AS4.1 | Pharmacology of Drugs Used in General Anaesthesia — Summary & Reflection

KEY TAKEAWAYS

General anaesthesia relies on a carefully balanced combination of agents. IV induction agents (propofol 1.5–2.5 mg/kg — most versatile; thiopentone 3–5 mg/kg — neuroanaesthesia; ketamine 1–2 mg/kg — haemodynamic instability/asthma, raises ICP; etomidate 0.2–0.3 mg/kg — cardiac stability, adrenal suppression) produce rapid unconsciousness. Inhalational agents (sevoflurane, isoflurane, desflurane, N₂O) are used for maintenance; potency is measured by MAC; low blood-gas partition coefficient = faster emergence. Opioids (fentanyl, morphine, remifentanil) provide analgesia and blunt laryngoscopy response; complemented by non-opioid adjuncts (paracetamol, NSAIDs, sub-anaesthetic ketamine). Muscle relaxants are classified as depolarising (suxamethonium — fastest onset, MH trigger, hyperkalaemia risk in denervation) or non-depolarising (vecuronium, rocuronium, atracurium — reversed by neostigmine+anticholinergic, or sugammadex for steroidal agents). The overall framework is balanced anaesthesia: multiple drugs at lower doses achieving all anaesthetic components while reducing individual drug toxicity. Malignant hyperthermia — triggered by volatile agents and suxamethonium — is managed with immediate trigger discontinuation and IV dantrolene.

REFLECT

You are called to assist in an emergency: a patient undergoing a laparoscopic cholecystectomy under isoflurane/suxamethonium anaesthesia is developing a rapidly rising end-tidal CO₂ (56 → 68 → 82 mmHg), a heart rate increasing from 78 to 122/min, and the anaesthesiologist notes increasing resistance to ventilation. Temperature is now 38.9°C and rising. What is your differential diagnosis? What immediate steps would you take to manage this crisis, and what is the specific pharmacological agent you would administer? Reflect on how the pharmacology you learned in this SDL directly informs each of your actions.