation and history to guide urgency - 10-20% require endoscopic removal, very few require open approach
* Approach to patients and relatives
* Focussed anaesthetic history and examination
* MDT, senior support, trained assistant
* Additional support needed e.g. ENT?
* Warm theatre, paediatric equipment if paediatrics case
* RSI vs inhalational induction - if needing theatre, likely GA recommended
Performing a Nerve Block
Generic
* Block type (anatomical name, nerves blocked)
* Consent
* Equipment
* Monitoring
* Venous access
* Skilled assistant
* Access to resus/intralipid
* Ultrasound and/or nerve stimulator (0.5mA/0.1ms)
* Asepsis - chlorhexidine 0.5%
* ?LA to skin
* PREP-STOP-BLOCK
Specific
* Patient position
* Probe orientation and location
* Ultrasound views - Structures identified
* Needle type and size, angle of entry
* Needle endpoint (in plane/out of plane)
* Injection method (max 20ml/minute ideally)
* Choice of LA and volume
* Post block instructions
Peripheral Vascular Surgery
Peripheral Revascularisation vs Amputations
Pre-operative
* commonly cardiovascular disease + diabetes
* multiple co-morbidities + usually elderly
* high mortality with critical limb ischaemia
Intra-operative
* anaesthetic technique tailored to patient + co-morbidities
* large IV access +/- invasive BP
* neuraxial/regional or GA + block
* keep MAP >55
* multimodal analgesia
* propofol TCI + sedation if needed
Post-operative
* ongoing regional blockade post-amputation
* likely to need ongoing opioids
* ?ongoing oxygen for 24hrs for revascularisation
Pituitary Surgery
Transphenoidal Hypophysectomy
Pre-operative
* present with either mass effects of hypersecretion of hormones
* special considerations for acromegalic patients or Cushings patients
Intra-operative
* as for craniotomy
* throat pack following intubation +/- OG tube
* ?Moffett’s solution to nose
* risk of major haemorrhage
Post-operative
* codeine phosphate
* anti-emetic (avoid dex)
* head up
* nasal pack
* avoid PPV/BMV
* high risk of post-op DI —> desmopressin
* d/w endocrine re: replacement
POCT - Viscoelastic Coagulation Tests (ROTEM vs TEG)
ROTEM = Rotational Thromboelastometry
TEG = Thromboelastography
- Assessment of clotting of whole blood
- Small amount of blood at body temperature added to a heated cuvette (a little cup)
- Pin is suspended into the cup
- TEG rotates the cup around the pin
- ROTEM rotates the pin in the cup
- Impediment to rotation develops as the blood clots
- Connected with a mechanical-electrical transducer
- Degree of impediment is recorded as “amplitude” and displayed on a time vs amplitude graph
Parameters
* CT/R - time taken for the amplitude to start climbing
– initiation of clotting
– prolonged if clotting factor deficient, heparin, warfarin, direct thrombin inhibitors
– replace factors e.g. FFP, concentrates or antagonise anticoagulants
* CFT/K - time from clot initiation to 20mm
– amplification phase
– activity of clotting factors, effectiveness of fibrin polymerisation, platelet activity and Factor VIII activity
– prolonged in thrombocytopenia, platelet dysfunction, low fibrinogen or severe deficiency of other factors
– shortened in hypercoagulable states
– give cryoprecipitate, fibrinogen or platelet transfusion
* a-angle - TEG - slope from 2mm-20mm, ROTEM - slope at 2mm amplitude - determined by rate of reaction between platelets, fibrin and clotting cascade factors
– used as measure of fibrinogen activity
– measure of the “thrombin burst” or propogation phase
– decreased angle in low fibrinogen, poor fibrinogen polymerisation, thrombocytopenia or platelet dysfunction
– give cryo/fibrinogen
* MCF/MA - the point where the clot is at its thickest
– usually correlated with platlet count
– consider giving platelets or DDAVP if decreased
* TMA/MCF-t - time it takes to reach maximum clot strength
– limited utility (e.g. how long to keep pressure on the groin wound after removing an IABP)
* A10/A30/A60 - amplitude at a specific time
– surrogate marker of platelet function, platelet numbers and fibrin concentration
– decreased A10 with low fibrinogen, thrombocytopenia, platelet aggregation inhibitors
* CL/LY30 - clot lysis
– consider TXA if accelerated lysis
Handy Guide
* brandy tumbler - do nothing
* red wine glass - give FFP
* test tube - give platelets
* champagne flute - give cryo
* upside down martini glass - give TXA
Point of Care Testing
Diagnostic testing that is performed at or near to the site of the patient, leading to a potential change in the care of that patient.
