Pearls:

Not all rattlesnake bites result in envenomation.

Bites that do result in envenomation can be categorized as mild, moderate and severe envenomations based on the tissue reaction, systemic signs and coagulation/bleeding abnormalities.

The severity of envenomation determines the need for treatment with CroFab, the antivenin for crotalid (pit viper) envenomation.

Most of the stories patients hear regarding first aid for snake bites are myths and are likely to do more harm than good.

CASE: An 8 year old boy presents after he was playing in the backyard with his friend when he felt pain at his ankle and saw that a baby rattlesnake had just bitten him. The patient’s mom called 911 and EMS found, killed and brought the rattlesnake in with the patient.

The patient arrives tachycardic and reporting tingling around his mouth.

The provider contacts Poison Control who helps determine that this patient shows signs of moderate envenomation and therefore would benefit from CroFab, the antivenin.

EPIDEMIOLOGY:

Boys and men of all ages are more commonly bitten than girls and women.

The majority of bites occur in boys between the ages of 5-18 years old.

VENOMOUS SNAKES found in the United States.

There are 4 venomous snakes in the United States.

Pit vipers (Crotalids):



Rattlesnakes - 40% of rattlesnake bites occur in California and Arizona





Copperheads





Cottonmouths - 33% of bites are in Texas and North Carolina



Coral snakes - 60% of bites occur in Florida.



Red, yellow and black stripes





“Red touch yellow, kill a fellow. Red touch black, venom lack”





Red on black is a milk snake or king snake which are not venomous

What about exotic snakes?

Different types of poisonous snakes exist in zoos and as personal pets, but bites from these types of snakes are very rare.



Schulte J, et al. Childhood Victims of Snakebites: 2000-2013. Pediatrics. 2016 Nov;138(5). [PMID 27940763]



Demonstrated that of 19,000 snake bites, only 2 of the cases were from exotic snakes.

ENVENOMATION vs DRY BITES

Will often see 2 puncture marks from a bite, but not always.

Venom is very physiologically demanding for a snake to make.

Adult snakes are judicious with their venom and will often bite without releasing venom just to scare an intruder. These are called dry bites



25% of rattlesnake bites are dry bites



Baby rattlesnakes are particularly dangerous because they are not as smart about when and how much venom to inject. Baby rattlesnakes are much more likely than adults to envenomate, and are likely to release their full amount of venom when they do.

Venom evolved to help snakes obtain food. It functions to immobilize the prey and contains proteolytic enzymes to begin the process of digestion.

It is the proteolytic enzymes that result in the skin necrosis we see in human victims.

Venom from pit vipers is hemotoxic and results in intense pain, edema, swelling, tachycardia, ecchymosis, oral paresthesias, metallic taste, vomiting and confusion

The venom of rattlesnakes is the most toxic and is the most in need of CroFab. The venom of copperheads is the weakest and rarely requires CroFab.

Coral snakes have much weaker fangs than pit vipers so they have to chew on their victims to release venom rather than a single skin-puncturing bite.

The venom of coral snakes is more neurotoxic, so these patients will have less pain and swelling and more paresthesias, weakness, diplopia, ptosis, dysphagia, hyporeflexia and respiratory depression.

FIRST AID

There are a lot of myths about what we should be doing in the wilderness if we or someone else sustains a venomous snake bite.

Arterial tourniquets? - no



The venom released by crotalids is locally damaging. Tourniquets function to trap the venom in the extremity and allow it to cause worse damage.



Suck the venom out? - no



Freezing the site? - no



Electrocute the area? - no

What should we do?

Immobilize the extremity at cardiac level and get the patient to an Emergency Department with CroFab.



Coral snakes and exotic snakes that have neurotoxic venom which can cause respiratory depression if absorbed systemically. These are the cases that may benefit from a pressure immobilization technique to prevent lymphatic drainage. Not an arterial tourniquet.

ASSESSMENT - Severity of Envenomation

There are 3 categories of envenomation based on skin findings, systemic signs and coagulopathy/bleeding effects.

Minimal - observe



Skin findings: localized tissue reaction very near the bite-site (swelling, pain, ecchymosis)





Systemic signs: none at all including no no tachycardia, hypotension or hypertension





Coagulation/bleeding: normal coagulation parameters without any bleeding



Moderate - give CroFab



Skin findings: swelling, pain and ecchymosis that involves less than the full extremity or less than 50cm if the bite is on the head, neck or trunk.





Systemic signs: evidence of systemic involvement, but vital sign. abnormalities are not life-threatening as well as nausea/vomiting/diarrhea, oral paresthesias, unusual taste, mild tachycardia, tachypnea, mild hypotension (SBP>90).





Coagulation/bleeding: Can have abnormalities in coagulation parameters but no actual bleeding including no gum bleeding, epistaxis or hematuria.



Severe - give Crofab



Skin findings: swelling, pain and ecchymosis that involves more than the entire extremity that is rapidly progressive, >50cm if the bite is on the head, neck or trunk, signs of compartment syndrome.





Systemic signs: significant vital sign abnormalities that may be life-threatening including marked tachycardia and severe hypotension, as well as airway compromise or respiratory distress, confusion and seizures.





Coagulation/bleeding: markedly abnormal coagulation parameters with bleeding including at the gums, epistaxis, hematuria.

MANAGEMENT

Labs including coagulation panel and fibrinogen to evaluate for possible DIC.

CBC with platelets (can have thrombocytopenia).



Basic metabolic panel for BUN/creatinine because renal failure can result from the venom or from rhabdomyolysis.



CK



PT/INR, PTT



Fibrinogen level



D-dimer

EKG for the rare cardiotoxicity

Evaluate immunization status. Patients may require tetanus immunoglobulin if they are under-immunized or non-immunized.

CroFab - contact poison control for guidance

The decision to give CroFab is a big deal because it is very expensive. We do not want to hold back if the patient needs it, but we do not want to give it if it is not necessary.



CroFab is $25,000 per vial and most patients require several vials. There must be documentation of systemic effects to justify the use of CroFab.

Monitor for compartment syndrome - but it is very rare.

The venom is nearly always injected subcutaneously and not into the facial plane, so even though the swelling can be significant, it usually does not cause arterial compromise and fasciotomies are rarely helpful.

DISPOSITION