Cause of Device-Related Incident
Device factors; External factors; User errors

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering; OR / Surgery

Device Factors
Design / labeling error; Device failure; Improper maintenance, testing, repair, or lack or failure of incoming inspection

Document Type
Hazard Reports

External Factors
Medical gas and vacuum supplies

Mechanism of Injury or Death
Barotrauma

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
Failure to perform pre-use inspection

UMDNS
Anesthesia Unit Gas Scavengers [10-142]; Anesthesia Unit Absorbers, Carbon Dioxide [10-140]

Use of Inadequate (Old) Anesthesia Scavenger Interfaces



Hazard [Health Devices Dec 1993;22(12):592]

Problem

ECRI investigated an incident in which a patient undergoing a laparotomy under general anesthesia suffered a bilateral pneumothorax at the end of surgery, requiring ventilation with a resuscitator. The pneumothorax developed immediately after the selector switch of an anesthesia absorber was shifted from "Ventilator" to "Bag/APL" (adjustable pressure limit) and the flush valve was pressed to fill the bag. The bag did not fill, and the flush and fresh gas then flowed directly into the patient. An old scavenger interface was in use at the time of the incident.

Discussion

This old scavenger interface draws in air, controlled by a pressure-relief valve, to reduce vacuum system pressures (typically at least -300 cm H2O) to levels that can be safely used for scavenging anesthetic gases (e.g., -0.5 cm H2O). Failure of this interface resulting in application of full system vacuum can occur when the port that allows room air to enter, which is a 22 mm conical fitting, becomes occluded. This can occur when, for example, a flattened reservoir bag is placed over the interface or a piece of plastic film from a package wrapper near the port is sucked tight against the opening. When the port is occluded, full system vacuum is applied to the anesthesia ventilator and APL valve; vacuum applied to the APL valve will be transmitted to the absorber's Bag/APL port.

Beneath the selector switch on the absorber are two arms (which remain at right angles to each other) with valve cups that are intended to occlude the Ventilator port when the switch is in the "Bag/APL" position or that occlude the Bag/APL port when the switch is in the "Ventilator" position. In the reported incident, a valve cup had apparently dislodged from one arm and remained in position over the Bag/APL port when the anesthesiologist attempted to shift from "Ventilator" to "Bag/APL," and the vacuum caused the switch to fail. This left both the Ventilator and Bag/APL ports occluded. Consequently, activation of the oxygen flush valve resulted in a high breathing circuit pressure that caused the bilateral pneumothorax. The ventilator high-pressure alarm did not activate because the ventilator had been switched out of the circuit and turned off.

Scavenger interface failure resulting in application of full system vacuum can also place patients at risk in other ways; for example, in some ventilators, it can alter breathing circuit pressures, possibly increasing them to harmful levels.

Currently available scavenger interfaces have multiple ports for venting the vacuum or other mechanisms to protect against accidental occlusion and resultant application of full system vacuum. In addition, they avoid use of standard port configurations (such as the 22 mm conical fitting) so that tubing or other components cannot be misconnected, even momentarily.

Recommendations

  1. Dispose of all vacuum system scavenger interfaces with venting ports that can be easily occluded or that allow connection of tubing or other components. In addition to checking components on anesthesia systems in use, also check drawers and storage areas.
  2. Conduct a pre-use check of the full anesthesia system before each case (see ECRI's Pre-Use Checklist for Anesthesia Units.
  3. During scheduled inspection and preventive maintenance (IPM) procedures, verify that an appropriate scavenger interface is in use.
  4. Use a breathing circuit pressure monitor that has a sensing port at the patient connection and an alarm (at least for high pressure) that is functional even when the ventilator is not in use. The monitor can be part of an integrated anesthesia system or can be a stand-alone monitor.

UMDNS Terms

  • Anesthesia Unit Gas Scavengers [10-142]
  • Anesthesia Unit Absorbers, Carbon Dioxide [10-140]

Cause of Device-Related Incident

Device factors: Design/labeling error; Device failure; Improper maintenance, testing, repair, or lack or failure of incoming inspection

User error: Failure to perform pre-use inspection

External factor: Medical gas and vacuum supplies

Mechanism of Injury or Death

Barotrauma


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