- Blood gas analysis - see separate card
- Blood glucose - reaction with a chemical reagent produces a current which is measured and is directly proportional to the glucose concentration
- Blood ketones - measures beta-hydroxybutyrate in the blood through an electrical current produced when blood is mixed with a reagent
- Urinalysis - pads with reagent on are soaked with the urine sample and the color measured using reflectance colorimetry apart from specific gravity which uses a fibreoptic refractive index method
- INR testing - coaguchek - blood mixes with reagent and current is created until the blood has clotted
- ROTEM (rotating pin)/TEG (rotating cup) coagulation - see separate card
- Hb - haemocue - microcuvette contains 2 reagents which convert Hb into methaemoglobinazide, photometer than measures absorbance at 570 and 880nm
- Activated Clotting Time (ACT) - sample of blood mixed with coagulation activators - end point determined by the optical or mechanical properties of the clotting blood
- Urine pregnancy tests
- HbA1c
Advantages
* rapid data
* increase potential for real time management
* usually simple to use
* usually low risk
Disadvantages
* cost
* unauthorised use
* staff training
* sample handling errors
* potential to lead to serious health consequences if not performed properly
Post Op Nausea and Vomiting
Risk Factors
APFEL score
Patient related
- female
- age (not under ~3), teenage/young adult
- non smoker
- history of PONV
- history of motion sickness
- ?obesity
- preoperative anxiety
- intestinal obstruction, metabolic disturbance, uraemia
Anaesthesia related
- volatiles
- N2O
- opioids
- untreated pain
- increased doses of neostigmine
- mask ventilation causing gastric distension
Surgery related
- procedure - eyes, ENT, gynae, neuro, laparoscopic
- longer duration of surgery
Management
* Non pharmacological
– avoid gastric distension
– ensure adequate hydrate, minimise fasting
– acupressure
- Pharmacological
– minimise exposure to opioids/volatile e.g. multimodal analgesia, regional anaesthesia, TIVA, avoid N2O
– prophylactic antiemetics - single individual antiemetics reduce risk by ~20-40% (RR cyclizine/ondanstron 0.6, dex 0.55, droperidol 0.65, metoclopramide 0.8, prochlorperazine 0.7)
— avoid sedating anti-emetics in day case
— second antiemetics are additive not synergistic
— use multiple antiemetics with different mechanisms (70% reduction in relative risk is best that can be expected)
— rescue antiemetics are ineffective if already used prophylactically
– active treatment of hypotension if awake
Posterior Fossa Surgery
Pre-operative
* may have decreased GCS and impaired airway reflexes - assess pulmonary function
* assess ICP, fluid status, electrolytes and BM
* assess cardiovascular function
Intraoperative
* as for craniotomy
* NG if risk of post-op bulbar dysfunction
* monitor for VAE and nerve tract injury - SSEPs, MEPs
* avoid nitrous
* TIVA or volatile + remi
— TIVA - reduces CMRO2 and maintains auto regulation, reducing ICP, easily titrated during different phases of surgery, rapid smooth emergence with reduced PONV. Risk of awareness if IV dislodged, may be slow to wake, needs depth of anaesthesia monitoring
— volatile + remi - no effect on auto regulation in the normal clinical range, possible ischaemic preconditioning
* positioning - sitting/prone/lateral
* often long procedures
* increase analgesia/anaesthesia for pinning
* NMBA or remi to prevent coughing
* N.Saline maintenance - avoid dextrose containing solutions
* Vasopressor infusion to maintain MAP (metaraminol/phenylephrine)
* fully reverse with neuromuscular monitoring
* maintain anaesthesia until supine and out of pins
* deep emergence/airway exchange/remi technique to limit cough and hypertensive response
Post-operative
* can usually extubate and manage on neurosurgical ward
* if significant oedema or loss of bulbar function - keep asleep and allow recovery in ITU
* risk of airway obstruction
* risk of post-op impairment of respiratory drive
* post-op analgesia as for craniotomy
* oxygen
* anti-emesis
Prehabilitation (4-8 weeks)
Process of enhancing an individual’s functional capacity to enable them to withstand a forthcoming stressor through an MDT approach
Benefits include decreased length of stay, decreased post op pain and decreased post op complications.
