Level 2 of 6Must-remember

Snake bite: envenoming, antivenom and supportive care

Assess, manage and stay safe — enough on its own

1 / 6

The card — assess, manage, caution

Assessment— look, ask, measure

Take the history in one minute: what bit (if seen), when, where on the body, what the patient was doing (walking barefoot, working in paddy fields or undergrowth, moving at night without light, sleeping on the ground, reaching into a hole, handling a snake — even an apparently dead one can deliver a reflex bite).
Ask what was done before arrival: tourniquet or constricting band, incision, cut-and-suck, suction device, cryotherapy, electric shock, chemicals, snake stones, traditional healer — each changes what you must do next.
A bite is not an envenoming: venom is metabolically expensive and used sparingly, so dry bites account for 20–25% of pit viper bites and up to 75% of sea snake bites; antivenom is given only for a clear indication.
Do not stall over the species: three questions matter — is this a snake bite, is there significant envenoming, and what species — but only the second alters management in the first hour, and no department should stall over identification while a patient bleeds.
Timing rule: time to onset of first symptoms ranges from minutes to 24 hours, so a normal initial assessment carries almost no predictive weight and must be repeated many times during the first 24 hours.
Inspect the bite site: fang marks may be absent, trivial or single — elapid fangs are fixed, erect and small, which often results in fewer or less distinct puncture wounds — and their absence excludes nothing.
Local envenoming: pain, progressive soft tissue swelling and ecchymosis, with haemorrhagic or serum-filled vesicles and bullae developing over hours to days; painful enlargement of the draining regional lymph nodes is a common early sign of envenoming.
Measure progression objectively: mark the leading edge of swelling, ecchymosis and tenderness with the time, and measure limb circumference at three points — bite site, proximal joint, distal joint — every 15 minutes until local effects stabilise, then every 1–2 hours.
Look under the lip for five seconds: spontaneous gum bleeding is the commonest early sign of haemostatic failure; also look for oozing from venepuncture sites, bruising, epistaxis and haematuria, and fear intracranial or retroperitoneal haemorrhage.
20-minute whole-blood clotting test (20WBCT): put 2–3 mL of venous blood in a clean glass container that is new or washed with water only (never detergent, never plastic), leave undisturbed for 20 minutes, then tip once — clot present is negative, blood still liquid is positive and means coagulopathy.
Bilateral ptosis is the usual first clear sign of neurotoxicity: then external ophthalmoplegia with medial gaze failing early, fixed dilated pupils, drooling, dysarthria and dysphagia — a descending flaccid paralysis reaching limbs, neck (the broken-neck sign) and finally the diaphragm, sometimes in under 30 minutes.
Bedside respiratory surrogates replace spirometry: ptosis on sustained upgaze, ability to lift the head from the pillow, single-breath count, ability to swallow saliva and speak a full sentence, respiratory rate and pattern, saturation — a falling single-breath count is an early surrogate for falling vital capacity.
Vital signs and output: blood pressure (hypotension or shock), pulse (tachycardia or bradycardia), respiratory rate, saturation; catheterise any patient with systemic features and chart urine volume and colour hourly, aiming above 0.5 mL/kg/h.
Dark urine: black or red-brown urine means myoglobinuria or free haemoglobin — dipstick positive for blood with no red cells on microscopy — whereas frank haematuria suggests coagulopathy; both demand antivenom.
Danger signs demanding immediate action: hypotension or shock; airway compromise or respiratory insufficiency; any cranial nerve sign, especially bilateral ptosis; inability to swallow saliva; spontaneous systemic bleeding; incoagulable blood; altered conscious level or focal deficit; black or red-brown urine; oliguria; rapidly progressing swelling; intractable vomiting; limb ischaemia from a constricting first-aid device.
Two thresholds are severity markers and antivenom indications in their own right: swelling involving more than half the bitten limb, and incoagulable blood on the 20-minute whole-blood clotting test.

