On this page
Study tools
Write your answer
Saved on this device. No marking — you are the marker.
Stem
A 35-year-old rice farmer from rural West Bengal is brought to the emergency department at 2 a.m. after being bitten on the foot while sleeping on a mat on the floor. He complains of vague abdominal pain and difficulty opening his eyes. On examination he is conscious and afebrile, pulse 96/min, BP 110/70 mmHg, RR 22/min, SpO2 96% on air. There is no visible bite mark swelling at the foot. Neurological examination reveals bilateral ptosis, restricted external ocular movements (diplopia), a weak voice and pooling of oral secretions; limb power is 4/5 proximally. His single breath count is 25. A 20-minute whole blood clotting test clots normally. The accompanying relative has brought the dead snake, which is glossy black with white bands.
Questions
a) What is the most likely diagnosis, and which two features clinch it? (2 marks)
Most likely diagnosis: common krait (Bungarus caeruleus) envenomation — a neurotoxic ELAPID bite. The two features that clinch it are: (i) the descending flaccid paralysis with NO local swelling (ptosis, ophthalmoplegia, bulbar palsy) and a normal 20WBCT — the classic neurotoxic-elapid syndrome; and (ii) the clinical setting — a nocturnal, painless bite while sleeping on the floor, abdominal pain, and the snake's appearance (glossy black with white bands). Krait venom is predominantly presynaptic phospholipase A2 (beta-bungarotoxin) plus postsynaptic alpha-neurotoxin.
b) Outline your immediate resuscitation and the single most life-saving supportive measure. (2 marks)
ABCDE: secure the airway, give oxygen, obtain IV access, and send bloods (CBC, coagulation, U&E, CK, group and cross-match). Because the bulbar palsy is causing pooling of secretions and the single breath count has fallen to 25 (indicating evolving neuromuscular respiratory compromise), the single most life-saving measure is EARLY ELECTIVE ENDOTRACHEAL INTUBATION AND MECHANICAL VENTILATION — do NOT wait for respiratory arrest; monitor single breath count, peak flow and forced vital capacity closely. Krait presynaptic neurotoxicity does NOT respond well to antivenom, so ventilation is the life-saver while the nerve terminal regenerates over days to weeks.
c) Give the drug, dose, route, timing and rationale for specific antivenom, and the precaution you must take before giving it. (2 marks)
Drug: Indian polyvalent anti-snake venom (ASV) (raised in horses; active against the Big Four). Dose: 8–10 vials (the same dose as an adult — antivenom neutralises the venom load, not body weight). Route and timing: reconstitute each vial in 10 mL sterile water, dilute in 100–200 mL normal saline, and infuse IV over 1 hour. Rationale: the polyvalent ASV neutralises circulating krait venom; efficacy is limited by the presynaptic toxin but it is still indicated. PRECAUTION before starting: have adrenaline drawn up, oxygen and IV fluids running, and resuscitation equipment at the bedside because ASV causes early anaphylactic/anaphylactoid reactions in 10–40% of recipients.
d) Describe the management of an acute reaction to the antivenom if it occurs. (2 marks)
Stop or slow the ASV infusion. Give IM adrenaline 0.5 mg (0.5 mL of 1:1000) into the anterolateral mid-thigh, repeated every 5 minutes as needed. Give high-flow oxygen and IV crystalloid (10–15 mL/kg) for shock, plus IV hydrocortisone 200 mg and chlorphenamine 10 mg. Once the patient is stable, resume the ASV cautiously at a slower rate — the indication for antivenom has not disappeared, and untreated envenomation is more dangerous than a controlled reaction. Counsel the patient about serum sickness at 5–14 days (fever, rash, arthralgia).
e) Name three harmful first-aid practices you must counsel the family against in future, and why each is harmful. (2 marks)
- Tourniquet — causes ischaemia and reperfusion injury and worsens local necrosis; if applied, sudden removal can trigger catastrophic systemic envenomation.
- Cutting and oral suction at the bite site — removes no meaningful venom, introduces infection, and worsens bleeding if there is coagulopathy.
- Application of ice, electric shock, herbal pastes, or alcohol — ice increases tissue necrosis; electric shock has no scientific basis; herbal pastes and alcohol delay definitive hospital care. (Other acceptable: washing the bite site, giving food/drink before assessment.) The correct first aid is reassure, immobilise the limb, pressure-immobilisation bandage, and rapid transport.