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
- Pain
- Swelling
- Compartment Syndrome (see Compartment Syndrome, [[Compartment Syndrome]])
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
- Acute Kidney Injury (AKI) (see Acute Kidney Injury, [[Acute Kidney Injury]])
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