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HTM ComDoc 12

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Countering the "Great Electrical Safety Scare of the 1970s" - an historic, early use of probabilistic analysis to quantify risk.

(This document was last revised on 10-2-18)


12.1 The theoretical vulnerability to electrocution during cardiac catheterization


The decade of the sixties saw both the advent of open heart surgery and the increasing use of cardiac catheterization procedures. More and more patients with externalized transarterial catheters, usually enclosing leads that could be quickly connected to an external cardiac pacemaker, were appearing in the new Cardiac Care or Special Care Units of hospitals. Once it was realized that this highly conductive pathway not only bypassed the usually protective layers of relatively resistive body tissues, but that it also had the effect of directing current to the most electrically sensitive areas of the inner walls of the heart, there was concern about the possibility that these patients could be “electrocuted” by currents much smaller than those required to achieve the same result when applied to the exterior of the body surface.

Patients with these externally accessible conductive pathways connecting directly to the heart came to be known as electrically susceptible or electrically sensitive patients (ESPs). The theoretical phenomenon in which an ES patient might be induced into fatal ventricular fibrillation by the passage of a level of current through the transarterial catheter much smaller than that required to electrocute the patient by external contact became known as “silent electrocution” or “microshock”.

Concern about this potential scenario was published as early as August 1961 in an editorial in the journal Circulation titled “Hidden Hazards of Cardiac Pacemakers”. Laboratory experiments indicated that the levels of current that could trigger potentially fatal ventricular fibrillation were indeed several orders of magnitude below the the levels associated with conventional electrocution – on the order of tens of microvolts. It was also established that the now-familiar phenomenon of current “leakage”, as well as relatively large currents passing through even low resistance grounding conductors, could easily generate potentials capable of injecting currents of this magnitude into the exposed conductive pathways.

The concept of equipotential grounding, in which substantial (green) grounding conductors are used to connect all exposed conductive surfaces to a central grounding point in a star configuration, was developed as a prime defensive measure against this new theoretical hazard. Others championed the use of isolation transformers as the best way to reduce leakage current in the ground circuits of the hospital’s electrical distribution system. Several regulatory and standards-making organizations began taking notice !

12.2 The 1968 Workshop on Electrical Hazards in Hospitals


In April,1968, the Division of Medical Sciences of the National Research Council (NRC) held a two-day workshop on “Electrical Hazards in Hospitals” that was attended by more than a hundred interested individuals. The proceedings of this workshop were edited by Dr. Carl Walters and later published by the influential National Academy of Sciences. Carl Walter was a renowned surgeon at the Peter Bent Brigham Hospital in Boston, a member of the faculty at Harvard Medical School, and Chairman of the Committee on Hospitals of the National Fire Protection Association (NFPA). Dr. Walter has been credited with establishing, in 1934, one of the world’s first blood banks in a basement room at Harvard, and later - in 1949 - with the invention of the blood bag which made it possible to end the cumbersome and dangerous procedure by which doctors pumped blood directly from donor to patient via paraffin-coated glass tubes. In addition to this he provided the insight, and pioneering work with the Castle company, that led to the introduction of high pressure steam sterilizers (sometimes called autoclaves) for reprocessing surgical instruments. Before the autoclave, surgical instruments were simply “sterilized” in boiling water.

It was at the NRC-sponsored workshop that Dr. Walter first speculated on the probable incidence of death by “microshock” in US hospitals. The following is a statement he made during a discussion of the national statistics on electrocution that were available at the time:

“As Chairman of the Committee on Hospitals of the National Fire Protection Association, I sought to convince the NFPA to broaden the scope of the Committee’s responsibilities. An insurance actuary, whose statistical hobby is electric shock and electrocautery injuries assured me that there were 1200 misdiagnosed electrocutions annually in hospitals during 1964 and 1965. That amounts to a “misadventure” annually in one of seven hospitals in this country. These were classified as cardiac arrest. But the deaths occurred during resuscitation efforts unrelated to the patient’s primary disease or during application of electric appliances. These were culled to demonstrate prevalence and also to show why the medical profession has not recognized the problem. During a lifesaving venture, those involved may not perceive what is going on. I have encountered three such instances in a recovery room. When the situation is recreated, you can see exactly which device is causing the trouble. There are a dozen or so astute analyses in the literature that describe similar settings. Now the profession is becoming cognizant of the problem; that is why so many doctors are interested in electric shock”.

