Dynamics of Electrical Hazards of Particular Concern to Operating-Room Personnel

Dynamics of Electrical Hazards of Particular Concern to Operating-Room Personnel

Dynamics of Electrical Hazards of Particular Concern to Operating-Room Personnel PAUL F. LEONARD, M.D. ALLAN B. GOULD, JR., M.D. Most physicians have...

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Dynamics of Electrical Hazards of Particular Concern to Operating-Room Personnel PAUL F. LEONARD, M.D. ALLAN B. GOULD, JR., M.D.

Most physicians have a rather limited understanding of the hazards of electricity. We know that high tension wires should be avoided and that flashlight batteries are rather innocent sources of electricity, but we read of people dying from very small amounts of electricity during cardiac catheterization. We find that electricity may initiate ventricular fibrillation and is used to terminate it. This paper is an attempt to define simply the hazards of electricity as used in the operating room and the effects of electric shock.

BACKGROUND: CHARACTERISTICS OF ELECTRIC CURRENT

A flow of electrons along a conductor is termed an electric current. Such a current may be direct (DC) or alternating (AG). Direct current is a steady unidirectional flow of electrons. A source of direct current, as for example a battery, has one pole which possesses a surplus of electrons and a second pole deficient in them. When a pathway connects the two poles, electrons flow in one direction, from the site of the surplus to that of the deficit. By contrast, the electron flow in alternating current is not unidirectional. The electrons surge in one direction and then in the other as the polarity of the current source periodically reverses. The rate at which these reversals of polarity and electron flow occur is the frequency of the alternating current. Ordinary house current goes through one complete cycle (a surge in one direction and then the other) in 1/60 of a second. It therefore has a frequency of 60 cycles per second. On the other hand, alternating currents

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Figure 1. Illustrative analogy of water flow to electric current. Rate of flow (Ampere?

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employed in diathermy may have frequencies of 50 million cycles per second. The rate of flow of electricity is measured in amperes. When 6.28 X 1018 electrons flow past a given point in a conductor each second, a current of one ampere is flowing. The electrical resistance of a substance is a measure of the ease with which it conducts electric current. If electrons flow through a substance readily, it is said to be a good conductor and to exhibit low resistance. If the substance resists the flow of an electric current., it has a high resistance. If its resistance is sufficiently high-if current is conducted only very poorly-the substance is termed an insulator. The unit of electrical resistance is the ohm. The unit of electrical force or pressure is the volt. The higher the voltage of a source of electricity, the more pressure it can exert to force a flow of current. Thus a source having a low voltage might be able to force only a fraction of an ampere of current flow through a conductor of moderately high resistance. But a source of high voltage, because of its greater pressure, could force several amperes of current flow through the same resistance. A rough analogy is often drawn between the flow of electrons in an electric circuit and the flow of water in pipes (Fig. 1). In this analogy, the rate of current flow ,or amperage is comparable to the rate of water flow. The electrical resistance is compared to the opposition to the flow of water offered by a valve-the smaller its orifice, the greater its resistance. The voltage is analogous to the height of the water tower which determines the pressure tending to force the flow of water through the valve.

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The three electrical parameters are related to each other by an expression known as Ohm's Law: Force (volts) Current (amperes) = R . h) eSlstance (0 ms

Thus, if the resistance in a given circuit is doubled and the voltage of the source is kept constant, the rate of current flow is cut in half. To restore the original rate of current flow in the face of the doubled resistance, it would be necessary also to double the voltage. A capacitor (formerly termed a "condenser") is a device which can store electrical energy. In its simplest form it consists of two conductive plates separated by an insulator. If one such plate is connected to the positive pole of a source of DC potential, such as a battery, and the other plate to the negative pole, current will flow momentarily so that the positive plate becomes deficient in electrons while the negative plate possesses a surplus. The capacitor is then said to be "charged"-for even after the battery is disconnected, the condenser contains electrical energy drawn from the battery. If a resistor is then connected from one plate to the other, electrons will flow through the resistor until the number of electrons on each plate is equal. The capacitor is then discharged, having dissipated its electrical energy into the resistor. The concept of grounding seems often a bit obscure. We speak of grounding equipment for safety, both to prevent electric shock and to prevent build-up of static charges. On the other hand we sometimes hear that the victim of an accidental electrocution might have survived had he not been so well grounded (by standing on a wet floor, for example). To understand the basis for these apparently conflicting statements, it is necessary to appreciate the fact that one of the electric wires supplying power to a house is connected to the earth; it is termed the "ground wire." This practice is uniformly observed by electric power companies. One reason for grounding the circuits is to provide a pathway for electrical charges induced in wiring during thunderstorms to bleed off harmlessly. Without this protection dangerous voltages could build up in the house wiring. Such grounding also prevents the appearance of very high voltages on house wiring should an equipment failure occur in the high-voltage systems by which power is transmitted cross country. Because of this arrangement, however, it becomes possible to sustain a shock when contact is made with only one electric wire; it is not necessary to touch both wires of the electric service simultaneously. Electric shock can occur if a person is grounded and touches the ungrounded (or "hot") side of an electric line, because the circuit is completed through the conductivity of the earth (Fig. 2). Probably the most common cause of human contact with a hot wire-is an insulation failure in an electrical appliance. In this event an electrical connection can exist between the hot wire in the cord supplying power to the

