Snake Bites: Do You Know What To Do?
Envenomation is the result of the injection of a highly specialized toxic secretion, called venom, by a venomous snake into a human, usually in accidental situations. Venom is injected through the snake’s fangs, which are teeth connected via a duct to a venom gland. The composition of snake venom shows high complexity and diversity, resulting in variable biochemical and toxicological profiles that determine a wide range of clinical manifestations.
Currently, the only accepted treatment for snakebite envenomation involves intravenous administration of conventional antivenoms comprising antibodies or antibody fragments derived from the plasma of large mammals (generally horses, but also sheep, goats, or rabbits) that have been previously immunized with non-lethal venomous doses.
According to the Centers for Disease Control and Prevention (CDC), an estimated 7000 to 8000 snakebites occur annually in the United States (CDC 2018). The 2017 annual report of the American Association of Poison Control Centers (AAPCC) showed around 7000 snakebites. Copperheads (2035), Crotalids, (1028), and rattlesnakes (753) were reported as the predominant species involved in envenomation; however, death is a rare outcome and only 5–10 deaths were reported.
There are 5000-10,000 snake envenomations (snake bites where the venom is injected vs a dry bite where no venom in injected by the bite) annually in the United States. Fortunately, few are fatal. We identified 101 fatal bites from native snakes. Rattlesnakes accounted for 74 (90.2%) of the 82 deaths for which the species was known or which occurred where rattlesnakes are the only native crotalids. There were five fatalities attributed to copperheads, two due to cottonmouths, and one caused by an eastern coral snake. Males were disproportionately affected. The median age for victims was 40 years old.
From the 2021 paper entitled, Snake Bite Management: A Scoping Review of the Literature
Common symptomatology can be identified across snake species.
Presenting symptoms of any envenomation (injection of venom via the snake bite) can include generalized weakness, numbness, paresthesia, and pain.
A snake’s venom is composed of a variety of enzymes and proteins that are responsible for both local tissue damage and systemic manifestations. Each species has altering levels of gene expression that control which proteins and enzymes are expressed. For example, certain species’ venom primarily expresses metalloproteinases, which can lyse (destroy) membranes and cellular adhesions, causing rubor (redness), calor (heat), tumor, and tissue necrosis (death).
This can present clinically as tachycardia (fast heartbeat), petechia (small red/purple spots on the skin), confusion, vomiting, disseminated intravascular coagulation (small blood clots throughout the body), acute renal failure, shock, and compartment syndrome.
Commonly, laboratory values show depleted fibrin levels, anemia (intravascular hemolysis), thrombocytopenia, and elevated BUN, creatinine, and prothrombin time/partial thromboplastin time
Alternatively, gene expression of either alpha protein or phospholipase A2 can give the venom a neurotoxic effect in which presynaptic or postsynaptic blockade prevents signal transmission. This can lead to visual disturbance like ptosis - drooping upper eyelid) and diplopia (double vision), dysphagia (difficulty swallowing), diaphoresis (profuse sweating), peripheral nerve palsy (damage to the nerves in your limbs and organs), diminished reflexes, and in severe cases, respiratory depression, and paralysis.
Field Management: What Do You Do?
After sustaining a snake bite, victims and bystanders should move out of the snake’s striking distance and take a picture of the snake, if possible.
The victim’s airway, breathing, and circulation should be assessed as envenomation can affect these vital functions within minutes.
Current recommendations for field treatment include limiting the victim’s activity while lying them flat and keeping the bitten extremity immobilized at heart level.
If local swelling, erythema, or pain are progressing, the affected extremity can be elevated as long as no systemic symptoms are present.
Importantly, the medical facility should be called in advance to allow enough time for the antivenom to be prepared or transferred as it is not universally stocked.
Common misconceptions about snake bite management abound.
The use of a tourniquet, thought to reduce the return of venom to the central circulation, actually restricts essential blood flow to the affected tissue, increasing local edema and potentiating the venom’s local effects.
A venous tourniquet can be beneficial when kept below a pressure of 30 mm Hg (2 fingers under band), limiting spread of systemic absorption; however, improper application limits its use in the field.
Wound compression, which involves wrapping the affected extremity distal to proximal at an optimal pressure of 55 mm Hg, has been shown to be error prone and is not recommended.
Initial treatment of wound incision and suction or suction alone was thought to withdraw a portion of the venom load, thus limiting the quantity of absorbed venom; however, studies have shown it can actually worsen patient outcomes and is therefore no longer recommended.
Application of medicinal herbs, chemicals, and intense scrubbing/cleaning of the wound is also not recommended.