Quick Recap
Toxicology System, Protocol 5/8. Covers both the neurotoxic (Elapidae — cobra, krait, coral snake) and hemotoxic/vasculotoxic (Viperidae — viper, pit viper) envenomation patterns, given global ICU practice encounters both.
1. General Principles
Most snakes are non-venomous, and even venomous snakebites often do NOT result in envenomation ("dry bites") — not every bite requires antivenom. Outcome depends on species, body region bitten, and venom volume injected. Treatments that are NO LONGER recommended: tourniquets, prophylactic antibiotics, prophylactic fasciotomy, pressure immobilization (regionally variable recommendation), cutting or suctioning the wound, ice application to the bite site — do not perform any of these, even if taught historically or requested by the patient/family based on folk practice.
2. Envenomation Syndromes by Snake Family
Syndrome | Typical culprits |
Local effects (swelling, pain, ecchymosis) | Vipers, cobra, sea snakes (usually ABSENT with krait bites — a diagnostic trap, since minimal local findings can falsely reassure) |
Coagulopathy | Vipers (Russell's viper, hump-nosed viper, saw-scaled viper) |
Neurotoxicity | Cobra, common krait, sea snakes, Russell's viper (in some cases/regions) |
Renal toxicity | Russell's viper, hump-nosed viper |
Myotoxicity | Sea snakes, some krait species |
Viperidae envenomation (North American: rattlesnake, water moccasin/cottonmouth, copperhead): local tissue/hematologic toxicity — rapidly progressive swelling, ecchymosis, coagulopathy, rhabdomyolysis, hypotension, nonspecific systemic symptoms (nausea, vomiting, diaphoresis, weakness).
Elapidae envenomation (North American: coral snake; globally: cobra, krait): moderate local effects with RAPID-ONSET neurotoxicity — ptosis, ophthalmoplegia, dysarthria, dysphagia, dysgeusia, fasciculations, paralysis, respiratory failure, seizures. Mnemonic for neurotoxic symptom screening: the "4 Ds" — Diplopia, Dysphagia, Dysphonia, Dyspnea.
3. Immediate Stabilization (ABCDE) — Airway Is Paramount in Neurotoxic Envenomation
Airway is THE critical priority in neuroparalytic snakebite. Assess for: pooling of secretions, inability to open mouth/protrude tongue, weakness of neck flexors ("broken neck sign"), or single breath count <10 — any of these, or a compatible clinical trajectory, warrants IMMEDIATE intubation using standard technique, before respiratory failure becomes an emergency rather than an anticipated event.
Breathing: monitor SpO2; supplemental O2 for hypoxia; assisted ventilation if the patient cannot maintain oxygenation independently.
Circulation: good peripheral IV access, crystalloid resuscitation; vasopressors if hypotension persists despite adequate fluids. Be careful with venipuncture in coagulopathic patients (viper envenomation) — avoid non-compressible sites, minimize needle sticks.
Checklist:
4. Severity Grading (Regional/WHO-style Framework)
Severity | Local findings | Systemic findings |
Nonenvenomation (dry bite) | None or puncture wounds only | None |
Mild | Puncture wounds, pain, swelling confined to bite site | None |
Moderate | Swelling beyond bite site | Mild nausea/vomiting/fasciculations, paresthesia, microscopic hematuria |
Severe | Severe pain/swelling | Respiratory failure, hypotension, or bleeding |
Mild-severity patients should still be OBSERVED for at least 24 hours given the potential for delayed progression, particularly with krait bites where local findings can be deceptively absent early.
5. Investigations
CBC with platelets, bleeding time, clotting time, 20-minute whole blood clotting test (20WBCT) — a simple, rapid bedside coagulopathy screen: place fresh whole blood in a clean glass tube, leave undisturbed 20 minutes, then check for clot formation — failure to clot indicates significant coagulopathy/venom-induced consumption coagulopathy. PT/INR/aPTT, fibrinogen, FDP, D-dimer. Urinalysis (hematuria, or myoglobin if urine is dipstick-blood-positive with absent RBCs on microscopy — suggesting myoglobinuria/rhabdomyolysis rather than true hematuria). Renal function (regularly monitored if renal failure present). Electrolytes, ABG. ECG (arrhythmia screening). CK/aldolase and aminotransferases (myotoxicity/rhabdomyolysis assessment).