12.3 1969 - The first published reports on "microshock"


On January 27, 1969, a report titled “Accidental Electrocutions Claim 1200 Patients a Year” was published in Electronic News. The report quoted microshock statistics obtained from Dr. Walter during a telephone interview. These same statistics were repeated again during presentations made by Dr. Walter and others at the 71st Annual Meeting of the American Hospital Association in Chicago in August, 1969. After the proceedings of the NRC workshop were published in 1970, these statistics were again repeated at a special press conference and widely reported throughout the national press.

In June, 1970 a report was distributed by the UPI wire service that attorney and consumer activist, Ralph Nader, had alleged in a speech that 5000 deaths attributable to microshock occurred each year in the nation’s hospitals. To this day Mr. Nader has not provided any independent substantiation for his figure.

In March, 1971 the Ladies Home Journal ran an article quoting Ralph Nader titled “Ralph Nader’s Most Shocking Expose’” which contained the statements that: “at the very least 1200 Americans are electrocuted annually during routine diagnostic and therapeutic procedures” and that “medical engineers such as Professor Hans von der Mosel, co-chairman of the Subcommittee on Electrical Safety of the Association for the Advancement of Medical Instrumentation and safety consultant to New York City’s Health Services Administration, believe that the number might be ten times as high as the conservative estimate of 1200”. (This is the source of the sometimes-quoted “estimate” of 12,000 deaths per year).

Interestingly, this same article states that “Only three hospitals in the country have biomedical engineers on their staffs to supervise the operation and maintenance of complex machines: Downstate Medical Center in New York City; Sinai Hospital in Baltimore; and Charles S. Wilson Hospital in Johnson City N.Y.”

12.4 1971 - Costly proposed amendments to the National Electric Code


By mid-1970, the NFPA’s Committee on Hospitals had developed and distributed for public comment some proposed amendments to Article 517 of the 1971 edition of the National Electric Code (NEC) that would require all hospitals to be provided with isolation transformer-based “Safe Patient Power Centers” in all Special Care Areas of the nation’s approximately 6000 hospitals. The potential financial impact of this proposal shocked the healthcare community. The technical inadequacy of the proposed solution also shocked the embryonic clinical engineering community.

In the Spring of 1971, shortly before the Annual NFPA Meeting in San Francisco at which the Committee on Hospitals’ proposed amendment would be voted upon, the Hill-Burton Program Committee convened a private meeting in Rockville, Maryland at which ten experts in “electronics in hospitals” were invited to debate with Dr. Walter and his technical advisors about the merits of the proposed new requirements. A written report generated by one of the ten experts summarized part of Dr. Walter’s presentation at that meeting as follows: “Dr. Walter’s “estimate” of 1200 deaths per year due to microshock had come about in the following way. In his (Dr Walter's) hospital in Boston a patient died under circumstances leading to his belief that the death was due to electrocution from microshock. Dr. Walter estimated that his hospital cared for about one in 1200 of all US patients yearly. Multiplying one suspected death by 1200 resulted in his widely-reported estimate of 1200 deaths per year!”

When it was pointed out at that same meeting that the proposed solution was technically inadequate because the isolation monitor, which the National Electric Code required to be used with an isolation transformer, injects far more current into the circuit than the “safe” level of 15 microamps, Dr. Walter’s team was unable to rebut the criticism. The report goes on to state that “The Hill-Burton Program Committee‘s findings were never publicized, but the Committee did inform the NFPA that if isolated power in all Special Care Areas was required by the NFPA in its forthcoming standards, the committee would terminate its long-standing requirement that hospitals receiving its funds comply with NFPA’s standards”. This was a substantial threat because at that time virtually all new hospital construction and renovations were subsidized with federal funds from the Hill-Burton Program.

When the proposed amendments to the NEC were presented at the NFPA Annual Meeting in San Francisco, in May 1971, they prompted a very lively floor debate, after which adoption was deferred and they were returned to committee by a 106 to 38 vote of the membership of the Electrical Section.

