Mislocated Pop-Off Valve Can Produce Airway Overpressure in Manual Resuscitator Breathing Circuits
Hazard [Health Devices May-Jun 1996;25(5-6):212-4]
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
Also, an adjustable pop-off valve is frequently included to provide
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.
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.
- 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
- 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.
- 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.
- Breathing Circuits [15-562]
- Resuscitators, Pulmonary, Manual [13-367]
- Resuscitators, Pulmonary, Manual, Disposable
- 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