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This study was evaluated to the pattern of presentation, the outcome and efficacy of Prazosin in scorpion sting envenomation at a tertiary care hospital, Bagalkot, India. A total of 240 consecutive children were prospectively studied. Data included demographics, time of presentation to the hospital, clinical features, and premedication given before coming to the hospital, response to the oral Prazosin and hospital outcome. Local pain, sweating and peripheral circulatory failure were the common clinical presentation. Complications like acute pulmonary edema, myocarditis, shock and encephalopathy were also seen. These were treated with combination of Prazosin with either inotropes or vasodilators. Mortality was seen in 18 (7.5%) children. Usage of antihistaminics and steroids in these children had higher mortality. Oral Prazosin, a postsynaptic alpha -1 blocker is highly effective drug for scorpion sting envenomation. Early presentation to the hospital and early intervention with Prazosin will hasten the recovery in scorpion sting victim.
KEY WORDS: Scorpion sting, Children, Prazosin
Scorpion sting envenomation is an acute life threatening, time limiting medical emergency, if left untreated. It is a frequent event in tropical, subtropical and temperate zones of the world and poses a public health problem in certain parts of India . Mesobuthus tamulus or Indian red scorpion is the most lethal scorpion species. These are found abundantly in western Maharashtra, northern Karnataka, Andhra pradesh, Saurashtra and Tamilnadu [2, 3]. Children are at greater risk of developing severe envenomation like cardiac, respiratory and neurological complications as compared to adults. Clinical manifestations of scorpion envenomation are vomiting, profuse sweating, cold extremities, pulmonary edema and death [4, 5]. The deaths in scorpion sting envenomation are attributed to cardiopulmonary complications like myocarditis and acute pulmonary edema [6, 7, 8].
Prazosin, a postsynaptic alpha -1 blocker counteracts the effects of excessive catecholamines and early administration of prazosin arrests the development of severe systemic features. It has been found to be an effective drug for scorpion sting envenomation and has reduced the mortality rate to 1% as compared to 30% in pre-prazosin era [9, 10, 11]. The present study was done to observe the pattern of presentation, and also the outcome and efficacy of prazosin in scorpion sting envenomation in children admitted at tertiary care center.
MATERIALS AND METHOD:
This prospective study was conducted at S. Nijalingappa Medical College, Bagalkot, a tertiary care hospital in North Karnatka, India, during the period from January 2007 to December 2010(4 years). All the cases aged between 0-14 years presented to the emergency department with history of scorpion sting envenomation, presence of sting mark and sting or scorpion seen in vicinity of child by parents or near family members were admitted. In total around 240 cases were studied during this 4-year period. Informed consent was taken from parents or relatives. The details of the clinical features and treatment given at PHC/ referring hospital were noted from reference letter. All clinical details including blood pressure, heart rate, chest findings and temperature of extremities were recorded on interval and thereafter at one hourly on a pretested standard proforma.
The diagnosis of various systemic involvements was done based on clinical manifestations and investigations. Myocarditis was diagnosed, if the child had tachycardia, muffled heart sounds, gallop rhythm and systolic murmur, ECG changes (low amplitude, ST segment changes, and presence of arrhythmias), elevated LDH, cardiomegaly on Chest X-ray and decreased ejection fraction on 2 D Echocardiography. Acute pulmonary edema was diagnosed on the basis of presence of tachypnea, pinkish frothy sputum, bilateral crepitations and radiological findings, complemented with ABG analysis. Autonomic storm was diagnosed on the basis of sweating, vomiting, excessive salivation, priaprism, shivering and hypotension or hypertension.
Patients were continuously monitored in intensive care unit for pulse rate, respiratory rate, blood pressure, temperature, SPO2, capillary refilling time and signs of systemic involvements like development of pulmonary edema, myocarditis, encephalopathy and shock. Complete hemogram, serum electrolytes, blood sugar, arterial blood gas analysis, renal function test, ECG and chest radiographs were done in all children. 2D Echocardiography was done in all patients with myocarditis.
Cases with a history of scorpion sting that came within 6 hours were given paracetamol for pain and a dose of prazosin (30ug / kg) tablet either through naso-gastric tube or per oral and, were given 4 hourly till all the symptoms subsided. Asymptomatic cases that came after 6 hours of scorpion sting were kept under observation and received only symptomatic treatment without Prazosin. All the symptomatic cases were given prazosin and supportive care. Children with acute pulmonary edema were managed with judicious use of vasodilators and inotropes along with supportive measures and ventilated when required. All the cases were observed for a minimum period of 24 hours. Cases with complications were discharged after they were off the drugs for 24 hours and were stable for 48 hours. Analysis was done in relation to complications, time interval between the scorpion sting and admission, and mortality.
240 children between the age group of 0 -14 years were studied during the study period. 80 children had local involvement i.e. pain and swelling at sting area. Hence observed for 24 hours and discharged as per protocol. Remaining 160 children were symptomatic and were treated with Prazosin, IV fluids and symptomatic treatment whenever required vasodilators and inotropes were used. Most of the cases were within 2 -7yrs of age i.e.180 (75%), followed by 8-12 years. Males being affected in 140 (58.3%) and females in 100(41.7%) cases. Maximum numbers of cases were from rural areas accounting for 214 (89.2%) with peaks during summer. Indian red scorpion (Mesobuthus tamulus) species accounted for 175 (72.9%) cases. Most of the bites were during night time 164 (68.3%). Most common site of the sting was on extremities, mainly over lower limbs accounting 171(71. 5%) cases, followed by upper limb in 57 (23.8%) cases and face in 12 (4.7%) cases.