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Hot wire

110

volts

Ground wire

Figure 2. Completion of circuit through body by touching hot wire while in contact with ground.

appliance and the metal frame or case of the unit. A potential of 110 volts then exists between ground and metal surfaces of the appliance. The stage is set for severe shock-even electrocution-of any person who touches it while he is also in contact with an electrical ground. To reduce this danger, the frames of such appliances often are connected to an external ground-sometimes via a third wire in the cord which is connected to a third pin on the power plug. When such ground wires are connected, only minimal voltage can exist between the appliance and other grounded surfaces. Should an insulation failure occur and the hot wire touch the frame, the result would be a blown fuse rather than a potentially lethal device. Of course such ground wires must actually be connected to an external ground to afford any protection-none whatever is furnished by insertion into a so-called cheater plug which provides no connection between the third pin and external ground. OPERATING-ROOM DANGERS AND COUNTERMEASURES STATIC ELECTRICITY. A rather special hazard exists in operating rooms. As is well known, a spark from a static electrical charge can touch off an explosion when flammable anesthetic agents are used. One means of reducing this hazard is electrically connecting all persons and objects in the operating room. This distributes electrical imbalances as they arise, preventing the buildup of static potentials. Such connections are effected by use of not only conductive shoes and flooring but also a Horton inter-

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Contact with single wire

Hot wire

110 vo Its with

110 volts

neither wire grounded (Floating circuit)

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No current flow through body

Isolation Transformer

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Conductivity/ of earth Figure 3. Circuit with isolation transformer. Even though body is grounded, no current flows unless both wires are contacted simultaneously.

coupler. The conductive floor mayor may not be connected directly to ground, but considerable conductivity to ground is incidental to ordinary construction. WIRE CONTACTS. The grounding by conductive shoes and flooring means, of course, that conditions are ideal for a severe electrical shock should contact be made with a hot wire. Therefore electrical wiring in the operating room must be arranged so that no wires are hot with respect to ground. This is accomplished by use of isolation transformers (Fig. 3). These transformers are so constructed that the input and output circuits are electrically isolated from each other-no electrical connection exists between them. The two output terminals have 110 volts between them, but neither terminal is connected to ground. Thus no voltage difference exists between either of the terminals and ground. The output terminals are connected to the lights and electrical outlets in the operating room. Electrical shock is, of course, still possible. But receiving such a shock would require an almost deliberate effort in touching both sides of the isolated power line simultaneously. Touching one side-or a device with faulty insulation-would not suffice even though the individual was well grounded. HARMFUL EFFECTS OF ELECTRICITY ON THE BODY

It is recognized that electrical currents may flow innocuously through various parts of the body; indeed, the same currents may be harmless to

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one person and fatal to another. Clarification of the factors that determine the eventual outcome of an electrical shock must begin by emphasizing that pre-existing disease states-particularly those resulting in relative myocardial ischemia-reduce tolerance to electrical currents. When man contacts a source of electricity, the end results of current flow through the body are influenced by many factors, 7 of which the most important are (1) voltage of the source, (2) resistance of the body tissues and of the electrode contacts, (3) amperage of the current, (4) the type of current-alternating or direct, (5) the position and size of the electrodes, and (6) the duration of current flow. VOLTAGE. The voltage of the source is important because, in conjunction with the body resistance, voltage determines total current flow in accordance with Ohm's law. RESIS'l'ANCE. Skin resistance varies, and this variation is important in determining the quantity of current forced through the body by a given voltage. Changes in resistance in any tissue may be brought about by sweating, variation of blood flow through the tissue, differences in its fluid content, or even carbonization due to a burn. These changes may take place very rapidly, with corrrespondingly swift alteration of resistance, current flow, and effect on other tissues. Resistance of the skin varies greatly from one area to another. Because the hands are frequently a site of contact with the electrical source, it is fortunate that the skin of the palms has the highest resistance, being usually between 1 and 2 megohms. Bone is the only tissue with higher resistance. Subcutaneous fat also has high resistance, but tissues deep to this are very vascular. Since blood and other body fluids have low resistance, vascular tissues are excellent conductors. If current is to flow through the body, there must be a point of exit as well as a point of entrance. The combined resistance of the two points is a primary factor in determining the amount of current flow. Because a frequent pathway of current through the body is via the foot to ground, the amount of the current is greatly decreased if there is a high resistance (insulator) at this point. For this reason rubber foot coverings or other nonconductive footwear are commonly worn when working in areas of possible electrical danger. In the operating room, conductive shoes and flooring must have a certain amount of resistance to reduce this hazard. The role of isolation transformers in this respect has already been discussed. AMPERAGE. The amount of current, or amperage, that flows through an organ is a major factor in determining the effect of the current on that organ. As the current leaves an electrode and spreads through the body, its density decreases as it is dispersed over multiple pathways. Thus, although a 20-microampere (millionth of an ampere) 60-cycle alternating current applied directly to the heart may cause ventricular fibrillation, a much larger amount of current must be applied to the skin to produce this effect. This dispersion of current is not uniform, however; blood is

