Anaesthetics Flashcards
Why are patients fasted before GA/operations?
- Empty stomach reduced reflux into oropharynx + aspirating into trachea
- Prevent pneumonitis and aspiration pneumonia
How long before operations are patients fasted for?
- 6 hours-> no food
- 2 hours before-> no clear fluids
What is pre-oxygenation?
- Few minutes of 100% oxygen during GA
- Gives O2 reserve for when unconscious + intubating
What is the triad of general anaesthesia?
Hypnosis + muscle relaxation + analgesia
What ‘premedications’ are given in GA?
- Benzos (eg midazolam)-> relax muscles + anxiety, amnesia
- Opiates (fentanyl)-> analgesia + reduce response to laryngoscope
- Alpha-2 adrenergic agonists (eg clonidine)-> sedation + pain
What is rapid sequence induction and when is it done?
- Quick + safe control of airway using drugs to induce neuromuscular blocking + immediate unresponsive + cricoid pressure
- Emergencies or when reflux risk (not fasted or pregnancy)
- Higher risk of aspiration
What is used for the hypnosis aspect of GA?
- IV-> propofol, ketamine, thiopental sodium
- Volatile agents-> sevofluorane
- Often IV for induction + inhaled to maintain
- Or TIVA (total IV anaesthetic)
What is TIVA?
Total IV anaesthesia-> propofol usually + better recovery
What is used for the muscle relaxation aspect of GA?
- Depolarising-> suxamethonium
- Non-depolarising-> rocuronium, atracurium
- Block NMJ
How can muscle relaxant agents used in GA be reversed?
- Neostigmine for NMJ blockers
- Sugammadex-> for non-depolarising
What is used for analgesia in GA?
Opiates-> fentanyl, alfentanil, morphine
What antiemetics are commonly used in GA?
- Ondansetron-> 5HT3 antagonist
- Dexamethasone-> steroid
- Cyclizine-> H1 receptor antagonist
When should ondansetron be avoided?
Long QT syndrome (or risk of)
When should dexamethasone be avoided?
Diabetes or immunocompromised
When should cyclizine be avoided?
Heart failure or elderly
How can the wearing off of muscle relaxants be tested during GA emergence?
Nerve stimulator-> test muscle response (ulnar/facial nerve) + see if train-of-four (if strong after 4 goes)
What are some of the risks of GA?
- Sore throat
- N+V
- Awareness
- Aspiration
- Dental injury
- Anaphylaxis
- CV events
- Malignant hyperthermia
What is Malignant hyperthermia?
Rare but fatal hypermetabolic response to anaesthetics (volatile + suxamethonium usually)
What can put a patient at risk of Malignant hyperthermia?
Family history-> autosomal dominant mutation
What are the symptoms and signs of Malignant hyperthermia?
- Increased temp
- Increased CO exhalation
- Tachycardia
- Muscle rigidity
- Acidosis
- Hyperkalaemia
What is a peripheral nerve block?
- Local anaesthetic into area around nerve
- Distal area numbed
- Done under US guidance
- May use nerve stimulator to check
What is a spinal block?
- Central neuraxial anaesthesia
- Local anaesthetic into CSF within subarachnoid space (L3/4 or L4/5)
Where is a spinal block inserted?
L3/4 or L4/5-> below spinal cord
How is a spinal block tested?
Cold spray along area
When might spinal block be performed?
- Caesarian
- TURPs
- Hip fracture repair
What is epidural anaesthesia?
- In labour or post-op after laparotomy
- LA infused into epidural space (outside dura)
- Goes into spinal cord + tissues
What medications are used in epidural anaesthesia?
Levobupivacaine +/- fentanyl
What is a dural tap?
When dura punctured + CSF leaks during epidural
What are the side effects of epidural anaesthesia?
- Hypotension
- Motor weakness in legs
- Nerve damage
- Infection
- Haematoma
- Headache (dural tap)
What are the risks of using epidural anaesthesia in labour?
- Prolonged 2nd stage
- Increased probability of instrumental delivery
What might indicate that epidural anaesthesia has been inserted into the wrong place?
Unable to straight leg raise-> may be in CSF (spinal block)
What is used for LA?
Lidocaine
When might LA be used?
- Skin sutures
- Minor surgery
- Dental + hand surgery
- LP
- Central line
What is endotracheal intubation?
- ETT is flexible tube with cuff (balloon) inflated by syringe
- Used for mechanical ventilation in GA
How might an endotracheal tube be guided in?
