Veterinary Anesthesia: Core Physiology and Drug Selection
What the exam expects
A candidate must integrate anesthetic depth assessment, cardiorespiratory physiology, and pharmacology rather than memorize isolated facts. Know the MAC concept (alveolar concentration at which 50% of patients do not move to a noxious stimulus), its species differences, and the factors that shift effective dose: hypothermia, hypotension, concurrent opioids, and age reduce MAC; young healthy animals and hyperthermia raise it. Understand the dose-response consequences of decreased cardiac output on IV induction agents-reduced hepatic clearance and slower redistribution prolong effect.
Monitoring and depth
Be fluent in depth signs (jaw tone, palpebral reflex, eye position, respiratory pattern) and their limits; no single sign is reliable across species and drug combinations. Tie monitoring to physiology: capnography reflects ventilation and perfusion, pulse oximetry fails in poor perfusion and motion, and blood pressure interpretation depends on the measurement method (Doppler vs oscillometric vs direct).
Common traps
Questions often test whether you can identify which parameter changes first. A classic trap is assuming an anesthetized patient with a normal SpO2 is adequately ventilated-hypoventilation raises PaCO2 before desaturation appears. Another is attributing bradycardia to depth when it reflects a vagal response to traction or an opioid effect.
Worked rule of thumb
Use the "MAC fraction" approach: end-tidal agent concentration divided by species MAC estimates depth. A dog at 1.4% isoflurane with MAC ~1.3% is at ~1.1 MAC-adequate for surgery but light for a noxious stimulus; adding an opioid or local block lowers the required MAC substantially, allowing reduction of vaporizer setting before reaching for a second inhalant.
Key concepts to name
Uptake and distribution, second gas effect, concentration effect, ventilation-perfusion mismatch, functional residual capacity, induction agent redistribution, and species-specific MAC values.