Snakebite and Envenomation for NEET PG Medicine: MoHFW First Aid, 20WBCT, ASV Dosing, Atropine–Neostigmine, Scorpion Sting

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🎯 Exam priority: High (India-specific). Expect: the four common venomous snakes, krait features, neuroparalytic vs vasculotoxic signs, first-aid errors (tourniquet, incision), 20WBCT method and repeat, ASV indications and doses, no test dose, adrenaline, AN injection doses and stopping rule, no AN in krait, FFP when coagulopathy persists, scorpion sting and prazosin.

CBME mapping: GM 21.1–21.9. Snake identification and medicolegal aspects are in Forensic Medicine; ASV production in Pharmacology; epidemiology in Community Medicine.

Snakebite syndromes, first aid, ASV, 20WBCT and AN injection. Drawn by TrackNation.

Snakes, Syndromes and First Aid

• Medically important Indian snakes: Indian cobra (Naja naja), common krait (Bungarus caeruleus), Russell's viper (Daboia russelii), saw-scaled viper (Echis carinatus). About 70% of bites are non-venomous.

• Neuroparalytic (cobra, krait): ptosis, diplopia, dysarthria, dysphagia, dyspnoea, paralysis. Krait bites at night on people sleeping on the floor, with no local signs, abdominal pain; symptoms can appear after 6–12 h and ptosis as late as 36 h. Locked-in syndrome: quadriplegia and anarthria with preserved consciousness; vertical eye movements are retained.

• Vasculotoxic (Russell's and saw-scaled viper): local swelling, blistering, necrosis, bleeding, incoagulable 20WBCT, shock, AKI (not with saw-scaled viper); compartment syndrome.

• First aid: reassure; immobilise the limb like a fracture; remove rings, watches, tight clothing; don't let the victim run or drive. Do not tie a tourniquet (gangrene), incise, suck, rub, apply herbs, ice or chemicals, or inject ASV locally. A crepe bandage only by trained staff. Admit every suspected bite and observe for 24 h.

20WBCT, ASV and AN Injection

• 20WBCT: 2 mL fresh venous blood in a clean, dry glass tube, undisturbed for 20 minutes, then tilt; still liquid = incoagulable (venom-induced consumption coagulopathy). Repeat 6 hours after the loading dose (and at 6 h in neurotoxic bites).

• AN injection (neuroparalytic): atropine 0.6 mg then neostigmine 1.5 mg IV; repeat neostigmine 0.5 mg with atropine every 30 min for 5 doses, then taper. Response = ≥ 50% recovery of ptosis in 1 h; stop if no response after the 3rd dose. No AN in confirmed krait bite. Ventilate if needed.

• Persistent coagulopathy after adequate ASV: FFP or cryoprecipitate (fresh whole blood if neither). Prophylactic antibiotics are unnecessary. No specific Indian ASV for sea snake or pit viper bites.

• Scorpion sting (MSD): prazosin may prevent pulmonary oedema from extreme hypertension in serious stings.

Traps the Examiner Sets

• No ASV test dose — ever.

• Local swelling alone is not an indication for ASV.

• Krait: night, floor, no fang-mark swelling, late ptosis; no AN.

• Saw-scaled viper does not cause AKI; starting ASV dose is 6 vials.

• No tourniquets — they cause gangrene.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 Krait 'Kills in the dark, Keeps no marks' — krait

• 🧠 20WBCT '2-20-tilt': 2 mL, 20 minutes, tilt — 20WBCT

• 🧠 ASV: 'No test, No local, No incomplete' — ASV rules

• 🧠 Neuro ASV '10 + 10' — neuroparalytic dose

• 🧠 AN: 'A before N, half the droop in an hour' — AN injection

• 🧠 Saw-scaled: 'Six vials, Spares the kidney' — saw-scaled viper

Rapid-Revision Cards

• Big four

  Cobra, krait, Russell's viper, saw-scaled viper.

• Non-venomous

  ~70% of bites.

• Krait

  Night, floor, no local signs; late ptosis (36 h).

• Neuroparalytic

  Ptosis, diplopia, dysphagia, paralysis.

• Vasculotoxic

  Bleeding, 20WBCT incoagulable, shock, AKI.