- Laryngoscope (eg McGrath)
- Bougie-> plastic
- Stylet-> stiff metal wire
- Awake fibre-optic intubation-> through nose or mouth, eg during trismus
What are supraglottic airway devices?
- Laryngeal mask airway (LMA) or I-Gel
- Alternative to ETT
- Tip at top of oesophagus + cuff around larynx
What is an oropharyngeal airway?
- Guedel-> rigid + create air passage between teeth + base of tongue
- Use to ventilate with face mask + bag before SAD/ETT
How are guedel airways inserted?
- Measured from centre of mouth to angle of jaw
- Upside down + rotate past tongue
What is a nasopharyngeal airway?
Flexible tube through nose + create airway to pharynx
How is nasopharyngeal airway measured?
Edge of nostril to tragus of ear
What is a major risk of nasopharyngeal airway?
Epistaxis
What is a contraindication of nasopharyngeal airway?
Base of skull fracture
How is a tracheostomy performed?
- Direct access to trachea through hole
- Held in place with stitches or soft tie
- Under GA or LA
- Outer (stays in place) + inner (can clean/change) tube
What are the 4 steps of managing a difficult airway?
- Laryngoscopy + tracheal intubation
- Supraglottic airway device
- Face mask ventilation + wake up
- Cricothyroidotomy
What is an arterial line and why is it used?
- Cannula in artery (eg radial)
- Accurately monitor BP
- Take ABGs
- NOT to put meds in
What is a central line?
- Central venous catheter
- Long thin tube with 3-5 lumens
- In large vein-> internal jugular, subclavian, femoral-> vena cava
- Give medications
- Take samples
What is a PICC line?
- Peripherally inserted central catheter
- Long thin tube into peripheral vein-> tip into IVC or RA
- 1-2 lumens
What is a tunnelled central venous catheter?
- Eg-> Hickmann line
- Long + thin-> enters skin on chest + into SC tissue-> tip in SVC/RA
- Cuff when more permanent
What is a pulmonary artery catheter?
- Through central vein, right heart then pulmonary artery
- Close cardiac function monitoring
What is a portacath?
- Type of central venous catheter
- Port under skin of chest to access
- Tip in SVC or RA
- Needle through skin into port for injections/infusions
- Long term eg chemo
What is the definition of pain?
Unpleasant sensory + emotional experience associated with or resembling acute or potential tissue damage
What should be considered even though pain is thought to be subjective?
- Everyone handles differently
- Accept the patient’s experience even when no underlying cause/tissue damage
What is a pain threshold?
The point at which a sensory input is described as pain
What is allodynia?
Pain experienced with sensory inputs that don’t normally cause pain
What is pain tolerance?
- The person’s response to pain
- 2 people may be affected differently to same stimulus
- Many biopsychosocial factors
What is the basic physiology of pain?
- Sensory (signal to pain receptors) + affective (emotional) aspects
- Nociceptors at ends of nerves detect damage-> along afferent nerves (primary afferent nociceptors)-> spinal cord
- Up cord via spinothalamic + spinoreticular tract-> to brain (thalamus + cortex)
- May be C fibre or A-delta fibres
What are C-fibres and what do they transmit?
- Unmyelinated + small
- Slow transmission
- Dull + diffuse pain
What are a-delta fibres and what do they transmit?
- Myelinated and large
- Fast transmission
- Sharp/local pain
What main sensory inputs generate a pain response?
- Mechanical (pressure)
- Heat
- Chemical (prostaglandins)
What is referred pain and why does it happen?
- Pain in 1 area that isn’t at site of damage
- As nerves can share innervation of multiple body parts
- Pain in 1 area creates more sensitivity in spinal cord from signals in other areas
What is neuropathic pain?
Abnormal function or damage to sensory nerves causing pain
What are the features of neuropathic pain?
Burning, tingling, pins + needles, electrick shocks, loss of touch sensation
What can be used to assess if pain is neuropathic?
DN4 questionnaire-> likely is if answer 4/10 or more
What can be used for neuropathic pain?
- Amitriptyline
- Duloxetine
- Gabapentin
- Pregabalin
- Tramadol-> for rescues/flares
- Physio
- Psych input
- Capsaicin cream
- Carbamazepine-> trigeminal neuralgia
What medications should be stopped pre-surgery?
CHOW
- Clopidogrel
- Hypoglycaemics
- OCP/HRT-> 4 weeks before
- Warfarin-> 5 days before + bridging
What medications should be altered pre-surgery?
