Snake bite carries high degree of morbidity and mortality. About thirty to fifty thousand deaths due to snake bite occur every year in India.
The common families of poisonous snakes are
(a) Elapidac which includes common and king cobra and Kraits
(b) Viperidae (vipers and pit vipers) and family Hydrophiidae which primarily consists of sea snakes.
Majority of the Snake bite are by non-poisonous ones and it is important to identify the poisonous ones. The poisonous ones are covered with large scales covering greater part of the ventral surface. The mouth contains only one pair of poisonous fangs in the upper jaw placed anteriorly in case of Krait and cobra and posteriorly in viper. As compared to them the non-poisonous ones have small teeth.
In poisonous snakes there are two fang marks along with local reaction while in nonpoisonous there are multiple teeth marks with hardly any local reaction. In biting it strikes with great speed, opens its jaws, rotates forward the fangs, snaps the jaws together and ejects its venom from the poison gland via the duct and fang into the tissues in one instantaneous movement.
Snake venoms are not single toxins but mixture of many components, enzymes such as phosphatidases, proteases, cholinestrases, hyaluronidases, ribonucleases, deoxyribonucleases, lecithinase, polynucleotides toxins and biogenic amines. Most of the time these venoms have diversified and complicated toxic effects. The poison of Indian cobra and Krait also contains distinct substances, a neurotoxin haemolysin, a cardiotoxin, a cholinesterase and non-enzymatic components which produce neuromuscular block.
The venom of vipers contains substances which produce severe haemorrhage, haemolysis, fibrinolysis and extensive damage to various organs while venom of sea snakes damages nerves and muscles producing necrosis of the muscles (Rhabdomyolysis, myoglobinuria). The severity of snake bite depends on various factors like age and health of the victim. Children and elder nourished persons are liable to suffer more from its ill effects. Site of strike is equally important.
A direct strike of the fang is more dangerous than a scratch. Similarly if the poison directly enters the blood stream, the effect is more dangerous. Clothing affords protection. Thus a strike through the cloth shall be less serious.
Bites by large kinds are more dangerous since large snakes inject more poison. Exertion or physical activity like running immediately after a bite is dangerous since it accelerates the dissemination of poison in the body.
The clinical picture depends on the quantity of the poison injected. But even if it is non-poisonous, fright and agitations are always present accompanied by tachycardia, sweating and restlessness.
In a bite by a poisonous one symptoms generally appear within a few minutes to as late as 2 hours. There is pain swelling at the site, nausea, vomiting, faintness and cardiovascular collapse. There is often ecchymosis, discoloration and exudation of a sero sanginuous fluid from the site. In a few hours bullae over the effected site appear with enlargement of lymph nodes. Rarely gangrene may develop.
Bites by all snakes produce systemic effects like vomiting, abdominal pain, headache, syncope and cardio vascular collapse. The distinctive features when bitten by various common forms of snakes are:
Cobra and Krait Bite
There is severe pain at the site, local necrosis and sloughing. Neurotoxic effects (Drowsiness, respiratory paralysis, Blurring of vision, paralysis of palate, tongue and flaccid paralysis of limbs) arc the predominant features and appear after 8-12 hours of bite. These effects are completely reversible provided they are treated at the earliest. Coma and death due to respiratory paralysis may occur.
There is severe local reaction in the form of swelling and necrosis at the site . Hemorrhagic complications are major manifestations in the form of bleeding from various sites, epistaxis, hematuria, haematemesis and malena. Blood becomes in-coagulable because of consumption coagulopathy. Hypo tension, shock, myocarditis and cardiac failure are other complications.
Renal involvement is a deraded complication and it may be in the form of direct nephrotoxicity acute tubular necrosis and interstitial nephritis. Death generally is due to shock, cardiovascular collapse and renal failure.
Sea snake bile
The local reaction is not much and signs of poisoning occur within one to 2 hours and are characterized by generalized stiffness, muscle aches, Trismus, Ptosis, paralysis and renal failure later on.
Laboratory investigations. In severe cases there is rise in polymorph leucocyte count with fall in platelet count. There is hypo-fibrinogenemia with abnormal tests of coagulation. Micro Elisa kit for the detection of snake venom and venom antibodies helps in detecting exact circulating venom.
Snake bite is a medical emergency and first aid be provided immediately and then patient shifted to a nearly hospital.
The bitten part should be immobilized by using an improvised splint. The bitten part should be washed well with soap and water. A tourniquet be applied nearest to the site of bite so as to impede the lymphatic flow as well as venous return. The toumiquet should be loosened periodically so that arterial supply of the part is not affected.
It is oft held view that incision and suction of the wound removes the poison but this is no longer recommended. Applying ice over the bitten site delays the absorption of venom but again there is a view that cooling may result in irreparable damage of injured tissues by causing ischemia so cooling of the part is not recommended by some authorities.
Besides local measures, general treatment be instituted. It consists of re assurance, sedation, (diazepam) antibiotics to cover infection, tetanus toxiod and treatment of shock. An intravenous drip should be set up immediately to correct fluid and electrolyte imbalance. Cardiac, respiratory and renal complications have to be managed appropriately.
It is very essential to give anti venom treatment at the earliest. There may be a case where no poison has been injected by the snake and it is non poisonous in all such cases close observance of the patient is required for next 24 hours to detect any toxic effects of snake venom.
In all cases of snake bite who are in shock or show neurological effects or bleeding tendencies, anti venom must be given immediately. It can neutralize venom if given early and the amount of anti venom is in excess of venom.
Antivenin available in our country is a lyophilized polyvalent product prepared from sera of horse’s hyper-immunised with the poison. Antivenom is constituted by diluting 1 ml with water to form 10 ml per vial.
The total dose of antivenin shall depend on the severity of condition. On an average 50-100 ml (5-10 amps) are required initially, to be given intravenously. Antivenin may have to be repeated after 6-12 hours. Larger doses are to be used in a child if it is big and there are severe effects.
There is always risk of an allergic reaction with use of antivenin so whenever it is administered. Injection Adrenaline (1% 0.5 mg) antihistamine (Inj chlorpheniramine Maleate 10 mg) and Injection Hydrocortisone (100 mg) should be available and administered at the first sign of anaphylaxis.
For patient developing neurotoxicity with respiratory paralysis anticholinestrase therapy with neostigmine and atropine is indicated. Respiratory failure shall require incubation and mechanical ventilation. Renal failure may require peritoneal or haemodialysis.
Besides this surgical debridement of necrotic tissue to prevent spread of infection is advocated. Patients with bleeding tendencies may require fresh blood transfusion. Snake bite carries high degree of morbidity and mortality and only prompt and early treatment can save a human life.
Check out the video below on how to deal with Snake Bites: