Cause of Device-Related Incident
User errors

Clinical Specialty or Hospital Department
Anesthesia; CCU / ICU / NICU; Nursing; Obstetrics and Gynecology; Pulmonary / Respiratory Therapy

Device Factors
*Not stated

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Barotrauma; Suffocation

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

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

Breathing Circuits, Ventilator [15-003]

Misassembly of Supplemental IMV and Breathing Circuits

Hazard [Health Devices Dec 1986;15(12):340]


ECRI received a problem report concerning misassembly of supplemental intermittent mandatory ventilation (IMV) gas circuits. While the patient was being mechanically ventilated, a nurse misassembled an IMV system after it had been accidentally disassembled. The patient was unable to breathe spontaneously and was later discovered in a hypoxic state. Although the patient in this case was not adversely affected, permanent injury or death could result under similar circumstances.


IMV is a mode of ventilation that allows a patient to breathe spontaneously between mandatory machine breaths while being weaned from the mechanical ventilator. Supplemental IMV circuits are used with older ventilators that lack integral IMV capability. These circuits can be purchased or assembled by the hospital from 22 mm connectors, one-way valves, and an anesthesia bag.

All IMV circuits use one-way valves. Improper valve orientation of the IMV system will occlude the flow of gas to the patient and prevent spontaneous breathing. We are unaware of any IMV circuits that are either permanently bonded to prevent disassembly or keyed to prevent misassembly. The IMV circuits available for purchase that we examined were easy to take apart and could be reassembled in a number of ways that resulted in improper operation. IMV systems constructed by hospitals are susceptible to the same problem.

Most respiratory therapists are familiar with IMV systems and breathing circuits and are unlikely to misassemble them. However, nonrespiratory therapy personnel (e.g., nurses, aides) are often responsible for reassembling systems that have been disconnected. Therefore, all clinical personnel attending a mechanically ventilated patient should be trained to reassemble disconnected breathing circuits and check for their proper operation. In addition, when ventilation monitors are used, clinical personnel should ensure that the alarm limits are set properly. (A carbon dioxide monitor could be used to detect the lack of spontaneous ventilation when ventilation monitors are inappropriate—an airway-pressure monitor cannot detect a decrease in spontaneous ventilation, and an exhaled-volume monitor cannot be used with continuous-flow IMV systems.)


  1. Alert all clinical personnel who may be attending ventilator patients to this report and instruct them in the proper assembly and operational testing of ventilator breathing circuits, including supplemental IMV systems.
  2. When ventilation monitors are used, clinical personnel should ensure that they are properly set.


Breathing Circuits, Ventilator [15-003]

Cause of Device-Related Incident

User errors: Device misassembly; Failure to perform pre-use inspection

Mechanism of Injury or Death

Barotrauma; Suffocation

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