- Insulin-> switch to variable rate
- Long term steroids-> give IV hydrocortisone
What medications should be started pre-surgery?
- VTE prophylaxis
- Antibiotic prophylaxis
- Bowel prep
What are the common sources of infection and problems post-surgery?
- Respiratory-> 1-2 days
- Urine-> 3-5 days
- Walk-> 4-6 days
- Wound-> 5-7 days
- Drugs-> 7+ days
What are some common post-op problems?
- Confusion
- Decreased UO
- N+V
- Bleeding
- DVT/PE
What does the WHO analgesic ladder consist of?
- Step 1-> non-opioids (paracetamol, NSAIDs
- Step 2-> weak opioids (codeine, tramadol)
- Step 3-> strong opioids (morphine, oxycodone, fentanyl, buprenorphine)
- Adjuvants can be used throughout
What are ‘adjuvant’ medications?
- Amitriptiline-> TCA
- Duloxetine-> SNRI
- Gabapentin-> anticonvulsant
- Pregabalin-> anticonvulsant
- Capsaicin creams
What dose of opioids are used for breakthrough pain?
1/10 to 1/6 of patient’s daily background dose (over 24 hours)
How much IV/IM/SC morphine is equivalent to 10mg of oral morphine?
5mg-> 1/2 dose for same effect
How much oral codiene or tramadol is equivalent to 10mg of oral morphine?
100mg-> 10x dose for equivalent
How much oral oxycodone is equivalent to 10mg of oral morphine?
6.6mg
How much IM/IV/SC diamorphine is equivalent to 10mg of oral morphine?
3mg
How much buprenophine (patch) is equivalent to 12mg/24 hours of oral morphine?
5mcg/hour
How much fentanyl (patch) is equivalent to 30mg/24 hours or morphine?
12mcg/hour
What benefits does post-op analgesia have for the patient?
- Pain relief
- Helps mobilise
- Ventilate lungs-> reduce infection + atelectasis
- Good oral intake
What is patient-controlled analgesia?
- IV strong opiate bolus when press button
- Stops responding for set time after each-> prevent overuse
- As required opiates stopped when on this
- Need naloxone, antiemetics + atropine around
What is chronic pain?
Pain present or recurring in 1 or more areas over 3 months or longer
What is the pathophysiology of chronic pain?
- Sensitisation of primary afferent nociceptors by frequent stimulation
- Increases activity of sympathetic NS
- Increased muscle contraction in response to pain
What are some options for managing chronic pain?
- Group exercise
- Acceptance and commitment therapy (ACT)
- CBT
- Acupuncture
- Antidepressants
- WHO analgesic ladder (when secondary to disease)
What can be used to predict a patient’s mortality on ICU?
APACHE-> acute physiology + chronic health evaluation
What is a complication of TPN?
Thrombophlebitis-> prevented by using central not peripheral line
What are the potential complications of ICU admission?
- Ventilation-associated lung injury
- Ventilation-associated pneumonia
- Catheter-related blood infections
- Catheter-related UTIs
- Stress-related mucosal disease (upper GI)
- Delirium
- VTE
- Critical illness myopathy
- Critical illness neuropathy
What is a normal pH value on ABG?
7.35-7.45
What is a normal PaO2 value on ABG?
10.7-13.3 kPA
What is a normal PaCO2 level on ABG?
4.7-6.0 kPa
What is a normal HCO3 level on ABG?
22-28 mmol/L
What is a normal base excess on ABG?
-2 to +2
What is a normal lactate level on ABG?
0.5-1mmol/L
What is FiO2?
- Fraction of inhaled O2
- 21% in room air
- Can increase with venturi masks
What does type 1 respiratory failure look like on ABG?
Normal pCO2 + low PaO2
What does type 2 respiratory failure look like on ABG?
High pCO2 + low PaO2
What does respiratory acidosis look like on ABG?
- Low pH
- High PaCO2
- Acute CO2 retention-> makes blood acidic (broken down to H2CO3)
What does respiratory alkalosis look like on ABG?
- High pH
- Low Co2
- High O2
- Raised RR or hyperventilation or PE
What does metabolic acidosis look like on ABG?
- Low pH
- Low bicarb
- Causes-> high lactate, high ketones, increased H+ (renal failure), low bicarb (diarrhoea or renal failure)
What does metabolic alkalosis look like on ABG?
- High pH
- High bicarb
- Loss o
What can cause respiratory alkalosis?
Raised RR or hyperventilation or PE
What can cause metabolic acidosis?
