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