Basic Sciences Applied to Anesthesia (Anatomy, Physiology, Pharmacology, Physics and Equipment)
Anatomy
The candidate must know the surface landmarks for neuraxial and regional blocks: the cricothyroid membrane at C5–C6, the Tuffier line (intercristal line) usually crossing L4 or the L4–L5 space, and the anatomy of the brachial plexus relative to the anterior and middle scalene muscles and the subclavian artery. Know that the recurrent laryngeal nerve loops around the subclavian artery on the right and the aortic arch on the left, and that the phrenic nerve lies on the anterior scalene.
Physiology
Master oxygen delivery (DO2 = CO × CaO2), the alveolar gas equation, the oxyhemoglobin dissociation curve and its shifts, and the determinants of mean arterial pressure. Understand closing volume, functional residual capacity, and how induction alters FRC. Know the renal handling of sodium and the physiology of third spacing.
Pharmacology
Know receptor pharmacology of neuromuscular blockers, the context-sensitive half-time concept, and the hepatic and renal elimination of common agents. Understand the mechanism of malignant hyperthermia (ryanodine receptor 1) and the interaction of volatile agents with the sympathetic nervous system.
Physics and Equipment
Understand the ideal gas law, Boyle's law, laminar versus turbulent flow (Poiseuille and Reynolds), the Venturi effect, and the principles of pulse oximetry and capnography. Know the safety features of the anesthesia machine: the oxygen failure protection device, the pressure-relief valve, and the scavenging system.
Traps
Questions often confuse the level of the cricothyroid membrane, ask which nerve is at risk in a specific block, or test the difference between context-sensitive half-time and elimination half-life. Another classic trap is the effect of a left shift of the oxyhemoglobin curve on tissue oxygen delivery.
Worked Example
If a patient's hemoglobin is 10 g/dL and SaO2 is 100%, CaO2 ≈ (1.34 × 10 × 1.0) + (0.003 × 100) ≈ 13.4 + 0.3 = 13.7 mL/dL. If cardiac output is 5 L/min, DO2 ≈ 685 mL/min. A fall in hemoglobin to 7 g/dL reduces DO2 to about 480 mL/min, illustrating why anemia is a major determinant of oxygen delivery.