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among the best conductors in the body and provides a low resistance pathway directly to the heart. Burchell has pointed out that electrical equipment used in the medical fields has a special hazard for the patient. If two pieces of equipment are attached to the patient and one is improperly grounded with a small current leak, the leakage current may flow toward the ground of the normally functioning equipment. Since this equipment is usually connected to the patient in such a manner as to minimize resistance, it is especially hazardous. A cardiac catheter filled with saline may serve as a conductor, carrying current directly to the heart. Thus electrical currents that would scarcely be felt if applied to the skin become potentially lethal. Pacemakers not having a self-contained source of power, electrocardiograph apparatus, and electrocautery equipment are among the potential electrical hazards in the anesthetizing areas. ALTERNATING AND DIRECT CURRENT. The type of current has a definite effect on the outcome in a case of electric shock. It has been stated that production of ventricular fibrillation requires approximately three times as much flow of direct current as of alternating. 5 A possible explanation for the difference is that the direct current flowing through the heart acts as one overwhelming stimulus causing instant depolarization of the entire heart and blotting out the heart's own electrical mechanism for stimulating contraction, but leaving the heart's normal electrical mechanism again dominant when the current flow is discontinued. With lowfrequency alternating current, each reversal of current acts as a new overwhelming stimulus, and slight differences in contractility and refractory periods from one muscle fiber to another may initiate an uncoordinated response-ventricular fibrillation-upon the cessation of the stimulating alternating current flow. The frequency of alternating current is very important. The range of 40 to 150 cycles per second is the most dangerous, and unfortunately the usual household current frequency falls within this range. As the frequency increases above 150 cycles per second, the danger of ventricular fibrillation decreases. With 400,000 to 1,000,000 cycles per second, up to 3 amperes has no adverse effect on humans. High-frequency currents tend to travel largely on the surface of conductors (in this case the skin) and are beyond the frequency at which muscle fibers can respond; hence ventricular fibrillation is not induced. Defibrillation. Prevost and Battelli in 1899 observed that the canine heart could be defibrillated by electric currents. They reported success both with alternating current and with current obtained from capacitor discharge. The first successful defibrillation of a human heart with complete recovery of the patient was reported by Beck, Pritchard, and Feil in 1947. Alternating current was used. Since that time many lives have been saved

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by defibrillation, using 60 cycle AC in both the open and the closed chest techniques. Until recently there has been less study of defibrillators using capacitor discharge as a source of current. Such units are often referred to as "DC defibrillators," and it is true that the primary flow of current is unidirectional. However, the rate of current flow (amperage) decreases abruptly from its initial value and some units are designed to provide a small reverse current flow following the first surge. Probably because clinical success with AC defibrillators was widespread and because earlier reports regarding the efficacy of DC defibrillators were contradictory, the latter method was neglected for a time. In 1962, however, Lown and associates 9 concluded from their studies that DC is superior to AC for defibrillation. They reported both modalities generally effective in terminating fibrillation in dogs. In a few cases, however, AC failed to accomplish defibrillation and DC was effective subsequently. They also studied adverse effects of countershock at defibrillating levels in animals initially having normal sinus rhythm. They found a significantly lower incidence of arrhythmias and of electrocardiographic changes consistent with acute myocardial infarction in those dogs countershocked with DC than in those which received AC. Since that time numerous additional reports have confirmed the effectiveness of capacitor-discharge defibrillators. There are also reports of successful clinical defibrillation with DC after failure with AC, and studies indicating that less myocardial damage follows the use of DC. However, it should be pointed out that the question of which modality is 8uperior is still debated; AC defibrillation continues to have its advocates. Other Applications. Lown and associates8 further reported that direct current applied across a closed chest is of value in terminating certain other cardiac arrhythmias. The mechanism of action is presumed to be the same as that postulated for DC defibrillation: instantaneous depolarization of the entire heart with resultant erasure of aberrant stimuli, permitting the normal sinus mechanism to resume control of the cardiac rhythm. 'When capacitor-discharge devices are used to terminate arrhythmias, a timing circuit is included to trigger the discharge at the correct instant in the electrocardiographic cycle. It. has been found that such a stimulus applied during the first part of the T wave (the vulnerable period) can induce ventricular fibrillation, and the timing circuit synchronizes the discharge so that the vulnerable period is avoided. Electrical anesthesia has been achieved by use of AC and DC and even by a combination of the two. lO Frequencies from 50 to 700 cycles per second have produced general anesthesia, but presently acceptance of this technique is not widespread. Convulsions, lack of muscle relaxation,

