Cause of Device-Related Incident
Device factors; Support system failures; User errors

Clinical Specialty or Hospital Department
Anesthesia; CCU / ICU / NICU; Clinical/Biomedical Engineering; CSR / Materials Management; Nursing

Device Factors
Design / labeling error; Device interaction

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Burn (electrical, thermal, chemical); Failure to deliver therapy; Fire

Support System Failures
Poor prepurchase evaluation

Tampering and/or Sabotage
*Not stated

User Errors
Failure to read label

Breathing Circuits, Anesthesia [10-139]; Breathing Circuits, Ventilator [15-003]; Humdifiers, Heated [12-050]

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[5], 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 delivered breath.

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 heated-wire humidifiers.


  1. 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.
  2. 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.
  3. 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.
  4. Use a ventilation monitor to warn of leaks in or occlusion of the breathing circuit.
  5. 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

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