12.5 First electrical safety requirements


In spite of this period of spirited discussion about the reality or non-existence of this new, perhaps life threatening hazard - and the uncertainty about whether or not the various proposed counter-measures and elaborate safety tests could in fact eliminate or reduce the threat, a battery of new electrical safety requirements came into being anyway. Many of these requirements persist today in various regulations in only slightly modified form. The Joint Commission on Accreditation of Hospitals issued new standards that prescribed quarterly documented electrical safety testing for all of the facility’s patient care equipment. In California, the State Department of Health issued stringent electrical safety measures as part of its new requirements for general acute care hospitals in Title 22 of the State Administrative Code, introducing the soon-to-be-obsolete concept of the “electrically sensitive patient” and a host of related tests. It was a time of absurdities such as festoons of green grounding wires connecting every piece of exposed metal surface within the vicinity of any special care bed (even in the adjacent bathrooms) to substantial central grounding posts. However, diligent, dedicated investigations over the next several years for possible occurrences of microshock failed to turn up any credible evidence that this ingeniously conceived but still theoretical hazard was in fact claiming any lives at all.

12.6 1973 - ECRI's classic rebuttal submitted to Senate sub-committee


In September, 1973, in a statement made during hearings before a Senate sub-committee on the proposed Medical Device Amendments of 1973, Dr. Joel Nobel, Director of the Emergency Care Research Institute, said: “ The issue of microshock electrocution, its real versus claimed incidence, its widespread publicity, the enactment of codes and laws to combat it, and the economic fortunes of the electrical transformer industry, are inextricably intertwined. Phony statistics have been used to promote the sales of safety equipment and manipulate the National Electric Code to require the use of specific products. We are not suggesting that the microshock electrocution issue was fabricated by the industrial and code-making camps and consumer advocates. Each, however, capitalizing on the issue has distorted both the technical problems and priorities rather badly. The result is that many millions of dollars have been diverted from more critical areas of health care. This electrical safety issue has, however, performed a useful catalytic function in drawing attention to other problems associated with the use of technology for health care. It has helped hospitals to understand the broader needs for engineering support of patient care , including the judicious purchase, inspection and preventive maintenance of medical equipment".

In later testimony he added: “Our information and priorities are sometimes distorted by special interest groups, however, and this is acceptable. By way of example, consider how much attention has been devoted to the problem of electrical safety in hospitals during the last 5 years, especially by the engineering community and the manufacturers of safety devices and equipment. Speculation is often translated into reality, or at least belief, by the very fact of statement or publication. Bogus statistics on electrocution in hospitals have been proclaimed and republished without end or confirmation, for 5 years. Many millions of words have been written about microshock and many millions of dollars spent to avoid it. It is obvious, however, that we still know nothing of its real incidence. Is it a widespread problem or a phantom ? We are not suggesting that the electrical safety problem is nonexistent. Our data shows that it does exist, and it is significant; but its characteristics and magnitude are rather different than is generally believed. Our biggest problem is not electrocution by microshock but, instead, inadequate or unreliable power. Not too much electricity but too little".

And in August, 1975 the following report appeared in the journal The Medical Staff under the heading “ The Myth of Iatrogenic Electrocution: Its Effect on Hospital Costs”

“A decade or so ago, a well-known surgeon made the widely publicized statement that there were 1200 electrocutions a year in US hospitals. The charge appeared regularly thereafter in the lay press. Evidence supporting the charges has never been produced". At the AMA annual scientific assembly in Atlantic City in June, 1975, John R. Bruner, MD, assistant professor of anesthesia, Harvard Medical School, stated flatly that “contrary to erroneous, if not willfully fabricated, reports in family magazines and the press, there has been no documented death due to electricity in a US hospital in more than a decade.” Dr. Bruner admitted that he “was among those who raised the specter of iatrogenic (physician-caused) electrocution nearly a decade ago. “Since then” Dr. Bruner said, ”there has developed little evidence to support fears that silent electrocution is a common occurrence”. He said that fear has led to the discarding of useful equipment in favor of “safety featured gadgetry at much greater costs. Bureaucrats and inspectors, whose good intentions exceed their knowledge, insist that clinical care areas be festooned with green wires like charms to ward off evil spirits. And isolation transformers and fancy wiring are foisted upon the medical consuming public at great expense.” He saw no safety benefits in these escalating costs since “the magnitude of the hazard was largely imaginary in the first place.” He did stress that there is potential for injury wherever electricity is used. He said that haste, stress, and moisture, depending upon the special characteristics of the medical situation, may further enlarge the opportunities for injury to the patient around whom multiple appliances are commonly clustered. “Electrocution occurs when, and only when, an individual becomes the component that closes the circuit in which a lethal current can flow.” Dr. Bruner said.

