Pulmonary edema :

This is a common cause of fatality in scorpion sting victims, if not intervened in time .It occurs 4-36 hours after sting. Even sudden development of pulmonary edema in a hospitalized patient has been reported necessitating a close vigilance and monitoring of these victims. Clinically pulmonary edema can be suspected when respiratory rate is >24 per minute, orthopnea, intractable cough, low volume fast thready pulse, summation gallops, systolic murmur and basal moist rales which may be auscultated over the dependent part or at times all over chest. 12% victims if remain untreated or reported too late after sting or at periphery if they received atropine, excessive steroids, antihistamine, digoxin and intravenous fluid or massive doses of furosemide develop acute dyspnea, cyanosis, bring copious massive blood stained froth in mouth and nostril. Moist bubbling rales with tracheal death rattles are heard all over chest. At times, this patient has marked tachycardia with hypotension.

Tachycardia :

In hospitalized children recovering from vasoconstriction usually after 12-18 hours develop marked tachycardia (HR 110-240 per min.) with warm extremities. Such child has air hunger, delirium, may throw convulsive movement, moist basal rales in chest, summation gallops with murmur in the heart. After 20-30 hours in a case recovering from autonomic storm, he develops warm extremities, bradycardia (heart rate 50-60 per minute), split second heart sound with hypotension (70-90 Mm hg) with prolonged QTC (500-650 msec.) with no complaints. This is result of depletion of tissue catecholamines due to autonomic storm, usually it takes 72-96 hours for recovery.

Other features are pain in abdomen which may be due irritation of worm (round worm infestation is common in villagers) by scorpion venom, in addition to smooth muscle contraction due to acetylcholine excess. Hyperglycemia, raised serum amylase suggestive of acute pancreatitis is transient and reversible. Hemiplegia, aphasia, cerebral infarction and subdural hematoma due to disseminated intra-vascular coagulation have been reported. Acute renal failure has also been reported. Persistent or prolonged hypoxia due to low output state, marked tachycardia, respiratory failure due to pulmonary secretion and edema may result in irreversible cerebral anoxic injury with subsequent persistent cerebral insufficiency and low intelligence rest of life.

Fatality:

Victim can die suddenly due to lethal ventricular arrhythmias, which occur within 15-30 minutes of sting. Many cases died due persistent pulmonary edema, tachycardia, hypotension and convulsion and brought to hospital in moribund, comatose condition, pin point pupils with massive pulmonary edema.

Investigations :

Total leucocytes count is raised to 14000-21000 resulting in liberation of inteleukin-6 cytokines and tumor necrosis factor alpha. Cardiac enzymes are raised. Serum amylase must be investigated in all cases with upper abdominal pain with vomiting and tachycardia. Serum potassium is raised in early hypertensive phase. In a few cases there is reduction in serum calcium level. If facilities are available, serum insulin detection is helpful for further research. Chest X-ray shows bilateral batwing, patchy or interstitial pulmonary edema. At times, secondary respiratory infection in form of pneumonitis is often seen in a hospitalized patient recovering from pulmonary edema. On 4th day, mild cardiomegaly is seen in a case recovering from pulmonary edema.

Electrocardiography changes :

Hyper-acute tented T waves, bradycardia, first degree heart block, transient ventricular and atrial ectopics, runs of ventricular VPC's can be observed and detected if case is monitored by cardio scope. PQRST or T waves alternans, acute myocardial infarction like pattern, sinus tachycardia with ST segments depression, left anterior hemi-block, bundle branch block are also seen. Many times left bundle branch block with marked tachycardia is confused for ventricular tachycardia. In such a situation the bundle branch block is tachycardia dependent. Complete heart block, low voltage, widened QRS complexes with tachycardia carries poor prognosis. Prolonged QTc interval (0.50-0.60 seconds) with broad base and round top T waves with bradycardia with hypotension are seen 12-24 hours after sting in a hospitalized patient. Most early changes in ECG such as left axis deviation, Tented T waves and ST segment elevation in lead I and AVL should be closely monitored for possibility of development of acute pulmonary edema.

Pathophysiology :

The clinical manifestations, pathological lesions and electrocardiographic changes are due to sudden massive liberation of catecholamines in to circulation similar to pheochromocytoma. Cool extremities with severe vasoconstriction (like Raynaud's phenomenon), dilated pupils, cold extremities, inhibition of insulin secretion, hyperglycemia, acute myocardial infarction like pattern (spasm of pericardial coronary vessels), pulmonary edema are due to alpha-1 receptors stimulation due to catecholamine excess. Scorpion venom increases the membrane permeability to sodium by opening the voltage sensitive sodium channels, which is accompanied with calcium entry, and blockade of calcium activated potassium channels resulting in relative hyperkalemia. Hyperkalemia further induces the release of catecholamines. Stimulation of alpha-receptors causes potassium efflux from the liver. Hyperkalemia, hypocalcaemia can explain the electrocardiographic changes-tall T waves, prolonged QTc and ST segment changes. Initial short lasting hypotension is due to hypovolaemia, peripheral cholinergic and central vagus stimulation. Delayed long lasting hypotension occurs as result of vasodilatation and depleted catecholamines. Pulmonary edema in scorpion sting is of homodynamic origin and is related to severe impairment of left ventricular systolic function. Local pain is due to sodium channel activation and stimulated of C fibers with local liberated prostaglandins.