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Caring for patients with venomous Crotalinae snakebites

Miller, Ariel; Parsh, Bridget EdD, RN

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doi: 10.1097/01.NURSE.0000651632.09894.b4
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Figure

VENOMOUS SNAKEBITES are surprisingly common worldwide.1 On average, between 7,000 and 8,000 venomous snakebites and about six fatalities are reported annually in the US alone.1-3 These injuries are most likely to occur when people are caring for captive snakes or trying to catch (or kill) wild snakes.2,4 This article provides an overview of clinical manifestations, treatments, and nursing considerations for patients experiencing a venomous snakebite, with a focus on North American pit vipers such as rattlesnakes.

Background

Pit vipers, or Viperidae, are a subfamily of Crotalinae snakes.5 They are native to all states except Alaska, Maine, and Hawaii. These venomous snakes, which include water moccasins (cottonmouths), copperheads, and rattlesnakes, are characterized by their triangular head, elliptical pupils, hinged fangs, and venom glands.2,6-8 The composition of venom varies depending on the species of snake and may include hemotoxins, neurotoxins, and myotoxins, among other components.2,4

Rattlesnakes account for approximately 65% of venomous snakebites in North America.1 Adult snakes range in size from less than 26 in (66 cm) to longer than 6.5 ft (2 m) and can accurately strike at up to one-half their body length when coiled.2,3 Most snakebites occur on the extremities. Upper extremity bites typically result from intentional handling and lower extremity bites from accidental encounters.2,4 Bites are most common between May and October, when snakes and humans are both more active.2 In the US, venomous snakebites are most frequently reported in Texas, Florida, California, and Arizona.9

First aid

If bitten by a venomous snake, individuals should move to safety away from the snake and call 911.2,3 While waiting, they should try to remain calm and still.2,3 They should also try to remember the general appearance of the snake, but they should not attempt to catch or kill it and risk a second bite.2,3 A cell phone picture may help to identify the snake later, but this should be taken only at a safe distance of at least 6.5 ft (2 m).2,4

Many individuals, including some healthcare providers, have the mistaken belief that placing a tourniquet and trying to suck venom from the wound are effective first aid responses, but these methods are contraindicated because they can do more harm than good.2,4,10 If a patient arrives at the ED with a tourniquet in place above the puncture wound, do not remove it quickly. Instead, loosen it gradually to reduce the risk of a venom bolus.2,11 Antivenom infusions can be initiated before the tourniquet is removed.11 Poison control should be contacted immediately in all cases for consultation with a toxicology expert.2,6

Similar to tourniquets, which can injure nerves, tendons, and blood vessels, several other treatment methods once used are no longer recommended. These include incisions, cryotherapy, and electrotherapy. Both oral and mechanical suction should be avoided, as the efficacy of these techniques is minimal and oral suction may even put patients at risk of infection.5

Signs and symptoms

Bites from snakes in the Crotalinae family can result in envenomation syndromes.5 Patients bitten by pit vipers may present with ecchymosis, progressive edema, and blistering at the site, leading to tissue necrosis, severe pain and/or burning, coagulopathy, and paresthesias in the affected extremity.1,2,5,6,12 They may also experience generalized symptoms such as nausea, chills, weakness, light-headedness, and diaphoresis.5 Coagulopathy is a serious sign of envenomation and should be treated with the appropriate type and quantity of antivenom.2,4

Systemic signs and symptoms of a pit viper bite include hypotension, weakness, diarrhea, angioedema, vomiting, neurotoxicity, oral paresthesias, coagulopathy, and systemic bleeding.2,5,6,12,13 Neurotoxicity is characterized by paresthesias, fasciculations, cranial nerve paresis, seizures, and respiratory failure.2,4,12

Diagnostic studies

Patients who have been bitten by a pit viper such as a rattlesnake, copperhead, or cottonmouth will require diagnostic testing. Blood specimens should be obtained from the unaffected extremity.2,6 Complete blood cell counts, prothrombin times, partial thromboplastin times, and international normalized ratios should be closely monitored, both in the hospital and for 4 weeks postdischarge.5 Additionally, assessments of serum electrolytes, creatinine, blood urea nitrogen, and fibrin degradation products are typically performed, as well as urinalysis and an ECG.5

Snakebite severity

The severity of a bite varies according to the snake's type, size, age, and recent feeding activity; geographic location; the amount of venom injected; and the time of year in which the patient was bitten.2,6 Snakebite severity can be divided into four grades: no envenomation (dry bite), minor, moderate, and severe.2,4

With a dry bite, or one in which no venom was injected, fang marks are present but no local and systemic signs or symptoms are observed for a minimum of 8 hours.2,4Minimal envenomation does not typically result in progressing local or systemic signs and symptoms, including coagulopathies.2,4,6 Signs and symptoms of moderate envenomation include acute local pain, progressive edema, and mild-to-moderate systemic signs, such as hypotension, systemic bleeding, and/or neurotoxicity.4Severe envenomation produces critical illness, including significant edema and pain, abnormal coagulopathies with acute bleeding, and life-threatening systemic signs that can lead to end-organ damage.4 Patients with moderate or severe envenomation require treatment with antivenom, as do patients with mild envenomation that is progressive or worsening.2,4

