Cause of Device-Related Incident
Device factors

Clinical Specialty or Hospital Department
Anesthesia; CCU / ICU / NICU; CSR / Materials Management; Emergency Medicine; Nursing; Pulmonary / Respiratory Therapy

Device Factors
Manufacturing error

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Barotrauma

Support System Failures
Lack or failure of incoming and pre-use inspections

Tampering and/or Sabotage
*Not stated

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

UMDNS
Breathing Circuits [15-562]; Resuscitators, Pulmonary, Manual [13-367]; Resuscitators, Pulmonary, Manual, Disposable [17-592]; Resuscitators, Pulmonary, Manual, Reusable [17-591]; Valves [14-325]

Mislocated Pop-Off Valve Can Produce Airway Overpressure in Manual Resuscitator Breathing Circuits



Hazard [Health Devices May-Jun 1996;25(5-6):212-4]

Problem

ECRI has learned that manufacturers of manual resuscitator breathing circuit accessories have provided hospitals with setups with a mislocated pop-off valve. When this valve is positioned incorrectly, patients can be subjected to dangerously high airway pressures that are not indicated to the caregiver.

One reported circumstance involved a Jackson-Reese (Mapleson F) breathing circuit attached to a breathing bag used to manually ventilate neonates. When this circuit is used, a mechanical pressure gauge is routinely attached (by small-diameter tubing) to the patient connector between the bag and the airway to measure pressure at the patient's airway opening. Also, an adjustable pop-off valve is frequently included to provide overpressure protection.

When set up correctly, the pop-off valve is placed in the breathing circuit at, or close to, the patient connector (see the "Acceptable Arrangement" depicted in the figure). However, in the reported instance, as well as in other instances we are aware of, the hospital received a setup in which the pop-off valve had been placed at the distal end of a length of small-diameter tubing connecting the pressure gauge to the breathing circuit (see the "Incorrect Arrangement" shown in the figure). (Note that hospitals could also assemble such an improper arrangement from separately purchased parts.)

When the pop-off valve is positioned incorrectly as shown, the pressure in the breathing circuit when the valve opens can be much higher than the pressure at the valve (which will be the valve's set release pressure), thus creating the potential for overpressurization. Also, once the valve opens, the pressure displayed by the gauge (which will reflect the pressure at the pop-off valve) can be much lower than that actually in the breathing circuit, thus misleading caregivers.

Discussion

An overpressure-relief pop-off valve is designed to open when the pressure at its inlet exceeds the set limit, venting sufficient gas to the atmosphere to bring the pressure down to, and maintain it at, the set limit. However, to provide adequate protection, the valve must be positioned so that it can freely vent the circuit. This does not occur when the pop-off valve is connected to the circuit through small-diameter tubing, which may be unable to carry the high flows typically needed to relieve overpressure through such a valve.

Once the valve opens, for a substantial amount of gas to flow toward the valve through small-diameter tubing, the pressure at the patient end of the tubing (i.e., in the breathing circuit) must be significantly higher than that at the pop-off valve because of the tubing's high flow resistance. Because this high resistance causes the pressure at the pop-off valve to be lower than that in the breathing circuit, the valve's ability to vent enough gas to adequately relieve the pressure in the circuit itself is limited—even though the valve is responding appropriately to the pressure in the vicinity of its inlet.

Furthermore, incorrect positioning of the pop-off valve can result in misleading pressure readings. When the pressure gauge and pop-off valve are connected to the circuit through the same small-diameter tubing as shown in the "Incorrect Arrangement" in the figure, pressure in the circuit can be measured effectively only while the pop-off valve remains closed. That is, with no flow through the pressure tubing, pressure changes will be faithfully transmitted from one end to the other so that the pressure displayed on the pressure gauge is that in the breathing circuit. However, once the pop-off valve opens, gas will flow through the tubing and out through the valve. In this way, the valve maintains, at its inlet, the pressure to which it was set. However, as described above, the flow resistance of the tubing will require the pressure at this inlet to be lower than that in the breathing circuit. Thus, the pressure in the vicinity of the gauge inlet will reflect the set pressure of the pop-off valve, instead of the higher pressure in the breathing circuit.

These circumstances combine to prevent 1) the pop-off valve from effectively regulating the pressure in the breathing circuit and 2) the pressure gauge from informing the caregiver of this problem.

Recommendations

  1. Ensure that any breathing circuit pop-off valve vents the circuit directly, with no interposed small-diameter tubing (as illustrated in the "Acceptable Arrangement" in the figure). Correct or remove from service any setups that are not so configured. (Also be alert for any pop-off valves that have a small-diameter tubing connector at their inlet if they are to be used as the pressure-limiting valve in a breathing circuit. A small-diameter connector encourages the inappropriate use of small-diameter tubing and can also create similar flow-resistance problems.)
  2. Explain the problem to responsible technical and clinical staff, demonstrate the proper configuration, warn them against improvising an improper setup, and caution them against vendors' suggestions that they use products having the hazardous configuration.
  3. Use only those pop-off or other pressure-relief valves with the capacity to vent flow sufficient to limit the pressure in the system in which they are used. To quickly check the suitability of a valve being considered for use in a manual breathing circuit, perform the following check before using the setup on a patient: block the patient connection, set the valve at a desired release pressure, compress the bag with the highest force that will be used clinically, and measure the pressure in the circuit. Repeat this procedure at several pressure settings over the range used in practice. If, in your clinical judgment, the measured pressure at any setting is dangerously higher than the set pressure, seek a different valve.

UMDNS Terms

  • Breathing Circuits [15-562]
  • Resuscitators, Pulmonary, Manual [13-367]
  • Resuscitators, Pulmonary, Manual, Disposable [17-592]
  • Resuscitators, Pulmonary, Manual, Reusable [17-591]
  • Valves [14-325]

Cause of Device-Related Incident

Device factor: Manufacturing error

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

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

Mechanism of Injury or Death

Barotrauma


[Home]    [About]    [Help]    [Site Map]
Copyright © 2017 ECRI
All rights reserved
www.ecri.org