SNAKEBITE POISONING ( Health Tips)

Snakebite is a common emergency in our hospitals, patients usually come from the rural areas, most of the time they are aware of the snake species. Students may get patient of snakebite as a long case in exams.

Common types of poisonous snakes

Poisonous species of snake fall into three families:

1. Viperideae: such as Russel viper, pit viper.
2. Elapidae: such as cobra, krait, and coral snake.
3. Hydrophidae: such as sea snake.

PATHOGENESIS & CLINICAL FEATURES

Poisonous snakes have a pair of enlarged teeth called fangs in their upper jaws that inject venom into the tissues of their victim.

Snake venoms are complex mixtures of proteins and small polypeptides with enzyme activity.

Effects of venoms may be:

• Hematotoxicity: They cause the vasculature leaky resulting in local or systemic bleeding leading to hypotension and shock.
• Cytotooxicity: causing local tissue necrosis, mygolinuria and renal failure.
• Coagulopathy: causing bleeding or clotting disorders.
• Cardiotoxicity: causing myocardial depression and reduced cardiac output.
• Neurotoxicity: inhibiting peripheral nerve impulses leading to paralysis.

Viperidae:

• Local swelling, echymosis and blistering at the site of bite.
• Systemic involvement within 30 min including vomiting, hypotension and shock.
• Bleeding and clotting disturbances (Coagulopathy): bleeding gums or venepuncture sites, bleeding may be fatal.

Elapidae:

• Usually no swelling at the site of bite.
• Vomiting, salivation.
• Hypotension and shock resulting from loss of intravascular fluid into the soft tissues.
• Neurological symptoms: muscle weakness causing ptosis, diplopia and dysphagia, with paralysis of respiratory muscles in severe cases.
• Myocardial depression causing reduced cardiac output and rhythm disturbances.

Hydrophidae (sea snake)

Muscle involvement causing rhadomyolysis with myalgia and myoglobinuria the may lead to acute renal failure. Cardiac and respiratory paralysis may occur.

INVESTIGATIONS

1. Blood grouping and cross matching: as soon as possible before the effect of circulating venom interfere the blood grouping.
2. Complete blood count: to evaluate degree of hemorrhage and hemolysis.
3. Urea, creatinine and electrolytes: for renal status.
4. Liver function tests (LFT’s)
5. PT, APTT, BT, CT, FDP:  to asses Coagulopathy.
6. Urine analysis: for hemoglobinuria and myoglobinuria.
7. ABGs may be required in severe cases.
8. ECG: to look for rhythm disturbances.
9. Chest X-ray.

MANAGEMENT

·         All patients with suspected snake bite should be observed for 12-24 hours, as    initial manifestations may be delayed, especially with elapid bites.

• Reassuring the patients, not all snakes are poisonous and even bite by the poisonous snake may be “dry bite” i-e no venoum in the bite.
• Try to identify the type of snake.
• Immobilize the bitten area to minimize the venom spread.
• Application of firm bandage to occlude lymphatic drainage (not the arterial supply); use of tourniquet is discouraged because they do not prevent spread of venom.
• Incisions at the site of bite and attempts to such out the venom with mouth should not be made.
• Pain and vomiting: symptomatic treatment. Aspirin should not be used for pain since this may aggravate bleeding.
• Saline and dopamine for hypotension.
• Monitor blood pressure, coagulation, renal, neurological and cardio respiratory status.
• Large bore IV canulla should be inserted on un affected limb.

Antivenin:

• Antivenin is indicated in patient with severe or progressing local tissue local reaction at the site of bite, clinical or laboratory evidence of systemic involvement.
• In about 50% of snake bites no venom is injected (Dry bite) and antivenoms are generally not indicated. However when indicated antivenoms should be given early, as the antivenoms only neutralize venom they can not reverse the effects of venom. Allergic reaction is the frequent complication of antivenin.
• Antivenom should be given slow IV, the same dose being given to children and adults.
• Before starting antivenom a test does is given; 0.02 ml of saline-diluted antivenom is injected subcutaneously and observed for at least 10 min for redness, hives, pruritus or other allergic reactions. A syringe containing 0.5 ml of 1:1000 adrenaline must be available to combat anaphylaxis whenever antivenin is administered. Adrenaline is given subcutaneously. However skin test does not always predict which patients will have allergic reaction to anti venom; a skin test may be false positive or false negative.
• Intravenous antihistamine and ranitidine should be given before starting antivenin infusion to limit the acute allergic reaction.
• In severe cases the anti venom infusion should be continued even with allergic reaction with closely controlled conditions and adrenaline, antihistamine and steroids.
• Antivenin should be diluted in 1000 ml of saline, Ringer’s lactate or 5% dextrose water and should be given slowly, in children 20ml/kg.
• Physician should be at the bedside to intervene in the event of an acute allergic reaction. Total dose may be given in 1-4 hours. Further antivenin may be necessary if clinical abnormalities worsen.
• Anti venom is usually available in big government hospital. Administrators are requested to make sure the availability of this life-saving medicine. 

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