In this article we will discuss about:- 1. Introduction to Snake Bite 2. Pathogenesis of Snake Bite 3. Clinical Symptoms 4. Treatment.
Introduction to Snake Bite:
The snakes are among the most widely distributed reptiles. They inhabit all tropical, subtropical and most temperate zones of the earth. As a result of this broad distribution and their relatively great numbers, there are more accidents involving snakes than any other kind of venomous animals. Among the 2,000 species of snakes about 400 species are venomous.
They are classified into four families:
1. Elapidae (Cobras, krait, coral snakes, membas)
2. Hydrophlidae (Sea snake)
3. Crotalidae (rattle snakes, pit vipers)
Venomous snakes possess a complete venom apparatus, containing highly specialized glands and venom ducts draining into the fangs. Snakes are indeed more timid than aggressive towards humans. They only bite if they are threatened, frightened or stepped upon when hidden under grass or leaves.
Estimate of the Problem:
According to statistics based on hospitalized cases only (but not taking into account the USSR, Cuba and Europe), there are 40,000 fatalities per year, nearly 50% of this occur in the Indian subcontinent. In reality the number of cases may be higher as many cases go unreported.
These are unofficial estimates, for the Asian subcontinent (comprising India, Bangladesh, Pakistan and adjoining areas) of approximately 1,00,000 fatalities per year. Hence it is imperative to be thoroughly conversant with the clinical presentation and management of these cases.
Pathogenesis of Snake Bite:
The venoms of most species which have been analysed have been found to be a mixture of several toxic proteins, and enzymes with diversified and complicated pharmacological effects. Venomous properties come from specific toxins, peptides with 60-70 amino acids. Most of these are cardiotoxins or neurotoxin.
In addition to the toxins, the crude venoms contain many enzymes, e.g. phospholipases, endopeptidase, exopeptidases, proteinases. These are also toxic causing rapid decrease of blood pressure, change in the clotting properties of blood or damage to blood vessels and tissues.
Clinical Symptoms/Features of Snake Bite:
The clinical symptoms of snake bite depend upon three factors:
1. On the amount of venom injected:
In defensive bite relatively little venom is ejected, but just the opposite is true in predation.
2. Relative toxicity of venom in different species.
3. Symptoms depend on the site of the bite:
Venom injected into a muscle produces less dangerous symptoms than if a blood vessel has been punctured.
4. The general physical condition of the victim is very important, since cardiac and/or circulatory distress are frequent. Primary shock and collapse are not rare occurrences.
Venomous snakes leave characteristically two or occasionally one fang mark at the site of bite whereas bites from non-poisonous snakes produce a semi-circular set of teeth mark.
(a) Local Effects:
Pain and swelling around the bite is a prominent symptom of cobra bite but not of other elapid bite. Tissue necrosis is particularly likely in bites from viperadal and crotalidae.
(b) Systemic Effects:
Venom may cause the following effects:
Vague pain abdomen, necrosis vomiting, excessive salivation;
(ii) Cardiovascular System:
Hypertension and circulatory collapse due to vasodilatation and hypovolaemia;
(iii) Haematological System:
Increased blood coagulability may occur in rattle snake bite. In others these may be increased tendency for bleeding, extensive echymoses and disseminated intravascular clotting.
Acute renal failure may occur following shock or due to disseminated intravascular clotting.
Central Nervous System:
In elapid bite especially due to Krait, ptosis is very quick to occur followed by total external ophthalmoplegia and bulbar palsy and difficulty in handling the secretions. This in turn is followed quickly by respiratory difficulties and flaccid paralysis affecting neck in 2 to 5 days. Recovery occurs in reverse order with power in limbs improving first and ptosis last.
Sea Snake Bites:
Are characterized by little pain and swelling at local site. There is massive necrosis of voluntary muscles with myoglobinuria and hyperkalemia. The renal failure may occur.
Some of the clinical features have been summarised in Table 19.10.
Treatment of Snake Bite:
(1) Careful cleansing of the wound with sterile saline or water.
(2) Most of the authorities now feel that there is no evidence that there is any value in the use of tourniquets or incision and suction of the injection site, in fact these may be harmful in unskilled hands.
(3) Tetanus toxoid booster injection should also be given.
(4) Reassurance is very important.
(5) Antivenin- Polyvalent anti-snake venom serum (Haffkine Institute, Bombay or similar product should be given I.V. in dosage of 20 ml initially, after proper test dose, and repeated six hourly. A total dosage of 100 to 200 ml may be required.
(6) In cases of neuromuscular paralysis neostigmine has been advocated by some, but majority of workers have not found it of much use.
(7) As in other poisonings, maximum stress should be given to intensive supportive care of respiratory and circulatory parameters.