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

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering; Obstetrics and Gynecology; OR / Surgery

Device Factors
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
*Not stated

UMDNS
Cables/Leads Electrosurgical Unit [11-496]

Damaged Reusable ESU Return Electrode Cables



Hazard [Health Devices May 1985;14(7):214-5]

Problem

We investigated an incident (and have documentation on another similar incident and unsubstantiated reports of four others) in which a patient was burned during electrosurgery when arcing within the dispersive electrode cable ignited the cable's insulation, the foam backing of the dispersive electrode, and nearby surgical drapes. Although this incident involved a specific model of electrosurgical generator and reusable dispersive electrode cable, the factors that led to this incident could occur with other combinations of ESUs and cables.

Before the incident, repeated stressing of the reusable cable near its junction with the clamp that attaches the cable to the dispersive electrode probably resulted in the fracture and separation of both conductors in the cable. When the ESU was activated, the open-circuit voltage across the separation was apparently sufficient to cause arcing, which led to the fire and the injury. Since the separation in the cable conductors was hidden beneath the surgical drapes, the staff could not see the arcing in time to prevent the fire. An ESU equipped with a dispersive electrode cable continuity monitor (also called a return cable sentry) would ordinarily have sensed and alerted the user to such an interruption of either or both dispersive cable conductors. However, the ESU in this incident lacked such a monitor.

The ESU involved in this incident has an isolated output. Although most manufacturers now include a cable continuity monitor (or its functional equivalent) in isolated-output as well as ground-referenced ESUs, in the past its inclusion was not considered to be necessary in isolated output ESUs. It was accepted that a continuity monitor was not necessary in isolated-output ESUs because a failure in the return path from an isolated unit does not substantially increase the risk of burns at alternate return sites, and because an interruption of the return path (e.g., cable/electrode disconnection) should be immediately obvious by the noticeable drop in output power or electrosurgical effectiveness. However, arcing within the cable may not result in any noticeable change in ESU performance. (Some low-power, special purpose ESUs also do not include such a safeguard because they either do not use a return electrode or their manufacturers believe that they have such low output power that the probability of a burn is low.)

Discussion

Isolation does not provide protection against the type of incident reported here. Even though relatively few burns result from arcing within a return electrode cable, if a system such as a return cable sentry will substantially reduce the likelihood of this type of incident, it should be incorporated into ESUs.

Reusable return electrode cables are typically supplied to the hospital by the manufacturer of the disposable return electrode. Suppliers of reusable cables typically do not specify how long the return cables can be used, since it is difficult to predict when a cable will fail. Cable life is dependent on the mechanical stress to which the cable is subjected and possibly on the sterilization methods or cleaning agents (e.g., alcohol, glutaraldehyde) that are used on the cable. It is common for cables to be used until they exhibit some defect.

In some hospitals, clinical engineers periodically inspect reusable return electrode cables using an ohmmeter. This procedure is not likely to detect cable faults where the conductor wire strands are severed but remain in physical contact with one another, unless the cable and connector are placed under tension while their conductivity is tested (such repeated stress may increase the likelihood of failure). Alternatively, the nurse who attaches the return electrode to the patient may visually inspect the cable for damage, but it is difficult to reliably detect severed wire strands within the cable insulation with a simple visual inspection. Further, despite these measures, cable stress and resulting fractures may occur during a surgical procedure.

We tested two isolated-output ESUs that have return cable sentries to see if the sentries would detect a cable fault before the cable insulation ignited. We found that the sentries would alarm and deenergize the output of the ESU just before or as soon as arcing started. Additionally, we circumvented the cable sentry and allowed arcing to start within the cable. We then returned the cable sentry to its normal mode of operation while the arc continued. In all instances, the sentries immediately alarmed and deenergized the ESU.

We have not received any reports of similar incidents with reusable active cables. We believe that the likelihood of injury in the event of arcing in an active cable is much lower because the areas of the active cable subject to the greatest mechanical stress (cable-connector interfaces) are visible and do not normally come in contact with other flammable materials while activated.

We have also considered the need for return cable sentries in low-power ESUs. Our preliminary testing indicates that the risk of arcing resulting in ignition, although lowered, still exists at power levels substantially below 50 W. In view of the lower risk, especially in those instances where the return electrode/cable junction is in plain view and not in contact with other flammable materials (e.g., emergency room, gastroenterology, dental procedures, outpatient procedures on non-anesthetized patients), we would concur with hospitals that choose to cautiously use low-power ESUs without provisions for monitoring the continuity of the return cable. Of course, a cable sentry is not required on low-power units that use no return electrode.

Many ESUs in the field do not have any form of cable continuity monitor. Some also lack a conventional patient cable sentry but come equipped with a return electrode monitoring (REM) system (evaluated in Health Devices 14:115ff.). This system is designed to monitor patient/return electrode contact quality when used with a REM-compatible two-part (split area) electrode. As a result, it inherently monitors the continuity of the return electrode cable and guards against this type of incident.We are not aware of any currently marketed general-purpose ESUs that lack a return cable sentry.

 If a standard return electrode is used with a REM-equipped generator, the ESU will not monitor the patient/return electrode contact quality but will monitor the continuity of the return cable. Some older model ESU generators can be retrofitted to include the REM system.

We believe that our recommendations, though in conflict with some manufacturers' recommendations, will substantially reduce risks, assure availability of ESUs to meet surgical needs, and minimize expense.

 

Recommendations

  1. Inspect all ESUs to determine whether any lack cable sentries. If return cable adapters are used with units that have sentries, verify  that the adapters do not circumvent the cable sentry (i.e., that the unit will indeed alarm if a conductor in either cable breaks or if the cable becomes disconnected from the dispersive electrode).
  2. ESUs that lack a cable sentry should be modified to include one if the ESU can be easily and economically retrofitted by the manufacturer. All ESUs that can be retrofitted with the REM system should be, but need not be used with the higher priced REM-compatible electrode unless the hospital decides it needs the added protection of a contact quality monitor (see "Who Needs It?" Health Devices 14:121). Standard electrodes can be used with the REM system, provided the proper adapters are available. In this configuration, the REM circuit will act as a return cable sentry.
  3. If ESUs that lack a return cable sentry cannot be modified easily and economically, we suggest the following alternatives:
    • If your hospital currently uses single-use, disposable electrodes with reusable cables, the risk of cable failure can be substantially reduced by using disposable electrodes with preattached (single-use) cables.
    • Where economic considerations dictate continued use of reusable cables with disposable electrodes, or when using reusable dispersive electrodes with their associated cables, a vigorous program of regular inspection of cables should be practiced. Inspect cables quarterly and replace them at least annually, regardless of condition. Use only cables with strain reliefs at the electrode clamp end, and ones that are made with wire that contains many fine strands (as opposed to a few thicker strands) to promote flexibility without breakage.
  4. Do not purchase new ESUs that lack cable sentries. Low-power units that lack a cable sentry may be purchased for use in areas where the portion of the return cable that inserts into the electrode connector is visible and not in contact with flammable materials (e.g., surgical drapes).

UMDNS Term

Cables/Leads Electrosurgical Unit [11-496]

Cause of Device-Related Incident

Device factors: Device interaction

Support system failure: Poor prepurchase evaluation

Mechanism of Injury or Death

Burn (thermal); Failure to deliver therapy; Fire


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