Medical optimisation
* pre-op smoking cessation
* reduction in alcohol intake
* weight optimisation
* management of anaemia
* control of blood glucose
* optimisation of pharmacological therapy
Pre-operative physical exercise
* strength and aerobic exercises
Nutritional support
* pre-operative enteral nutritional support if malnourished
* pre-operative carbohydrate loading
Stress/anxiety reduction
* psychological support
* maximise patients motivation
* provision of information
Prep-Stop-Block
Step 1: Prep - preparation
- perform WHO sign in
- prepare LA solution, place in dedicated tray + hand to assistant
- position patient + equipment
- pre-scan if required
- don gloves + prep site (keep mark visible)
Step 2: Stop - stop moment
- “I’ve completed my prep, let’s stop before you block”
- Assistant - “let’s stop before you block”
- check block side - view surgical site mark, verbally confirm side + check consent form (+ ask patient if awake and unsedated)
Step 3: Block - perform block
- assistant hands tray back
- immediately perform black
- any delay = re-start (hand tray back to assistant)
Aims to decrease incidence of wrong side blocks.
Prevention of VTE
Risk factors
* Stasis-endothelial injury - indwelling venous device, surgery, major trauma/burns, prolonged travel, paralysis, varicose veins
* Thrombophilias e.g. factor V leiden, antiphospholipid syndrome, protein C/S deficiency
* Medical conditions - malignancy, pregnancy, postpartum, MI, CHF, CVA, obesity, IBD, nephrotic syndrome, personal history of VTE
* Drugs - COCP, HRT, chemotherapy e.g. tamoxifen
* Other factors - increasing age, smoking
Pathophysiology
* site of vascular trauma or sluggish blood flow
* accumulation of fibrin and platelets causes rapid growth of clot
* organisation of thrombus, reducing venous return and narrowing the lumen
Prevention of VTE
* Mechanical methods
– graded anti-embolism stockings - increase blood velocity, promote venous return
– intermittent pneumatic compression - mimic muscle pump effect of walking and promote fibrinolysis
– foot impulse devices - compress plantar venous plexus
* Pharmacological methods
– LMWHs
– UFH
– Warfarin
– Factor Xa inhibitors
* Patient education
* Use of regional anaesthesia
* Physiotherapy and nursing care
* Avoidance of dehydration
Prone Positioning
General management
* minimum 6 staff to prone (head, feet, 2 each side)
* disconnect infusions, monitoring and breathing system when proning to minimise injuries, accidental dislodgement
* roll with arms by side, arm care to avoid brachial plexus injury
* protect +/- pad eyes
* securely fastened reinforced cuffed tracheal tube
* care to avoid head rotation
* chest and pelvis support with abdomen free
* careful padding of pressure areas
* CPR + defib in prone position
Options for positioning
* Pillows
* Chest roll
* Pelvic roll
* Thoracic support/Montreal mattress
* Allen table/Jackson table
* Wilson frame
* Mayfield clamp and pins
* Pre-formed foam head support
* Gel ring/gel support/gel horseshoe
Adverse Effects
* Limited access to airway
* Increased airway pressure if abdomen splinted and reduced venous return
* Displacement of tubes/lines during proning
Complications
* Direct pressure injuries - skin necrosis, contact dermatitis, tracheal compression, salivary gland swelling, breast injury, injury to the genitalia, compression of the pinna, compression of the femoral neurovascular bundle
* Indirect pressure injuries - macroglossia and oropharyngeal injuries, swelling, mediastinal compression, visceral ischaemia - liver, pancreas, avascular necrosis of femoral head, peripheral vessel occlusion, limb compartment syndrome and rhabdomyolysis