• Saw-scaled viper

  No AKI; ASV start 6 vials.

• First aid

  Reassure, immobilise, remove rings.

• Never

  Tourniquet, incision, suction, herbs, local ASV.

• Observe

  Admit all; 24 h.

• 20WBCT

  2 mL, glass tube, 20 min, tilt.

• Repeat 20WBCT

  6-hourly.

• ASV now

  Spontaneous bleeding > 20 min after bite.

• Not ASV

  Purely local or old swelling.

• Test dose

  None.

• Neuro ASV

  10 vials, repeat 10 at 1 h.

• Vasculo ASV

  10 (6 SSV) then 2 q6h (low) or 6 q6h (high).

• Total ASV

  10–30 vials.

• Adrenaline

  Premed (not in HTN); reaction 0.5 mg IM.

• AN injection

  Atropine 0.6 + neostigmine 1.5 mg IV; 0.5 mg q30 min × 5.

• AN response

  ≥ 50% ptosis recovery in 1 h; stop after 3 failed doses.

• No AN

  Krait.

• Persistent coagulopathy

  FFP or cryoprecipitate.

• Antibiotics

  Not prophylactic.

• Scorpion

  Prazosin.

Sources

Facts in this article were checked against these documents.

• Standard Treatment Guidelines: Management of Snake Bite — Quick Reference Guide — Ministry of Health & Family Welfare, Government of India, July 2016 (link)

• MSD Manual Professional: Scorpion Stings — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• Competency Based Undergraduate Curriculum, General Medicine (GM 21) — National Medical Commission, 2024

Test Yourself: Practice Questions

Thirty questions in NEET PG style, most of them clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. The medically most important venomous snakes of India include all EXCEPT

• (a) common krait

• (b) the python

• (c) Indian cobra

• (d) Russell's viper

Q2. A villager sleeping on the floor wakes with severe abdominal pain and later develops ptosis; no fang marks or swelling are seen. The likely snake is

• (a) python

• (b) Russell's viper

• (c) common krait

• (d) saw-scaled viper

Q3. Approximately what proportion of snakebites are by non-venomous species (MoHFW)?

• (a) 30%

• (b) 95%

• (c) 70%

• (d) 10%

Q4. Correct first aid for a snakebite on the leg is

• (a) incise and suck the wound

• (b) reassure and immobilise the limb like a fracture, remove rings and tight items

• (c) apply ice and herbs

• (d) tie a tight tourniquet

Q5. A relative has tied a tight cord above a snakebite. The MoHFW guideline warns that tourniquets

• (a) prevent all envenoming

• (b) should be tightened every hour

• (c) may cause gangrenous limbs

• (d) are recommended for 6 hours

Q6. A snakebite victim with no symptoms reaches hospital. Per MoHFW he should be

• (a) given antibiotics only

• (b) sent home immediately

• (c) admitted and observed for 24 hours

• (d) given ASV prophylactically

Q7. The bedside test of venom-induced coagulopathy is

• (a) D-dimer

• (b) 20-minute whole blood clotting test: 2 mL blood in a clean dry glass tube, tilted after 20 minutes

• (c) bleeding time

• (d) platelet count only

Q8. After the loading dose of ASV in a vasculotoxic bite, the 20WBCT is repeated

• (a) every 30 minutes

• (b) every 6 hours until clotting returns

• (c) never

• (d) after 3 days

Q9. A man bitten by a viper has spontaneous gum bleeding 30 minutes after the bite. The next step is

• (a) observe for 24 h

• (b) wait for 20WBCT

• (c) give vitamin K only

• (d) start ASV without waiting for the 20WBCT

Q10. A patient has only mild swelling around fang marks 8 hours after a bite, with normal 20WBCT and no systemic signs. ASV is

• (a) not indicated — purely local swelling is not a ground for ASV

• (b) indicated, 2 vials

• (c) indicated, 10 vials

• (d) indicated as test dose

Q11. Before giving ASV, a skin or conjunctival test dose is

• (a) mandatory

• (b) required only in children

• (c) done with 1 vial

• (d) not recommended — it does not predict reactions

Q12. The MoHFW dose of ASV for neuroparalytic envenomation is

• (a) 1 vial every 6 hours

• (b) 50 vials at once

• (c) 2 vials only

• (d) 10 vials over 30 minutes, repeated once after 1 hour if no improvement

Q13. In the low-dose regimen for a saw-scaled viper bite with coagulopathy, the initial ASV dose is

