Snakebite and Environmental Emergencies

Medicine — Snakebite and Environmental Emergencies, NMC MBBS licence examination syllabus (Nepal Medical Council).

Snakebite and environmental emergencies

The commonest fatal error in snakebite happens before the patient reaches you.

Snakebite is a serious and neglected cause of death and disability across South Asia, and it is unusual among emergencies in that a large share of the harm is done by first aid and by delay rather than by the venom alone. Tourniquets cause limb loss. Cutting and sucking the wound achieves nothing and introduces infection. And hours spent seeking traditional treatment are hours during which the only effective therapy — antivenom, in a hospital — is not being given.

Clinically, the subject simplifies into two syndromes. Venom that attacks the nervous system produces descending paralysis beginning with the eyelids; venom that attacks the blood produces bleeding and incoagulable blood. Recognising which you are looking at, and knowing that minimal local signs do not mean minimal envenoming, covers most of what is examinable.

🩺 Where this lives: Most snakebite deaths in this region are preventable, and the preventable factors are almost all logistical. The bite happens in a field or a house at night, far from a facility that stocks antivenom. First aid measures that are actively harmful are applied. The family seeks traditional treatment first. By the time the patient reaches a hospital, they are paralysed or bleeding. None of that is a failure of pharmacology — which is why community education about what not to do, and about going straight to hospital, saves more lives than any refinement of treatment.

💡 A note on numbers and species. This chapter gives no doses, no antivenom vial numbers and no species-specific identification rules. Antivenom dosing is product-specific and set by national guidance; the species implicated vary by region; and a species-based decision made from memory could be dangerous. What is taught here is the syndromes, the first-aid rules and the observation principles — all stable — with everything quantitative taken from the national snakebite management guideline. General poisoning principles are in the Poisoning chapter.

First aid

The whole of pre-hospital snakebite care reduces to three things: reassure, immobilise, transport. Anxiety raises the heart rate and speeds systemic spread, so calming the patient is genuinely therapeutic. Keeping the bitten limb still slows absorption. And everything else — the tourniquet, the incision, the ice, the herbal poultice — either does nothing or does harm. A tourniquet is not a neutral intervention: it causes ischaemic damage, and releasing it can deliver a bolus of venom into the circulation.

The two syndromes

RECOGNISING ENVENOMING NEUROTOXIC — a DESCENDING paralysis PTOSIS is characteristically the first sign, and it is easy to miss unless you look for it. Then external ophthalmoplegia, difficulty swallowing and speaking, weakness of the neck. Then RESPIRATORY MUSCLE PARALYSIS — which is what kills. CRUCIALLY: local signs at the bite may be MINIMAL or absent. Some bites, particularly at night indoors, are barely painful and the patient may not even be certain they were bitten. A patient with unexplained ptosis and progressive weakness in an endemic area should raise the question. HAEMOTOXIC — bleeding and clotting failure Bleeding from the gums, nose and the bite site, bruising, haematuria. INCOAGULABLE BLOOD — which can be demonstrated with a simple bedside WHOLE BLOOD CLOTTING TEST where no laboratory is available. Marked local swelling, blistering and tissue necrosis. Acute kidney injury may follow. THE ESSENTIAL WARNING: MINIMAL LOCAL SIGNS DO NOT MEAN MINIMAL ENVENOMING. Judging severity by how the bite site looks is a recognised route to a preventable death. Some patients develop features of both, and some have no envenoming at all — a "dry bite" — which is why every bite is observed rather than either ignored or reflexively treated.

Hospital management

💡 Exam angle: two principles carry most of the marks. Every snakebite is observed, because envenoming can declare itself hours later — discharging a well-looking patient early is the classic error. And antivenom is indicated for systemic envenoming, not for every bite: neurotoxic signs, coagulopathy or bleeding, or severe progressive local swelling. Since antivenom carries a real risk of anaphylaxis, adrenaline and resuscitation equipment must be at the bedside before the infusion begins.

