DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY.
1977, 19
ELECTRICAL INJURY IN CHILDHOOD ELECTRICAL injuries during childhood are not uncommon, but the incidence is difficult to ascertain because only fatal cases are notified. Statistics of mortality from such injuries in England and Wales for the quinquennium 1969 to 1973' illustrate the expected preponderance of males, particularly in the age range 5 to I5 years, and also the higher incidence in the first four years of life, when curiosity outweighs experience (Fig. 1). This paper outlines some of the factors involved in producing injury from electricity, with some comment regarding prevention. There is general agreement that the magnitude of current passing through the body determines the degree of damage2. 3. The electrical resistance of the pathway through the body determines the magnitude of applied voltage necessary to cause a dangerous or lethal current to flow (Ohm's Law). Internal resistance of the body seems to vary little, and a figure of 500 Ohms (0) seems a good approximation*. Skin resistance, however, depends on several factors, including age and wetness. We have examined the influence of age upon combined body and skin resistance in the age-group up to 14 years and found a significant increase in resistance with increasing age. The mean resistance for the group, measured with electrodes applied to dry hands, was approximately 20,000 i 7000 (SD)R4,illustrating the wide person-to-person variation. Re-testing with wet hands produced a significant fall in mean resistance of about 50 per cent. The degree of tissue damage caused by a current is influenced by the following factors: ( a ) Polarity. Alternating current (AC)shock is more dangerous than direct current shock. When a nerve impulse or an electric current reach a motor end-plate acetylcholine is released, and until this is destroyed by cholinesterase the muscle is in a refractory state. At 50Hz (UK mains voltage: 1Hz = 1 cycle/sec) the electron flow through the conductor (the current) reverses direction one hundred times each second and the neuromuscular j unction therefore remains refractory. Thus, if an AC electrical source is grasped the muscles remain in spasm ; as forearm flexors are more powerful than the extensors the victim is unable to let go. (b) Frequency. The lower the frequency the lower will be the threshold of sensation. At a frequency of 60Hz,a current of 0.36mA was perceived by 50 per cent of a group of men3. This level of current is only important in that it may cause involuntary movements, leading to falls. A larger current causes muscular contraction leading to the 'cannot-let-go' phenomenon. At the same frequency (6OHz), 50 per cent of a group of men could not let go when
Fig. 1. Mortality from electrical injury in England and Wales for quinquennium 1969-1973: (Iefi) birth to 15 years; (right) birth to five years.
1
72
ANNOTATIONS
a current of 16mA was passed through a wire. At a higher frequency of IkHz, the current required for this effect rises to 24mA5, and with frequencies above lkHz the risks of electrical injury diminish considerably. (c) Currenrpathway. Death caused by mains voltage can usually be attributed to ventricular fibrillation, asphyxia or respiratory arrest. The sites of contact with electrical source and earth are important in determining the pathway of current through the body. About 10 per et ul.' cent of total current flow in hand-to-foot shock passes through the hearta. RAFTERY observed the effects of 50Hz leakage currents from catheters in the right ventricle during cardiopulmonary by-pass in humans and anaesthetised dogs. The smallest current producing fibrillation from the right ventricle was 80pA. A similar figure is given by DOBBIE~, though WHALEN et aL9 induced fibrillation in dogs by currents as small as 20pA. Passage of current through the thorax may cause contraction of the chest muscles, with consequent asphyxia. At 60Hz, currents of 40 to 60mA will produce asphyxia, though much lower currents of 18 to 22mA may be dangerous5. Experimental work suggests that respiratory arrest caused by passage of current through the respiratory centre is uncommonlo. ( d ) Durarion of exposure. Studies in dogs suggest that the threshold level for ventricular fibrillation falls as the duration of shock increasesll. For periods shorter than 10 milliseconds, current greatly in excess of threshold is necessary to produce fibrillation. Much of the current is carried by blood vessels. Damage to vessel walls may result in haemorrhage, and elevation of the intima is considered pathognomonic12. Cavity formation around blood vessels may occur in the brain, particularly after