SCORPION STING
Scorpion sting is more common than snake-bite in rural and costal regions of India, though mortality is rare except in young children. Out of ~80 species in India, only two scorpions are toxic - Mesobuthus tamulus (red scorpion) and Palamnaeus swammerdami (black scorpion).
Pathophysiology of scorpion-sting is related to:
• Release of chemical mediators, e.g. catecholamines (automonic storm), cytokines and platelet-activating factors; and,
TABLE 27.24: Complications of scorpion sting
• Local reactions
• Transient autonomic storm (lt; 6 hours)
• Late systemic reactions (gt; 6 hours)
- CVS: Myocarditis, arrhythmia, heart blocks
- Resp.: Pulmonary edema, ARDS
- CNS: Acute encephalopathy, seizures, stroke
- Blood: DIC, bleeding tendencies
- Renal: Hematuria, renal failure
- Others: Anaphylactic shock, hypoglycemia
• Altered permeability of cell membranes, specially at pre-synaptic terminals, due to stimulation of sodium channels and inhibition of calcium-dependent potassium channels.
Sympathetic #945;-receptor stimulation appears to be the critical event in systemic manifestations of scorpion sting, which may be blocked by competitive antagonists, e.g. Prazocin.
Clinically, most scorpion stings are limited to local reactions, e.g. burning pain, itching, swelling or ecchymosis, lasting for 24-48 hours. Systemic reactions are more common in young children or some adults, which begin as “autonomic stormquot; within a few minutes to 6 hours of envenomation, characterized by tachycardia, hypertension, perspiration, mydriasis and hyperglycemia. Priapism, due to sympathetic vasodilatation of penile vascular bed is a useful indicator of autonomic storm in scorpion sting.
Untreated cases may deteriorate rapidly with complications due to: (a) myocardial dysfunction, e.g. hypotension, shock and arrhythmia, and (b) increased capillary permeability, e.g.
pulmonary edema and ARDS (Table 27.24). Overall mortality is lt;2%.Diagnosis depends on history, examination of scorpion if possible and clinical evaluation for signs of autonomic storm or systemic complications with relevant investigations.
Management: Hospitalization is preferable in all but mildest scorpion bites till 24 hours for close supervision. Currently, no anti-scorpion venom is available in India and treatment is largely supportive and symptomatic, with following steps:
a. Local pain relief to allay anxiety and myocardial stress with Diazepam (PO/IV 0.5-2.0 mg/kg). Local infiltration of xylocaine is useful in severe cases.
b. Treatment of autonomic storm with Prazocin (PO 30 #956;g#8725;kg#8725;dose at 0, 3, 6 hours). Prazocin- #945;-1 adrenergic antagonist, decreases myocardial load by peripheral vasodilatation as well as counteracts metabolic effects of adrenergic stimulation. It should be started as soon as first sign of autonomic storm appears, though prophylactic therapy is not advisable. Calcium-channel blockers, e.g. verapamil and/or ACE
inhibitors, e.g. nifedipine may also be used in cases with severe hypertension.
c. Myocardial dysfunction usually manifests after 6-24 hours with hypotension and poor perfusion (cold extremities), which needs oxygen supplementation, fluid/electrolyte correction, inotropic agents, e.g. dopamine and after-load reducing agents, e.g. IV sodium nitroprusside (2-5 mg/kg/min).
d. Pulmonary edema and ARDS are other important complications, which needs positive pressure ventilation, along with other supportive measures.
27.5.7