White Booklet - Anaesthetics Flashcards
What is the importance of knowing if a px has had previous anaesthetic?
- Hx of difficult intubation.
- Perioperative problems = awareness, dreams, jaundice.
- PONV
- Enquire about: suxamethonium apnoea and malignant hyperthermia.
What is suxamethonium apnoea?
Some px lack the enzyme ‘plasma cholinesterase’ in the blood which metabolises suxamethonium. In a normal person - metabolism is usually complete in 5-10 mins.
Px with SA remain paralysed for many hours after a standard dose of suxamethonium - they must be kept anaesthetised + ventilated until it is eliminated.
Genetic = E1u (must ask in anaesthetic + family history).
What is malignant hyperthermia?
Rare autosomal dominant inherited disease of skeletal metabolism (1 : 10-40,000).
MH is due to the release of abnormally high levels of calcium from the sarcoplasmic reticulum = causing increased muscle activity + rapid generation of ATP. This results in a rise in core body temperature and release of K+ = hyperkalaemia + risk of arrhythmias.
MH = Ca+ release from sarcoplasmic reticulum = muscle activity + ATP generation = rise in body temp = release of K+ = hyperkalaemia + arrhythmias.
What are the common triggers for MH?
Halothane and suxamethonium.
What mutation is thought to cause MH?
RYR1 mutation (ryanodine receptor gene).
What is the Rx for MH?
- Dantrolene 1mg/Kg (inhibits Ca2+ release)
- Wet sponge + fanning
- Hyperventilation (100% FiO2)
- Treat acidosis = 8.4% sodium bicarbonate
- Treat hyperkalaemia
What anaesthesia should be used for known MH?
- Regional anaesthesia
- Vapour free = propofol, thiopentone, opiods, atracurium, vecuronium
- TIVA
- Dantrolene = pretreatment
How long should an adult be fasted for prior to elective surgery?
Solids = 6 hours (milk is considered a solid).
Clear fluids = 2 hours
Is there a difference between children and adult fasting times before surgery?
With regards to solids - no. However breast milk = 4 hours (less fatty than normal milk).
Why are px fasted before surgery?
To avoid the risk of aspiration caused by vomit.
Silent regurgitation = neonates or neurological disorders.
What is Mendelson’s syndrome and which condition is this usually seen in?
Chemical pneumonitis caused by aspiration during anaesthesia - especially during pregnancy.
What are the effects of prolonged fasting?
- Hypoglycaemia - particularly a problem in children/ elderly/ diabetics.
- Hypovolaemia - due to dehydration.
- Increases organic response to trauma = increased insulin resistance, acute-phase response + loss of lean body mass.
What:
- Metabolic
- Anatomical
- Mechanical
Factors delay gastric emptying?
- DM, end-stage renal failure, obesity.
- Pyloric stenosis
- Increased IAP, pregnancy, obesity, trauma
Why is gastric emptying delayed in DM?
Peristalsis is delayed in diabetes.
Approximately how long does it take for:
- Gastric emptying
- Water to move through the stomach
- 4 hours
2. 10-20 minutes
How is the airway assessed and why is it important?
- Teeth = false or any missing?
- Mouth opening = less than 2 fingers breadth = difficult. (Wilson Score).
- Jaw protrusion = can lower incisors be brought anterior? (Calder Test).
- Neck = level of movement? (Wilson Score).
- Thyromental distance should be >6cm.
- Mallampati Score = I: soft palate + uvula + side pillars, II: soft palate + uvula, III: soft palate + base of uvula, IV: hard palate only. (III + IV = difficult intubation).
Important to assess how difficult it will be to intubate px.
What are the criteria for the Wilson Score?
- Fat
- Reduced head + neck movement
- Reduced mouth opening
- Receding mandible
- Buck teeth
= difficult intubation
Describe the Calder Test and what it suggests as difficult intubation?
Px asked to protrude mandible as far as possible = lower incisors can either progress anterior, in line with upper or posterior to upper.
In line + posterior to upper = difficult intubation.
Which conditions lead to difficult intubation?
Achondroplasia (dwarfism), Marfan’s syndrome, Noonan’s syndrome (no neck), obesity, rheumatoid arthritis.
What are the aims of pre-operative assessment?
- Check right px for surgery
- Plan appropriate anaesthesia
- Check they are optimised for surgery (identify co-morbidities)
- Assess airway
= all to prevent cancellation of surgeries due to the px not being fit for operation.
What risks should be considered in pregnancy anaesthesia?
- Increases risk of spontaneous abortion in early pregnancy.
- Increases risk of aspiration.
- Consider X-ray risk
What problems may smokers suffer through GA?
