Describe snake bite with the identification of venomous snakes, first aid and treatment.

Epidemiology and the Venomous Snakes of India

• India has the highest burden of snakebite mortality in the world, with estimates of the order of 50,000 deaths a year, overwhelmingly among agricultural workers in rural areas, and largely at night and during the monsoon. It is now recognised by the World Health Organization as a neglected tropical disease
• Of some 300 species in India, about 60 are venomous, and four account for the great majority of deaths — the "big four": the spectacled cobra (Naja naja), the common krait (Bungarus caeruleus), russell’S viper (Daboia russelii) and the saw-scaled viper (Echis carinatus). Indian polyvalent antivenom is raised against these four only, which matters where other species are involved

First Aid and Investigation

• Reassure the patient — a large proportion of bites are by non-venomous snakes or are "dry" bites with no envenomation, and much of the early distress is fear → immobilise the limb with a splint, as for a fracture, and keep it below heart level
• movement accelerates venom absorption through the lymphatics → Remove rings, bangles and anything constricting before swelling develops → get to hospital quickly, carrying the patient rather than letting them walk → tell the doctor of any symptoms
• bring the snake only if it is already dead and can be transported safely — never attempt to catch or kill it → Remembered as "Do it R.
• I. G.
• H. T.
• " — Reassure, Immobilise, Get to Hospital, Tell the doctor
• What must not be done, all of which are traditional, widespread and harmful: tourniquets, which cause ischaemia, gangrene and a bolus release of venom on removal; incision and suction, which introduce infection and cause bleeding in a coagulopathic patient; washing the bite site, which removes venom traces needed for identification; cauterisation, cryotherapy and electric shock; the application of "snake stones"; and delay in seeking treatment while a traditional healer is consulted, which is a major and remediable cause of death
• The 20-minute whole blood clotting test (20WBCT) is the single most useful bedside investigation, and requires nothing but a tube: place 2 mL of fresh venous blood in a clean, dry glass tube, leave it undisturbed for 20 minutes, then tip it once. If the blood has not clotted, there is a coagulopathy, which indicates viper envenomation and is an indication for antivenom. It must be a glass tube, since plastic does not activate the clotting cascade, and it must not be shaken
• Other investigations — prothrombin time and fibrinogen, platelet count, renal function, creatine kinase, urine for myoglobin and haemoglobin, and an electrocardiogram

Treatment

• Antivenom is the only specific treatment, and Indian polyvalent ASV covers the Big Four. It is indicated on signs of systemic envenomation — a positive 20WBCT or other coagulopathy, spontaneous bleeding, any neurotoxic sign such as ptosis, cardiovascular abnormality, or rapidly progressing local swelling — not on the fact of a bite alone
• Dose — usually 8 to 10 vials as an initial infusion, repeated according to response. The dose is the same for a child as for an adult, since it neutralises a quantity of venom and the snake injects the same amount regardless of the size of the victim — a point frequently and dangerously misunderstood
• Anaphylaxis is common with antivenom; adrenaline must be drawn up and ready before the infusion starts, and low-dose subcutaneous adrenaline given prophylactically has been shown to reduce reactions
• Neostigmine with atropine for neurotoxic envenomation — it prolongs the action of acetylcholine at the junction. cobra envenomation responds well; krait envenomation responds poorly, because krait venom acts presynaptically and irreversibly
• Supportive care is what saves the paralysed patient — intubation and mechanical ventilation, continued for as long as necessary, since recovery of neuromuscular function is complete if the patient is ventilated through it; and dialysis for acute kidney injury
• Local care — elevation, analgesia (avoiding aspirin and non-steroidal drugs, which worsen bleeding), tetanus prophylaxis, and watching for compartment syndrome, which must be confirmed by pressure measurement before any fasciotomy, since fasciotomy in a coagulopathic patient is catastrophic and is done far too readily

Cobra Compared with Krait Envenomation

Applied Aspects

• Do not apply a tourniquet, incise or suck; all three are harmful, all three are widely practised, and unlearning them saves more lives than any drug
• Do the 20WBCT on arrival and repeat it; it needs only a glass tube, identifies viper envenomation, and is the indication for antivenom
• Give the same antivenom dose to a child as to an adult; the dose neutralises venom, not body weight, and halving it for a child is a fatal error
• Have adrenaline drawn up before starting antivenom; anaphylaxis is common and the reaction may be immediate
• Suspect krait in unexplained early-morning paralysis in someone who slept on the floor; there is nothing to see at the bite site and the diagnosis is made on the pattern alone
• Ventilate and wait in neurotoxic envenomation; recovery is complete if the patient is supported through it, and death is from giving up too early
• Confirm compartment syndrome by measurement before any fasciotomy; a swollen limb in a coagulopathic patient is not an indication, and unnecessary fasciotomy causes severe bleeding and disability
• Indian polyvalent antivenom covers the big four only, which matters where another species is involved
• Elapid fangs are short and fixed, viper fangs long and hinged, and the bite marks differ accordingly
• Russell viper causes hypopituitarism from pituitary infarction, which may present months later and is easily missed
• Sea snake venom is myotoxic, causing rhabdomyolysis with myoglobinuria and renal failure rather than paralysis or bleeding
• Many bites are dry or by non-venomous snakes, so antivenom is given on signs of systemic envenomation and not on the bite alone
• Do not wash the bite site; venom traces on the skin can be used to identify the species
• Avoid aspirin and non-steroidal analgesics, which worsen bleeding in a coagulopathic patient
• Delay while a traditional healer is consulted is a major and remediable cause of death, and deserves direct community counselling
• Krait venom acts presynaptically, which is why neostigmine fails and ventilation must be prolonged until the terminal regenerates
• Ptosis is the earliest neurotoxic sign, and should be looked for specifically in anyone bitten or found paralysed
• Snakebite is a WHO neglected tropical disease, and India carries the largest share of the global mortality
• Carry the patient rather than let them walk; muscular activity accelerates lymphatic absorption of venom
• Recovery from neurotoxic envenomation is complete if the patient is ventilated through it, which justifies prolonged support
• Remove rings and bangles early, before swelling makes them tourniquets in their own right
• Fasciotomy in a coagulopathic patient is catastrophic, so compartment syndrome must be confirmed by pressure measurement first
• Give adrenaline prophylactically before antivenom in low dose subcutaneously; it reduces the frequency of reactions
• The 20WBCT needs a clean dry glass tube and must be left undisturbed; plastic does not activate clotting and shaking invalidates it
• Repeat the 20WBCT six-hourly after antivenom; recurrence of coagulopathy indicates the need for a further dose
• Community education prevents more deaths than any drug — footwear, torches, sleeping on a cot, and going straight to hospital