Anesthesia machine checkout and intraoperative failures
Stem
A 58-year-old woman, 70 kg, with COPD, is your first case of the day for an open ventral hernia repair under general anesthesia. Overnight the anesthesia machine in your room was moved for floor cleaning, and a technician swapped one of the vaporizers. The patient is waiting in the holding area, and the room is otherwise set up.
Question
What does your machine checkout include before she comes into the room, and what is your plan if the machine fails during the case?
Ideal answer
HeadlinePatient before machine: a working self-inflating bag and auxiliary oxygen cylinder first, then the full 2008 ASA daily checkout, as it was moved.
- Supply and power: suction adequate, AC power, machine-mounted spare cylinder full, pipelines at least 50 psig,1 a backup for supply failure.
- Gas path: vaporizers filled, swapped one too, low-pressure leak check between flowmeters and common gas outlet, scavenging tested, fresh absorbent,1 because a reseated vaporizer can leak.
- Oxygen monitor calibrated, low-oxygen alarm checked: it catches a hypoxic mixture.
- Before every case, the subset: suction, monitors and alarms, vaporizer levels, absorbent, breathing-system pressure and leak test, flow test through both valves, documentation, ventilator settings as an anesthesia time-out.1
- Failure mid-case: ventilate first, troubleshoot later. Disconnect, bag on room air or cylinder, propofol to keep her asleep, help, a technician; then fix or replace the machine.
Breaking down the answer
- Why the bag leads — independent of machine, gas supply and electricity, it buys unlimited time to think; failures have one right first move, and saying it first shows organization and adaptability.
- TIVA when the vaporizer is in question — if I cannot deliver or measure volatile, propofol prevents awareness, with processed EEG monitoring added.
- Low inspired oxygen — I trust the analyzer, required with a low-concentration alarm on every machine general anesthetic;2 cylinder open, pipeline disconnected, as a crossed or contaminated pipeline keeps delivering; bag on room air if the cylinder is suspect too.
- Pipeline failure — backup oxygen cylinder open, fresh gas flow reduced, ventilator to manual if oxygen drives it, and time remaining estimated: an E cylinder at 2000 psi holds about 660 L.
- Leak or disconnect — low-pressure alarm and lost capnography; the standard requires an audible disconnect alarm during mechanical ventilation.2 Patient end first (cuff, circuit connections), then canister seating, vaporizer seating, ventilator bellows.
- Stuck valve — an incompetent expiratory or inspiratory valve gives rebreathing: inspired CO2 above zero, a baseline that does not return. Exhausted absorbent looks the same, so I check its color and raise fresh gas flow, which flushes CO2 either way.
- Power failure — about 30 minutes of battery; manual ventilation, flashlight, portable monitors, and the ventilator off to reduce battery load.
Follow-up question
An hour into the case, the inspired oxygen fraction alarm sounds at 18%, the SpO2 falls to 89% and the pipeline gauge reads 50 psi. What do you do?
Follow-up answer
HeadlineNormal pipeline pressure with hypoxic gas is a pipeline crossover; I tell the room, open the cylinder and disconnect the pipeline hose.
I ventilate by hand with low fresh gas flows to preserve the cylinder and start propofol in case vaporizer output changes with the reduced flow. Someone fetches more cylinders and the surgeon pauses. I call biomedical engineering and facility management, because other rooms are affected, and do not reconnect until the analyzer confirms the supply. If the cylinder fails too, the self-inflating bag on room air.
Pitfalls that cost points
- Forgetting that the patient will wake up when the vaporizer stops delivering.
- Leaving the pipeline on after a crossover: 50 psi closes off the cylinder (about 45 psi), and the patient continues to receive the wrong gas.
- Treating a rising inspired CO2 as hypoventilation.
Rapid-fire
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 use 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.
Q: What is item 1 of the daily checkout? A: A self-inflating bag and auxiliary oxygen available and working.1
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, Capnography: waveforms and sudden loss of ETCO2, Ventilator modes, PEEP and IMV vs. pressure control, Intraoperative awareness and depth monitoring, 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.