• (a) 10 vials then 10 hourly

• (b) 6 vials, then 2 vials 6-hourly

• (c) 1 vial

• (d) 20 vials

Q14. The usual total ASV requirement in Russell's viper envenomation is

• (a) not quantifiable

• (b) 1–2 vials

• (c) 100 vials

• (d) 10–30 vials (each neutralises 6 mg venom)

Q15. Before ASV, routine prophylactic adrenaline is recommended EXCEPT in

• (a) women

• (b) known hypertensives (or BP > 140/90)

• (c) patients with bleeding

• (d) children

Q16. A patient develops an anaphylactic reaction during ASV infusion. The dose of adrenaline for an adult is

• (a) 1 mg subcutaneously daily

• (b) 0.05 mg orally

• (c) 5 mg IV push

• (d) 0.5 mg IM

Q17. ASV has

• (a) absolute contraindication in children

• (b) absolute contraindication in asthma

• (c) absolute contraindication in pregnancy

• (d) no absolute contraindications

Q18. The AN injection for a neuroparalytic bite in an adult starts with

• (a) pralidoxime 1 g

• (b) adrenaline 1 mg

• (c) atropine 0.6 mg then neostigmine 1.5 mg IV

• (d) physostigmine 2 mg

Q19. A positive response to the AN injection is

• (a) pupil dilation

• (b) rise in BP

• (c) ≥ 50% recovery of ptosis within 1 hour

• (d) complete recovery in 5 minutes

Q20. In confirmed krait bite, the AN injection is

• (a) given every 30 minutes

• (b) given as a single large dose

• (c) replaced by pralidoxime

• (d) not given

Q21. After a krait bite, ptosis has been recorded as late as

• (a) never after 1 hour

• (b) 5 minutes only

• (c) 1 week

• (d) 36 hours after hospitalisation

Q22. A paralysed snakebite patient cannot move limbs or speak but has preserved consciousness and vertical eye movements. This is

• (a) hysteria

• (b) brain death

• (c) coma

• (d) locked-in syndrome — not brain death

Q23. Acute kidney injury is a feature of vasculotoxic envenoming EXCEPT after bites by

• (a) both vipers

• (b) Russell's viper

• (c) saw-scaled viper

• (d) none

Q24. Despite adequate ASV, a Russell's viper victim still has incoagulable blood and bleeding. The next step is

• (a) fresh frozen plasma or cryoprecipitate

• (b) give heparin

• (c) give aspirin

• (d) stop ASV forever

Q25. Prophylactic antibiotics after snakebite are

• (a) required before ASV

• (b) required for all krait bites

• (c) always required

• (d) unnecessary

Q26. ASV should NOT be

• (a) given intravenously

• (b) given in full dose

• (c) injected locally at the bite site

• (d) given to children

Q27. Rapid development of swelling after a bite indicates

• (a) dry bite

• (b) envenoming (consider ASV)

• (c) allergy only

• (d) non-venomous snake

Q28. ASV available in India does not specifically cover bites by

• (a) sea snakes and pit vipers

• (b) Russell's viper

• (c) saw-scaled viper

• (d) cobra

Q29. Which wound practice is recommended after snakebite?

• (a) apply chilli paste

• (b) leave the wound alone — no incision, suction, rubbing, herbs, ice or cautery

• (c) incise and drain

• (d) cauterise

Q30. In a serious scorpion sting with extreme hypertension, a drug that may prevent pulmonary oedema is

• (a) prazosin

• (b) adrenaline

• (c) atropine

• (d) propranolol

Active Recall

From memory: name the big four snakes, describe neuroparalytic and vasculotoxic syndromes and krait clues, list first-aid do's and don'ts, explain the 20WBCT, give ASV indications, non-indications and regimens, the adrenaline rules, the AN injection schedule and response, and management of persistent coagulopathy and scorpion sting.