- Carbon monoxide in cigarette smoke + Hb = carboxyhaemoglobin. This reduces the oxygen carrying capacity of RBC = hypoxia, HTN.
- Nicotine stimulates sympathetic nervous system (fight or flight) = tachycardia.
- More likely to have broncho- / laryngo- spasm.
- More prone to post-operative atelectasis (lung collapse) = reduced FRC + increase mucus secretion. This also increases risk of pneumonia.
- V/Q (ventilation:perfusion) mismatch + pulmonary shunt.
Are smokers more likely or less likely to suffer PONV?
Less likely!
How long should you advise a px to stop smoking before surgery?
4-6 weeks - reduces the risk of peri-operative complications.
8 weeks = improves airway
2 weeks = reduces irritability - less chance of bronchospasm
24 hours = decreases carboxyhaemoglobin levels!
What needs to be considered in alcoholics with regards to GA?
> 50 units a week = induces liver enzymes - greater tolerance to anaesthetic drugs, therefore will require more.
Must consider physiological withdrawal effects - can give chlordiazepoxide.
How can these anti-hypertensives affect the px and the anaesthetic?
- ACEi
- Beta-blockers
- CCB
- Diuretics
- Anti-coagulants
ACEi
- Okay to take before + on the day of surgery + IV dose during.
- Some anaesthetists stop on the day as causes drop in BP.
Beta-blockers
- Okay to take before + on the day of surgery + IV dose during.
- Abrupt withdrawal may adversely affect HR + BP and precipitate MI.
CCB
- Okay to take before + on the day of surgery + IV dose during.
- BUT may exaggerate myocardial depressant effects of volatile agents + prolong non-depolarising muscle relaxants.
Diuretics
- Stop the day before surgery
- Check U+E before surgery = hypokalaemia? - lead to arrhythmias.
- Potentially cause diuretic-induced volume depletion (hypovolaemia) + hypokalaemia.
What considerations should be taken with regards to px taking anti-coagulants and anaesthetics?
- Why are they taking them and what surgery are they having?
- Check their INR
- Swap warfarin to heparin pre-operatively = allow INR to reach <1.5
What should be the INR of px having an epidural / spinal?
<1.3 = can result in bleeding into the spinal cord (epidural haematoma) + causing cord compression.
Which antibiotics prolong neuromuscular blockade?
Aminoglycosides + tetracyclines
What information do these investigations provide and when are they necessary?
- FBC
- U+Es
- LFTs
- Coagulation screen
- Group & save
- ECG
- CXR
- Echo
- Hx of bleeding loss, major surgery, cardioresp disease, men >50 years.
- Renal function = If on diuretics, digoxin, steroids, major trauma, burns, hepatic / renal disease, severe diarrhoea / vomiting.
- If jaundiced, malignancy, alcoholic.
- Liver disease, hx bleeding, on warfarin / heparin.
- All major surgery
- For cardiopulmonary disease, diabetes, age >50
- Known cardiopulmonary disease, pathology/symptoms i.e. pneumonia, thoracic surgery.
- Cardiac disease (LV function, valves).
What drug is given to carry out a ‘stress echo’ and what is its MOA?
Dobutamine (acts on B receptors in the heart) is given to increase HR and myocardial work and can assess the body’s response - type of CPX.
How long does it take for induction agents to induce loss of consciousness? What is the duration of action?
10-20 seconds.
Duration of action = 4-10 minutes.
What px can etomidate be used on and why?
Px with heart conditions - etomidate has haemodynamic stability therefore no rise in BP/HR.
What condition should etomidate NOT be used for and why?
Septic shock = continuous IV etomidate leads to adreno-cortical suppression (72 hours after a single bolus). Increased mortality in px with septic shock.
Which inducing agents:
- Px requiring a burn dressing change?
- Px undergoing arm operation under GA with an LMA?
- Px with a history of HF requires a GA?
- Px with intestinal obstruction requires emergency laparotomy?
- Px with porphyria comes for an inguinal hernia repair?
- Ketamine (used for single short procedures).
- Propofol (excellent airway suppression).
- Etomidate (haemodynamically stable).
- Thiopentone (for rapid sequence induction - emergency).
- Propofol (NOT thiopentone).
What is TIVA and what drug is used for this?
Why are these drugs NOT used?
- Ketamine
- Thiopentone
- Etomidate
‘Total IV Anaesthesia’ = IV drugs alone given for induction and maintenance anaesthesia.
Drug used = Propofol
- Hallucinogenic effect (“emergence phenomenon”).
- Hangover effects.
- Adreno-cortical suppression.
What are the disadvantages of induction agents?
