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
Briefly explain the history of anaesthetics
• No modern anaesthetics were used before the mid-19th century
o Early forms:
Alcohol
Strangulation
Mesmerism
o Ether and nitrous oxide (N2O) had been used recreationally; serendipitous finding as anaesthetics
1842: first reported surgery with ether
1844: first reported use of dental surgery with N2O as analgesic
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
