Anesthesia machine checkout and intraoperative failures
Why examiners ask this
Equipment failures are the classic additional topic because they have one right first move: the patient comes before the machine. The examiner wants to hear that you keep the patient oxygenated and anesthetized with a self-inflating bag and IV agents while you troubleshoot, and that you know what the checkout would have caught. It tests organization and adaptability.
The 60-second answer
I follow the 2008 ASA pre-anesthesia checkout. Daily, or after the machine is moved or a vaporizer changed: a self-inflating bag and auxiliary oxygen cylinder available and working, suction adequate, AC power confirmed, the machine-mounted spare cylinder full, pipeline pressures at least 50 psig, vaporizers filled, a leak check of the low-pressure system between the flowmeters and the common gas outlet, scavenging tested, the oxygen monitor calibrated with its low-oxygen alarm checked, and fresh absorbent.1 Before every case I repeat the subset that changes between patients: suction, monitors and alarms, vaporizer levels, absorbent, a breathing-system pressure and leak test, a flow test through both valves, documentation, and a final review of ventilator settings as an anesthesia time-out.1 When the machine fails during a case, I do not troubleshoot first. I disconnect the patient, ventilate with the self-inflating bag on room air or the cylinder, switch to propofol so the patient stays asleep, and call for help and a technician. Once the patient is safe I work backward through the system to find the fault, or I replace the machine.
Decision points and the "why"
- Self-inflating bag first — it is independent of the machine, gas supply and electricity; it buys unlimited time to think.
- TIVA when the vaporizer is in question — if I cannot deliver or measure volatile, I prevent awareness with propofol and add processed EEG monitoring.
- Low inspired oxygen — I trust the analyzer, which the monitoring standard requires with a low-concentration alarm during every general anesthetic on a machine;2 I open the cylinder and disconnect the pipeline, because a crossed or contaminated pipeline continues to deliver the wrong gas even with the cylinder open; I ventilate with the bag on room air if the cylinder is suspect too.
- Pipeline failure — I open the backup oxygen cylinder, reduce fresh gas flow to conserve it, switch the ventilator from oxygen-driven to manual if it uses oxygen as a drive gas, and estimate time remaining: an E cylinder at 2000 psi holds about 660 L.
- Leak or disconnect — a low-pressure alarm and loss of capnography; the standard requires an audible disconnect alarm whenever ventilation is mechanical;2 I check the patient end first (tube cuff, circuit connections), then absorbent canister seating, vaporizer seating and the ventilator bellows.
- Stuck valve — an incompetent expiratory or inspiratory valve gives rebreathing: an inspired CO2 above zero and a capnogram baseline that does not return to zero. Exhausted absorbent gives the same picture, so I check its color and raise fresh gas flow, which flushes CO2 either way.
- Power failure — the machine runs on battery for about 30 minutes; I switch to manual ventilation, use a flashlight and portable monitors, and reduce battery load by turning off the ventilator.
The complication they will inject
Midway through a laparoscopic colectomy, the inspired oxygen fraction alarm sounds at 18%, the SpO2 falls to 89% and the pipeline gauge reads 50 psi. I tell the room the oxygen supply has failed, open the backup cylinder, and disconnect the pipeline hose. I ventilate by hand with low fresh gas flows to preserve the cylinder and start propofol in case the vaporizer output changes with the reduced flow. I send someone for more cylinders and inform the surgeon to pause. I call biomedical engineering, notify facility management because other rooms are affected, and I do not reconnect to the pipeline until the analyzer confirms the supply. If the cylinder fails as well, I ventilate the patient with the self-inflating bag on room air.
Pitfalls that cost points
- Describing troubleshooting steps before ensuring ventilation and oxygenation.
- Forgetting that the patient will wake up when the vaporizer stops delivering.
- Keeping the pipeline connected after a crossover: the higher pipeline pressure (50 psi) closes off the cylinder (regulated to about 45 psi) and the patient continues to receive the wrong gas.
- Not mentioning the self-inflating bag in the checkout; it is item 1 of the daily list.1
- Treating a rising inspired CO2 as hypoventilation.
Rapid-why
Q: Why does a hypoxic guard not guarantee safe gas? A: It ensures oxygen flow relative to nitrous but not that the gas in the oxygen pipe is oxygen; only the analyzer measures what is delivered.
Q: Why does a cylinder not drain when the pipeline is connected? A: Its regulator reduces pressure to about 45 psi, below the 50 psi pipeline, so the check valve stays closed.
Q: Why do vaporizers need correct seating? A: A poorly seated vaporizer is a common low-pressure leak and dilutes both the agent and oxygen.
Q: Why low flows on a cylinder? A: At 2 L/min an E cylinder lasts over 5 hours; at 10 L/min it lasts about an hour.
Numbers to know
| Item | Value |
|---|---|
| Pipeline pressure | ≥50 psig at checkout1 |
| Full O2 E cylinder | ~2000 psi, ~660 L |
| Cylinder time remaining | (psi/2000 × 660 L) ÷ flow |
| Low-pressure leak test | Daily, flowmeters to common gas outlet, method per manufacturer1 |
| Machine battery backup | ~30 min, model-dependent |
Links
- Hypoxic gas mixture and oxygen supply failure (coming), Capnography: waveforms and sudden loss of ETCO2, Ventilator modes, PEEP and IMV vs. pressure control, Intraoperative awareness and depth monitoring (coming), Malignant hyperthermia
- ASA Recommendations for Pre-Anesthesia Checkout Procedures (2008)
Sources
- 1.New Guidelines Available for Pre-Anesthesia Checkout · APSF, 2008 · apsf.orgReproduces the 2008 ASA Recommendations for Pre-Anesthesia Checkout Procedures, Tables 1 (daily, 15 items) and 2 (before each procedure).
- 2.Standards for Basic Anesthetic Monitoring · ASA, 2025 · asahq.orgLast amended October 15, 2025.
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.