lightning injury. Focal myelin degeneration and cerebral oedema are common. Burns account for 95 per cent of electrical injurieP. Contact with a live conductor accounts for half the total number14. Flash (arc) burns are usually industrial and more severe, involving higher voltages. Ignition of clothes or equipment by spark or heating effect may also occur. The extent of skin involvement should never be used as an indicator of severity. Serious muscle necrosis may underlie intact skin. Swelling or oedema are important warning signs. Tissue necrosis may not be complete until 10 days after injuryIg. Myoglobinuria and renal failure may result from extensive tissue damage. The mouth is involved in as many as two-thirds of children with electrical b u m l a ; half of these are caused by mouthing a 'female' plug disconnected from an appliance (e.g. a kettle) but switched on at a wall socket. Secondary haemorrhage from labial arteries occurs in as many as 25 per cent" and may appear as late as four days after the original injury. Microstoma is a particularly troublesome complication. Other effects of electrical injury have recently been summarised by HORSFIELD and WILLIAMS'*. Interestingly, cataracts may appear as late as three years afterwardsl9. There is increasing concern over the risk of shock from monitoring equipment and other electrical devices in hospitals (including reading lamps and television sets). Fatalities are well documented, especially with intracardiac pacemakers2'22. Small leakage currents in the pA range usually flow in conductors within equipment. Earthing of the patient's circuit disperses these currents through a low-resistance escape pathway. If this protective connection is broken, current may flow through the patient. If two or more pieces of equipment are connected to a patient the potentials of each cabinet or chassis relative to the power-line neutral may be different; this will allow current to flow from one apparatus to another via the patient and thence to the power-line neutral. The risk of fibrillation is high if an intracardiac pacemaker is in use, and this may occur with intact skin if the current is large enough. 73
DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY.
1977, 19
The introduction of British Standard 1363 13A three-pin plugs, together with regular maintenance, has almost eliminated electrical hazards in hospital. Battery-operated pacemakers have also reduced the chance of intracardiac passage of current, though cardiac et U I . used ~ ~ larger than normal ground catheterisation may be dangerous. STARMER (earthing) wires to provide lower resistance pathways and encourage dissipation of leakage currents. Recently the concept of earth-free patient monitoring has been introducedz4, but neither perfect earthing nor absolute electrical isolation of the patient are yet possible in practice. The availability of a defibrillator in the risk situations outlined above should therefore be mandatory. Domestic accidents can be minimised by wider education, especially in schools, about electrical safety. Firm legislation and inspection of electrical appliances and household wiring to ensure compliance with appropriate laid-down standards are necessary. Where such standards do not exist, consideration shodd be given to their introduction. A. J. WILLIAMS P. HORSFIELD Department of Child Health, Alder Hey Children’s Hospital, Eaton Road, Liverpool L12 2AP. REFERENCES I . Registrar General Statistical Review of England and Wales, 1973. London: H.M.S.O. 2. Bruner, J. M. R. (1967) ‘Hazards of electrical apparatus.’ Anesthesiology, 28, 396425. 3. Bernstein, T. (1973) ‘Effects of electricity and lightning on man and animals.’ Journal of Forensic Sciences, 18, 3-1 1. 4. Williams, A. J., Horsfield. P. (1977) ‘Measurement of electrical impedance in childhood.’ (In preparation.) 5. Dalziel, C . F., Lee, W. R. (1968) ‘Re-evaluation of lethal electric currents.’ IEEE Spectrum, 4,467476. 6. Butterfield, W. H. (1975) ‘Electricshock hazards in aversive shock conditioning of humans.’ Behavioural Engineering, 3, 1-28. 7. Raftery, E. B., Green, H., Gregory, I. (1973) ‘Electrical safety: fibrillation thresholds with 50Hz leakage currents in man and animals.’ British Heart Journal, 35, 864. 8 . Dobbie, A. K. (1972) ‘Electricity in hospitals.’ Biomedical Engineering, 7, 12-20. 9. Whalen, R. E.. Starmer, C. F., McIntosh, H. D. (1964) ‘Electrical hazards associated with cardiac pacemaking.’ Annals of the New York Academy of Sciences, 111, 922-931. 10. Lee, W. R., Zoledziowski, S. (1964) ‘Effectsof electric shock on respiration in the rabbit.’BritishJournal of Industrial Medicine, 21, 135-144. 