PH3.1 | PH3.1 | General Anaesthetics and Pre-Anaesthetic Medication — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

General anaesthesia is a pharmacologically engineered state of unconsciousness, analgesia, and muscle relaxation (the anaesthetic triad), achieved by balanced use of multiple agents. Mechanistically, most agents (except ketamine) act via GABA-A potentiation (Cl⁻ influx) or NMDA inhibition. Inhalational agents (halothane, isoflurane, sevoflurane, desflurane, nitrous oxide) are characterised by their MAC (potency) and blood-gas partition coefficient (speed of onset/recovery). IV agents include thiopental (barbiturate), propofol (anti-emetic, TIVA), etomidate (haemodynamic stability, adrenal suppression), ketamine (NMDA antagonist, dissociative, contraindicated in raised ICP/hypertension), and midazolam (benzodiazepine, reversible with flumazenil). Pre-anaesthetic medications include anticholinergics (atropine/glycopyrrolate), benzodiazepines, opioids, antiemetics, and aspiration prophylaxis. Malignant hyperthermia — triggered by volatile agents + succinylcholine — requires immediate dantrolene.

REFLECT

Consider a scenario where you are asked to recommend a pre-operative medication chart for a 45-year-old patient with poorly controlled hypertension and known coronary artery disease, scheduled for an elective laparoscopic cholecystectomy. Which general anaesthetic agents would you specifically recommend avoiding and why? Think through each limb of the anaesthetic triad and how the patient's cardiovascular risk changes your agent selection for each. What would you write in the pre-medication orders to reduce the cardiovascular risk of induction?