Cause of Device-Related Incident
External factors; User errors

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

Device Factors
*Not stated

Document Type
Hazard Reports

External Factors
Medical gas and vacuum supplies

Mechanism of Injury or Death
Barotrauma

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

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

UMDNS
Continuous Positive Airway Pressure Units [11-001]; Pressure Alarms, Airway [14-351]; Pressure Monitors, Airway [17-425]; Valves, Positive End-Expiratory Pressure [14-337]

Barotrauma from CPAP Systems Lacking Pressure Relief



Hazard [Health Devices Sep 1996;25(9):343-5]

Problem

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.

Discussion

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.

Recommendations

  1. 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.
  2. 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 pop-off valve.
  3. 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.

UMDNS Terms

  • 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 supplies

Mechanism of Injury or Death

Barotrauma


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