6. ICU Admission Indications
Circulatory shock/cardiac dysfunction/pulmonary edema; hemorrhage/hypovolemia; coagulopathy/DIC; coma/seizures/intracranial hemorrhage; cranial nerve dysfunction; rhabdomyolysis/renal failure/hyperkalemia; GI bleeding; respiratory failure; anaphylaxis (to venom component or to antivenom itself).
7. Antivenom (ASV) — Central Definitive Therapy
Indicated for hematologic toxicity, neuromuscular toxicity, progressive edema, or hemodynamic instability — NOT given prophylactically or in patients lacking envenomation signs, given real anaphylaxis risk (Section 8).
Global (polyvalent ASV, horse-serum-derived) dosing: usual initial dose 10 vials, given by slow injection (max 2mL/min) or IV infusion (diluted in NS/dextrose, 5mL/kg body weight, over 30-60 minutes). Do NOT inject ASV locally at the bite site. Repeat the initial dose if: blood remains non-coagulable at 6 hours, OR spontaneous bleeding persists at 1 hour, OR neurotoxic/cardiovascular signs persist or worsen. Children receive the SAME dose as adults — venom volume injected is independent of victim size, so dosing is not weight-based.
North American (Crotalidae-specific ASV) approach: starting doses vary with clinical scenario and specific antivenom product — contact poison control or a toxicology expert to guide dosing. Be aware exotic snake collectors may have non-native species not covered by standard Crotalidae antivenom, requiring specific alternative antivenom sourcing.
Efficacy pattern — an important expectation-setting point: ASV will NOT have a dramatic effect on established neuroparalysis (the neuromuscular junction damage from neurotoxin binding is not rapidly reversed by antibody neutralization of circulating venom) — but ASV DOES have a dramatic, often rapid effect on stopping bleeding/coagulopathy. Low-dose ASV has been shown as effective as high-dose ASV in severe neurotoxic envenoming — do not assume more antivenom equals better neurologic outcome.
Response monitoring: test for coagulopathy reversal 1 hour after antivenom administration; redose/maintain per response until "control" is achieved — defined as arrest of progressive edema, hemodynamic stability, resolution of systemic toxicity, and partial/complete coagulopathy reversal.
8. ASV Reaction Management
ASV is a foreign (horse-serum-derived) protein — allergic reactions including anaphylaxis are a real, expected risk. Skin testing before ASV infusion is NOT recommended (poor predictive value for infusion reactions). H1/H2 blockers and hydrocortisone pretreatment do NOT reduce infusion reaction incidence. Prophylactic adrenaline (0.25mg of 1% adrenaline, i.e., 0.25mL, given SUBCUTANEOUSLY before starting ASV) IS recommended to reduce infusion reaction incidence — a genuinely different (and less intuitive) premedication strategy than the antihistamine/steroid approach used for many other infusion-reaction-prone therapies.
Always keep an adrenaline syringe ready BEFORE starting ASV infusion.
If a reaction occurs during infusion: STOP the ASV infusion immediately -> give adrenaline 0.5mg of 1:1000 dilution IM -> simultaneously give H1 blocker (chlorpheniramine) + H2 blocker (ranitidine) + hydrocortisone 100mg (understanding steroids take 4-6h to act, so this is adjunctive, not the primary rescue) -> adrenaline can be repeated 2-3 doses, or an infusion started at 1:50,000 dilution if needed -> treat hypotension with fluids, inotropes if overt myocardial dysfunction present.
9. Neuroparalytic Envenomation — Specific ICU Management
Mechanical ventilation initiated at the appropriate time significantly reduces mortality in neuroparalytic envenomation — do not delay intubation awaiting further deterioration once the airway warning signs in Section 3 are present.
Anticholinesterase therapy (edrophonium, neostigmine) has been recommended as an ADJUNCT for neuroparalytic envenomation, particularly where the neurotoxin has a postsynaptic (competitive, potentially reversible) mechanism: 10mg edrophonium IV OR 0.5mg neostigmine IM, given over 2-3 minutes, WITH ATROPINE PRETREATMENT (0.6mg) to counter the cholinergic side effects of the anticholinesterase agent itself. If the patient improves with this test dose, continue neostigmine/atropine maintenance dosing over the next 24-48 hours.
Most patients with neuroparalytic envenomation recover within 48 hours with appropriate supportive care — useful for family counseling/expectation-setting once the acute crisis is controlled.
General ICU supportive care: propped-up nursing position, stress ulcer prophylaxis, DVT prophylaxis, glucose control, appropriate sedation/analgesia.
10. Complications and Their Management
Wound debridement: consider if local swelling/necrosis is severe enough to threaten limb/life viability.