- high lactate
- high ketones
- increased H+ (renal failure)
- low bicarb (diarrhoea or renal failure)
What can cause metabolic alkalosis?
- Loss of H+ (vomiting)
- High aldosterone causing H+ loss-> Conn’s, cirrhosis, HF, loop or thiazide diuretics
What can cause high bicarb?
Chronic CO2 retention-> takes a while to be produced in kidneys so not raised if not chronic
What is acute respiratory distress syndrome?
Severe inflammation of lungs secondary to sepsis or trauma
What is the pathology of acute respiratory distress syndrome?
- Atelectasis-> alveoli + tissue collapse
- Pulmonary oedema
- Decreased lung compliance-> less inflation
- Fibrosis
What are the symptoms and signs of acute respiratory distress syndrome?
- Distress
- Hypoxia not responding to therapy
- Bilateral infiltrations on CXF
How is acute respiratory distress syndrome managed?
- Respiratory support
- Prone-> improves blood flow + secretion clearance
- Fluid management
- PEEP-> positive end expiratory pressure to prevent further lung collapse
What is PEEP?
- positive end expiratory pressure -> pressure remains in airways after exhalation
- to prevent further lung collapse
- can use in nasal cannulae, NIV, mechanical ventilation
What are some options for respiratory support?
- High flow nasal cannulae
- Venturi mask
- Face mask
- Non-rebreathe mask
- NIV-> CPAP or BiPAP
- Mechanical ventilation-> ETT, tracheostomy
- Extracorporeal membrane oxygenation?
What is BiPAP?
Cycle of high + low pressure used-> IPAP + EPAP (inspiratory + expiratory)
What is CPAP?
- Continuous pressure to keep airway expanded
- Maintains when likely to collapse
- Similar to PEEP
What are the settings on mechanical ventilation machines that can be altered?
- FiO2
- RR
- Tidal volume
- Inspiration:expiration
- Peak flow rate
- Peak inspiratory pressure
- PEEP
What are the different modes on mechanical ventilation machines?
- Volume-controlled-> tidal per breath
- Pressure controlled
- Assist controlled-> breaths triggered by patient or machine
- CPAP
What is extracorporeal membrane oxygenation?
- Blood through machine where O2 added + CO2 taken
- Like dialysis
- Rarely used
What is cardiac output?
- Stroke volume x heart rate
- Preload + afterload + contractility + heart rate
- Volume of blood exiting heart after each contraction
What is preload?
Amount that the heart muscle is stretched when filled with blood (pre-contraction)
What is afterload?
- Resistance the heart overcomes to eject blood from the LV
- Resistance after aortic valve
What can raise the afterload?
- Aortic stenosis
- HTN
What is contractility?
Strength of the heart muscle contraction
What is systemic vascular resistance?
Resistance in circulation that the heart overcomes to pump blood around
What is the stroke volume?
Volume of blood ejected with each beat
What is the mean arterial pressure?
- CO + SVR
- Average BP through whole cycle
- Need for adequate tissue perfusion
When should fluid status be monitored?
- Acutely unwell eg sepsis
- When suspect overload-> CHF, pulmonary oedems
- Before giving inotrope + vasopressor meds
How can fluid status be monitored?
- Input-output chart
- Weight after diuretics
- Central venous pressure-> estimates preload
What are inotropes?
Meds that alter the contractility of the heart
What are positive inotropes?
- Increase heart contractility, output + MAP
- Given when low cardiac output
- Egs-> adrenaline, milrinone, levosimendan
What are negative inotropes?
- Reduce contractility of heart
- Egs-> CCBs, beta blockers, flecainide
What are vasopressors?
- Vasoconstrict + increase SVR
- To improve BP + tissue perfusion
- EGs-> noradrenaline, vasopressin, adrenaline, ephedrine, metaraminol, phenylephrine
What are antimuscarinics?
- Block acetylcholine receptors
- Egs-> Glycoryronium, atropine
What is an intra-aortic balloon pump?
- Used in cardiogenic shock, ACS or surgery
- Mimic heart contractions-> inflate in diastole + deflate in systole
What are the indications for acute dialysis?
AEIOU
- Acidosis
- Electrolyte imbalance-> eg hyperkalaemia
- Intoxication
- Oedema
- Uraemia
What is haemodialysis?
- Blood through semi-permeable membrane + solute out into dialysate (fluid)
- Acute, continuous (24 hours) or intermittent (eg 3-12 hours then break)