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HIGH-TENSION ELECTRICAL INJURY
978
extending health services in poor countries. Let us hope that pharmaceutical companies, governments, and aid organisations will take the point.
ary cover for the vital structures, a flap being constructed later. Microscopy of doubtful tissue has been recommended as a guide to excision5 but even with this guide another look is probably still necessary.
HIGH-TENSION ELECTRICAL INJURY HIGH-TENSION shocks cause only a small proportion of electrical injuries but the results are serious (the voltage is usually 11 000 or more, though high tension means anything higher than the domestic supply). Depressingly often the outcome is amputation of a limb. Luce and others’ have lately reported the loss of 11 upper limbs in 18 patients, most of whom were young men. The tissue damage is largely due to the conversion of electrical energy to thermal energy.2 According to Joule’s law, when a current passes through a conductor the power (heat) is proportional to the amperage squared times resistance; thus bone and skin, which are poor conductors of high resistance, will very efficiently convert electrical energy to thermal energy. This accounts for the severe damage to periosseous muscles beneath viable tissue. When the current in a high-tension accident arcs, commonly from the palm to the volar aspect of the wrist, there is a voltage drop absorbing much of the electrical energy as the air particles become ionised. The temperature in such an arc can reach 4000 °C, with burning of tissue and ignition of clothing3. Thus tissue damage can result from both the heat of the electric arc and the flow of current. The patient with a high-tension injury needs careful initial examination. The shock may have thrown him and caused other injuries;3 and extensive flame burns may obscure the lesions at the site of contact. When fluid requirements are calculated the percentage area burned may not be a good criterion, since the death of tissue simulates a crush injury in which additional fluid is needed to prevent renal failure.4 Particular attention must be paid to the tissue damage at the site of contact. Immediate decompression by escharotomy and fasciotomy must be followed by debridement of dead tissue. There has been much argument about the timing and extent of the debridement. The usual policy with burns is to watch for progressive necrosis of muscle and to debride periodically. In high-tension injuries this policy is inappropriate because excision tends to be inadequate or delayed, and skin cover is not achieved early enough to preserve the function of nerves and tendons. Clearly, any progressive necrosis of muscle cannot be due to the high-tension injury; it results from infection and hypoxia and is prevented by thorough debridement of all dead muscle-especially around bone. Nerves and tendons, even if apparently not viable, should be spared since some regeneration is possible if good cover is provided early with a skin flap; this is especially so in children, who have remarkable powers of recovery. After the excision, early application of a skin flap is essential to provide a good blood-supply and cover, and it can be raised at the first operation. The wound can thereafter be inspected by lifting the flap from the wound and resuturing. Alternatively, xenograft can be used as temporDowden, W. L., Hoopes, J. E. Surgery, Gynec. Obstet. 1978, 147, 38. 2. Hunt, J. L., Mason, A. D., Masterson, T. S., Pruitt, B. A. J. Trauma, 1976, 16, 335. 3. Skoof, T. ibid, 1970, 10, 816. 4. Hartford, C. E., Ziffren, S. E. ibid. 1971, 4, 331.
THE ANOMALY THAT WOULDN’T GO AWAY CORRELATIONS can be treacherous. Textbooks warn that a correlation coefficient must be interpreted with caution-that its statistical significance need not mean cause. An aura of implicit cause and effect may hang over a good correlation, nonetheless. Perhaps it is because of this aura that the problems inherent in correlation analysis do little to deter their use. Give a man a weapon-and he’ll use it. Multiple regression is more treacherous still. So impressive. So elegant in its multidimensional space. So easy to do on a computer. And, some say, the logistic function can now rescue it from the fallacy of linearity. Thus, despite the difficulties in sorting out the meaning of partial regression coefficients when predictor variables are inter-related, it is used. Give a man a weapon ... Correlation and regression analysis of international differences in mortality against a wide variety of dietary, social, and economic variables has a depressing history. It began with, and repeatedly returns to, the enthusiastic interpretation of a few points purporting to represent the diets and coronary disease of millions of people of diverse backgrounds.l The assertions of causality on the basis of such evidence have been at times extreme. But give a man three weapons-correlation, regression, and a pen-and he will use all three. Against this background we must set a display by Cochrane and his colleagues,2 who have taken up the old arms in yet another assault on international differences in mortality. And their results are indeed as they describe them-"both interesting and amusing". One might add sobering, as well, like so many displays of weaponry. For though high levels of educational standards and a high percentage of health expenditure covered by public funds both correlate satisfyingly with low levels of mortality in 18 developed countries, not all the results are so comforting. Oddly enough, higher numbers of paediatricians per birth are correlated with higher infant death rates. This is but a taste of the ultimate paradox: the more doctors per person, the higher the death-rates in general. Such anomalies may well interest or amuse. On the other hand, the authors tell us that, despite extensive juggling of the figures, the anomalies would not go away. These associations are eloquent in questioning the expanding use of multivariate analysis in the medical sciences. But the reasons for the sobering results are only partly statistical. There are the problems of distributions all around: of variables which are not normally distributed, as the statistician would have them; of causes of death which are not uniformly distributed, as . the inter-country comparisons would have them; and of doctors and health services which are not equably distributed, as justice would have them. Indeed, much in this world is attributable to anomalous distributions.
1. Luce, E. A.,
5.
W. C., Burke, J. F., Trelstad, R. L., Caulfield, J., ibid.1978, 18, 423. 1. Keys, A. Atherosclerosis, 1971, 14, 193. 2. Cochrane, A. L., St. Leger, A. S., Moore, F. J. Epidem. Comm. Hlth, 1978,
Quinby,
32, 200.
extending health services in poor countries. Let us hope that pharmaceutical companies, governments, and aid organisations will take the point.
ary cover for the vital structures, a flap being constructed later. Microscopy of doubtful tissue has been recommended as a guide to excision5 but even with this guide another look is probably still necessary.