Children who came late were having features of excessive sympathetic activity (tachycardia, intense vasoconstriction and carditis). Those children presenting immediately after the sting (within 30 minutes) had features of parasympathetic hyperactivity (i.e. sweating, salivation bronchospasm and vomiting). All these symptoms indicates autonomic storm at presentation. Most common presenting symptoms were irritability and profuse sweating, hurried breathing, cold extremities followed by altered sensorium. Most common clinical signs were tachycardia, tachypnea, cold extremities, perspiration and hypotension (Table 1). Majority of cases approached the hospital after 6-12 hours of scorpion sting.
Myocarditis was detected in 48 (20%) of cases clinically could be diagnosed in 40% of cases after other investigations like ECG finding like ST segment depression in 25% cases. 48 cases (20%) has pulmonary edema with myocarditis. Acute pulmonary edema with myocarditis, shock and encephalopathy were found in 30(12.5%) patients and 25 of them required mechanical ventilation. Out of 25 patients, 18 of them died. All the 18 patients who died had received intravenous dexamethasone and antihistaminics prior to the hospital and they had presented6-12 hours after sting.
Mortality and complications were seen in those patients who presented to hospital after 6 hours of sting. Most of the deaths (75%) were in the age between 1-5 years. Highest mortality was due to cardiovascular complications i.e. myocarditis in 74%, pulmonary edema in 22% and encephalopathy in 4% cases. 5 cases were complicated with thromboembolic features (deep vein thrombosis and arterial thrombosis). In 2 cases on follow up echocardiography showed ventricular dilatation.
Indian red scorpion (Mesobuthus tamulus) venom is potent sodium channel activator  and resulting in stimulation of autonomic nervous system, which in turn leading to sudden release of endogenous catecholamines into circulation . The venom initially leads to transient cholinergic phase followed by sustained adrenergic hyperactivity, which is venom dose dependent phenomenon . Clinical manifestations depend upon the dose of venom, age of the child, season of sting and time lapse between sting and hospitalization .
Of the 240 cases, 140 (58.3%) were boys and 100 (41.7%) were girls, as also reported by Biswal et al . 214 (89.2%) cases of scorpion stings came from rural areas and 164 (68.3%) cases had sting over foot-leg, similar to Bosnak et al  where 71% were from rural areas and 55.6% had sting over foot-leg. Peripheral circulatory failure cases with cold extremities were seen in 180 (75%) of cases, similar to 83% reported by Bawaskar et al . This is due to early stage of compensated shock due to excessive catecholamine resulting in peripheral vasoconstriction, but without significant myocardial dysfunction.
Most of the cases with myocarditis had acute pulmonary edema and many had S3 gallop. Late onset acute pulmonary edema could have been due to acute myocardial injury and left ventricular failure caused late onset acute pulmonary edema and the toxin induced autonomic storm. There was no significant difference between means of basic parameters such as age, blood pressure, GCS, hemoglobin level, total leukocyte count and serum electrolytes among both survivors and non-survivors.
Time gap between scorpion sting and presentation to hospital is one of the significant risk factor determining the better outcome and mortality. Children who presented after 6 hours of sting had significantly higher mortality as also reported by Biswal et al . Most of the cases with acute pulmonary edema, encephalopathy and myocarditis came to us after 6 hours of the sting had higher mortality and morbidity. However, some studies [6, 11] have shown higher mortality in those patients admitted between 30 min to 3 hours of sting.
Mortality observed in this study was 18(7.5%) cases as compared to 1% to 10.7% reported by various authors from different places [14, 16, 17]. The causes for higher mortality may be late presentation, use of intravenous dexamethasone and antihistaminics and associated multiple systemic involvements. Dexamethasone alone or in combination with antihistaminics is known to potentiate the effect of catecholamine on cardiovascular and CNS and worsen encephalopathy as observed by other authors [14, 18].
Mortality was less in cases treated with Prazosin alone in comparison to others who received dobutamine, dopamine or SNP along with Prazosin. This could be due to the protective effect of Prazosin on cardiovascular and respiratory system. Early administration of Prazosin also reduces the mortality associated with encephalopathy which is due to neutralizing the adverse effect of catecholamine released in the brain, as the catecholamines released outside the brain does not crosses the blood brain barrier.
Scorpion sting envenomation is an acute life threatening emergency in children and timely referral and early therapy with Prazosin may be life saving. The presence of metabolic acidosis, myocarditis, encephalopathy and acute pulmonary edema are important determinants of mortality and morbidity in children. Treatment with steroids and antihistaminics before admission was associated with poor outcome.
Oral Prazosin is fast acting, easily available, cheap, free from any anaphylaxis and is highly effective. Early intervention with oral Prazosin and appropriate use of dobutamine and SNP will hasten the recovery in scorpion sting victim.