* Ophthalmic complications - corneal abrasian, visual loss - central retinal artery occlusion, ischaemic optic neuropathy (? due to reduce venous drainage and increased interstitial fluid around the optic nerve)
* Peripheral nervous system - all superficial peripheral nerves are at risk from stretch or external compression (especially ulnar nerve, brachial plexus and lateral cutaneous nerve of the thigh)
* Central nervous system - caution not to overextend or overflex the c-spine, log roll if necessary. Risk of ischaemic stroke of brain and spinal cord with hypotension and arterial hypoperfusion
Rigid bronchoscopy
including management of inhaled foreign bodies
Pre-operative
* check for airway obstruction
* check for reflux - pretreat with PPI
* suitable as day case in some
* warn about post op cough, haemoptysis, sux myalgia
* may be emergency FB inhalation in child
Intra-operative
* full pre-oxygenation
* inhalational induction with maintenance of spontaenous ventilation
* benzo/opioid/propofol induction with FM or temporary use of SAD
* maintenance - TIVA, intermittent IV bolus, intermittent/continuous volatile - deep anaesthesia required
* local anaesthesia to the airway - spray lidocaine to cords
* oxygenation - jet (manual/high frequency), spontaneous assisted ventilation, HFNO (apnoeic oxygenation), IPPV through ventilating bronchoscope
* sux just prior to bronch/roc then sugammadex
* may need gas induction in theatre if potential obstruction
Post-operative
* biopsied side down
* sit fully upright once awake
* risk of blood clot causing obstruction
* risk of stridor in recory - nebulised adrenaline + ENT involvement
Robotic Assisted Surgery
Risks
* Pneumothorax
Scavenging
The removal and safe disposal of waste anaesthesia gases from the breathing circuit to avoid contamination of the theatre environment.
Continuous exposure of staff to anaesthetic gases has been implicated in:
* Cognitive impairment
* Spontaneous abortion
* Infertility
* Haematological malignancy (lymphoid)
Aldasorbers
* charcoal canisters containing activated charcoal - efficiently adsorb volatile agents (adsorb = molecules present in gas or liquid adhere to the surface of another phase)
* cannot remove nitrous oxide
* very low resistance
* cheap and easy to install in the expiratory limb of a breathing system
* not recommended for current use
Consists of
* gas collection assembly
– connects to APL valve and ventilator relief valve, collects gas vented from the circuit
– uses a 30mm connector - prevents accidental connection to the breathing system
* transfer tubing (wide bore)
* scavenging interface - structure depends on type of system
– open interface –> active scavenging systems use a pump or fan to generate a pressure gradient, drawing gas to the disposal assembly (open to air to prevent negative pressure being transmitted to the patient) –> must be low pressure and high flow to remove up to 75L/min
– closed interface –> passive scavenging systems use a series of positive and negative pressure relief valves (when gas pressure in the collection assembly is increased, positive relief valve opens and gas enters a reservoir bag, when gas pressure in the disposal assembly falls, negative relief valve opens and gas enters disposal assembly)
* more transfer tubing
* disposal assembly (high flow)
Passive disposal systems are no longer recommended because their outlets for waste anaesthetic gases cannot be strictly controlled, problems may arise due to direction/strength of wind, water vapour running back into the system or waste gases from one theatre passing back into another.
