Cause of Device-Related Incident
Device factors; User errors

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering

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

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Suffocation; Underdose

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
Failure to perform pre-use inspection; Inappropriate reliance on an automated feature

UMDNS
Anesthesia Unit Vaporizers [10-144]; Breathing Circuits, Anesthesia [10-139]

Vaporizer Leak with Mapleson Breathing Circuits



Hazard [Health Devices Dec 1986;15(12):344]

Problem

A member hospital reported that a leaky vaporizer caused a child to suffer a cardiac arrest when used in a system composed of a humidifier and a breathing circuit. A pre-use test had disclosed a leak in the humidifier. The leak was tightened, and this supposedly corrected the problem. The leak test was performed only on the complete system, which is permitted a higher leakage rate, not on the anesthesia unit alone.

Discussion

A blood gas measurement made at the time of resuscitation showed that the patient had an acceptable PO2, but also had an excessive PCO2. This result is consistent with the characteristic of a Mapleson E breathing circuit to exhibit rebreathing (and increased CO2) in inverse proportion to fresh gas flow. In this case, the fresh gas flow must have been much lower than the normal range.

Further testing disclosed a leak at the back cover plate of the vaporizer. This plate, which is the primary mounting fixture for the vaporizer, supports its entire weight in the configuration used. Two of the four screws holding the plate to the vaporizer and sealing the gas flow passages in the vaporizer were loose. The pressure drop through the humidifier and fresh gas inspiration line to the Mapleson circuit were sufficient to cause much of the fresh gas flow to be lost through the leak. The leak was found to increase with repeated application of downward force on the vaporizer.

When using Mapleson circuits, including Bain circuits, under conditions that can develop high back pressures in the anesthesia unit, leaks in the unit can be especially hazardous. Although some oxygen was able to reach the patient, the rebreathed carbon dioxide continued to build up to an excessive level.

Recommendations

  1. Whenever Mapleson or Bain circuits are used, pay special attention to the machine and system pre-use leak tests of the anesthesia unit Bain circuits (see ECRI Pre-Use Checklist for Anesthesia Units (Machines and Accessories) to detect disconnections within the coaxial hose. Any fresh gas leak will increase rebreathing and carbon dioxide levels in the breathing circuit.
  2. Consider using a carbon dioxide monitor for excessive carbon dioxide in the rebreathed gas when using Mapleson or Bain circuits (see our evaluation of carbon dioxide monitors, Health Devices 15:255-85).
  3. Be sure all anesthesia equipment is on a regular inspection and preventive maintenance program.

UMDNS Terms

  • Anesthesia Unit Vaporizers [10-144]
  • Breathing Circuits, Anesthesia [10-139]

Cause of Device-Related Incident

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

User errors: Failure to perform pre-use inspection; Inappropriate reliance on an automated feature 

Mechanism of Injury or Death

Suffocation; Underdose 


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