Anaesthesia Flashcards
Explain, from the perspective of the patient and of the surgeon, why we need anaesthetics
• For the patient: o No pain o No traumatic memory of surgery • For the surgeon: o Patient is immobile; can perform complex procedures more easily
What are the 3 key components of anaesthesia? Are there other effects - if so, what are they? Are these effects reversible?
• 3 key components: o Hypnosis – loss of consciousness o Amnesia – no memory formation o Immobility – no response to a painful stimulus • Other effects: o Analgesia o Sedation o EEG slows o Heart rate stabilises • Effects are reversible • Not just one state; it’s the culmination of multiple effects
Describe the theory of the 4 stages of anaesthesia
4 stages:
- Analgesia – dream-like state
- Excitement – increased muscle tone, heart rate, and blood pressure
- Anaesthesia – loss of consciousness; immobility; no memory formation
- Cessation of breathing – can be fatal, is avoided based on dosage alterations
Describe the stages of anaesthesia in practise
In practice:
1. Induction – normally via propofol
2. Maintenance – via N2O (a volatile anaesthetic)
3. Recovery
• Induction gets you to stage 3; may not notice stage 1-2
List the ideal qualities of an anaesthetic from the patient’s perspective
• Unconscious; no pain, memory, or anxiety • Fast induction with fast recovery • No undesirable side effects, e.g.: o Airway irritation o Nausea o Vomiting o Acidity
List the ideal qualities of an anaesthetic from the surgeon’s perspective
• Immobility
• Relaxed muscles
o Easy to slice into and operate on
• Non-inflammable and non-explosive
List the ideal qualities of an anaesthetic from the anaesthesiologist’s perspective
- Potent
- Can quickly adjust the depth of anaesthesia
- Regular breathing and heart rate
- High safety margin – no deaths
- Cheap, stable, easily stored
List the types of intravenous anaesthetics
- Etomidate
- Alphaxalone
- Propofol
- Ketamine
- Pentobarbital
- Thiopental
List the types of inhalant anaesthetics
- Nitrous oxide
- Halothane
- Xenon
- Isoflurane
- Desflurane
- Sevoflurane
- Enflurane
Why is classifying anaesthetic by administration route not ideal?
- Not the best way to classify them
- Large structure diversity and no obvious relationship between structure and function
- Neurosteroids are the only known endogenous anaesthetics
Explain the history and use of inhalational anaesthetics
• N2O – first in use; still used today
• Ether had side-effects and chloroform was worse
• Cyclopropane was highly unstable
• 1950s-now:
o Fluorine-based inhalants
o Halothane not used much anymore – causes liver toxicity
Explain the history and use of intravenous anaesthetics
• Barbiturates: have been used, even for death penalty and as a sedative/anxiolytic
o Mostly replaced as anaesthetic by propofol
• Benzodiazepines: sedative, anxiolytic
• Short duration of action – good for anaesthetics
o Notably etomidate, propofol
• Long duration of action – good as sedatives
Define and explain MAC and the applications of MAC
• MAC = minimum alveolar concentration
o Minimum concentration of vapour in the lungs which produces immobility/hypnosis in 50% of subjects
High MAC50 = low potency
Low MAC50 = high potency
o MAC for inhaled anaesthetics producing immobility (MAC-immobility) is considered a standard measure of anaesthetic potency
Plasma concentrations (Cp50-immobility) for intravenous agents can be evaluated in a similar manner
• Analogous potency measurements for hypnosis (MAC-awake or Cp50-awake) have been documented for many anaesthetics
• 1 atmosphere is the maximum alveolar concentration you can get; anything above 1 can never reach MAC
Describe the unitary theory of anaesthesia
• Meyer-Overton correlation shows that all anaesthetics have a hydrophobic site of action
o Suggests:
Anaesthetics act on hydrophobic sites of proteins or on lipid membranes
o Together with the diversity of anaesthetic structures, it suggests that:
All anaesthetics act through a common molecular mechanism
The assumption was that anaesthetics dissolve in the lipid membrane of neurons, and affect neuronal activity by perturbing their membrane
List the issues with the unitary theory of anaesthesia
- Recently discovered anaesthetics are less potent than predicted by their lipid solubility
- Anaesthetics can bind to proteins (in a way consistent with Meyer-Overton correlation)
- Mutations in some proteins impair anaesthetic effects
- Enantiomers (S- and R-) pairs of chiral anaesthetic molecules have different potencies