WHY VENTILATION MATTERS SO MUCH In neurotoxic envenoming, the patient dies of respiratory muscle paralysis — not of brain injury. The paralysis is REVERSIBLE, both spontaneously as venom is cleared and more rapidly with antivenom. So a patient who is ventilated through the paralysis can make a complete recovery, even from total flaccid paralysis in which they appear unresponsive. THE PRACTICAL CONSEQUENCES: Monitor respiratory function repeatedly — a falling ability to speak in full sentences, weak cough, and inability to lift the head off the pillow are warning signs BEFORE the oxygen saturation falls. Prepare for airway support before it is needed. Do not assume that an apparently unresponsive paralysed patient is unconscious — they may be fully aware while unable to move. Speak to them accordingly. In haemotoxic envenoming, the priorities are antivenom, monitoring of clotting, avoiding unnecessary intramuscular injections and invasive procedures while the blood is incoagulable, and watching renal function. Doses, vial numbers and repeat criteria come from the national guideline.

Heat illness

The distinction between heat exhaustion and heat stroke is mental state. A hot, unwell but mentally clear patient has heat exhaustion and needs cooling, rest and rehydration. A hot patient who is confused, agitated or unconscious has heat stroke, which is a medical emergency with a real mortality and needs immediate aggressive physical cooling. Note that antipyretics do not work here — the hypothalamic set point is normal, and the problem is that heat cannot be lost.

Altitude and cold

💡 Exam angle: altitude illness is worth knowing in Nepal specifically. Acute mountain sickness is a headache with nausea and fatigue after ascent, and usually settles with rest at the same altitude. The two that kill are high altitude cerebral oedema — recognised by ataxia and confusion — and high altitude pulmonary oedema, recognised by breathlessness at rest. For both, the treatment that matters is immediate descent; oxygen and drugs are adjuncts that buy time.

Clinical reasoning: four presentations

🔍 Case 1 — the tourniquet

PresentationA farmer arrives three hours after a snakebite with a tight cloth tied around his upper arm. The forearm is cold, pale and pulseless. He was also taken to a traditional healer before coming.

Two harmsThe tourniquet, and the delay.

ReasoningTourniquets cause limb ischaemia and can release a bolus of venom when removed. Delay in reaching antivenom is a major cause of death.

AnswerRemove the tourniquet with the patient monitored and resuscitation available, assess for systemic envenoming including a clotting test, and manage per the national guideline. Educate the family and community — this is where lives are saved.

🔍 Case 2 — drooping eyelids and a trivial bite

PresentationA man wakes with mild discomfort on his foot and by morning has drooping eyelids, double vision and difficulty swallowing. The foot looks almost normal, with barely a mark. He is thought unlikely to have been envenomed.

TrapJudging envenoming by the bite site.

ReasoningThis is neurotoxic envenoming. Ptosis is characteristically the first sign, and local signs may be minimal or absent — especially with night-time bites indoors.

AnswerTreat as systemic envenoming per the national guideline, with antivenom and preparation for airway support. Monitor respiratory function closely — paralysis is reversible if the patient is ventilated through it.

🔍 Case 3 — bleeding gums after a bite

PresentationA woman bitten on the hand has marked swelling, is bleeding from the gums and the puncture site, and has passed dark urine. A bedside clotting test shows the blood does not clot.

DiagnosisHaemotoxic envenoming with coagulopathy.

ReasoningIncoagulable blood is definitive evidence of systemic envenoming and an indication for antivenom. Acute kidney injury is a recognised complication.

AnswerAntivenom per the national guideline with adrenaline and resuscitation equipment ready, monitor clotting and renal function, and avoid unnecessary intramuscular injections and invasive procedures while the blood is incoagulable.

🔍 Case 4 — confused in the heat

PresentationA labourer collapses during hot weather. He is very hot to touch and is confused and agitated. He is given paracetamol and moved to a shaded area to rest.

The key signAltered mental state.

ReasoningConfusion converts heat exhaustion into heat stroke, a medical emergency. Antipyretics are ineffective because the hypothalamic set point is normal — the problem is failure of heat loss.

AnswerImmediate aggressive physical cooling, resuscitation, check the glucose, and monitor for rhabdomyolysis, acute kidney injury and coagulopathy.