Strabismus Surgery
Pre-operative
* kids, ex-prem, post hyperthyroid, ?MH
Intra-operative
* GA, avoid sux
* oculocardiac reflex - glyco, ?block, normocapnia
* anti-emetic
Post-operative
* multimodal analgesia (clonidine)
Surgery for Epilepsy
Procedures aimed at resecting epileptogenic foci, disconnection surgeries to reduce seizure frequency and propagation and procedures aimed at reducing seizure frequency via neuromodulation.
History of chronic seizures that are refractory to medical therapy. MRI, EEG, neuropsychological evaluation required.
Types of surgery
* temporal resection - resection of anterior temporal lobe, amygdala and part of the hippocampus
* extratemporal resection - focal lesion, lobar or multilobar resections in the frontal, occipital and parietal lobes
* hemispherectomy - diffuse disease pathology affecting one cerebral hemisphere, risk of large volume blood loss
* laser interstitial thermal therapy - fibroptic catheter via a burrhole for MRI guided laser ablation of selected epileptogenic foci (GA required)
* disconnection surgery - total corpus callostomy, fewer risks than hemispherectomy
* seizure modulation devices - vagal nerve stimulators - exact mechanism of action unclear, usually left sided - battery replacement is quick and can be undertaken as a day case with a SAD
* deep brain stimulation - possibly reduces neuronal activity in the target area
Pre-operative
* thorough preoperative assessment
* look for sodium/platelet/white cell and LFT abnormalities associated with long term antiepileptic use
* FBC, U+Es, coagulation, LFTs, X match
* ECG - Brugada type ST changes common and J wave abnormalities associated with sodium channel blocking AEDs
* Clarify patients regular seizure type and pattern
Intra-operative
* maintenance of adequate cerebral perfusion pressure
* avoid increases in ICP
* arterial access and large bore peripheral access for craniotomies
* remifentanil infusion helpful
* consider use of normal saline rather than CSL if ketogenic diet being followed
* intraoperative invasive EEG monitoring may be required - do not give benzos, potent short acting mu-agonists may be required to activate interictal epileptiform activities (alf 20-100mcg/kg)
* reduce depth of anaesthesia during this period, warn of small risk of awareness, NMBAs may be used to prevent movement and interference
* intraoperative functional neuromonitoring - TIVA, reinforced ETT and bite block if MEPs monitored
* if seizures develop, cease stimulation, irrigate surgical field with ice cold saline, propofol boluses +/- benzos (in conjunction with neurophysiologist)
Post-operative
* delayed emergency common
* avoid large doses of opioids
* NSAIDs can be given if large blood loss not occurred and no other contraindications
Temperature Monitoring
Non electrical
* mercury - increases in volume proportionally as temperature increases, much higher usable range than alcohol
* alcohol - increases in volume proportionally as temperature increases, safer than mercury but measurable range less convenient
* bimetallic strips - different metals expand at different rates as they warm up, causing the strip to bend in one direction or the other
* bourdon gauge - as temperature increases, volume of gas in a tube increases, trying to turn the gauge
* liquid crystal - contains heat sensitive liquid crystals that change colour to indicate different temperatures
Electrical
* resistance wire thermometer (usually platinum) - resistance of materials increases with increases in with temperature, slow but highly accurate
* thermocouple - voltage produced when two disimilar metals come together, the voltage varies with temperature (usually copper/nickel alloy and copper construction) - linear response
* thermistor - semiconductor,as temperature increases, the resistance to flow of electrical current through the material decreases - non linear response
* thermography (IR thermometer) - detects proportion of radiation which is emitted in the IR specturm, proprtional to the amount of thermal energy present in the item being measured
Thoracic Surgery
Pre-operative
* respiratory assessment including functional capacity, lung function tests, exercise testing
* assessment of active cardiac conditions + cardiac risk factors
* prediction of perioperative mortality e.g. thoracoscore
Intra-operative
* indications for lung isolation (DLT vs BB)
* plan regional anaesthesia according to surgical approach e.g. thoracic epidural
* invasive monitoring (consider site of CVC)
* temperature + fluid management
* consider TIVA
* IV access in non dependent arm (if lateral)
Post-operative
* avoid post-op ventilation if possible
* multimodal analgesia
* physiotherapy
* post-op humidified oxygen
* HDU/ITU as appropriate
* CXR in recovery
Thyroid Surgery
Pre-operative
* thyroid status - history, examination, investigations - thyrotoxic?
