Use of Inadequate (Old) Anesthesia Scavenger Interfaces
Hazard [Health Devices Dec 1993;22(12):592]
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.
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.
- 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.
- Conduct a pre-use check of the full anesthesia
system before each case (see ECRI's Pre-Use Checklist for Anesthesia Units.
- During scheduled inspection and preventive
maintenance (IPM) procedures, verify that an appropriate scavenger interface
is in use.
- 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
- Anesthesia Unit Gas Scavengers [10-142]
- Anesthesia Unit Absorbers, Carbon
Cause of Device-Related Incident
Device factors: Design/labeling error;
Device failure; Improper maintenance, testing, repair, or lack or failure of
User error: Failure to perform pre-use inspection
External factor: Medical gas and vacuum supplies
Mechanism of Injury or