HIGH-TENSION ELECTRICAL INJURY HIGH-TENSION shocks cause only a small proportion of electrical injuries but the results are serious (the voltage is usually 11 000 or more, though high tension means anything higher than the domestic supply). Depressingly often the outcome is amputation of a limb. Luce and others’ have lately reported the loss of 11 upper limbs in 18 patients, most of whom were young men. The tissue damage is largely due to the conversion of electrical energy to thermal energy.2 According to Joule’s law, when a current passes through a conductor the power (heat) is proportional to the amperage squared times resistance; thus bone and skin, which are poor conductors of high resistance, will very efficiently convert electrical energy to thermal energy. This accounts for the severe damage to periosseous muscles beneath viable tissue. When the current in a high-tension accident arcs, commonly from the palm to the volar aspect of the wrist, there is a voltage drop absorbing much of the electrical energy as the air particles become ionised. The temperature in such an arc can reach 4000 °C, with burning of tissue and ignition of clothing3. Thus tissue damage can result from both the heat of the electric arc and the flow of current. The patient with a high-tension injury needs careful initial examination. The shock may have thrown him and caused other injuries;3 and extensive flame burns may obscure the lesions at the site of contact. When fluid requirements are calculated the percentage area burned may not be a good criterion, since the death of tissue simulates a crush injury in which additional fluid is needed to prevent renal failure.4 Particular attention must be paid to the tissue damage at the site of contact. Immediate decompression by escharotomy and fasciotomy must be followed by debridement of dead tissue. There has been much argument about the timing and extent of the debridement. The usual policy with burns is to watch for progressive necrosis of muscle and to debride periodically. In high-tension injuries this policy is inappropriate because excision tends to be inadequate or delayed, and skin cover is not achieved early enough to preserve the function of nerves and tendons. Clearly, any progressive necrosis of muscle cannot be due to the high-tension injury; it results from infection and hypoxia and is prevented by thorough debridement of all dead muscle-especially around bone. Nerves and tendons, even if apparently not viable, should be spared since some regeneration is possible if good cover is provided early with a skin flap; this is especially so in children, who have remarkable powers of recovery. After the excision, early application of a skin flap is essential to provide a good blood-supply and cover, and it can be raised at the first operation. The wound can thereafter be inspected by lifting the flap from the wound and resuturing. Alternatively, xenograft can be used as temporDowden, W. L., Hoopes, J. E. Surgery, Gynec. Obstet. 1978, 147, 38. 2. Hunt, J. L., Mason, A. D., Masterson, T. S., Pruitt, B. A. J. Trauma, 1976, 16, 335. 3. Skoof, T. ibid, 1970, 10, 816. 4. Hartford, C. E., Ziffren, S. E. ibid. 1971, 4, 331.
THE ANOMALY THAT WOULDN’T GO AWAY CORRELATIONS can be treacherous. Textbooks warn that a correlation coefficient must be interpreted with caution-that its statistical significance need not mean cause. An aura of implicit cause and effect may hang over a good correlation, nonetheless. Perhaps it is because of this aura that the problems inherent in correlation analysis do little to deter their use. Give a man a weapon-and he’ll use it. Multiple regression is more treacherous still. So impressive. So elegant in its multidimensional space. So easy to do on a computer. And, some say, the logistic function can now rescue it from the fallacy of linearity. Thus, despite the difficulties in sorting out the meaning of partial regression coefficients when predictor variables are inter-related, it is used. Give a man a weapon ... Correlation and regression analysis of international differences in mortality against a wide variety of dietary, social, and economic variables has a depressing history. It began with, and repeatedly returns to, the enthusiastic interpretation of a few points purporting to represent the diets and coronary disease of millions of people of diverse backgrounds.l The assertions of causality on the basis of such evidence have been at times extreme. But give a man three weapons-correlation, regression, and a pen-and he will use all three. Against this background we must set a display by Cochrane and his colleagues,2 who have taken up the old arms in yet another assault on international differences in mortality. And their results are indeed as they describe them-"both interesting and amusing". One might add sobering, as well, like so many displays of weaponry. For though high levels of educational standards and a high percentage of health expenditure covered by public funds both correlate satisfyingly with low levels of mortality in 18 developed countries, not all the results are so comforting. Oddly enough, higher numbers of paediatricians per birth are correlated with higher infant death rates. This is but a taste of the ultimate paradox: the more doctors per person, the higher the death-rates in general. Such anomalies may well interest or amuse. On the other hand, the authors tell us that, despite extensive juggling of the figures, the anomalies would not go away. These associations are eloquent in questioning the expanding use of multivariate analysis in the medical sciences. But the reasons for the sobering results are only partly statistical. There are the problems of distributions all around: of variables which are not normally distributed, as the statistician would have them; of causes of death which are not uniformly distributed, as . the inter-country comparisons would have them; and of doctors and health services which are not equably distributed, as justice would have them. Indeed, much in this world is attributable to anomalous distributions.
1. Luce, E. A.,
5.
W. C., Burke, J. F., Trelstad, R. L., Caulfield, J., ibid.1978, 18, 423. 1. Keys, A. Atherosclerosis, 1971, 14, 193. 2. Cochrane, A. L., St. Leger, A. S., Moore, F. J. Epidem. Comm. Hlth, 1978,
Quinby,
32, 200.