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July 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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It should come as no surprise that in the
pre-safety-ground era which included the 1960s that electrical shocks of patients
in hospitals was not uncommon. If the jolt came intentionally from a cardiac defibrillator,
then it would be a good thing. However, these shocks, which were the subject of
a Time magazine story in the
April
18th, 1969 issue cited by Mac's technician, Barney, were being administered
unintentionally by patient monitoring and ancillary life-sustaining equipment. Per
the article, no Underwriter's Laboratory (UL) certification was required for hospital
equipment. Maybe it was felt that it wouldn't be so bad if someone got zapped in
the hospital since there would be a doctor on-hand to resuscitate the zapee. Since
that time medical equipment has been required to undergo stringent safety conformance
requirements that makes electrocution virtually impossible. Now, if we could just
keep doctors from cutting off the wrong limb or removing the wrong organ...
Mac's Service Shop: Safety in Medical Electronics
By John Frye
Increased use of electronic equipment in medicine is creating a demand for meaningful
safety standards.
"Mac," Barney said to his employer, "did you see that story a while back claiming
that some 1200 hospital patients were accidentally electrocuted every year?" "Yes,"
the older man replied, taking a final swipe with the cleaning cloth at the face
of the portable TV he had just serviced.
"As I remember, the story first appeared in the January 27th issue of Electronic
News. The figure was given by John A. Hopps, Radio & Electrical Engineering
Division, National Research
Council, Canada, at the Reliability Symposium held in Chicago the week before.
He was quoting Dr. Carl W. Walter, surgeon at the
Peter Bent Brigham Hospital in Boston, who said he received the figures from
an actuary of an insurance company who had made a computer study of the situation."
"Ask for a slice of bread and you get a bakery!" Barney exclaimed. "You know
more about it than I do. I was talking about a
Time
story that ran in the April 18th issue. Anyway, can you believe that 'shocking'
figure? A guy goes to the hospital to get well, not electrocuted."
"One more bad pun like that and you may go to the hospital yourself," Mac growled.
"I, of course, have no way of judging the validity of the figure, but the original
story concluded with the comment that throughout the survey conducted by the newspaper
'no one denied the figure of 1200 deaths or made a lower estimate.' Dr. Walter,
who is recognized as a man of stature in the medical field, sticks with the figure
and contends it would be a lot higher if it included patients who suffered cardiac
arrest from shock but were resuscitated."
"The Time story says a spokesman for the AMA claims the figure is exaggerated
by about 1175 cases," Barney offered.
"On the other hand," Mac countered, "Richard Merris, sales manager for Dallons
Instruments is quoted as saying the figure sounds about right to him. As Dr. Walter
points out, many hospitals are unaware of the cause of death in these electrocution
cases. Death is attributed to other causes, and that is why it is difficult to get
hard figures regarding these electrocution deaths."
"I got the idea most of the deaths were caused by incompatible grounding systems
used on different kinds of complex equipment and on such simple things as frayed
cords or broken plugs," Barney said.
"That's partly oversimplification," Mac answered. "Leakage of any sort between
two different pieces of electrical equipment with which the patient is in contact
could produce death, especially when the attachments of the instrument bypass the
skin resistance by being inserted in a vein or artery or deliberately reduce the
skin resistance through the use of moisture or conducting paste."
"Know what you mean," Barney offered. "I read an article in the September, 1968,
issue of QST written by Melville M. Zemek of the Associated Factory Mutual Fire
Insurance Companies in which he said the resistance of the human body varies from
100,000 ohms down to 1000 ohms or less, and most of this is made up of contact resistance.
A value of approximately 500 ohms is usually accepted as the average resistance
of the human body between the major extremities.
"He went on to point out that while high voltage produces severe surface tissue
destruction at high resistance contact points, it's the current flowing through
the body that kills you. Danger of electrocution depends on the magnitude, duration,
and path of this current through the body.
"The most dangerous path is through the chest, for this is likely to cause the
heart to lose its life-sustaining rhythm and to go into a condition of ineffective
quivering called ventricular fibrillation in which the heart feels, in the almost-too-graphic
words of a surgeon, 'like a handful of worms, just squirmy.' Experiments on animals
to determine the amount of current through the chest to produce usually fatal fibrillation
have been projected into a theoretical criterion of danger for man in terms of current
and time duration. This data produces a straight line graph on log-log paper from
400 mA for 0.005 second down to 75 mA for 5.0 seconds."
"Electricity can produce death in other ways, can't it?"
"Oh sure. Shocks can cause respiratory inhibition, heart block, and severe damage
to the nervous system. These other mechanisms of death, however, ordinarily require
a lot more current than that needed to initiate the deadly ventricular fibrillation;
and that's why the latter is more likely to be cause of death in a hospital electrocution.
A current that only tickles the hands of a doctor or technician may be more than
enough to bring death to a weakened patient when the electrodes are applied in such
a manner as to bypass his protective skin resistance."