* airway - history, examination, investigations - FNE/CT/USS)
— ask re: voice, positional dypnoea, exercise
— trache narrowed/deviated
— retrosternal
Intra-operative
* induction - NMBAs? Remi?
* intubation - specialised ETT for monitoring recurrent laryngeal nerve
* optimise surgical conditions - head up, hypotensive anaesthesia
* haemostasis challenge prior to extubation - supraglottic exchange
Post-operative
* PACU/HDU - monitor airway
* keep sat up
* monitor neck for bleeding
* measure calcium (PTH) - 2hrs post op
* prescribe T4
* analgesia - paracetamol/NSAIDs +/- opioids
* complications
— vocal cord palsy
— pneumothorax
— laryngeal oedema
— tracheomalacia
— thyroid storm
— haematoma - oedema causing obstruction
— hypocalcaemia
Tracheostomy
A tracheostomy is a surgical procedure that creates and opening in the anterior wall of the trachea to facilitate airway access and ventilation. Most tracheostomies are placed between the second and third tracheal rings.
Indications
Emergency
* acute upper airway obstruction with failed intubation or where intubation is impossible
* people who have undergone an emergency cricothyroidotomy
* select fractures of the oropharynx, face and neck (e.g. LeFort III fracture of the mid face)
* penetrating laryngeal trauma
Elective
* In critical care
— to assist weaning from artificial ventilation
— to facilitate withdrawal of sedation
— ongoing airway toilet/reduce secretion retention
— long term ventilation in patients with chronic conditions
— protect airway in neurological dysfunction
* Planned surgical traches
— severe OSA refractory to other therapies
— severe subglottic stenosis or vocal cord paralysis not responsive to conventional therapies
— prior to planned head and neck procedures
Contraindications
* Absolute - local sepsis of the anterior neck, absence of the cervical trachea, uncorrectable bleeding diathesis, patient refusal, tumour
* Relative - haemodynamic instability, severe hypoxaemia, severe coagulopathy/anticoagulation, platelet dysfunction/thrombocytopenia
* Percutaneous contraindications - gross distortion of the neck, suspected tracheomalacia or cartilage abnormalities, inability to palpate landmarks (short, fat neck), inability to extend neck, C-spine instability, immature trachea, blood vessels crossing the surgical field
Techniques
* Informed consent, monitoring, trained assistant, sterile field
* Increased FiO2 prior to procedure
* Palpation/ultrasound
* Lidocaine/adrenaline
* Open under GA though can be performed under local anaesthesia
— incision made above the cuff of the ETT
— cuff then deflated and pulled back slightly
— tracheostomy tube placed through the incision
— tracheostomy cuff inflated and tubing connected to ventilator/anaesthetic circuit
— capnography to confirm placement before removal of ETT
— bronchoscope to confirm device at least 2cm above the carina
* Percutaneous dilational with single dilator (Seldinger wire/Rhino) usually under sedation and paralysis
— tapered dilator modified Seldinger approach
— bronchoscope at ETT tube tip to visualise whole process
— bronchoscope tracheostomy tube after insertion to confirm position and to suction blood/secretions
* Percutaneous dilation all with multiple dilators (Seldinger wire/Ciaglia)
* Percutaneous with guidewire and dilating forceps
Complications
* Immediate
— Bleeding
— Pneumothorax or pneumediastinum from false passage creation or guide wire puncture
— Oesophageal perforation
— Tracheal ring fractures
— Loss of airway
— Airway fire (open procedure using electrocautery)
— Failure
* Early - bleeding, dislodgement, obstruction
