Basic Sciences Relevant to Anaesthesia Practice
What you must understand
Expect integrated physiology, pharmacology, and physics. Key areas: respiratory (compliance, resistance, V/Q mismatch, shunt vs dead space, oxygen cascade, hypoxic pulmonary vasoconstriction), cardiovascular (Frank-Starling, preload/afterload, cardiac output determinants), renal and fluid compartments (Starling forces, osmolality vs tonicity), and acid-base (Henderson-Hasselbalch, anion gap, compensation logic). For physics, know gas laws (Boyle, Charles, Dalton, Henry), flow regimes (laminar vs turbulent, Poiseuille vs Reynolds), and the behaviour of gases in cylinders and vaporisers.
Traps in questions
- Confusing shunt (perfused, unventilated - poorly responsive to oxygen) with dead space (ventilated, unperfused).
- Mixing osmolality (particles per kg solvent) with tonicity (effective osmoles).
- Forgetting that hypoxic pulmonary vasoconstriction diverts blood from poorly ventilated lung.
- Applying laminar flow equations where turbulence dominates.
Worked rule of thumb
Use the oxygen cascade rule: delivered oxygen depends on FiO2, then alveolar ventilation, then diffusion, then V/Q matching, then carriage. If a patient is hypoxaemic despite high FiO2, suspect shunt - oxygen therapy has limited effect because blood bypasses ventilated alveoli.