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

Clinical Specialty or Hospital Department
Anesthesia; Clinical/Biomedical Engineering; Emergency Medicine; Facilities Engineering; Obstetrics and Gynecology; OR / Surgery

Device Factors
*Not stated

Document Type
Hazard Reports

External Factors
Medical gas and vacuum supplies

Mechanism of Injury or Death
Barotrauma; Suffocation; Wrong drug

Support System Failures
Lack or failure of incoming and pre-use inspections

Tampering and/or Sabotage
*Not stated

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

Fittings/Adapters [11-726]; Fittings/Adapters, Pneumatic, Quick-Connect [11-731]; Medical Gas and Vacuum Systems [18-046]

Crossed Connections in Medical Gas Systems

Hazard [Health Devices Jul 1984;13(9):22]


ECRI received two reports of cross-connected medical gas lines. In both reports, nitrous oxide and oxygen couplers had been unscrewed at the threaded fittings that connect the back of the coupler housing to the gas supply hose. When reassembled, the couplers were reversed. While both reports involved one brand of quick-connect hose couplers, similar cross-connections can occur with virtually all other manufacturers' systems. The purpose of this Hazard Bulletin is not simply to discuss the two specific incidents, but to remind hospitals how easily (and innocuously) cross connections can occur in any medical gas system.

The first incident occurred after attempted modification of an anesthesia machine's gas supply lines and resulted in the deaths of two patients. Legal action surrounding this incident was previously described in the literature (Biomed Saf Standard 1984;14 [Feb 5]:15-6).

In the second incident, the quick-connect couplers had been removed so that the cover plate of a ceiling-mounted gas hose reel system could be installed just prior to occupancy of a new operating room suite. Although the gas system had already undergone final inspection and certification, the seemingly trivial installation of the cover plate required the couplers to be temporarily removed from the hoses.

Improper replacement of the couplers led to crossed connections. Fortunately, a vigilant anesthesia department double-checked the medical gas system and noticed the crossed connections before clinical use.

Many types of quick-connect couplers have these threaded fittings. The threaded fittings are the same design for many manufacturer's couplers, and a variety of crossed connections are possible between oxygen, vacuum, nitrous oxide, air, and carbon dioxide.

The coupler face plates are usually color coded to correspond with the color of the gas hose or outlet. While this decreases the risk of misassembly and undetected crossed lines, it may not always be effective protection, as demonstrated by the reported cases.

We believe that this hazard exists with other manufacturers' couplers, as well as other types of medical gas system connectors. Any fittings that are accessible to service personnel or users and are not gas-specific throughout their design (e.g., pin indexed, unique threading) have the potential for crossed connections. We have also investigated a similar problem involving crossed connections with duplex cover plates for gas wall outlets (Health Devices 10:222, July 1981).

While the reported incidents occurred during system installation or modification, many quick-connect couplers must also be disassembled at threaded fittings to periodically replace O-rings in the connector. This increases the likelihood that they may be reconnected to the wrong gas line or inadequately tightened.

We believe that many couplers or connectors in use may not be adequately tightened. In a ECRI survey of a hospital's operating rooms, 13 of 160 couplers could be loosened by hand. Loose or hand-tightened threaded fittings could be used improperly as the primary disconnection point of the connector.

According to the manufacturer or the incident couplers, some models of its quick-connect couplers now have gas-specific fittings at the back of the coupler. Couplers that require disassembly to replace O-rings are no longer available. New couplers allow access to the O-rings through the front panel. Threaded fittings are factory tightened and cannot be unscrewed by hand.

The potential for these incidents underscores the importance of a complete final inspection of the gas system (in accordance with National Fire Protection Association [NFPA] NFPA 56F) following any repair, maintenance, or modification of a medical gas system. We believe that, ideally, the threaded or internal design for all connectors should be unique for each type of gas or secured so that the connectors cannot be removed by hand or with simple hand tools. However, because many connectors with the potential for easy removal are in widespread use and may continue to be used in the future, hospitals must ensure that these connectors are reassembled correctly, tightened securely, and inspected after any disconnection prior to clinical use.


  1. Immediately inspect every gas supply hose coupler and connector throughout the hospital and ensure that threaded fittings cannot be disassembled by hand. Mark all connectors with a surface sealant (e.g., Glyptol) that will indicate (i.e., with a broken seal) if a threaded connector has been disassembled. Also, ensure that all connectors and hoses are color coded.
  2. Whenever any part of a medical gas system is modified or serviced, alert the department using the equipment and ensure that the system is inspected by qualified personnel before use. Inspect only after all work on the system has been completed. If the system cannot be inspected immediately, prominently label the connectors (e.g., place tape over each outlet) to warn users that the system has been serviced and must be inspected before use.
  3. When replacing O-rings in the connectors, disassemble only one connector at a time. Retighten all fittings securely, so that they cannot be removed by hand.
  4. In accordance with good clinical practice, always use an oxygen analyzer during inhalation anesthesia.


  • Fittings/Adapters [11-726]
  • Fittings/Adapters, Pneumatic, Quick-Connect [11-731]
  • Medical Gas and Vacuum Systems [18-046]

Cause of Device-Related Incident

User errors: Accidental misconnection; Failure to perform pre-use inspection

External factor: Medical gas and vacuum supplies

Support system failure: Lack or failure of incoming and pre-use inspections

Mechanism of Injury or Death

Barotrauma; Suffocation; Wrong drug

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