Emergency Medicine Hub / Toxicology & Environmental • 3 min read • 3 sections

Envenomations, Bites & Marine Stings

Comprehensive emergency protocol for venomous snakebites, spider bites, and marine toxin exposures. Covers clinical staging and antivenom indications for North American pit vipers (Crotalinae), delayed respiratory paralysis in coral snake bites, the rigid abdomen of latrodectism (black widow) vs. loxoscelism (brown recluse), and the immediate hot-water immersion protocol for stingray and marine envenomations.

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Pit Viper Antivenom Triggers

Swelling crossing a major joint, systemic shock/angioedema, or coagulopathy (platelets < 100k, fibrinogen < 100 mg/dL)

CroFab vs Anavip Dosing

CroFab: 4-6 vials IV initial load over 60 min. Anavip: 10 vials IV initial load; longer half-life prevents late recurrence

Harmful First-Aid Prohibition

NEVER apply tourniquets, arterial constriction bands, ice, electric shocks, or wound incisions (worsens local necrosis)

Coral Snake ICU Rule

'Red on yellow, kill a fellow'; admit to ICU for 24-48 hours; neurotoxin causes delayed diaphragmatic paralysis

Stingray Hot Water Immersion

Immerse affected extremity in hot water (45°C/113°F) for 30-90 minutes; heat instantly denatures protein toxin

Bottom-Line Clinical Pearl

In pit viper envenomations (rattlesnakes, copperheads, cottonmouths), measure and mark the leading edge of swelling every 15 to 30 minutes; progression crossing a major joint, systemic toxicity, or coagulopathy mandates immediate Crotalidae antivenom (CroFab 4-6 vials or Anavip 10 vials). Never apply tourniquets, ice packs, or suction devices. For stingray envenomations, immerse the affected extremity immediately in non-scalding hot water (45°C) to denature heat-labile protein toxins.

1. North American Pit Viper Envenomations (Crotalinae)

Pit vipers (Rattlesnakes, Copperheads, Cottonmouths/Water Moccasins) account for 99% of venomous snakebites in North America. They possess elliptical pupils, heat-sensing facial pits between the eye and nostril, and retractable hinged fangs. Their venom is a complex mixture of proteolytic enzymes, metalloproteinases, and thrombin-like glycoproteins that cause local tissue necrosis, capillary leak, and severe consumptive coagulopathy:

Clinical Feature	Findings & Progressive Stages	Emergency Action & Antivenom Protocol
Local Tissue Injury	Fang marks (one or two puncture wounds), rapid-onset severe pain, erythema, expanding edema, ecchymosis, and hemorrhagic bullae.	Serial Tracking Protocol: Mark the leading edge of swelling with a surgical pen every 15 to 30 minutes, recording the exact time. Measure extremity circumference at three fixed reference points.
Systemic Manifestations	Nausea, vomiting, diaphoresis, metallic taste in the mouth, facial paresthesias, muscle fasciculations, severe hypotension, and angioedema.	Systemic signs indicate significant envenomation; obtain two large-bore IVs and begin aggressive isotonic fluid resuscitation.
Hematologic Venom-Induced Coagulopathy (VIC)	1. Severe Fibrinogen Consumption (often < 50-100 mg/dL) 2. Thrombocytopenia (platelet count < 50,000-100,000/mcL) 3. Prolonged PT/INR and PTT.	Serial laboratory monitoring every 4-6 hours: CBC, PT/INR, Fibrinogen, and CK (for rhabdomyolysis). Coagulopathy can persist or recur for up to 1-2 weeks.
Antivenom Therapy: CroFab vs. Anavip	Indications for Antivenom: 1. Progressive local swelling crossing a major joint (e.g., wrist, elbow, knee) 2. Any systemic symptoms (shock, fasciculations) 3. Any coagulopathy (platelets < 100k, fibrinogen < 100).	Dosing Regimens: - CroFab (Ovine Fab): 4 to 6 vials IV reconstituted in 250 mL Normal Saline over 60 min. Once initial control is achieved, administer 2 vials IV q6h for 3 maintenance doses (18h total). - Anavip (Equine F[ab']2): 10 vials IV reconstituted in 250 mL NS over 60 min. Repeat 10 vials if no control. Anavip has a 5-day half-life; zero maintenance infusions required, with significantly lower late recurrence rates!

