Snake bite in Pakistan: the tourniquet, the clotting test, and the dose rule

A farmhand is carried into casualty with a cord tied hard around his upper arm. Someone tied it within a minute of the bite, and they are proud of it. The arm below is dusky and the pain is unbearable.

Your first clinical decision is not about the snake. It is whether to cut that cord off — and the answer is no, not yet.

The tourniquet you find already tied

WHO is unambiguous about tourniquets as first aid:

Tight (arterial) tourniquets must never be recommended or condoned! ... If applied tightly around the upper part of the limb, these bands, bandages or ligatures are extremely painful as the limb becomes ischaemic and are very dangerous if left in place for long periods. Many gangrenous limbs have resulted!

But that is advice about applying one. What you actually face in Pakistan is a tourniquet that is already on, and the guidance there runs the other way:

Delay the release of tight bands, bandages and ligatures: if the patient has already applied these very popular methods of first-aid, they should not be released until the patient is under medical care in hospital, medical staff and resuscitation facilities are available and antivenom treatment has been started.

The reason is on WHO's list of situations requiring urgent resuscitation: sudden deterioration, or rapid development of severe systemic envenoming, after releasing a tight tourniquet. Venom has been pooling distal to that band. Cutting it off delivers the lot in one bolus.

So: IV access, adrenaline drawn up, antivenom running if it is indicated — and then release the band, with resuscitation to hand.

What actually helps before hospital

Reassure the patient. A dry bite is common even from a venomous snake, severe envenoming usually evolves slowly, and treatment works — all three are legitimate grounds for reassurance, and a slower heart rate genuinely slows venom spread.

Then immobilise the whole patient, not just the limb. WHO: "Any movement or muscular contraction, even undressing or walking, will increase absorption and spread of venom by squeezing veins and lymphatics." Recovery position, splint or sling the limb, remove rings and bangles before swelling makes it impossible.

One point that is often taught backwards: WHO does recommend pressure-pad immobilisation unless an elapid bite can confidently be excluded, and cites evidence that the pressure-pad method reduced venom spread in Russell's viper bite victims. It is described as "preferred and recommended as being simpler and more practicable" than pressure-bandage immobilisation, which needs equipment and skill.

Everything else in the traditional repertoire — incision, suction, rubbing, herbs, ice, cautery, electric shock — falls under WHO's blanket verdict, printed in capitals: most traditional first-aid methods do more harm than good.

Resuscitate before you diagnose

ABCDE, vital signs, and one specific trap:

The Glasgow Coma Scale cannot be used to assess the level of consciousness of patients paralysed by neurotoxic venoms.

A patient with complete neurotoxic paralysis is fully awake and fully aware. Score them on GCS and you will document a deeply comatose patient, manage them as unconscious, and miss that they can hear every word being said over them.

The bite with nothing to see

The presentation that kills quietly is the one with no local signs at all. WHO's Syndrome 4 — paralysis with minimal or no local envenoming, bitten on land while sleeping on the ground, with or without abdominal pain — points to a krait.

There is no swelling to prompt the diagnosis. The patient wakes with abdominal pain, then develops ptosis, then stops breathing. If your mental trigger for "this is a snakebite" is a swollen limb, you will not reach for it.

The five syndromes in brief:

In Pakistan those genera mean Naja naja throughout and Naja oxiana in the north and north-west; Bungarus caeruleus and B. sindanus; Daboia russelii; Echis carinatus sochureki; and sea snakes along the Makran and Sindh coast.

Note what the syndromic approach is not: a species diagnosis. WHO warns that identifying a dead snake "requires skill and even experienced medical personnel may mistake harmless mimics for venomous snakes, or they may confuse different venomous species. As a result, the patient may be given antivenom unnecessarily." Do not let a phone photograph override the clinical picture.

The 20-minute test, done properly

Two millilitres of fresh venous blood into a small, new, dry, ordinary glass vessel. Undisturbed for 20 minutes at room temperature. Tip it once. If the blood is still liquid and runs out, that is incoagulable blood from venom-induced consumption coagulopathy.

And a genuinely useful discriminator: in this region, incoagulable blood is diagnostic of a viper bite and rules out an elapid bite.

The test fails in one predictable way. Plastic, polystyrene or polypropylene tubes, glass washed with detergent, a wet or contaminated vessel, or a glass syringe with anticoagulant lubricant — any of these prevents factor XII surface activation and the blood will not clot regardless of the patient. That is a false positive, and it sends antivenom into someone who does not need it.

