Anaesthesia and Pain Medicine: Pharmacology, Airway and Analgesia
Core concepts
Candidates must understand the pharmacokinetics and pharmacodynamics of induction agents, volatile agents, neuromuscular blockers, opioids and local anaesthetics. Know the context-sensitive half-time concept, minimum alveolar concentration and factors that alter it, and the triad of anaesthesia: hypnosis, analgesia and muscle relaxation. Be able to describe a structured airway assessment and a failed intubation algorithm, including supraglottic rescue and front-of-neck access.
Understand preoxygenation and apnoeic oxygenation, rapid sequence induction with an appropriate induction agent and suxamethonium or rocuronium, and the management of anaphylaxis, malignant hyperthermia and local anaesthetic systemic toxicity. For local anaesthetics, know maximum safe doses with and without adrenaline and the role of intravenous lipid emulsion.
Pain medicine requires familiarity with multimodal analgesia, the WHO analgesic ladder, opioid equivalence and adverse effects, neuropathic pain agents, and the biopsychosocial model of chronic pain. Understand patient-controlled analgesia, regional techniques and the assessment of pain in patients unable to self-report.
Traps in questions
- Confusing MAC with an equipotent dose for all agents; MAC values differ and are additive.
- Forgetting that adrenaline-containing solutions raise the maximum safe local anaesthetic dose.
- Assuming a normal airway examination excludes difficulty; predictors are poorly sensitive.
- Missing that local anaesthetic toxicity can present with perioral tingling and seizures before cardiovascular collapse.
- Underestimating opioid accumulation in renal impairment, particularly with morphine metabolites.
Worked example
A 70 kg patient requires lidocaine without adrenaline. Using 3 mg/kg, the maximum is 210 mg. A 1% solution contains 10 mg/mL, so the maximum volume is 21 mL. With adrenaline the limit rises to 7 mg/kg, giving 490 mg or 49 mL of 1%. Rule of thumb: always state the concentration-to-milligram conversion before calculating volume.