Management— do this, in order

Resuscitation takes precedence over antivenom: antivenom is important but never more important than an airway — A, B, C first, vials second.
Keep the patient still: immobilise the bitten limb with a splint in a neutral position of comfort at approximately heart level; the patient must not walk, because muscle-pump activity disperses venom through the lymphatics regardless of bite site.
Strip the limb early: remove rings, bangles and tight clothing before swelling makes them tourniquets; clean the wound with soap and running water and cover it with a dry dressing.
Releasing a constricting band or tourniquet is dangerous: there may be a sudden rush of venom into the circulation causing rapid deterioration and cardiorespiratory collapse, and release of stagnant acidotic blood may precipitate hypotension or dysrhythmia — release only with monitoring attached, IV access established, oxygen running and resuscitation drugs drawn up.Doctor / Nurse
Airway: bites to the face or neck may require early endotracheal intubation to pre-empt loss of patency from soft-tissue swelling, as may any patient with bulbar weakness, drooling or inability to swallow saliva — elective intubation of a ptotic patient is far preferable to emergency intubation of a swollen, paralysed one.Doctor / NurseNot available at your setup — Endotracheal intubation kit.
Oxygen: high-flow for neurotoxic signs, shock or bleeding, while watching for pulmonary oedema.
Access: two large-bore intravenous lines in unaffected extremities; minimise venepuncture attempts, avoid non-compressible sites such as the subclavian vein, and apply firm prolonged pressure after every puncture.Doctor / Nurse
Fluids: isotonic crystalloid 20–40 mL/kg intravenously for any haemodynamic instability, given as reassessed boluses; in children 10–20 mL/kg per bolus.Doctor / Nurse
Persisting shock: if shock persists after aggressive volume resuscitation and antivenom, add a vasopressor such as noradrenaline, and reconsider whether the patient is anaphylactic to the venom or to the antivenom.Doctor / NurseNot available at your setup — Infusion pump.
Give antivenom for any of these: shock, cardiac collapse or arrhythmia; respiratory compromise; rapidly increasing swelling, swelling involving more than half the bitten limb, swelling after bites on fingers or toes or by species likely to cause necrosis, extensive blistering or bruising; spontaneous systemic bleeding; incoagulable blood on the 20WBCT or an abnormal INR; developing paralysis — ptosis, diplopia, neck weakness, limb or respiratory paralysis, altered sensorium; black urine positive for blood or myoglobin; developing renal failure; intractable symptoms including recurrent vomiting.Doctor / Nurse
Dose: the appropriate dose is dictated by local experience and by the product — consult the package insert of the product in your hand for species covered, starting dose and redosing; children require the same dose as adults, because what is neutralised is the quantity of venom injected, which does not scale with the size of the victim.Doctor / Nurse
Route and rate: intravenous only — dilute in 0.9% sodium chloride (typically 250 mL for an adult) or give as a slow undiluted push, infusing over approximately one hour, starting at 25–50 mL/h for the first 10 minutes and increasing if no reaction occurs.Doctor / NurseNot available at your setup — Infusion pump.
Before the infusion starts: draw up adrenaline and have airway equipment immediately available, and observe the patient continuously during administration and for at least an hour afterwards; never perform a skin or test dose.Doctor / Nurse
Acute reaction (tachycardia, rigors, vomiting, urticaria, dyspnoea, laryngeal oedema, bronchospasm, hypotension): stop the infusion; adrenaline 1:1000 IM into the anterolateral thigh 0.5 mg (0.5 mL) in an adult, repeated after 5 min if no response, or 0.01 mg/kg to a maximum 0.5 mg in a child; chlorphenamine 10 mg or diphenhydramine 50 mg by slow IV injection (child diphenhydramine 1 mg/kg, maximum 50 mg); hydrocortisone 100 mg IV (child 2 mg/kg, maximum 100 mg); plus oxygen, supine with legs elevated and a crystalloid bolus (20 mL/kg in a child).Doctor / Nurse
Restart after a controlled reaction: the envenoming will kill the patient and a successfully treated reaction will not — restart at 5–10 mL/h and titrate upward as tolerated if the envenoming still warrants it.Doctor / Nurse
Redose: effective antivenom should halt progression and reverse coagulopathy within about 6 hours — repeat if life-threatening bleeding, shock or paralysis persists a few hours after the first infusion, or if the blood remains incoagulable when retested at 6 hours.Doctor / Nurse
Neurotoxic bites: give antivenom at the first sign of neurotoxicity, not at the point of breathlessness; once paralysis is established and intubation is required, further antivenom is unlikely to help and the patient must be ventilated until recovery, which may take days to weeks and occasionally several months.Doctor / NurseNot available at your setup — Endotracheal intubation kit.
Pain and wound care: paracetamol 1 g orally or IV 6-hourly to a maximum 4 g/24 h in adults, 15 mg/kg 6-hourly to a maximum 60 mg/kg/24 h in children; morphine 2.5–5 mg IV titrated against pain and respiratory rate for severe pain (children 0.05–0.1 mg/kg IV), used cautiously and in reduced doses if neurotoxic features are present; leave intact serum-filled vesicles and haemorrhagic blebs undisturbed, and once antivenom has been started elevate the limb to heart level.Doctor / Nurse

