Barotrauma from CPAP Systems Lacking Pressure Relief
Hazard [Health Devices Sep 1996;25(9):343-5]
ECRI is aware of several incidents in which the exhalation hose of certain
user-assembled continuous positive airway pressure (CPAP) systems has become blocked. When
this happens, the high gas flows and source-gas pressures used to provide CPAP can cause
the pressure in the system to rise to dangerous levels almost instantaneously. This abrupt
rise in pressure can cause barotrauma injuries to the patient before caregivers can
respond to an airway pressure alarm.
CPAP is used to improve ventilation in a spontaneously breathing patient.
The patient inhales through a mask or endotracheal tube supplied with a continuous high
flow of fresh gas. To maintain CPAP and to prevent the patient from rebreathing his or her
exhaled gas, the fresh gas flow is adjusted to exceed the patient's peak inspiratory flow.
Hospitals routinely assemble CPAP systems from components such as
breathing circuit hoses, connectors, humidifiers, and positive end-expiratory pressure
(PEEP) valves. In these systems, fresh gas is typically supplied from an air/oxygen
blender attached to piped medical gases or medical gas cylinders, which are regulated at
50 to 55 psig. (Although devices exist that are specifically designed to provide CPAP,
these are usually reserved for home use. They also operate at lower flows and source-gas
pressures than user-assembled hospital units and should not be susceptible to the problem
described in this report.)
The breathing circuit pressure at the patient connector is determined
primarily by the opening pressure of the PEEP valve (i.e., the pressure at which the valve
will allow gas to pass through). PEEP valves, which are connected to the end of the
exhalation limb of the circuit, are designed to provide a constant back pressure ranging
from 2.5 to 20 cm H2O at gas flows up to 60 L/min and to relieve any pressure
exceeding the set PEEP. However, the PEEP valve may be unable to relieve overpressure in
the system for several reasons, including the following:
- PEEP valve malfunction
- Reverse installation of the PEEP valve
- Inadvertent pinching or kinking of the exhalation hose sufficient to
defeat the PEEP valve (often a result of using longer exhalation circuits to
keep the PEEP valve, which can be noisy, away from the patient's head; this
increases the risk that the circuit will be pinched or kinked)
In the event of such a blockage, the high gas flows (40 to 60 L/min) and
source-gas pressures (50 to 55 psig) needed to maintain CPAP can cause the breathing
circuit pressure to rise almost instantaneously to pressures well beyond those normally
used for ventilation. This will likely subject the patient to barotrauma and its related
sequelae. Although an airway pressure monitor will detect these high pressures and alert
clinicians to the problem, the pressure rise can be so abrupt that barotrauma will occur
before anyone can respond to the alarm.
The only reliable means of preventing barotrauma when a CPAP system
becomes blocked is to provide an additional source of pressure relief. This can be
accomplished by adding a respiratory pop-off valve to the inspiratory limb of the circuit.
Such a valve is designed to open when the pressure at its inlet exceeds the set (pop-off)
limit, venting sufficient gas to the atmosphere to bring the pressure down to, and
maintain it at, the set limit. Adding a pop-off valve to the inspiratory, rather than the
expiratory, limb ensures that obstruction or kinking of the expiratory tubing will not
prevent pressure relief to the system. In a blocked CPAP system, the pop-off valve may not
return the breathing circuit pressure to the PEEP, but it will lower the pressure
sufficiently to protect the patient until the blockage can be remedied.
Even with a pop-off valve in place, airway pressure monitoring is a
necessary component of CPAP systems. For one thing, the system must still be monitored for
low pressure (i.e., a disconnection) or for PEEP exceeding the desired value. In addition,
a monitor is needed to alert clinicians to any system blockage; the high-pressure alarm
limit should be set below the pop-off valve limit and just sufficiently over the PEEP
setting to avoid creating excessive nuisance alarms.
- Add a respiratory pop-off valve to the inspiratory circuit. (Do not
install it in the expiratory circuit, where it can be defeated by blocked tubing just as
the PEEP valve can.) Ensure that it has sufficient capacity to vent the gas flows commonly
used for CPAP (up to 60 L/min). A valve having adjustable pop-off pressure is preferable
because it will permit the clinician to keep the pop-off pressure reasonably close to the
set PEEP. Regardless of whether the pop-off valve is adjustable, its opening pressure
should never exceed 30 cm H2O.
- Always include airway pressure monitoring in a CPAP system to alert
personnel to conditions of excessive PEEP. The pressure should be measured in the
inspiratory circuit adjacent to the patient wye or from a pressure port integral to the
wye connector. The high-pressure alarm limit of the pressure monitor should be adjusted a
few centimeters of H2O above the PEEP, but below the setting of the
- Before connecting the patient to the system, verify the following:
A. The PEEP is correctly set for the gas flow rate intended for the
patient, and the PEEP valve is correctly installed and functioning properly.
B. The high- and low-pressure monitor alarms function properly at the gas
flow rate intended for the patient.
C. The pop-off valve will correctly limit the airway pressure; verify this
by blocking the exhalation circuit and observing the airway pressure on the monitor's
pressure display or gauge.
- Continuous Positive Airway Pressure Units [11-001]
- Pressure Alarms, Airway [14-351]
- Pressure Monitors, Airway [17-425]
- Valves, Positive End-Expiratory Pressure [14-337]
Cause of Device-Related Incident
User errors: Device misassembly; Failure to
perform pre-use inspection; Incorrect clinical use
External factor: Medical gas and vacuum
Mechanism of Injury or Death