Emergency Medicine · Year 3 · from Emergency Medicine
Case 3: Snakebite Envenomation - The Pit Viper Bite
Patient Demographics
- Age: 42 years
- Sex: Male
- Occupation: Landscaper
Chief Complaint
"I got bit by a rattlesnake on my hand!"
History of Present Illness
A 42-year-old male landscaper presents 45 minutes after being bitten on the right hand by a snake while clearing brush. He reports seeing a rattlesnake (heard the rattle) that struck his right hand when he reached under a bush. He killed the snake with a shovel (brought the specimen). He is now experiencing severe pain and swelling in his hand progressing up his forearm.
Initial Assessment
ESI Level: 2 - Envenomation with progressive symptoms
First Impression:
- Appearance: Anxious, holding right arm
- Work of breathing: Normal
- Circulation: Appears well-perfused
Vital Signs:
- Heart rate: 112 bpm
- Blood pressure: 148/88 mmHg
- Respiratory rate: 18 breaths/min
- SpO2: 98% on room air
- Temperature: 37.2C
Primary Survey
Airway: Patent Breathing: Normal Circulation: Tachycardic (anxiety/pain), normotensive Disability: Alert, GCS 15 Exposure: Right hand with visible bite marks, progressive swelling
Snake Identification
Snake Brought to ED (confirmed):
- Western Diamondback Rattlesnake (Crotalus atrox)
- Pit viper (triangular head, heat-sensing pits, vertical pupils, rattle)
Pit Viper Envenomation Syndrome:
- Local: Pain, swelling, ecchymosis, necrosis
- Hematologic: Coagulopathy, thrombocytopenia
- Systemic: Hypotension, altered mental status (severe cases)
Local Examination - Severity Assessment
Right Upper Extremity:
- Two puncture wounds on dorsum of right hand
- Intense pain at bite site
- Edema: Hand + wrist + mid-forearm (progressing)
- Ecchymosis developing around puncture sites
- Bullae: None yet
- Necrosis: None
- Sensation: Intact
- Motor: Can make fist but painful
- Pulses: Present (radial 2+)
Mark the Leading Edge:
- Circumference measured and marked with time
- Forearm: 28cm at presentation
- Plan: Reassess every 30-60 minutes
Severity Classification
| Grade | Local Effects | Systemic Effects | Labs |
|---|---|---|---|
| None (dry bite) | Fang marks only | None | Normal |
| Mild | Swelling at bite | None | Normal |
| Moderate | Swelling beyond bite | Mild systemic symptoms | Abnormal |
| Severe | Entire limb swelling | Shock, bleeding | Markedly abnormal |
This patient: MODERATE envenomation (progressive swelling, mild tachycardia)
Secondary Survey
SAMPLE History:
- Symptoms: Pain, swelling, anxiety
- Allergies: None (no prior antivenom exposure)
- Medications: Lisinopril
- PMH: Hypertension
- Last Meal: Lunch 2 hours ago
- Events: Bite 45 minutes ago, progression of symptoms
What NOT to Do (prehospital myths):
- No tourniquet (ischemia)
- No ice (increases necrosis)
- No incision/suction (ineffective, causes harm)
- No electrical shock (ineffective)
Diagnostic Testing
Labs:
- CBC: WBC 14.2, Hgb 13.8, Platelets 128,000 (low)
- BMP: Normal
- Coagulation: PT 18.2, INR 1.5, PTT 42 (abnormal)
- Fibrinogen: 180 (low-normal)
- D-dimer: Elevated
Baseline Labs Abnormal = Envenomation confirmed, antivenom indicated
Management
Antivenom Indication:
- Progressive local swelling (beyond bite site)
- Abnormal coagulation studies
- Moderate severity
CroFab (Crotalidae Polyvalent Immune Fab):
- Mixed according to package insert
- Initial dose: 4-6 vials IV
- Infuse slowly initially (allergic reaction risk)
- Monitor for improvement
Antivenom Administration:
- Premedicaton: Not routinely needed, but have epinephrine available
- Started at slow rate, advanced as tolerated
- 6 vials CroFab given over 1 hour
Response to Antivenom
At 1 hour post-antivenom:
- Pain improving
- Swelling progression slowed
- Repeat labs: Platelets 142, INR 1.3, Fibrinogen 210
At 4 hours:
- Swelling stabilized at mid-forearm
- No new ecchymosis
- Labs normalizing
Maintenance Dosing:
- 2 vials CroFab at 6, 12, and 18 hours after initial control
Additional Management
Supportive Care:
- IV fluids
- Pain management (opioids, avoid NSAIDs)
- Tetanus prophylaxis
- Limb elevation
- Wound care
Monitoring:
- Serial exams every 4-6 hours
- Mark swelling margins
- Repeat labs at 6 hours, then daily
- Watch for compartment syndrome
Compartment Syndrome Consideration:
- Rare with snakebite (antivenom usually sufficient)
- Fasciotomy rarely needed
- Measure compartment pressures if concern
Disposition
- Admitted to ICU/monitored bed
- Completed antivenom protocol
- Swelling peaked at 36 hours, then improved
- Labs normalized
- Discharged day 3
- Return for repeat labs in 1 week (recurrent coagulopathy risk)
Teaching Points
- Identify the snake if safe: Helps guide management (not all bites envenomated)
- Dry bites occur: ~25% of pit viper bites have no envenomation
- Mark the swelling: Serial measurements track progression and response to treatment
- Antivenom indications: Progressive local swelling, coagulopathy, systemic symptoms
- CroFab vs. Anavip: Both available; Anavip may have lower recurrence rate
- Recurrent coagulopathy: Can occur days after antivenom; follow-up labs essential
- Fasciotomy rarely needed: Antivenom usually controls swelling; measure compartment pressures before surgery
- Don't delay treatment for labs: Start antivenom based on clinical progression
Clinical Image
Image Description: Photograph of upper extremity with pit viper envenomation demonstrating puncture wounds at bite site with progressive edema, ecchymosis, and bullae formation extending from the hand to the forearm.
Attribution: Image from Wikimedia Commons, Rattlesnake bite. Public domain. Source: https://commons.wikimedia.org/wiki/File:Crotalus_bite.jpg