1 I . Kouwenhoven, W. B.. Chesnut, R. W., Knickerbocker, G. G.. Milnor, W. R., Sass, D. J. (1959) ‘A-C shocks of varying parameters affecting the heart.’ Transcripts of the American Institute of Electrical Engineers. 78, 163-1 69. 12. Hughes, J. P. W. (1956) ‘Electric shock and associated accidents.’ British Medical Journal, 1, 852-855. 13. Oeconomopoulos, C. T. (1962) ‘Electrical burns in infancy and early childhood.’ American Journal of Diseases of Childhood. 103, 35-38. 14. Davies, M. R. (1959) ‘Burns caused by electricity.’ British Journal of Plastic Surgery, 11, 288-300. 15. Baxter, C. R. (1970) ‘Present concepts in the management of major electrical injury.’ Surgical Clinics of North America, 50, 1401-1418. 16. Thomson, H. G., Juckes, H. M., Farmer, A. M. (1965) ‘Electrical burns to the mouth in children.’ Plastic and Reconstructive Surgery, 35, 466477. 17. Gifford, G. H., Marty, A. T., MacCollum, D. W. (1971) ‘The management of electrical mouth burns in children.’ Pediatrics, 47, 113-1 19. 18. Horsfield, P.,Williams, A. J. (1977) ‘Recovery after electrical injury.’ Developmental Medicine and Child Neurology, (in press). 19. Adam, A. I., Klein, M.(1945) ‘Electrical cataract.’ British Journal of Ophthalmology, 29, 169-175. 20. Burchell, H. B. (1961) ‘Hidden hazards of cardiac pacemakers.’ Circulation, 24, 161-163. 21. Furman, S.. Schwedel. J. B., Robinson, G., Hurwitt, E. S. (1961) ‘Useof an intracardiac pacemaker in the control of heart block.’ Surgery, 49, 98-108. 22. Noordijk, J. A., Oey, F. T. I., Tebra, W. (1961) ‘Myocardial electrodes and the danger of ventricular fibrillation.’ Lancer. 1, 975-977. 23. Starmer, C. F., Mclntosh. H. D.. Whalen, R. E. (1971) ‘Electrical hazards and cardiovascular function.’ New England Journal of Medicine, 284, 181r186. 24. Pocock S. N. (1972) ‘Earth-free patient monitoring.’ Biomedical Engineering, 7, 21-25.
14
1977, 19
ELECTRICAL INJURY IN CHILDHOOD ELECTRICAL injuries during childhood are not uncommon, but the incidence is difficult to ascertain because only fatal cases are notified. Statistics of mortality from such injuries in England and Wales for the quinquennium 1969 to 1973' illustrate the expected preponderance of males, particularly in the age range 5 to I5 years, and also the higher incidence in the first four years of life, when curiosity outweighs experience (Fig. 1). This paper outlines some of the factors involved in producing injury from electricity, with some comment regarding prevention. There is general agreement that the magnitude of current passing through the body determines the degree of damage2. 3. The electrical resistance of the pathway through the body determines the magnitude of applied voltage necessary to cause a dangerous or lethal current to flow (Ohm's Law). Internal resistance of the body seems to vary little, and a figure of 500 Ohms (0) seems a good approximation*. Skin resistance, however, depends on several factors, including age and wetness. We have examined the influence of age upon combined body and skin resistance in the age-group up to 14 years and found a significant increase in resistance with increasing age. The mean resistance for the group, measured with electrodes applied to dry hands, was approximately 20,000 i 7000 (SD)R4,illustrating the wide person-to-person variation. Re-testing with wet hands produced a significant fall in mean resistance of about 50 per cent. The degree of tissue damage caused by a current is influenced by the following factors: ( a ) Polarity. Alternating current (AC)shock is more dangerous than direct current shock. When a nerve impulse or an electric current reach a motor end-plate acetylcholine is released, and until this is destroyed by cholinesterase the muscle is in a refractory state. At 50Hz (UK mains voltage: 1Hz = 1 cycle/sec) the electron flow through the conductor (the current) reverses direction one hundred times each second and the neuromuscular j unction therefore remains refractory. Thus, if an AC electrical source is grasped the muscles remain in spasm ; as forearm flexors are more powerful than the extensors the victim is unable to let go. (b) Frequency. The lower the frequency the lower will be the threshold of sensation. At a frequency of 60Hz,a current of 0.36mA was perceived by 50 per cent of a group of men3. This level of current is only important in that it may cause involuntary movements, leading to falls. A larger current causes muscular contraction leading to the 'cannot-let-go' phenomenon. At the same frequency (6OHz), 50 per cent of a group of men could not let go when
Fig. 1. Mortality from electrical injury in England and Wales for quinquennium 1969-1973: (Iefi) birth to 15 years; (right) birth to five years.