Fasciotomy: consider if clinical compartment syndrome develops, or if intracompartmental pressure exceeds 40mmHg (adults) — measure intracompartmental pressure proactively if compartment syndrome is suspected, given viper envenomation's propensity for severe local swelling.
Rhabdomyolysis: manage with adequate hydration, acidosis correction with bicarbonate, and alkaline diuresis (see also the Rhabdomyolysis protocol, Renal System, for the broader management framework, understanding that urine alkalinization's evidence base for rhabdomyolysis specifically is debated there — apply per current local/toxicology guidance).
11. Organ Support
Mechanical ventilation for neuroparalytic respiratory failure; blood product support for coagulopathy/hemorrhage (per general Coagulopathy protocol principles, Hematology System, understanding ASV itself is the primary coagulopathy-reversing intervention here); RRT for renal failure per standard AKI/CRRT indications; standard ICU supportive care.
12. Consultation Matrix
Consultation | Trigger | Timing |
Toxicology/Poison Control | All significant envenomation, antivenom dosing guidance | Immediate |
Surgery | Compartment syndrome, wound debridement, fasciotomy consideration | Urgent once suspected |
Nephrology | AKI/renal failure | As indicated |
13. Monitoring Framework
Reassess clinically every 15 minutes during active envenomation/antivenom administration; mark the leading edge of local edema to track progression; serial coagulation panel (test 1h post-ASV for reversal); vital signs (BP, oxygenation, cardiac rhythm, urine output); serial CK/potassium (rhabdomyolysis trend); intracompartmental pressure if compartment syndrome suspected.
14. Complications (Broader List)
Respiratory failure (neuroparalytic), hemorrhage/DIC (hemotoxic), compartment syndrome, rhabdomyolysis/AKI, anaphylaxis to ASV, delayed serum sickness (see Section 15), local tissue necrosis. Prevention: proactive airway assessment/intubation, appropriate ASV dosing with prophylactic adrenaline, intracompartmental pressure monitoring. Rescue: mechanical ventilation, repeat ASV dosing per response criteria, fasciotomy, standard anaphylaxis/DIC management.
15. ICU Discharge Criteria
Resolution of paralysis for >24 hours; 50% improvement in CK and potassium; peak expiratory flow rate >100 L/min; normal oximetry/blood gas on room air; normalized bleeding time/clotting time/capillary refill time and platelets >50,000; stable or improved urine output. Counsel the patient about late reactions (serum sickness) — can occur days after ASV exposure, treated with oral antihistamine or steroid.
16. Documentation & Medicolegal Checklist
17. Key Guidelines
World Health Organization. WHO Guidelines for the Management of Snakebite, 2nd ed, 2016.
18. Landmark Evidence
Aggarwal R, Aggarwal AN, Gupta D, et al. Low dose of snake antivenom is as effective as high dose in patients with severe neurotoxic snake envenoming. Emerg Med J. 2005;22:397-399.
19. Controversies
The role and evidence base for anticholinesterase therapy (neostigmine/edrophonium) in neuroparalytic envenomation varies by snake species/toxin mechanism (postsynaptic vs presynaptic neurotoxins respond differently) and is not universally effective — a trial dose with clear improvement criteria is the pragmatic approach rather than a blanket recommendation. Pressure immobilization technique recommendations vary meaningfully by region/snake family and are not universally endorsed. Optimal ASV redosing threshold and duration in severe hemotoxic envenomation continues to be refined by ongoing regional studies.
20. References
- Chaudhry D, Alavala SC, Jash D. Snakebite. ICU Protocols: A Step-wise Approach, 2nd ed. Springer; 2020 (Ch. 16).
- Toxicology (Snake Envenomation section). Washington Manual of Critical Care, 4th ed, 2025 (Ch. 36).
- World Health Organization. WHO Guidelines for the Management of Snakebite, 2nd ed, 2016.
- Aggarwal R, Aggarwal AN, Gupta D, et al. Low dose of snake antivenom is as effective as high dose in patients with severe neurotoxic snake envenoming. Emerg Med J. 2005;22:397-399.
- Naphade RW, Shetti RN. Use of neostigmine after snake bite. Br J Anaesth. 1997;49:1065-1068.
See also: Guillain-Barré Syndrome and Myasthenic Crisis (Neurology System) for the broader neuromuscular respiratory failure differential; DIC and Coagulopathy (Hematology System) for the shared coagulopathy management framework.