Commonly confused

Confusion	The distinction	Why it matters
Tourniquet vs immobilisation	Immobilise; never constrict	Tourniquets cause ischaemia and a venom bolus.
Local signs vs systemic envenoming	Minimal local signs mean nothing	Neurotoxic bites can look trivial.
Neurotoxic vs haemotoxic	Ptosis and paralysis versus bleeding	Different monitoring priorities.
Every bite vs every antivenom	Antivenom is for systemic envenoming	It carries a real anaphylaxis risk.
Well on arrival vs safe to discharge	Envenoming can declare hours later	Observe every bite.
Paralysed vs unconscious	Patients may be fully aware	Speak to them; ventilate and they recover.
Heat exhaustion vs heat stroke	ALTERED MENTAL STATE	One rests; one is an emergency.
Antipyretics vs physical cooling	The set point is normal in heat stroke	Paracetamol does not work.
Altitude symptoms vs HACE/HAPE	Ataxia, or breathlessness at rest	Both require immediate descent.

Rapid revision

MUST-KNOW FACTS 1. First aid = REASSURE, IMMOBILISE, TRANSPORT. 2. NO tourniquet · NO cutting · NO sucking · NO ice · NO herbal packs. 3. Tourniquets cause ischaemia and a venom surge on release. 4. Remove rings and tight items from the bitten limb. 5. DELAY, often for traditional treatment, is a major cause of death. 6. The only effective treatment is ANTIVENOM in hospital. 7. NEUROTOXIC envenoming causes a DESCENDING paralysis. 8. PTOSIS is characteristically the FIRST sign. 9. Then ophthalmoplegia, swallowing and speech difficulty. 10. Then RESPIRATORY PARALYSIS — which is what kills. 11. Local signs in neurotoxic bites may be MINIMAL or absent. 12. HAEMOTOXIC envenoming causes bleeding and INCOAGULABLE BLOOD. 13. Gums, nose, bite site, bruising, haematuria; local necrosis; AKI. 14. A bedside WHOLE BLOOD CLOTTING TEST works without a laboratory. 15. MINIMAL LOCAL SIGNS DO NOT MEAN MINIMAL ENVENOMING. 16. Some bites are DRY — no envenoming at all. 17. OBSERVE EVERY BITE — signs may appear hours later. 18. ANTIVENOM is for SYSTEMIC envenoming, not every bite. 19. Indications: neurotoxic signs, coagulopathy or bleeding, severe local progression. 20. Have ADRENALINE and resuscitation equipment ready BEFORE antivenom. 21. Neurotoxic paralysis is REVERSIBLE if the patient is ventilated. 22. Watch speech, cough and head lift — they warn before saturation falls. 23. A paralysed patient may be fully AWARE — speak to them. 24. Avoid unnecessary injections while blood is incoagulable. 25. HEAT EXHAUSTION: unwell but MENTALLY CLEAR — cool, rest, rehydrate. 26. HEAT STROKE: ALTERED MENTAL STATE — a medical emergency. 27. Cool aggressively and physically; ANTIPYRETICS DO NOT WORK. 28. Complications: rhabdomyolysis, AKI, coagulopathy, multi-organ failure. 29. ACUTE MOUNTAIN SICKNESS: headache, nausea, fatigue after ascent. 30. HACE: ATAXIA and confusion · HAPE: breathlessness AT REST. 31. The treatment for both is IMMEDIATE DESCENT. 32. Handle hypothermic patients GENTLY — rough movement risks arrhythmia. 33. Take all antivenom doses from the national guideline.

💡 Exam angle: for snakebite, remember that the examinable content is largely negative — what not to do in first aid, and why a normal-looking bite site proves nothing. For the environmental emergencies, one sign decides each: altered mental state for heat stroke, ataxia for cerebral oedema, breathlessness at rest for pulmonary oedema.

Syllabus points

First aid: reassure, immobilise, transport
Why tourniquets cause harm
Delay as a cause of death
Neurotoxic envenoming and ptosis
Descending paralysis to respiratory failure
Haemotoxic envenoming and coagulopathy
The bedside whole blood clotting test
Why minimal local signs mean nothing
Observing every bite
Indications for antivenom and anaphylaxis risk
Why ventilation allows full recovery
Heat exhaustion versus heat stroke
Altitude illness and immediate descent

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