Anesthesia Equipment, Monitoring, and Safety
What you must understand
Know the anesthesia machine as a gas-delivery system: oxygen supply (pipeline vs cylinder, fail-safe and hypoxic guard), vaporizers (variable bypass, agent-specific, interlock), the breathing circuit (circle system with CO2 absorber, unidirectional valves), and the ventilator (bellows, pressure vs volume modes). Understand the scavenging system and the low-pressure leak test. Learn the monitors: pulse oximetry principles (absorption of red/infrared light), capnography waveform and its phases (I–IV), ECG and ST analysis, NIBP vs invasive arterial pressure, and depth-of-anesthesia monitoring. Understand electrical safety (microshock, grounding, isolated circuits), alarm management, and the critical-incident framework (e.g., anesthesia awareness, malignant hyperthermia, oxygen failure).
Traps in questions
Capnography traps dominate: an abruptly absent waveform suggests disconnection or esophageal intubation, while a gradually rising baseline suggests exhausted CO2 absorbent or rebreathing. A "curare cleft" indicates spontaneous respiratory effort during paralysis. Pulse oximetry traps: it lags behind true saturation and is unreliable with poor perfusion, dyshemoglobinemias (CO poisoning reads falsely normal), and motion. Vaporizer traps: desflurane has a heated, pressurized design; interlock prevents two agents simultaneously. Watch questions that assume a low-pressure alarm means a leak - it may mean disconnection or a closed APL valve.
Rule of thumb
Use the capnography waveform as your first-line "is the tube in the trachea and is gas moving" monitor. For any unexplained desaturation, check DOPE: Displacement, Obstruction, Pneumothorax, Equipment failure.
Worked example: During maintenance, EtCO2 rises from 35 to 48 mmHg with a rising inspiratory baseline. This suggests rebreathing from exhausted absorbent; check and replace the CO2 absorber.