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Letters to the Editor Indian Pediatrics 2000;37: 1154-1157 |
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Scorpion Sting |
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The author has reviewed the literature on scorpion sting(1) extensively in the personal practices column. In addition he has presented his views on the management of scorpion envenomation. Unfortunately, he has not referred to our articles(2) on scorpion envenomation, a prospective study done in one of the medical units at the Institute of Child Health, Chennai, during eighties. Seventy one children who were symptomatic following scorpion sting were studied. the signs and symptoms included peripheral failure in 80.7%, persistent tachycardia in 87.3%, ECG changes suggestive of myo-cardial injury pattern in 56.5%, pulmonary edema in 5.6%, seizures in 2.8% and brady-cardia in 2.8% of cases. All the symptomatic children received lytic cocktail therapy and steroids as per a standard protocol for a period of 12 hours, and in an occasional child the treatment was extended upto 18 hours. Other supportive measures included IV fluids, symptomatic treatment for pulmonary edema and seizures. Digoxin was withheld based on past experience. In this particular study, only one child (1.4%) died of recurrent seizures at the end of 12 hours of hospital stay. From 1981, over a period of 19 years, a total of 3775 cases were treated for scorpion envenomation at the Institute of Child Health. The average mortality rate was only 3.7%. In the past 4 years inotropic agent like dopamine is being used in place of lytic cocktail.(30) We never concluded in our earlier article that pethidine may convert sublethal dose of scorpion venom into a lethal one and interfere with respiratory reflexes(4). In one of the studies of Bavaskar et al.(5) among the 34 children treated, 4 (11.7%) died. Most of them were treated with alpha blockers, vasodilators like prazosin, nitroprusside infusion, fruse-mide, etc. The children who died had circulatory failure with central cyanosis and their heart rate ranged from 136 to 215 per min and all of them had hypotension. Two of the victims received oral prazosin which is known to produce ‘first pass’ hypotension. It is necessary to monitor both systemic arterial pressure and central venous pressure when initiating vasodilator drug therapy. Clinical deterioration can occur if filling pressure falls excessively or the patient develops systemic hypotension(6). Is it safe to use prazosin claiming the drug as an antidote to scorpion venom? Indiscriminate use of vasodilators or alpha blockers are fraught with danger if there are inadequate facilities for continuous monitoring. It is simpler and easier to use lytic cocktail therapy even in primary and secondary care centers without the expensive modern monitoring systems, especially in the presence of hypotension. The experimental studies(7) using freshly extracted venom confirm our clinical experience. In the presence of hypertension which may be related to catecholamine induced auto-nomic storm, prazosin may be the drug of choice for children in Maharashtra whereas the complications as reported from Andhra Pradesh are related to consumptive coagulo-pathy. Hence, the treatment for scorpion envenomation must be individualized based on the nature of complications seen in the particular region. B.R. Santhanakrishnan*, *Deceased.
I thank Professor B.R. Santhanakrishnan for his comments on the article "Scorpion Sting"(1). While highlighting his views on lytic cocktail, he has raised doubts and concern about Prazosin therapy for scorpion sting. I do agree that treatment should be dictated by observed toxicity and known scorpions of the geographic area. However, it appears to me that most treatment ptotocols for scorpion sting are based on isolated, sometimes contro-versial observations and are not the results of controlled clinical studies. The beneficial effect of lytic cocktail was attributed to a state of artificial hibernation - an idea propagated by Labroit and Hugenard. It was documented that the course of lethal shock can be prevented or altered by administering phenoxy benzamine (dibenyline) which has a prolonged a-receptor blockages. The overall effect is one of vasodilation provided the circulating volume is adequate(2). Chlorpromazine in lytic cocktail exerted an improved dibenyline effect, lowering the cerebral metabolism giving enough time for scorpion venom effect to wear off?(3) Lytic cocktail (pethidine + chlorpromazine + promethazine) was a popular therapy for scorpion sting in pediatric units including ours(4). Out of 100 admissions for scorpion sting, 22 children died. The respiratory status of five children with increased secretions deteriorated after lytic cocktail. Twelve children had functional alteration of neuro-logical status which worsened on lytic cocktail. Their deaths were attributed to sedation or cardiac effects induced by lytic cocktail. We, no longer use lytic cocktail at our center. Drugs like pethidine and morphine are contraindicated because they enhance the toxic effects of scorpion venom(5). Con-current administration of drugs such as promethazine or chlorpromazine may greatly enhance pethidine induced sedation without slowing clearance of the drug. Intravenous pethidine more frequently produces a marked increase in heart rate. Such a tachycardia may worsen the systolic and diastolic dysfunction in these children with toxic myocardial changes. Chlorpromazine and other pheno-thiazines have a negative inotropic action and cause prolongation of QT intervals similar to scorpion venom action(6). Promethazine, a H1 blocker, tends to inhibit response to acetylcholine that is mediated by muscarinic receptors similar to atropine which has increased the mortality and morbidity in Bawaskar’s series(7). Similarly, the four fatal cases reported by Bawaskar were referred by peripheral doctors in moribund and comatosed condition. These children were treated with repeated atro- pine, steroids, antihistamines resulting in multi-organ failure. Antihistamine inhibits potassium channels similar to scorpion venom, prolonging QT interval and can result in sudden death. This was noted before advent of prazosin or treatment without prazosin(8,9). Steroids which were a part of lytic cocktail protocol mentioned by Prof. Santhanakrishnan are no better than placebo(10). It is not clear from the letter whether dopamine was used as inotropic support along with lytic cocktail or had replaced lytic cocktail at Institute of Child Health, Chennai. Positive inotropic support with dobutamine is practiced at our center whenever required for these cases. Dobuta-mine has a vasodilatory effect, improves ventricular-vascular coupling and reduces afterload. Tachycardia is more pronounced with dopamine than with dobutamine. At our center, we choose to treat victims of scorpion sting with prazosin. Prazosin is an antidote to venom action because at hyper-tension stage, it acts as an antihypertensive agent by reducing afterload while in hypo-tension, tachycardia and pulmonary edema it acts as a vasodilator and corrects hemo-dynamic pattern by reducing preload and afterload without reflex tachycardia. Even in hypo-tension with tachycardia due to scorpion sting, prazosin did reverse the changes(11). Fluid replacement must not be lost sight of, since hypovolemia is one of the proposed mechanism of shock syndrome in scorpion sting. Pulmonary edema and hypovolemia frequently co-exist in these patients. So management with loop diuretics without fluid replacement is a dangerous practice. Prazosin corrects metabolism by an increase in insulin secretion. Prazosin opens venom induced block of potassium channels. Prazosin alone has dropped the mortality to less than 1%(12). Prazosin administration is oral and easily available even at village level where a large number of victims come from. Pethidine of lytic cocktail is difficult to obtain and it is not available to a private practitioner in rural areas. The debates between old and new treatment protocols continues. Randomized controlled trials with prazosin and oral largactil (both with a-receptor blockage properties) may provide an answer to this debate. S. Mahadevan,
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