Caution— what harms

Never cut, suck or tie: incision, cut-and-suck, suction devices, cryotherapy, electric shock, chemicals, snake stones and tourniquets are useless or harmful — tourniquets in particular can cause catastrophic ischaemic distal limb injury.
Never give aspirin or non-steroidal anti-inflammatory drugs: they aggravate bleeding in a patient who may already be defibrinated.
Never give intramuscular tetanus toxoid until any coagulopathy is reversed, and keep all intramuscular injections to a minimum in a bleeding patient.
Never perform a skin or test dose of antivenom: test doses are neither sensitive nor specific and have no role; prophylactic antihistamines and glucocorticoids, though widely used, have not proved beneficial.
Never give antivenom by any route other than intravenous, and never start it without adrenaline drawn up and airway equipment at the bedside.Doctor / Nurse
Never mistake severe neurotoxic paralysis for brain death: with preserved respiratory function, fixed dilated pupils, absent reflexes, no withdrawal to pain and gross ptosis may coexist with a patient who is fully conscious and terrified — assume such a patient hears everything, and never base a prognostic judgement on this examination.
A normal first examination is falsely reassuring: some envenomings produce no signs at all and declare themselves only on laboratory testing, so repeat the full blood count and coagulation studies every 4 hours until it is clear that no systemic envenoming has occurred.Not available at your setup — Coagulation (PT/INR). if coagulation studies are unavailable, use the 20WBCT instead
A painless bite does not exclude lethal envenoming: some bites produce minimal or no local effects, not even pain, yet lethal systemic envenoming is present — the classic krait scenario of a person asleep on the floor at night who now has abdominal pain and drooping eyelids.
Do not redose because coagulopathy has not fully normalised on a 1–3 hour result: even after all venom is neutralised, coagulation may take hours to normalise, and thrombocytopenia may persist for days despite adequate antivenom and is by itself not a reason for further vials.Doctor / Nurse
Do not give blood products before adequate antivenom: venom-depleted factors and platelets usually rebound within hours of antivenom, and products given first simply fuel ongoing consumptive coagulopathy.Not available at your setup — Blood & blood products.
Do not reach for a fasciotomy: most envenomings deposit venom subcutaneously and the tense agonising limb is usually massive subcutaneous oedema — fasciotomy is required in fewer than 1% of cases, is overused, often disastrous and associated with poor functional outcomes; elevate, give antivenom, ensure coagulopathy has resolved, and remember that pressures above 30–40 mmHg indicate additional antivenom, not a knife, with published data supporting pressures up to 55 mmHg for up to 6 hours.
Opioids blur the neurological picture: opioid-induced respiratory depression cannot be distinguished clinically from advancing paralysis, so use reduced, cautious doses in any patient with neurotoxic features.Doctor / Nurse
The wrong antivenom is no antivenom: a product lacking antibodies to the relevant components will provide no benefit and may cause unnecessary complications — Indian polyvalent antivenom is unlikely to work against hump-nosed vipers or green pit vipers and is ineffective against African Echis species.
Watch for the complications that kill after the first hour: hyperkalaemia from rhabdomyolysis (peaked T waves and QRS widening on ECG), intracranial or retroperitoneal haemorrhage, capillary leak syndrome with pulmonary oedema heralded by conjunctival oedema, aspiration, and recurrent coagulopathy during the first 2–3 weeks.

Refer / escalate

Refer or transfer urgently any patient with shock, airway or respiratory compromise, any cranial nerve sign or ptosis, spontaneous systemic bleeding or incoagulable blood, black urine or falling urine output, rapidly progressing swelling, or a bite by a species your antivenom does not cover — and if your facility has no antivenom, no ventilator or no dialysis, move them before those needs arise, immobilised, with an IV line running and adrenaline drawn up.

The card — assess, manage, caution

Snake bite: envenoming, antivenom and supportive care — Level 1: CorePrevious Snake bite: envenoming, antivenom and supportive care — Level 3: Core practiceNext

Read the full lesson free

Create a free account to unlock every page, the level exams, and progress tracking.