Antivenom

Although they are expensive, antivenoms are a lifesaving treatment option for patients with moderate-to-severe pit viper bites.2,4,10 Only crotalidae polyvalent immune fab (CroFab) is approved by the FDA to treat all North American pit viper bites. More recently, the F(ab')2 equine antivenom (Anavip) has been approved for rattlesnake bites, but not for bites by copperheads or water moccasins at this time.6,14,15

Emergency services personnel should ensure patients are taken to a healthcare facility with antivenom in stock, and poison control should be consulted immediately.2,4,6 For cases of moderate to severe envenomation, as well as cases of minor envenomation that are worsening, antivenom should be administered as soon as possible to mediate the local and systemic alterations caused by the toxic pit viper venom.2,4

The dosage and administration of antivenom may vary based on envenomation grade, so follow manufacturer instructions exactly. Following administration, assess patients for their response, including signs and symptoms of a severe allergic reaction to the antivenom, such as bronchospasms, pruritis, or hypotension.2,13,16 Use caution when administering antivenom for anyone who has had a previous allergic reaction.5,16

Patient care

Monitor and support the ABCs in a patient with a suspected venomous snakebite, assessing for difficulty breathing, vomiting, and/or seizures.2,17,18 Administer antivenom as prescribed and be prepared to initiate cardiopulmonary resuscitation if necessary.2,4,6,19 Patients may require supplemental oxygen, and two large-bore venous access devices should be placed in the unaffected extremities for fluid infusion. Given the potential for systemic effects, continuous cardiac and BP monitoring are also recommended following a snakebite.2,6

Wash the bite with soap and water, keeping the affected area level with the heart.4 Remove anything tight from around the bite, such as clothing, rings, anklets, or bracelets, as significant localized edema may occur.2,4,18,19 Draw a circle around the affected area and mark the time of the bite and the initial reaction.2,4 By redrawing a circle around the injury, nurses can mark its progression.2,4

Patients with severe snakebites, especially those who have received antivenom, are typically admitted to the ICU for monitoring, but many do not stay longer than 48 hours.9 If they are experiencing severe pain, acetaminophen and/or an opioid analgesic may be prescribed, but nonsteroidal anti-inflammatory drugs are not recommended due to potential coagulopathies.2,4,6,19 Prophylactic antibiotics are sometimes prescribed, but they are not typically necessary.1,2 I.V. crystalloid solutions may be indicated to treat hypotension.2,6

Supportive care

Severe coagulopathies are a potentially life-threatening complication of pit viper bites.2,4,6,18,20,21 They can be managed with the appropriate quantity of antivenom, but blood products and platelet transfusions have not demonstrated efficacy as treatments.4 Recurrent coagulopathies, such as thrombocytopenia, are possible, as well as disseminated intravascular coagulation.2,6,18,20,21 Patients on antiplatelet medications or anticoagulants, as well as over-the-counter products such as garlic, ginger, gingko, and ginseng, may also be at risk for coagulopathies and should be monitored closely.2,9

Due to edema at the site of a snakebite, rattlesnake bites may mimic or cause compartment syndrome.22,23 Monitor patients carefully for the six Ps: pain, paresthesia, poikilothermia, paralysis, pulselessness, and pallor. Additional doses of antivenom and mannitol may reduce intracompartmental pressures.2,22 Additionally, poison control is a valuable resource and can provide recommendations for treatment, including whether a fasciotomy is the best option.2,22

Table
Table:
Dos and Don'ts2-4,10,17

Education and awareness

Educate patients to remain vigilant. Snakes can be found sunning themselves near logs, boulders, or in open areas in the warmer months.3 Advise patients to be cautious and alert when climbing rocks, as sunning snakes may be difficult to see.17,24

Rattlesnakes are known for the rattling sound produced by the end of their tail, which acts as a warning, but they sometimes strike without warning. Other pit vipers never provide such a warning.2,3

When hiking or spending time outdoors, people should consider wearing closed-toed shoes and long pants made from heavier fabrics and avoiding tall grass.2,17,24,25 Snakebites may be avoided with the use of hiking sticks, as the snake may attack the pole rather than the individual's lower extremity. Many individuals are bitten because they get too close or try to kill a snake, so advise them to leave snakes alone.2,4,17 (See Dos and Don'ts.)

Early intervention is key

A snakebite is a clinical emergency that requires close monitoring from the time of the bite through the administration of any antivenom until the patient is discharged. Early recognition of physical reactions and bite severity, as well as the application of appropriate treatments, can make the difference for these patients.

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    Keywords:

    antivenom; copperhead; cottonmouth; Crotalinae; envenomation; pit viper; rattlesnake; venomous snakebite; Viperidae; water moccasin

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