Failed Leak Test and Sticking Expiratory Valve Before a Paediatric List
At 06:40 in a Kuwait MOH tertiary hospital anesthesia workroom, you are assigned to check four anesthesia machines before a mixed elective list. On machine 2 (Datex-Ohmeda Aisys), the automated self-test passes the circuit leak test only after you change the CO2 absorber canister, but a manual 30 cmH2O sustained-pressure test shows a decay of 180 mL/min with the adjustable pressure-limiting valve closed and the Y-piece occluded. You also notice the expiratory unidirectional valve disk stays slightly open at rest and the soda lime is from a canister opened 9 days ago; the color indicator is still white. The first patient is a 6-year-old for adenotonsillectomy scheduled at 08:00, and the only spare machine is a transport ventilator without an anesthesia gas module. The surgeon is already in theatre and has asked why the list is delayed.
1. The automated test passed after the canister change, yet your manual test shows 180 mL/min decay. Is that machine fit for use? Explain what the valve finding adds and what you would check before condemning the machine.
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Interpretation. A sustained-pressure test at 30 cmH2O with the APL valve closed and the Y-piece occluded should hold pressure. Many anesthesia-machine service manuals allow a small leak, commonly up to 150 mL/min (some up to 200 mL/min); 180 mL/min is at or beyond the usual acceptance limit and must be checked against the Aisys service manual. It is not a trivial finding in a 6-year-old, where low fresh-gas flows may be used and even a small leak can cause rebreathing or inadequate ventilation.
The valve finding matters more than the number. An expiratory unidirectional valve that does not seat causes rebreathing of exhaled gas, unpredictable tidal volumes and hypercapnia. Common causes are moisture, detergent residue, a warped or swollen disk, or incorrect reassembly after cleaning. The 9-day-old soda lime is also relevant: colour indicators are unreliable, and an opened canister may already be partly exhausted.
Before condemning the machine, verify: correct valve assembly and seating, canister seals and absorbent dust, circuit and bag integrity, and repeat the test with a known-good circuit. If the leak and valve fault persist, remove the machine from service.
2. Sequence your actions and escalation over the next 20 minutes. What do you tell the surgeon, and how do you document the problem?
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First 20 minutes - sequence and escalation.
- Stop the check, label the machine 'DO NOT USE - fault', and remove it from the anaesthetic room.
- Tell the anesthesiologist and theatre coordinator immediately: machine 2 has failed the leak/valve check; the 08:00 paediatric start is at risk. Give facts, not guesses.
- Fully check another machine (machine 1, 3 or 4) including leak test, valves, absorbent, vaporisers, oxygen failure alarm, scavenging, suction and a self-inflating bag. Only release it when the whole checkout passes.
- Call biomedical engineering and log the fault number.
- Record on the machine-check sheet: time, test pressure, leak rate, valve finding, action, your name and the name of the person informed.
- Tell the surgeon a specific reason and a realistic revised start time; offer to move the list to another theatre if the second machine cannot be certified quickly.
Do not move the transport ventilator into theatre as a substitute for an anaesthesia machine: it lacks an anaesthetic gas module, scavenging and the required alarm package for a paediatric tonsillectomy.
3. If machine 2 cannot be certified in time, what is the safest backup plan for the 6-year-old?
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Backup plan if machine 2 cannot be certified. The list should move to another theatre with a fully checked anaesthesia machine, or start late. A transport ventilator is acceptable only for intra-hospital transfer or an emergency, not for a 60–90-minute adenotonsillectomy requiring volatile agent, CO2 absorption and gas monitoring. If no machine is available, the safest option is to postpone the elective case; the anaesthetist must be part of that decision. For an emergency, a self-inflating bag with 100% oxygen and a separate capnograph can ventilate the child, but this is a rescue plan, not a normal anaesthetic plan. Document the delay and the reason.