12.7 Electrical isolation as a cost-effective solution to "microshock" hazard and a shift in focus to equipment maintenance


In the meantime, someone had – with a stroke of genius – realized that this entire threat could be completely eliminated by the simple expedient of protecting the exposed conductive ends of the patient’s catheter. Proper terminations for transarterial catheters providing low impedance pathways to the heart and great vessels became the order of the day and electrically sensitive patients and their attendant need for special environmental consideration disappeared almost overnight. Articles on electrical isolation of the patient appeared. See, for example, Guidelines for Clinical Engineering Programs; Part I: “Guidelines for Electrical Isolation”; first developed in the 1970s and later published in the Journal of Clinical Engineering; Vol 5; No 4; 287 - 290; Oct - Dec 1980.

12.8 Using probabilistic analysis to estimate the risk of microshock

The debate was particularly interesting because advocates of the less costly approach required considerably more professional courage and belief in their analyses than those advocating the more extravagant "safety" measures. One issue that proved key to bringing some of the uncertain lay observers around to the more conservative position was the clinical engineering community's use of a probabilistic analysis to estimate the levels of risk. See Guidelines For Clinical Engineering Programs; Part III: The Risk of Electric Shock In Hospitals; first developed in the 1970s and later published in the Journal of Clinical Engineering; Vol 6; No 1; 53 - 58; Jan - Mar 1981.

A byproduct of this extended period of debate was the discovery that the existing quality of the maintenance of the typical hospital’s continually expanding inventory of electronic equipment was inadequate. A new high-intensity focus on equipment maintenance and safety was born.

12.9 The Great Debate about isolated power in ORs


Another interesting sidebar to this episode was the parallel debate about the rationale for perpetuating the requirement for isolated power in operating rooms where the use of flammable agents had been prohibited. The original requirement for isolated power had been introduced into the NFPA standard governing anesthetizing locations in 1941 along with other antistatic measures intended to reduce the number of accidents resulting from the ignition of flammable agents such as cyclopropane.

In 1970, the standard addressing anestetizing locations (NFPA 56 –Code for the Use of Flammable Anesthetics) had been renumbered as NFPA 56A and given the new title “Standard for the Use of Inhalation Anesthetics (Flammable and Nonflammable)”. In this new document anestetizing locations where the use of flammable agents was prohibited did not have to install or utilize any of the previously required antistatic safeguards, except the isolated power system. In retrospect this might appear strange, until one considers what other issues were preoccupying the NFPA’s Committee on Hospitals at this exact time. They were busy advocating the use of isolated power systems (IPSs) in other Special Care Areas of the hospital as a safeguard against microshock. This, often acrimonious debate ground on throughout the 1970s and well into the next decade(See Guidelines For Clinical Engineering Programs; Part IV: Isolated Power in Anestetizing Locations ? History of An Appeal; first developed in the 1970s and later published in the Journal of Clinical Engineering; Vol 6; No 1; 59 - 63; Jan - Mar 1981.) before the IPS advocates finally settled for permitting isolated power in anesthetizing locations but not requiring it.

As expected, there have been no significant adverse trends of electrical accidents in operating rooms over the past 20 years. The predominant categories of equipment-related misadventures in the operating room continue to be patients accidentally burned by poorly implemented electrosurgical procedures and patients injured by pressure sores resulting from extended contact with the unyielding surface of the surgical table - which are often misdiagnosed as accidental burns.


This material was later published as "The Great Debate on Electrical Safety - In Retrospect" by Malcolm G. Ridgway, Chapter 65 in The Clinical Engineering Handbook edited by Joseph F. Dyro; Elsevier Press; 2004 (HTM ComRef 5)


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