Rattlesnake Bite

Epidemiology

  • 20% of bites are dry (not associated with injection of any venom)
  • Venomous snakes are native to every state except Alaska/Hawaii/Maine
  • 45,000 snake bites occur annually in USA (8,000 are due to venomous snakes)

Etiology

  • Class: Crotalidae (pit viper): rattlesnake/copperhead/cottonmouth water moccasin
    • This class accounts for 95% of venomous snake bites
  • Class: Coral Snakes:

Physiology

  • Poisonous snake envenomation
  • Crotalidae Venom: contains phospholipase A (disrupts cell membranes), proteases (causes tissue destruction), and hyaluronidase (promotes rapid spreading of venom through tissues)
    • Mojave rattlesnake (Crotalus scutulatus) has a presynaptic neurotoxic venom component known as Mojave Type A toxin, which causes severe paralysis

Clinical

Local Bite Site Manifestations

Cardiovascular Manifestations

  • Hypotension/Distributive Shock (see Hypotension, [[Hypotension]])

Pulmonary Manifestations

  • Acute Lung Ninjury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]]
  • Acute Hypoventilation/Acute Respiratory Failure (see Acute Hypoventilation, [[Acute Hypoventilation]]: may be seen with neurotoxic envenomation with Mojave Rattlesnake bites

Hematologic Manifestations

  • Coagulopathy (see Coagulopathy, [[Coagulopathy]])
  • Hemorrhage

Renal Manifestations


Treatment

Constriction Band Proximal to Bite Site: effective to contain local spread (by compressing superficial veins and lymphatics) only if used within 30 min of bite
-However, avoid a tight tourniquet, as this may increase the risk of necrosis and amputation

Polyvalent Crotalidae Anti-Venin IV (see Crofab, [[Crofab]]): best results if given within 24 hrs of bite
-SE (anti-venin is from horse serum): immediate hypersensitivity (may need to treat through anaphylaxis with Benadryl, IV Epinephrine slow drip, fluids, and steroids) and serum sickness (can occur in <50% of cases)
–Skin testing is relatively insensitive and non-specific in predicting these reactions (although the package insert recommends skin testing prior to administration) -> give anti-venin even if skin test is positive

Wound Infection Prophylaxis: antibiotics/wound cleansing

Tetanus Prophylaxis: Tetanus toxoid

Surgical Fasciotomy: may be required in cases with a complicating compartment syndrome

Not Effective:
1) Vitamin K/Heparin: no role in treating DIC
2) Prophylactic Antibiotics: little evidence these improve outcome
3) Incision and Drainage of Wound in Field: not recommended (due to risks of infection and bleeding)
4) Local Cryotherapy: not recommended (worsens local and systemic manifestations in animal studies)


Prognosis

  • Mortality: 0.2% (previously 10-35% prior to availability of anti-venin)

References

  • Toxicology rounds: death from a rattlesnake bite. Am J Emerg Med 1985; 3:227-235
  • Snake venom poisoning in the United States. Experiences with 550 cases. JAMA 1975; 233:341-344
  • Antivenin therapy in the emergency department. Am J Emerg Med 1983; 1:83-93