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and ventilation problems are some of the difficulties that may be encountered with employment of these techniques. POSITION AND SIZE OF ELECTRODES. Size of the electrodes is important, for generally the larger the electrode, the lower the resistance to current flow. Guyton and Satterfield, applying 110 volt 60 cycle per second current to the dog's chest wall, found that electrodes 8 cm. in diameter caused fibrillation invariably, but electrodes 3 cm. in diameter caused ventricular fibrillation only 20 per cent of the time, and smaller electrodes were ineffective. The importance of electrode positioning has been demonstrated by Kouwenhoven and co-workers, who exposed dogs to 60 cycle alternating current and made the interesting observation that if the pathway is parallel to the body axis 9 to 10 per cent of the current passing through the body flows through the heart, whereas if the pathway is transverse (from foreleg to foreleg) only 3 per cent of the current flows through the heart. Thus ventricular fibrillation in dogs is caused by a smaller total current flow if the pathway is parallel to the body axis. This is further demonstrated by apparatus used for electroshock therapy and electrical anesthesia. In both instances, potentially lethal currents are introduced at one point on the head and removed at another. The current pathway is from one electrode to another and the direct effects are limited to the head. DURATION OF CURRENT FLOW. As a general rule, the longer a given current is allowed to flow through the body, the more serious are the possible consequences. The greater the duration of current flow, the more likely is the interval of the electrical stimulus to include the vulnerable period of the heart cycle and result in fibrillation. Further, even though fibrillation is not induced, electrical power flowing through the body is dissipated as heat. The longer the current flow, the more heat is produced and the greater is the resultant tissue damage.

EFFECT OF ELECTRICAL CURRENT ON SPECIFIC TISSUES

Alterations in cutaneous resistance have been discussed already, as has the influence of sweating and the vascular supply. Damage to the skin and tissues close to the skin is much greater when the voltage is more than 1000 than when it is in the lower range of household electrical supply. This is because an electrical arc with a temperature of 2500 to 3000° C. may form between the conductors and the tissues. Gas gangrene has been reported following such tissue damage. Jaffe reports that heat changes may form a negative impression of the conductor on the skin of the victim. The area of electrode contact may become necrotic, as may the underlying tissue and even bone. Holes

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through the skull have been reported. Because of the vascular changes about the site of contact, these necrotic wounds have a progressive character. The blood vesRels are described as becoming brittle and friable with thrombus formation and microscopic changes similar to those seen with radiation. The efferts of electrical current on the heart are of primary importance in the explanation of death following passage of electricity through the body. High currents may cause the heart to lock in spasm but allow resumption of a normal beat, provided the duration of the current has not been excessive. 4 Lower currents may induce ventricular fibrillation as described earlier. It has been found that 0.06 volt applied to the dog heart is capable of producing fibrillation. 12 Hypoxia secondary to respiratory arrest may ultimately cause ventricular fibrillation in accidents with high-tension wires, but this is not a primary effect of the electric current on the heart itself. It must be emphasized that a direct electrical stimulation of the heart with a given current is much more dangerous than the same current applied to the skin and dispersed among multiple pathways through the body. Reports of cardiovascular changes following legal electrocution vary. Jaffe stated that most necropsies in such cases show no cardiac pathology, but Taylor has declared that the heart and great vessels may show multiple perforations. He further reported that arrhythmias, angina, rupture of cardiac valves, and myocardial infarction all may follow accidental exposure to an electric current. The majority of neurologic manifestations, aside from transitory neurop!lychiatric disorders, result from accidents involving high voltage. They are due to heat-induced destruction of parts of the brain or spinal cord. Spinal-cord temperatures above 120 0 F. and brain temperatures up to 145 0 F. are not uncommon following legal electrocution using 500 to 2000 volts with a current of 4 to 8 amperes for two minutes. Occasionally after an electrical accident, a transitory paresis of an extremity may last several weeks. Unconsciousness is more common in high-voltage accidents. Cerebral edema and perivascular hemorrhages have been reported. Nerves may lose their irritability and conductivity and apnea may result from central inhibition or actual damage to the respiratory center. Contact with electrical conductors may cause a generalized tetanic muscular contraction. This is most commonly seen with 60 cycle alternating currents greater than about 20 milliamperes. Spasm of the muscles of the hands and arms may make it impossible for the victim to release his grasp of the conductors. "Hold on" electrical accidents usually are associated with other symptoms such as tightness of the chest, difficulty of breathing, and a sensation of suffocation. The victim may hold on to the conductors for several minutes. The longer he holds on, the greater the likelihood of chest Rymptoms and the chance for unconsciousness and death. Release from the conductors will result when current flow is stopped, or the victim's

