Volume 1, No. 4 • Winter 1986

Current Questions in Patient Safety – Isolated Power Systems in the OR

David E. Lees, M.D.

Question: We are in the process of designing new operating rooms at our community hospital. The architects have indicated that local building and fire codes require isolated power systems in the OR but our hospital biomedical engineer says isolated power systems are obsolete, expensive, and do not contribute to patient safety. Who is right?

Answer: In the most recent document from the National Fire Protection Association on standards for health care facilities (NFPA 99-1984), isolated power systems are no longer required in nonflammable anesthetizing locations. This document comprises a number of past NFPA individual pamphlets dealing with health care facilities and supersedes NFPA 56A. The NFPA is a not-for-profit organization that writes voluntary standards arising out of consensus among fire professionals, engineers, anesthesiologists, and other interested parties. As such, these standards have no weight of law, but are often adopted in part or as a whole by local governments and accrediting agencies having jurisdiction. Only then do they become “law” ‘The NFPA has no power or authority to police or enforce compliance with their standards.

Regrettably, there is often a several-year delay between when NFPA reviews a document and when a jurisdiction incorporates the changes into the municipal or state fire or health facility code. Also, a government or agency is not obligated to accept the most recent NFPA revision. Given the lead time between planning and actual construction, effort should be made to lobby the local government or authority having jurisdiction to accept the new NFPA standards; a conventional grounded power distribution system is far less costly to install and maintain than an isolated power system.

The absence of an isolated power system in a nonflammable anesthetizing location will not put your patients at any greater risk. Remember that

isolated power systems were originally developed to reduce the risk of flammable anesthetic explosions. All isolated power systems required the use of a line isolation monitor (LIM) which continuously indicated the current that might flow to ground and create a spark were there a connection between the isolated circuit and ground. This could be as high as 5 milliamperes (mA) be-fore triggering the audible and visual alarms in each operating room. An “acceptable” hazard current of 4 mA to the LIM still was far in excess of the safe current limits established by the Association for the Advancement of Medical Intrumentation for the prevention of microshock (AAMI: Safe Current Limits for Electromedical Apparatus [American National Standard] {ANSI/AAMI ESI-1985)). Isolated power systems were never effective in preventing a dangerous microshock, whose magnitude may be as small as 10 microamperes (uA) in a susceptible patient.

The removal of the requirement for isolated power systems, however, did not remove the need for isolation transformers in electromedical equipment that comes into contact with patients. Nor does the inclusion of an isolation transformer in the design of a device guarantee the safety of the unit. AU hospitals should have an active biomedical engineering/risk management alliance that ensures all equipment brought into the hospital, whether purchased or on loan from a manufacturer, has been screened for leakage currents and is on an annual surveillance program. This is particularly critical with the encroaching use of equipment in the operating room that was never intended for direct patient care support, specifically the microcomputer. Errors in design and/or construction may result in extremely dangerous current leaks from device chassis (metal cabinet) to ground of greater than 100 uA.

Answer by David E. Lees, M.D., Professor and Chairman, Department of Anesthesia, New York Medical College and Chief, Westchester County Medical Center, and a member of the Newsletter Editorial Board.