Where new glass tubes are unaffordable, WHO gives a workaround: recycled glass antibiotic bottles are acceptable if washed with normal saline only — no detergent — and hot-air dried.

It also has false negatives, becoming positive only below a fibrinogen of 0.5 g/L, so it misses early evolving coagulopathy. WHO's response is not to abandon it but to repeat it frequently, and:

Antivenom treatment should not be delayed if there is other evidence of anti-haemostatic disturbances (e.g. spontaneous systemic bleeding distant from the bite site).

Do not substitute a variant. The 30-minute WBCT, the "2,3,5 syringe test" and the capillary tube test "have not been standardised or validated" and carry the same false-positive risk.

When antivenom is indicated

Systemic envenoming — any one of: spontaneous systemic bleeding distant from the bite site, or coagulopathy (non-clotting 20WBCT, INR above 1.2, PT 4–5 seconds beyond control), or platelets below 100 × 10⁹/L; neurotoxic signs; hypotension, shock or arrhythmia; acute kidney injury; haemoglobinuria or myoglobinuria.

Local envenoming — swelling involving more than half the bitten limb within 48 hours in the absence of a tourniquet; swelling after a bite on a digit; rapid extension of swelling, such as beyond the wrist or ankle within a few hours; or an enlarged tender draining lymph node.

Absent all of those, antivenom is not indicated yet — which is not the same as no envenoming. Admit, observe, repeat the clotting test.

The dose rule that matters most

Snakes inject the same dose of venom into children and adults. Children must therefore be given exactly the same dose of antivenom as adults.

Antivenom neutralises venom, not body mass. Scaling it by weight is an instinct carried over from every other paediatric drug, and here it under-doses the patient who is least able to tolerate the venom load.

The second rule: if blood is still incoagulable on the 20WBCT six hours after the initial dose, repeat the same dose. The liver takes 3–9 hours to restore coagulable fibrinogen once the venom is neutralised, so six hours is the point at which persisting incoagulability means insufficient antivenom rather than insufficient time.

How many vials? Our tool deliberately does not tell you, and neither will this article. WHO states initial doses per manufacturer; Pakistan runs on a mix of NIH Islamabad, Indian and Saudi product; and WHO's own record for the Pakistani producer reads "no recent information available". Read the neutralising capacity printed on the vial you are actually holding, and follow your hospital protocol.

Reactions

Reaction rates for Indian polyvalent antivenoms have been reported as high as 81% in Sri Lanka, with severe reactions in up to 43%. Adrenaline should be drawn up at the bedside before the infusion starts.

Give it intramuscularly into the upper lateral thigh — 0.5 mg for adults, 0.01 mg/kg for children — at the very first sign: "even when only a few spots of urticaria have appeared or at the start of itching, tachycardia or restlessness." Chlorphenamine and hydrocortisone come after, not instead.

And do not bother pre-medicating. Antihistamines, corticosteroids and slowing the infusion rate "do not affect the incidence or severity of early antivenom reactions."

The limb

Two rules that get broken in that order.

No intramuscular injections into an incoagulable patient. That includes the tetanus toxoid. Give it once the coagulopathy has been corrected.

Fasciotomy needs all three criteria: haemostatic abnormalities corrected with antivenom, clinical evidence of a compartment syndrome, and a directly measured intracompartmental pressure above 40 mmHg in adults. Direct measurement is mandatory — palpable or Doppler-detectable pulses do not exclude compartment ischaemia. WHO notes that "many unnecessary, dangerous and debilitating fasciotomies are performed, especially where surgeons rather than physicians have the primary responsibility." Cutting into a patient with venom-induced coagulopathy causes catastrophic bleeding, and early antivenom remains the best way to prevent the muscle damage the fasciotomy was meant to avert.

Bottom line

Leave the tourniquet until antivenom is running. Immobilise the whole patient. Do not score a paralysed patient on GCS. Remember that the krait bite has nothing to see. Use ordinary glass for the clotting test and repeat it rather than trusting one result. Give a child the adult dose. Have adrenaline drawn up before you start, and skip the premedication. Give the tetanus after the coagulopathy corrects, not before. And measure the pressure before anyone reaches for a blade.

Our snake bite tool walks through this in six steps and will tell you whether antivenom is indicated — it just will not tell you how many vials, for the reason above. For the other common animal-contact emergency, see the rabies post-exposure prophylaxis tool.

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