* Late - erosion into vessels, tracheal dilatation, cuff-related stenosis, granule at a, stenosis related to traumatic insertion, cord/laryngeal dysfunction
National Tracheostomy Safety Project guidelines
Transfusion Reactions
Immediate Immunologic
* acute haemolytic reaction
* non haemolytic transfusion reaction (non haemolytic febrile reaction)
* allergic reaction to proteins, IgA
* anaphylaxis
* TRALI
Immediate Non-Immunologic
* bacterial contamination
* TACO (fluid overload)
* non immune haemolysis
* TRALI
* related to IV access - air embolism, thrombophlebitis
* related to infusion - hyperkaelamia, citrate toxicity –> hypocalcaemia, hypothermia
* coagulopathy - dilutional/consumptive
Delayed Immunologic
* acute haemolytic reaction
* transfusion associated graft vs host disease
* immune sensitisation
* immunomodulation
Delayed Non-Immunologic
* iron overload
* disease transmission - viral, bacterial, parasites, prion
______________________________________________________________________________________
Acute Haemolytic Reaction/ABO Incompatibility
* IgM binds to RBCs —> complement fixation
* intravascular haemolysis
* cytokine release, platelet activation, mast cell degranulation
* causes head/chest/flank pain, fever/chills/rigors, anaphylaxis, SOB, AKI, hypo/hypertension, N+V, urticaria, haemoglobinura, DIC
* stop infusion, support organs, maintain adequate renal perfusion, careful documentation and investigation
Delayed Haemolytic Reaction
* Minor incompatibilities
* IgG antibodies bind to surface antigen but do not activate complement
* extravascular haemolysis occurs over 7-21 days
* cause low Hb, jaundice (unconjugated hyperbilirubinaemia) and positive DAT test
Febrile Non Haemolytic (due to recipient antibodies reacting with donor antigens)
* leucocyte antigens bind to antibodies –> bind complement
* release of pyrogens IL-1/IL-6/TNF alpha
* causes pyrexia, shivering, general discomfort, headache, myalgia
* rarely may progress to hypotension, vomiting and respiratory distress
* slow or stop the infusion and give antipyretic
TRALI (due to donor antibodies reacting with recipient antigens)
* leucocyte antibodies in donor blood activate neutrophil granuloctye in immune form
* reactive lipid products released from the membranes of donor blood cells activate neutrophil granulocyte in non immune form
* activated neutrophil granulocytes –> lodge within pulmonary vascularture –> endothelial damage –> pulmonary capillary leak syndrome with exudation of fluid and protein into alveoli
* causes SOB, decreased sats, non cardiogenic pulmonary oedema, cyanosis, fever, tachycardia and hypotension
* ARDS either during or within 6hr of transfusion
Allergic Reaction
* common and usually mild
* presence of foreign proteins in donor plasma, IgE mediated
* cause pruritus and urticaria, with or without fever
* STOP transfusion and administer antihistamines
* if symptoms resolve in < 30 mins + no CVS instability –> restart (if symptoms recur, then abandon that unit)
* anaphylaxis may occcur in patients with hereditary IgA deficiency or pre-existing anti-IgA antibodies - reaction occurs immediately after commencing infusion - manage as per anaphylaxis
Transfusion Related Circulatory Overload (TACO)
* too much fluid or transfused too rapidly
* acute LVF - dyspnoea, tachypnoea, non productive cough, raised JVP, hypotension, tachycardia
* STOP transfusion, standard medical treatment for LVF diuretic, oxygen etc
Infections
* bacterial contamination - infrequent but can cause fulminant sepsis with high mortality
* caused by contamination during venepuncture or if an asymptomatic bacteraemia at time of donation
* causes high fever, rigors, erythema and cardiovascular collapse during or shortly after transfusion of the contaminated unit
