Anesthesia Equipment, Monitoring, and Safety
What this domain tests
This domain checks whether you can verify gas delivery, interpret monitoring waveforms, and recognize equipment failure before it harms the patient.
Core rules
- Machine check: ASA checklist; verify oxygen supply, fail-safe and proportioning systems, minimum oxygen concentration, vaporizers, circuit leak and compliance, suction, and a self-inflating bag.
- Gas supply: oxygen pin index 2,5; nitrous oxide 3,5; air 1,5. Cylinders are color-coded with pressure regulators. The oxygen failure alarm sounds at low supply pressure, and the fail-safe cuts nitrous oxide.
- Capnography: normal square waveform; sudden zero means disconnection, obstruction, or cardiac arrest; exponential decay suggests leak; curare cleft reflects spontaneous respiratory effort; rising baseline suggests exhausted absorber.
- Pulse oximetry: unreliable with poor perfusion, motion, methemoglobin (plateau near 85%), carboxyhemoglobin (falsely normal or high), and nail polish.
- Arterial line: square-wave test. Overdamping gives a slurred upstroke and underestimates systolic pressure; underdamping gives overshoot and ringing.
- Electrical safety: the isolated circuit and line isolation monitor protect against macroshock; microshock risk rises with intracardiac catheters.
Worked example
During laparoscopy, ETCO2 suddenly falls to zero and the capnogram is flat while SpO2 is 99%. The first action is not to assume hyperventilation; look at the patient and circuit. If the chest is not moving and no breath sounds are heard, the tube may be esophageal or disconnected. Disconnection is confirmed by reconnection and return of the waveform; esophageal intubation is confirmed by absent sustained CO2 and treated by re-intubation. This sequence prevents treating a mechanical failure as a physiologic change.
Traps
Dismissing a flat capnogram as artifact; ignoring a high baseline CO2 from absorber exhaustion; using an underdamped trace to guide vasopressors; forgetting that nitrous oxide diffuses into air-filled spaces; assuming a line isolation monitor substitutes for good grounding.
Key points
- The ASA machine check verifies oxygen, fail-safe, vaporizers, circuit, and suction.
- Sudden flat capnogram means disconnection, obstruction, or arrest until proven otherwise.
- Methemoglobin plateaus the oximeter near 85%; carboxyhemoglobin can read falsely normal.
- Overdamped arterial lines underestimate systolic pressure.
- Isolated circuits and line isolation monitors reduce macroshock risk.