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

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering

Device Factors
Design / labeling error

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death

Support System Failures
Lack of competent accident investigation

Tampering and/or Sabotage
*Not stated

User Errors
Device misassembly; Failure to perform pre-use inspection; Failure to read label

Anesthesia Units [10-134]; Anesthesia Unit Absorbers [17-616]; Anesthesia Unit Absorbers, Carbon Dioxide [10-140]

Risk of Barotrauma and/or Lack of Ventilation with Ventilatorless Anesthesia Machines

Hazard [Health Devices Jan-Feb 1994;23(1-2):54]


During our investigation of a case in which a patient sustained pulmonary barotrauma and subcutaneous emphysema, ECRI determined that, under certain circumstances, patients can be exposed to high pressures (approaching 5 psi) by anesthesia machines with an absorber module that has no ventilator attached.


The breathing of an anesthetized patient can be assisted by connecting to the patient circuit either 1) a gas reservoir bag with an APL (adjustable pressure limiting) valve, which limits the maximum pressure that can be applied at the patient's airway during manual compression of the bag, or 2) an automatic ventilator.

Some older asorbers have a nipple to which a reservoir bag can be attached and a port to which a ventilator can be attached, as well as a mechanical Bag/APL-Ventilator switch to select either ventilatory-assist mode. In such cases, when no ventilator is attached to the absorber, the Bag/APL-Ventilator switch must remain in the Bag/APL position for proper operation of the anesthesia system; if it is turned to the "Vent" position, the reservoir bag and APL valve will be shut out of the circuit. In addition, if the ventilator port is unblocked (as it should be), then all pressure in the patient circuit would be lost, and the patient would not be ventilated. Conversely, if the ventilator port is blocked, excess gas from the absorber will have no exit to the atmosphere. As a result, the normal gas flow and the flush flow (if used) from the common gas outlet would pressurize the patient circuit, as indicated on the absorber's pressure gauge. The circuit is protected only by the anesthesia machine's pressure-relief valve (if present) at the common gas outlet; this valve is set to release in accordance with international standards at approximately 5 psi (350 cm H2 O).

Although the reported problem was observed with a specific manufacturer's system, anesthesia machines from other manufacturers also have a Bag/APL-Ventilator-type switch, which may exhibit the same behavior when not used with a ventilator. A clinician who typically uses a ventilator-equipped anesthesia system in daily practice and only rarely uses a system without a ventilator may, by force of habit, inadvertently turn the Bag/APL-Ventilator switch to the "Vent" position when using a ventilatorless system. With the switch in this position and the ventilator port either unblocked or blocked, the operator must diagnose the nature of the resultant problem and take immediate action.


We believe that all anesthesia system manufacturers should provide a means to ensure that only Bag/APL operation is possible on units on which the ventilator either is not attached or is not switched on.


  1. Ensure that staff members are familiar with the operating instructions and configuration of the anesthesia system they are to use.
  2. Check that all protective caps (except for the required caps on some brands of scavenger interface valves) and packing material have been removed from the anesthesia machine.
  3. To reduce the risk that an open (unblocked) ventilator port will collect dirt or other debris or that it will invite an erroneous connection, attach an uninflated reservoir bag to it. This additional bag will inflate if the Bag/APL-Ventilator switch is placed in the "Vent" position during a procedure and may lessen the likelihood of barotrauma. An alternative would be to connect a bacterial filter to the port to protect against dirt and debris. In either case, be vigilant in monitoring the circuit pressure gauge, which can indicate a problem and may assist in detecting whether the Bag/APL-Ventilator switch is incorrectly placed in the "Vent" position during a procedure.
  4. Distribute this report to appropriate OR and anesthesia personnel.


  • Anesthesia Units [10-134]
  • Anesthesia Unit Absorbers [17-616]
  • Anesthesia Unit Absorbers, Carbon Dioxide [10-140]

Cause of Device-Related Incident

Device factor: Design/labeling error

User errors: Device misassembly; Failure to perform pre-use inspection; Failure to read label

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

Mechanism of Injury or Death


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