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