1
72
ANNOTATIONS
a current of 16mA was passed through a wire. At a higher frequency of IkHz, the current required for this effect rises to 24mA5, and with frequencies above lkHz the risks of electrical injury diminish considerably. (c) Currenrpathway. Death caused by mains voltage can usually be attributed to ventricular fibrillation, asphyxia or respiratory arrest. The sites of contact with electrical source and earth are important in determining the pathway of current through the body. About 10 per et ul.' cent of total current flow in hand-to-foot shock passes through the hearta. RAFTERY observed the effects of 50Hz leakage currents from catheters in the right ventricle during cardiopulmonary by-pass in humans and anaesthetised dogs. The smallest current producing fibrillation from the right ventricle was 80pA. A similar figure is given by DOBBIE~, though WHALEN et aL9 induced fibrillation in dogs by currents as small as 20pA. Passage of current through the thorax may cause contraction of the chest muscles, with consequent asphyxia. At 60Hz, currents of 40 to 60mA will produce asphyxia, though much lower currents of 18 to 22mA may be dangerous5. Experimental work suggests that respiratory arrest caused by passage of current through the respiratory centre is uncommonlo. ( d ) Durarion of exposure. Studies in dogs suggest that the threshold level for ventricular fibrillation falls as the duration of shock increasesll. For periods shorter than 10 milliseconds, current greatly in excess of threshold is necessary to produce fibrillation. Much of the current is carried by blood vessels. Damage to vessel walls may result in haemorrhage, and elevation of the intima is considered pathognomonic12. Cavity formation around blood vessels may occur in the brain, particularly after lightning injury. Focal myelin degeneration and cerebral oedema are common. Burns account for 95 per cent of electrical injurieP. Contact with a live conductor accounts for half the total number14. Flash (arc) burns are usually industrial and more severe, involving higher voltages. Ignition of clothes or equipment by spark or heating effect may also occur. The extent of skin involvement should never be used as an indicator of severity. Serious muscle necrosis may underlie intact skin. Swelling or oedema are important warning signs. Tissue necrosis may not be complete until 10 days after injuryIg. Myoglobinuria and renal failure may result from extensive tissue damage. The mouth is involved in as many as two-thirds of children with electrical b u m l a ; half of these are caused by mouthing a 'female' plug disconnected from an appliance (e.g. a kettle) but switched on at a wall socket. Secondary haemorrhage from labial arteries occurs in as many as 25 per cent" and may appear as late as four days after the original injury. Microstoma is a particularly troublesome complication. Other effects of electrical injury have recently been summarised by HORSFIELD and WILLIAMS'*. Interestingly, cataracts may appear as late as three years afterwardsl9. There is increasing concern over the risk of shock from monitoring equipment and other electrical devices in hospitals (including reading lamps and television sets). Fatalities are well documented, especially with intracardiac pacemakers2'22. Small leakage currents in the pA range usually flow in conductors within equipment. Earthing of the patient's circuit disperses these currents through a low-resistance escape pathway. If this protective connection is broken, current may flow through the patient. If two or more pieces of equipment are connected to a patient the potentials of each cabinet or chassis relative to the power-line neutral may be different; this will allow current to flow from one apparatus to another via the patient and thence to the power-line neutral. The risk of fibrillation is high if an intracardiac pacemaker is in use, and this may occur with intact skin if the current is large enough. 73
DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY.