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muscles become hypoxic or fatigued. The. initial muscular contraction may be so violent as to throw the victim off the conductors. Broken bones and ruptured muscles may result from the violence of contraction.

SUMMARY One of the two wires supplying electrical power from the generating station is connected to the earth, or "grounded." Because the earth is conductive, an individual who is also grounded need touch only one wirethe ungrounded or "hot" wire-to receive a shock. Grounding the metal surface of an electrical appliance reduces the chance of shock by ensuring that accidental circumstances can produce only a very low voltage between the appliance and ground. Because persons in operating rooms are well grounded, extra precautions against shock are needed. Electrical power is supplied through an isolation transformer which isolates the electrical system so that no voltage difference exists between either electrical wire and the ground. The end result of the flow of electricity through the body depends upon a number of factors-principally the amount of current flow (which in turn depends upon the voltage and the resistance), the type of current (whether alternating or direct), the pathway of current through the body, and the duration of flow. Although fibrillation can be induced by the passage of electricity through the heart, defibrillation also can be accomplished electrically. Both alternating and direct current have been used for this purpose. Besides the possibility of inducing ventricular fibrillation, electricity may damage the body by producing violent muscular contractions, injuring nerves, and overheating tissue.

REFERENCES 1. Beck, C. S., Pritchard, W. H., and Feil, H. S.: Ventricular fibrillation of long duration abolished by electric shock. J.A.M.A. 135:985-986 (Dec. 13) 1947. 2. Burchell, H. B.: Electrocution hazards in the hospital or laboratory. (Editorial.) Circulation 27: 1015-1017 (June) 1963. 3. Guyton, A. C., and Satterfield, J.: Factors concerned in electrical defibrillation of the heart, particularly through the unopened chest. Am. J. Physiol. 167: 81-87 (Oct.) 1951. 4. Hughes, J. P. W.: Emergencies in general practice: Electric shock and associated accidents. Brit. M. J. 1:852-855 (April 14) 1956. 5. Jaff6, R. H.: Electropathology: Review of pathologic changes produced by electric currents. Arch. Path. 5:837-870 (May) 1928. 6. Kouwenhoven, W. B., Hooker, D. R., and Langworthy, O. R.: The current flowing through the heart under conditions of electric shock. Am. J. Physiol. 100:344-350 (April) 1932. 7. Langworthy, O. R., and Kouwenhoven, W. B.: An experimental study of abnormalities produced in the organism by electricity. J. Indust. Hyg. 12: 31-65 (Feb.) 1930.

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8. Lown, Bernard, Bey, S. K., Perlroth, M. G., and Abe, Tadaaki: Cardioversion of ectopic tachycardias. Am. J. M. Sc. 246:257-264 (Sept.) 1963. 9. Lown, Bernard, Neuman, Jose, Armarasingham, Raghavan, and Berkovits, B. V.: Comparison of alternating current with direct current electroshock across the closed chest. Am. J. Cardio!' 10:223-233 (Aug.) 1962. 10. Smith, R. H.: Electrical Anesthesia. Springfield, Illinois, Charles C Thomas,Publisher, 1963, 54 pp. 11. Taylor, C., and Stoelting, V. K.: Cardiac rupture following electrocution. J. Indiana M. A. 55:1502-1505 (Oct.) 1962. 12. Weinberg, D. I., Artley, J. L., Whalen, R. E., and McIntosh, H. D.: Electric shock hazards in cardiac catheterization. Circulation Res. 11: 1004-1009 (Dec.) 1962.