- Px become apnoeic = need manual ventilation.
- Varying effects on BP (hypotension).
- May lose airway patency.
What are inhalation agents?
- Halogenated hydrocarbons
- Used to maintain amnesia + administered via vaporisers.
Which inhalation agents are INSOLUBLE? What are their advantages?
Sevoflurane and desflurane.
- Rapid onset of action
- Less hangover effect
- Faster emergence from anaesthesia
- Small blood-gas partition co-efficient
= lower blood-gas partition coefficient, faster onset and quicker recovery.
What is the only SOLUBLE anaesthetic and what is its disadvantage?
Halothene
- Require higher blood-gas partition co-efficient = larger amount of gas needed to be taken up in the blood before passing onto brain = more needed to take effect.
- Low MAC means that a higher/lower concentration will be needed for maintenance induction.
- Compound with low potency with have high/low MAC? - name a compound.
- Compound with high potency will have high/low MAC? - name a compound.
- LOWER
- High = Desflurane, Sevoflurane
- Low = Haloflurane
Halothane and Enflurane are older inhalation agents - therefore have high/low solubility?
High = higher blood:gas partition coefficient - need more to take effect.
Describe Sevo/Desflurane with regards to:
- Potency
- Solubility
- MAC
- Recovery time
- Low potency
- Low solubility
- High MAC
- Rapid recovery (doesn’t stay in tissues for long)
Why does the ‘hangover effect’ occur?
GA that is highly fat soluble accumulates in fat, slowly diffuses out, thus the effects carry on.
Why is Desflurane NOT recommended in children?
Very irritant = cough, breath holding, apnoea, laryngospasm + increased secretions.
What are the advantages and disadvantages of Isoflurane?
Advantages = Medium potency (low MAC), stable HR (least effect on organ blood flow), enhancement of muscle relaxation, less incidence of arrhythmias than halothane, CHEAP.
Disadvantages =
hypoxia/hypercapnia, initial respiratory irritation, hepatotoxicity (small chance - less than Halothane).
What are the indications for muscle relaxant use?
- If surgery requires it (e.g. open abdo surgery).
- RSI
- Endotracheal tube insertion
- Endoscopic examinations
- Ortho procedures
How can we assess the adequacy of neuromuscular blockade?
Electrode stimulator = on tragus (VII nerve) or wrist (Ulnar nerve).
Train-of-four stimulation.
What are the problems with using Suxamethonium?
What is suxamethonium also known as?
Muscle pains, suxamethonium apnoea, hyperkaemia = arrhythmia, malignant hyperthermia, histamine release (anaphylaxis).
- Succinylcholine
How are muscle relaxants reversed?
Neostigmine (2.5mg IV) + Glycopyrrolate
- Name 3 commonly used vaso-active drugs.
Fall in BP
- Px HR low give?
- Px HR high give?
- Ephedrine
- ^HR + ^contractility = ^BP
- acts on alpha and beta receptors
- indirect + direct action - Phenylephrine
- Vasoconstriction = ^BP
- direct action on alpha receptors
- drops HR - Metaraminol
- Vasoconstriction = ^BP
- most alpha receptors
- direct and indirect action - HR low = ephedrine
- HR high = metaraminol (longer acting than phenylephrine)
What vasopressors are used in severe hypotension / ICU?
- Noradrenaline
- Adrenaline
- Dobutamine
How does Dobutamine work and what conditions is it used for?
- Directly stimulates beta-1 adrenoreceptors = increases HR and force of contractions.
- HF due to reversible causes + Congestive HF (positive inotropic action).
Best vaso-active agent:
- Low BP, low HR
- Low BP, high HR
- Intensive care / severe sepsis
- Ephedrine.
- Metaraminol or Phenylephrine (only via vasoconstriction - smaller effect on heart).
- Adrenaline / noradrenaline / dobutamine.
What type of drug is adrenaline and what is its method of action?
- Endogenous catecholamine
2. Alpha receptors in BV to increase SVR + beta receptors in the heart to increase contractility + rate (SV).
Why is adrenaline used with LA? Where should it not be used?
- Reduce toxicity
- Reduce blood flow
- Extends duration
(Prolonged duration of anaesthetic action because less blood flow to remove LA from the area).
DO NOT use at extremities.
What 2 categories do LA fall under and name them.
- Esters
- Tetracaine (amethocaine) = AmeTop
- Cocaine
- Procaine - Amides
- Lidocaine
- Bupivacaine
- Prilocaine
- Ropivacaine
- Mepivacaine
Two ‘i’ = Amides
Which of the 2 LA groups are more likely to cause allergic reactions?
Esters
