Snake Bites 101

Author: Samantha Selesny, PGY-3
Associate Editor of Emergency Medicine Toxicology, EMRounds

Background:

Reported snake bites in the US: 5,000/year
- Reporting is not mandatory
- Only about 5 or 6 result in death
25% of bites are from venomous snakes
Victims are typically male, ages 17-27
- Alcohol is significantly associated with many snake bites
Venomous snakes are found everywhere in the US except Maine, Alaska and Hawaii.
Most bites occur in the southwest
Most bites occur between May and October (snakes hibernate in the winter)
Pearl: Snakes are called “venomous” not “poisonous”
- Venomous – toxins are INJECTED into prey
- Poisonous– toxin causes harm by INGESTING or TOUCHING it
Thousands of species of snakes worldwide

2 families of Venomous Snakes in the United States:

Viperidae (Crotalinae, Pit Vipers):

Account for 99% of venomous snakebites in the US
Named for heat sensing pit organs
Pit vipers are different from true vipers, which are not endemic to the US
Crotalinae subfamily includes:
- Rattlesnakes (see Figure 1 below)
- Cottonmouths (water mocassins) (see Figure 2 below)
- Copperheads (see Figure 3 below)

Can identify a Pit Viper with 3 main features:
1. Heat Sensing Pits
2. Elliptical Pupils
3. Triangular Shaped Head

Elipidae (Coral Snakes):

Only account for ~1% of venomous snake bites:
- Not aggressive
- Live mostly underground (no contact with humans)
- Venom apparatus not as efficient (smaller mouths, need to maintain bite for longer to deliver enough venom)
Identifying a Coral Snake (vs non-venomous snake such as King snake)
1. Snout color
  - Coral Snakes- black snouts (see Figure 4 below)
  - King Snakes- red snouts (see Figure 5 below)
2. Ring Color
  - Coral Snakes- red and yellow rings adjacent
    - “Red touches yellow, kills a fellow”
  - King Snakes- red and black rings adjacent
    - “Red touches black, safe for Jack”

Viperidae (Pit Viper):

Venom is a complex solution of various proteins, peptides and enzymes
- allows the snake to kill its prey quickly and begin the digestive process
Clinical Presentation:
1. Cytotoxic: Severe pain and swelling at bite site
  - Ecchymosis,
  - Fluid filled or hemorrhagic bullae (Figure 6 below) or
  - Extensive tissue destruction
2. Hemotoxic: Consumption of coagulation factors
  - Low Platelets
  - High PT, and
  - LOW fibrinogen
3. Systemic toxicity (less common):
  - Oral Paresthesias
  - Metallic taste,
  - Fasciculations,
  - Hypotension, or
  - Anaphylaxis

Elapidae/Coral Snakes

Venom is an 𝝰-neurotoxin –> post-synaptic NMJ blockade –> systemic neurotoxicity
Causes serious systemic toxicity (rather than local findings found in crolatid bites)
Clinical Presentation
- Neurologic abnormalities:
  - weakness,
  - numbness,
  - respiratory paralysis (immediate cause of death)
- May require airway and respiratory management lasting several weeks
- Typically presents ~1-7 hours after envenomation
- Onset may be delayed up to 18 hrs, thus ALL patients with elapidae envenomation are admitted

For ALL BITES:

Viperidae/Pit Vipers:

Labs on arrival and after 4-8 hours:
- CBC (thrombocytopenia/anemia),
- PT/fibrinogen (coagulopathy),
- BMP (potassium/renal function),
- CK (rhabdomyolysis)
If no symptoms within 6-8 hours, the patient can be considered medically cleared.
Do not use torniquets, local debridement or cautery
Note: Because children have smaller body mass, smaller limbs, and less subcutaneous tissue, they can potentially receive more venom per kg body weight and therefore have more clinical severity than adults.
CroFab (Crotalidae polyvalent immune fab):
- Administer if:
  - severe local swelling/ecchymosis,
  - lab abnormalities (PT >15, fibrinogen <150, platelets <150), or
  - systemic symptoms (hypotension, airway edema, neurological symptoms)
- All patients who receive crofab should be admitted for observation
- Dosing CroFab antivenom (dosing units are by vials):
  - 1st dose: 4-6 vials,
    - Repeat dosing as needed
    - Maintenance dosing with 2-4 vials
  - Dosing is the same in pediatric patients
- Most common reaction: anaphylaxis (ensure patient is closely monitored)
Disposition:
- All patients who receive crofab should be admitted for observation
- Most patients who require admission can go to the medical floors
- ICU setting is reserved for those who require neuro checks or have severe systemic toxicity
- Consults: consider surgical consult for signs of compartment syndrome despite antivenom treatment.

Elapidae/Coral Snakes

Administer Antivenin (specific for coral snakes) for systemic toxicity
Disposition: ALL patients are admitted for observation (potentially delayed onset)

References:

Gold B.S., Dart R.C., Barish R.A. Bites of venomous snakes. N Engl J Med. 2002 Aug 1;347(5):347-56. doi: 10.1056/NEJMra013477. PMID: 12151473.
“Bites and Sings” Cydulka, R., Fitch, M., Joing, S., Wang, V., Cline, D., Ma, O. and Tintinalli, J., Tintinalli’s emergency medicine manual. 8th ed.
“Snakes and Other Reptiles” Riley, B.D., Pizon, A., Ruha, A.M., Goldfranks Toxicologic Emergencies, 9th ed., McGraw-Hill, 2002.
Spencer Greene et al. How Should Native Crotalid Envenomation Be Managed in the Emergency Department? J Emerg Med. 2021 Feb 20;S0736-4679(21)00029-9. doi: 10.1016/j.jemermed.2021.01.020.
Jacobi Medical Center’s Snakebite Protocol