"Let's see if we can figure out for ourselves how some of these deaths might
occur," Mac suggested. "In older hospitals or hospitals that have added wings at
different periods, there may not be a common ground for all outlets. If two pieces
of equipment are plugged into receptacles with different grounds, there may be a
'ground-loop current' flowing from one instrument to the other through the patient."
"Yeah, and suppose the grounded lead in the line cord is broken loose from the
plug prong, leaving the case ungrounded. Suppose further that a capacitor from the
hot side of the line to the case is leaky or has been actually shorted by a lightning
surge. Now if the patient touches the case or anything connected to the case and
also touches with his other hand a grounded object such as a radiator, water pipe,
or wall plate, the current flows to ground right through his chest."
"These are pretty obvious examples," Mac admitted.
"Quite likely the more subtle leakages are the ones that cause the most trouble.
We both know that the primary or secondary of a power transformer can short to the
core and thence to the case. An arc-over can establish a carbonized path that can
carry enough current to produce fibrillation and still be high enough in resistance,
especially when the instrument is not operating, to be hard to detect by a casual
examination.
"Dr. Leon Pordy, Assistant Professor of Medicine, Mount Sinai School of Medicine,
points out that patients in an operating room are often wired up for sixteen different
things. Every precaution is taken to avoid accidents, and the first consideration
is to make sure the patient is not grounded. Actually the patient is safer in the
operating room, even with all this equipment, because it is being used by experts.
He is in more danger from more ordinary equipment carelessly used by hospital personnel
with no training in electronics, equipment that is less rigorously examined. Few
hospitals in the country use expert electronics technicians to operate complicated
instruments. They usually scout around for some doctor with a smattering of electronics
and turn the job over to him."
"Hey, that's about as smart as finding a janitor with a first aid course and
turning the emergency ward over to him!" Barney exclaimed. "As I get it, there is
at present no pre-marketing clearance of medical electronic equipment such as the
UL tag on household equipment. How come?"
"There are a couple of reasons. For one thing, the doctors and the equipment
manufacturers can't agree on what is necessary. The doctors want foolproof equipment
that requires a minimum of maintenance and that can be operated by untrained personnel.
The equipment manufacturers want the medical profession to set up some standards
as to what constitutes safe leakage currents. But no doctor is willing to stick
out his neck and say this is x number of microamperes. Doctors say the fibrillation
level varies from individual to individual. They would prefer, of course, an impossible
leakage level of zero.
"The second reason for a lack of safety standards is that Congress will not pass
same. Starting in 1962, bills have been introduced every year requiring approval
of electrical medical equipment by some federal agency, and every year these bills
have died in committee. Two more bills were introduced in the House and Senate at
the present session, but no one will wager they will ever get out of committee.
However, the chance that some sort of legislation will be passed eventually is improving
as a result of the present publicity regarding the hospital electrocutions - especially
since Ralph Nader brought this subject up in testimony before the Product Safety
Commission in Washington last February. The pity is that several hundred - or perhaps
thousand - patients will die of electrocution while undergoing routine diagnostic
tests or treatment before that takes place."
"That reminds me that Professor Paul E.Stanley, a Purdue University professor
of aeronautical, aerospace, and engineering sciences, has spent the last few years
in researching the causes and prevention of these hospital electrocutions. He has
come up with both a long-range and a short-range plan for correcting the condition.
His long-range plan is a typical engineering approach: 1. Define the problem and
collect facts about the hazards of medical instrumentation. 2. Do research to determine
more precisely I the maximum nonfibrillibrating current. 3. Expand the study to
include such things as electrically operated beds, heating pads, TV sets, etc. 4.
Set up design standards and procedures that will reduce the accidental electrocution
rate in hospitals to zero.
"All this, he admits, will take time, precious time in which other lives will
be lost needlessly. To reduce this loss, he recommends that in the meantime all
personnel using electrically operated equipment in hospitals be trained in the fundamentals
of safety, that a positive earth ground and a single ground reference be used for
all equipment connected to one patient, that isolated and monitored ungrounded power
be provided for all hospital rooms where patient monitors are used or where cardiac
catheterization is performed, and that adequately trained personnel be employed
to provide specifications for the purchase of equipment and to provide preventive
maintenance on same."
"Makes sense," Mac observed. "The important thing is to fix the responsibilities.
Dr. Pordy said it well: 'Suppliers of electronic equipment have the first responsibility
to make sure their equipment is safe. Doctors have the second responsibility to
make sure the equipment is properly used.' If both groups accept their responsibility,
we should be able to bring a halt to this needless loss of life."
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive
technodrama™
stories was the brainchild of none other than John T. Frye, creator of the
Carl and Jerry series that ran in
Popular Electronics for many years. "Mac's Radio Service Shop" began life
in April 1948 in Radio News
magazine (which later became Radio & Television News, then
Electronics
World), and changed its name to simply "Mac's Service Shop" until the final
episode was published in a 1977
Popular Electronics magazine. "Mac" is electronics repair shop owner Mac
McGregor, and Barney Jameson his his eager, if not somewhat naive, technician assistant.
"Lessons" are taught in story format with dialogs between Mac and Barney.
