Cause of Device-Related Incident
Device factors; Support system failures; User errors

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering

Device Factors
Improper maintenance, testing, repair, or lack or failure of incoming inspection

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Exposure to hazardous gas; Failure to deliver therapy; Underdose

Support System Failures
*Not stated; Lack or failure of incoming and pre-use inspections

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated; Failure to perform pre-use inspection

UMDNS
Anesthesia Units [10-134]

Internal Leakage from Anesthesia Unit Flush Valves



Hazard [Health Devices Apr-May 1981;10(6-7):172]

Problem

A hospital reported that a large leak in the flush valve of an anesthesia unit resulted in delivery of a gas mixture with an excessive oxygen concentration to an anesthetized patient. Such delivery will result in lighter anesthesia than intended. The hazard was discovered only because an oxygen analyzer in the patient circuit, a standard ECRI recommendation (see Health Devices, Vol. 7, p. 147), indicated an oxygen concentration much higher than was calculated from flowmeter readings for the fresh gas flow.

Examination of the anesthesia unit showed that the core of the flush valve was loose in the housing that contains the valve and the fresh gas outlet. Oxygen was leaking around the core and into the fresh gas manifold, where it combined with the normal gas flow. The core may have been improperly tightened when last serviced (proper tightening requires a special tool, such as a tire valve core retractor). Further loosening may have occurred if the flush button was turned during operation.

Discussion

Such inward leakage can be easily detected during daily pre-use leak tests and during periodic inspection. Leaks in flowmeter control valves can be even more easily detected through observation because the flowmeter bobbin will not fall to zero. However, with a flush valve leak, the pressure in the machine and the patient circuit will begin to increase (indicating inward leakage) even though the flowmeters indicate no source of gas flow into the system. Prior to the leak tests, observe the system for about 15 seconds to see if the pressure rises before you turn on one of the gases.

Recommendations

  1. Perform pre-use tests, including leak tests, at least daily to detect malfunctions. Use the ECRI Pre-Use Checklist for Anesthesia Equipment to assess the amount of leakage. Squeezing the reservoir bag and feeling resistance does not necessarily indicate the absence of leaks; inward leaks, in fact, will create a greater feeling of resistance.
  2. If you detect leakage into the fresh gas circuit when all valves are shut off, a malfunctioning valve (or gasket on some older models) is indicated; take the anesthesia unit out of service until it can be repaired.

UMDNS Term

Anesthesia Units [10-134]

Cause of Device-Related Incident

Device factor: Improper maintenance, testing, repair, or lack or failure of incoming inspection

User error: Failure to perform pre-use inspection

Support system failure: Lack or failure of incoming and pre-use inspections

Mechanism of Injury or Death

Exposure to hazardous gas; Failure to deliver therapy; Underdose


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