1977, 19
The introduction of British Standard 1363 13A three-pin plugs, together with regular maintenance, has almost eliminated electrical hazards in hospital. Battery-operated pacemakers have also reduced the chance of intracardiac passage of current, though cardiac et U I . used ~ ~ larger than normal ground catheterisation may be dangerous. STARMER (earthing) wires to provide lower resistance pathways and encourage dissipation of leakage currents. Recently the concept of earth-free patient monitoring has been introducedz4, but neither perfect earthing nor absolute electrical isolation of the patient are yet possible in practice. The availability of a defibrillator in the risk situations outlined above should therefore be mandatory. Domestic accidents can be minimised by wider education, especially in schools, about electrical safety. Firm legislation and inspection of electrical appliances and household wiring to ensure compliance with appropriate laid-down standards are necessary. Where such standards do not exist, consideration shodd be given to their introduction. A. J. WILLIAMS P. HORSFIELD Department of Child Health, Alder Hey Children’s Hospital, Eaton Road, Liverpool L12 2AP. REFERENCES I . Registrar General Statistical Review of England and Wales, 1973. London: H.M.S.O. 2. Bruner, J. M. R. (1967) ‘Hazards of electrical apparatus.’ Anesthesiology, 28, 396425. 3. Bernstein, T. (1973) ‘Effects of electricity and lightning on man and animals.’ Journal of Forensic Sciences, 18, 3-1 1. 4. Williams, A. J., Horsfield. P. (1977) ‘Measurement of electrical impedance in childhood.’ (In preparation.) 5. Dalziel, C . F., Lee, W. R. (1968) ‘Re-evaluation of lethal electric currents.’ IEEE Spectrum, 4,467476. 6. Butterfield, W. H. (1975) ‘Electricshock hazards in aversive shock conditioning of humans.’ Behavioural Engineering, 3, 1-28. 7. Raftery, E. B., Green, H., Gregory, I. (1973) ‘Electrical safety: fibrillation thresholds with 50Hz leakage currents in man and animals.’ British Heart Journal, 35, 864. 8 . Dobbie, A. K. (1972) ‘Electricity in hospitals.’ Biomedical Engineering, 7, 12-20. 9. Whalen, R. E.. Starmer, C. F., McIntosh, H. D. (1964) ‘Electrical hazards associated with cardiac pacemaking.’ Annals of the New York Academy of Sciences, 111, 922-931. 10. Lee, W. R., Zoledziowski, S. (1964) ‘Effectsof electric shock on respiration in the rabbit.’BritishJournal of Industrial Medicine, 21, 135-144. 1 I . Kouwenhoven, W. B.. Chesnut, R. W., Knickerbocker, G. G.. Milnor, W. R., Sass, D. J. (1959) ‘A-C shocks of varying parameters affecting the heart.’ Transcripts of the American Institute of Electrical Engineers. 78, 163-1 69. 12. Hughes, J. P. W. (1956) ‘Electric shock and associated accidents.’ British Medical Journal, 1, 852-855. 13. Oeconomopoulos, C. T. (1962) ‘Electrical burns in infancy and early childhood.’ American Journal of Diseases of Childhood. 103, 35-38. 14. Davies, M. R. (1959) ‘Burns caused by electricity.’ British Journal of Plastic Surgery, 11, 288-300. 15. Baxter, C. R. (1970) ‘Present concepts in the management of major electrical injury.’ Surgical Clinics of North America, 50, 1401-1418. 16. Thomson, H. G., Juckes, H. M., Farmer, A. M. (1965) ‘Electrical burns to the mouth in children.’ Plastic and Reconstructive Surgery, 35, 466477. 17. Gifford, G. H., Marty, A. T., MacCollum, D. W. (1971) ‘The management of electrical mouth burns in children.’ Pediatrics, 47, 113-1 19. 18. Horsfield, P.,Williams, A. J. (1977) ‘Recovery after electrical injury.’ Developmental Medicine and Child Neurology, (in press). 19. Adam, A. I., Klein, M.(1945) ‘Electrical cataract.’ British Journal of Ophthalmology, 29, 169-175. 20. Burchell, H. B. (1961) ‘Hidden hazards of cardiac pacemakers.’ Circulation, 24, 161-163. 21. Furman, S.. Schwedel. J. B., Robinson, G., Hurwitt, E. S. (1961) ‘Useof an intracardiac pacemaker in the control of heart block.’ Surgery, 49, 98-108. 22. Noordijk, J. A., Oey, F. T. I., Tebra, W. (1961) ‘Myocardial electrodes and the danger of ventricular fibrillation.’ Lancer. 1, 975-977. 23. Starmer, C. F., Mclntosh. H. D.. Whalen, R. E. (1971) ‘Electrical hazards and cardiovascular function.’ New England Journal of Medicine, 284, 181r186. 24. Pocock S. N. (1972) ‘Earth-free patient monitoring.’ Biomedical Engineering, 7, 21-25.
14
