Give me a 7 mark answer on general anaesthesia From surgery standard book
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General Anaesthesia
(Bailey and Love's Short Practice of Surgery, 28th Edition)
Definition / The Triad
General anaesthesia is classically described as a triad of three components:
- Unconsciousness (Amnesia) - loss of awareness
- Analgesia - pain relief
- Muscle relaxation
Induction of General Anaesthesia
Induction is most frequently achieved by intravenous (IV) agents:
| Agent | Class | Key Features |
|---|---|---|
| Propofol | Di-isopropyl phenol | Smooth induction, haemodynamic stability, blunts autonomic reflexes, can be used as continuous infusion |
| Thiopentone | Barbiturate | Rapid induction, myocardial depression; reduces ICP - useful in neurosurgery |
| Etomidate | Steroid derivative | Good haemodynamic stability, brief action; concern over adrenocortical depression |
| Ketamine | Phencyclidine derivative | Preserves BP and respiratory reflexes, excellent analgesia - ideal for field anaesthesia; may cause emergence delirium |
Inhalational induction (e.g., sevoflurane - non-pungent) is preferred in:
- Children
- Needle-phobic adults
- Anticipated difficult airway
Maintenance of Anaesthesia
- Inhalational agents: isoflurane, sevoflurane, desflurane
- IV infusion: propofol (TIVA - Total IntraVenous Anaesthesia)
- Nitrous oxide: declining use due to risk of postoperative nausea/vomiting, expansion of air bubbles (harmful in eye/ear/abdominal surgery), mutagenicity concerns, and greenhouse gas effects
TIVA (Total Intravenous Anaesthesia) is popular for neurosurgery, airway laser surgery, cardiopulmonary bypass, and day-case anaesthesia due to lack of cumulative effect and excellent recovery profile.
Airway Management
Loss of muscle tone under GA means the patient cannot maintain their own airway. Options in order of escalation:
- Head tilt, chin lift, jaw thrust - short-term manoeuvres
- Guedel (oropharyngeal) airway - holds tongue forward, does NOT prevent aspiration
- Laryngeal Mask Airway (LMA) - supraglottic device developed by Dr Archie Brain; reliable, less traumatic than intubation; second-generation devices (ProSeal, i-gel) allow higher inflation pressures and have an oesophageal drain tube
- Endotracheal (ET) tube - secure, protected airway; cuff facilitates positive pressure ventilation and protects against aspiration
Complications of intubation:
- Failed intubation
- Accidental bronchial intubation
- Trauma to teeth, pharynx, or larynx
- Aspiration of gastric contents
- Delayed tracheal stenosis
Rapid Sequence Induction (RSI)
A predetermined IV dose + rapidly acting muscle relaxant to secure the airway quickly. Used when there is a high risk of regurgitation (e.g., emergency surgery, full stomach, delayed gastric emptying).
Muscle Relaxants
Neuromuscular blocking agents (NMBAs) allow surgical access by relaxing muscles, but require artificial ventilation.
| Type | Example | Mechanism | Use |
|---|---|---|---|
| Depolarising | Suxamethonium | Binds nicotinic ACh receptors → depolarisation | Rapid-sequence intubation (quick onset, short duration) |
| Non-depolarising | Atracurium, vecuronium | Competitive blockade at NMJ | Longer surgeries |
- Reversal: neostigmine or sugammadex at end of procedure
- Monitoring: peripheral nerve stimulator (to assess depth of block and confirm recovery before extubation)
- Suxamethonium adverse effects: hyperkalaemia, muscle pain, anaphylaxis, malignant hyperthermia (life-threatening)
Source: Bailey and Love's Short Practice of Surgery, 28th Edition, Chapter 23 (pp. 326-327)
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