Incompatibility of Disposable Heated-Wire Breathing Circuits and Heated-Wire Humidifiers
Hazard [Health Devices May-Jun 1993;22(5-6):300]
ECRI is aware of several incidents in which disposable heated-wire
breathing circuits have overheated before or during use because of incompatibility with
the heated-wire humidifiers with which they were being used, resulting in melting or
charring of the plastic breathing circuit. This problem prompted us to update our previous
generic report on the hazards of heated-wire breathing circuits ("Heated Wires Can
Melt Disposable Breathing Circuits," Health Devices, 18, May 1989).
A heated humidifier is used to humidify the gas delivered to a patient
during positive-pressure ventilation. During humidification, gas passes over a water
reservoir, where it is heated and saturated with water vapor. As the humidified gas passes
through the breathing circuit, it cools and condenses; to compensate for this, the gas in
the humidifier is heated above 37°
C. However, under some
circumstances, this hot gas may reach the patient without cooling, possibly causing
thermal injury. In addition, the accumulation of the condensate in the breathing circuit
changes the ventilator's flow dynamics and can be carried over to the patient by a
To improve humidification and reduce the amount of condensate, as well as
to eliminate the need to overheat the gas in the reservoir, clinicians can use a
heated-wire humidifier. In this type of humidifier, a heated, insulated wire in the
breathing circuit warms the gas and the walls of the breathing circuit. Heating of the
wire depends on the voltage supplied to it by the humidifier, its impedance, the heat
transfer between the breathing circuit and the surrounding environment, and the flow of
gas in the breathing circuit. A circuit may operate without any problems when first set up
for a patient, but may overheat when operating conditions change.
In our previous report, we noted that overheating of breathing circuits
can be caused by defects in or damage to the heated wire; bunching of the heated wire
within the breathing circuit; or inadequate heat transfer caused by low gas flow or the
draping of surgical drapes, towels, or bed linens over the breathing circuit. However, the
availability of heated-wire breathing circuits from vendors other than the humidifier
manufacturer introduces the potential for incompatibility that can cause overheating of
the heated wire and melting or charring of the breathing circuit. Melting can cause the
breathing circuit to leak or occlude, resulting in hypoventilation or barotrauma; charring
in the presence of oxygen-enriched gas poses a significant risk of fire.
Users of heated-wire humidifiers are often unaware that heated-wire
breathing circuits are not interchangeable or may have been purchased from suppliers who
have not adequately tested them for compatibility with specific heated-wire humidifiers.
Currently, no simple test is available for hospitals to check compatibility. While
purchasing heated-wire breathing circuits from independent vendors may offer a cost
saving, the potential adverse effect on patient safety and the added responsibility on the
user must be considered (see "Alternate Parts and Supplies," Health Devices
13[5-6 pt. I]:99-104, Mar-Apr 1984).
ECRI believes that vendors of generic heated-wire breathing circuits
should take steps to reduce the risks of incompatibility between their products and the
heated-wire humidifiers with which they can be used. For example, a standardized test
method could be developed that would take into account voltage differences in the
humidifier's heated-wire circuit and low- or no-flow conditions.
Purchasers and users of generic heated-wire breathing circuits must take
appropriate precautions to reduce the risk of overheating caused by incompatibility with
- Alert users of heated-wire humidifiers to the
potential of overheating and melting or charring of disposable plastic
heated-wire breathing circuits that are not compatible with the humidifier.
- Be sure that the heated-wire breathing circuit is
designed and labeled for use with the heated-wire humidifier. If purchasing
breathing circuits from an independent vendor, obtain written assurance that
the product has been designed and tested for use with the heated-wire
humidifier with maximum output and low- or no-flow conditions.
- Avoid covering the heated-wire breathing circuit
with bed linens, surgical drapes, or towels. If the breathing circuit is
kinked (e.g., by the bed rail), replace it to avoid overheating.
- Use a ventilation monitor to warn of leaks in or
occlusion of the breathing circuit.
- Consult the manufacturer of the heated-wire humidifier (or the
operator's manual for the humidifier), as well as the supplier of the
heated-wire breathing circuit, to determine the minimum flow requirement and
any other precautions that will decrease the likelihood of overheating. Do
not turn on the heated-wire humidifier until flow has been initiated.
- Breathing Circuits, Anesthesia [10-139]
- Breathing Circuits, Ventilator [15-003]
- Humdifiers, Heated [12-050]
Cause of Device-Related Incident
Device factors: Design/labeling error; Device interaction
User error: Failure to read label
Support system failure: Poor prepurchase evaluation
Mechanism of Injury or Death
Burn (thermal); Failure to deliver therapy; Fire