2. Coral Snakes (Elapidae): Delayed Neurotoxic Paralysis

North American coral snakes (Eastern and Texas coral snakes) belong to the family Elapidae (related to cobras and mambas). They are recognized by their brightly colored circumferential bands: 'Red on yellow, kill a fellow; red on black, friend of Jack' (applies only to indigenous North American species):

Feature	Clinical Characteristics	Emergency Management
Neurotoxic Mechanism	Venom contains alpha-neurotoxins that competitively block post-synaptic nicotinic acetylcholine receptors at the neuromuscular junction.	Produces minimal local swelling, zero tissue necrosis, and minimal pain at the bite site, often deceiving patients and clinicians into assuming a 'dry bite'.
Clinical Course	THE DELAYED PARALYSIS TRAP: Systemic neurotoxicity may be delayed by 12 to 18 hours post-bite. Initial signs include ptosis, ophthalmoplegia, dysarthria, and dysphagia, followed by rapid, flaccid diaphragmatic paralysis and fatal respiratory arrest.	Mandatory ICU Admission: Admit all confirmed or suspected coral snake bites to the ICU for continuous monitoring (negative inspiratory force and forced vital capacity) for at least 24 to 48 hours. Antivenom: Administer Micrurus fulvius antivenom (3 to 5 vials IV) early, ideally before the onset of neurotoxic respiratory failure.

3. Spider Bites & Marine Envenomations

Species/Creature	Venom & Clinical Manifestations	Emergency Treatment Protocol
Black Widow Spider (Latrodectus mactans)	Alpha-Latrotoxin: Opens presynaptic calcium channels, causing massive catecholamine and acetylcholine exocytosis. - Target lesion: central blanched area surrounded by erythematous halo. - Within 1-2 hours: Severe, agonizing muscle spasms, rigid board-like abdomen (mimicking surgical peritonitis!), facial grimacing (facies latrodectismica), hypertension, and diaphoresis.	First-Line Therapy: 1. Intravenous Opioids (Morphine or Fentanyl) 2. High-dose IV Benzodiazepines (Diazepam 5-10 mg or Lorazepam 2-4 mg) for muscle relaxation. 3. Antivenom (Latrodectus equine antivenom) is reserved for life-threatening refractory hypertension, cardiac ischemia, or pregnancy due to risk of anaphylaxis.
Brown Recluse Spider (Loxosceles reclusa)	Sphingomyelinase D: Cleaves cell membranes, triggering endothelial necrosis and massive complement activation. - 'Red, White, and Blue' Sign: Central violaceous/blue ischemia surrounded by a white blanched ring of vasospasm and an outer red erythematous flare. - Progresses over days to a deep, sunken, necrotic eschar. - Systemic Loxoscelism: Coombs-negative hemolytic anemia, hemoglobinuria, renal failure, and DIC.	Conservative Management: Cold compresses, elevation, and wound care. Avoid dapsone. DO NOT PERFORM EARLY SURGICAL EXCISION: Excision of acutely necrotic tissue causes extensive non-healing defects and disfigurement; debridement is delayed until the ulcer has fully demarcated (several weeks).
Stingray Envenomation	Caudal serrated spine punctures skin and injects a heat-labile protein toxin, producing excruciating, instantaneous, radiating pain out of proportion to exam.	HOT WATER IMMERSION: Immediately immerse the affected extremity in non-scalding hot water (45°C/113°F) for 30 to 90 minutes. Heat instantly denatures the protein toxin, providing immediate pain relief. Obtain plain radiographs to rule out radiopaque retained barb fragments.

Pit Viper Envenomation: Harmful First-Aid Interventions

Traditional field first-aid techniques for snakebites are not only ineffective, but actively dangerous and substantially worsen patient outcomes. NEVER apply arterial tourniquets or tight constriction bands (converts a local envenomation into total limb ischemia and gangrene); NEVER apply ice packs or cryotherapy (causes catastrophic frostbite and accelerates tissue necrosis); and NEVER incise the wound or apply mechanical suction devices (suction extractors remove less than 0.05% of venom while lacerating tendons and nerves). Keep the extremity immobilized in a neutral position at heart level, and proceed immediately to an emergency department for antivenom administration.

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