* contaminated bags may seem unusally dark in colour or contain gas bubbles
* viral transmission
– hep A - negligible risk per unit of transfused blood
– hep B - 1 in 100000
– hep C - < 1 in 1000000
– HIV 1/2 - < 1 in 4000000
* prion infection - theoretical risk
Transfusion-associated graft-vs-host disease
* very rare
* 90% of cases are fatal
* donor-derived immune cells mount an immune response against host tissue
* cause maculopapular rash, abdominal pain, diarrhoea and abnormal LFTs + pancytopenia
Ultrasound Guided Techniques
Physics
In-Plane
- can see needle tip
- direct visualisation of whole needle/catheter
- longer needle path (risk of damage to structures)
- possibility of unrecognised tip
Out-of-Plane
- shorter path, increased patient comfort
- easier for catheters
- familiarity (vascular access ultrasound)
- possibly decreases nerve injury
- difficult to identify tip of needle
Artefacts
* Acoustic - reverberation, comet tails, speckle, mirror image
* Anatomic - misinterpretation
* Patient factors - obesity, air, oedema, muscle atrophy, abnormal anatomy
Optimising Image
* P - pressure
* A - alignment
* R - rotation
* T - tilt
* Gain
* Depth
Ventricular Optimisation
Preload
- inadequate - low CVP - haemostasis, IV fluid
- excessive - high CVP - diurese, ?CVVH
Afterload
- excessive - raised PVR/PAP - inhaled nitric oxide, sildenafil/prostacyclin
Contractility
- impaired - raised CVP, reduced PAP, reduced RVSWI - inotrope, 2nd Inotrope, adrenaline
Heart Rate
- inadequate - low HR - pacing
- excessive - high HR - antiarrhythmic
Heart Rhythm
- abnormal - arrhythmia - DCCV, antiarrhythmia
Coronary Perfusion Pressure
- low MAP, low SVR - vasopressor, increase volume, IABP, ventricular assist device
Vitreoretinal Surgery
Pre-operative
* range of patients
* previous eye surgery
Intra-operative
* block (most commonly) or GA (scleral buckle requires GA - risk of Brady)
* avoid nitrous if GA + gas used
* avoid tetracaine, high volume Sub-Tenons
* dark room
Post-operative
* tends to be day case
* positioning (to hold retina in place for healing)
* no flying while bubble in eye
* simple analgesia
Weaning from Mechanical Ventilation
Weaning = the process of liberating the patient from mechanical ventilatory support.
Predictors of weaning failure
* advanced age
* prolonged mechanical ventilation
* COPD
* increased MV
* positive fluid balance
General requirements
* lung disease stable/resolving
* low FiO2 (<0.5)
* low PEEP requireement (<5-8cmH2O)
* haemodynamic stability (little to no inopressors)
* able to initiate spontaneous breaths - good neuromuscular function
* able to protect airway
Predictors of success
* RR <30
* TV >5ml/kg
* FVC >15ml/kg
* MV <15L/min
* Maximum insp pressure <-30
* Other indices focussing on lung function
Spontaneous breathing trial - on 5+5 support
Optimising weaning success
* optimise respiratory muscle power - nutrition, avoid NMBAs, decrease steroid use and other contributors to critical illness-induced weakness, avoid exhaustion, normal electrolytes, normal FRC, physiotherapy
* decrease respiratory work - sit up, recrease respiratory demand (decrease CO2, correct metabolic acidosis), decrease resistance, increase compliance
* optimise ventilatory drive (stop sedation, consider causes from the brain to the NMJ)
* increase oxygenation and carrying capacity (sit up, avoid atelectasis, correct anaemia, correct acid-base disturbance)
* address cardiac dysfunction - removal of positive pressure ventilation may unmask LV dysfunction, treat ischaemia
* address sputum clearance - treat infection, chest physio, suction, bronch, mucolytics
