Published in UAB Insight, Spring 2006
Timing and Toxicology Critical For Treating Snakebite Victims
ABSTRACT: Recommendations for first aid and treatment for snakebites have changed dramatically. Rapid transport to the closest hospital is critical.
CME ABSTRACT: The reader will understand sequelae and progression of symptoms from snake envenomations, proper first aid, and use of antivenom.
Erica L. Liebelt, MD, no conflict of interest; Ziad N. Kazzi, MD, no conflict of interest
Despite fears to the contrary, fatalities from snakebites in the United States are exceedingly rare. Of the 7000 to 8000 venomous snakebites reported each year, fewer than six result in death.
“Across the nation, the great majority of snakebites are caused by the Crotalidae family (pit vipers), which includes rattlesnakes, copperheads, and cottonmouths, or water moccasins,” says Erica L. Liebelt, MD, director of UAB’s Medical Toxicology Services. She is also secretary-treasurer of the American College of Medical Toxicology, and comedical director of the Regional Poison Control Center, located at Children’s Hospital of Alabama.
Pit viper bites classically appear as two fang punctures with local edema, redness, ecchymosis, and sometimes, progression to necrosis. Unless the snake is captured or accurately identified, clinicians must focus on objective signs and symptoms of envenomation to pursue the proper course of treatment. “Immediately contact the nearest poison control center with a description of the snake and details about the victim’s snakebite,” Liebelt says.
“Pit vipers can cause a wide range of symptoms,” she says. “Patients with severe envenomation can have nausea, vomiting, dizziness, altered sensorium, syncope, paresthesias around the mouth or affected limb, or be in frank shock. Evaluating victims for at least 6 hours is critical to determine local toxicity, coagulation abnormalities, and potential systemic toxicity,” she adds. “Envenomation can progress dramatically over time, and without observation and antivenom administration, can lead to death.”
In the West, rattlesnakes account for the majority of snakebites, but bites from copperheads and cottonmouths are more common in the Southeast. Historically, snakebites have been linked with outdoor activities and were most frequently reported from April to October. Today, bites occur throughout the year, often from deliberate exposure to captive snakes, including nonnative species.
Thousands of people are unintentionally bitten on the hand or lower extremities, but nearly half of reported snakebites occur while the victim intentionally handles or attempts to harm a snake. Many snakebite victims throughout the United States and United Kingdom are men younger than 30 years, who are particularly careless handling snakes when intoxicated or fatigued (BMJ. 2005;331:1244-1247 and N Engl J Med. 2002;347:347-356).
Unlike bites from pit vipers, coral snake envenomations cause potent neurotoxicity, possibly requiring ventilatory support. “Adverse effects from coral snake bites may develop hours after a victim is bitten,” Liebelt cautions. “When considering the possibility of coral snake envenomation, remember, local necrosis and coagulopathy do not typically occur. Instead, physicians should carefully monitor neurologic status, looking for paresthesias, muscle weakness, and paralysis.”
In the past, copperhead strikes were considered relatively benign, and early antivenom formulations were not recommended. “We now know copperhead bites can cause devastating functional outcomes, but a single dose of the proper antivenom decreases or prevents progression of local reaction, alleviates pain and swelling, and improves quality of life in mild-to-moderate and severe envenomations,” she says.
Initial Treatment
“Experts have radically revised first aid measures for snakebites to exclude arterial tourniquets, aggressive wound incisions, and ice, all of which may worsen a patient’s condition,” Liebelt says. “First, advise the patient to calm down, avoid excessive activity, remove jewelry or constricting clothing, immobilize the bitten extremity, and travel as quickly as possible to the nearest hospital.”
Experts recommend recording an initial circumferential measurement at several points surrounding the bite and repeating calculations every 15 to 20 minutes until local swelling subsides. Laboratory tests performed at baseline and following each antivenom dose may include a complete blood count with platelet count, coagulation profile with prothrombin time, activated partial-thromboplastin time, and fibrinogen level, measurement of fibrin degradation products, electrolytes, blood urea nitrogen, serum creatinine, and urinalysis to monitor for hemoglobinuria and myoglobinuria. Physicians should administer tetanus immunization if indicated by the patient’s history.
Poison Control
Because an increasing number of people in the Southeast keep nonnative snakes, UAB Medical Toxicology Services and Regional Poison Control Center have established a formal relationship with the Birmingham Zoo, Liebelt says. “The zoo has many exotic snakes and is legally required to have an on-site antivenom supply for a variety of species, as available. No one has been envenomated at the Birmingham Zoo in more than 28 years, but a protocol is in place to ensure any victim and the appropriate antivenom are promptly transported to UAB’s Emergency Department or Children’s Hospital of Alabama.” Liebelt notes UAB medical toxicologists can also procure exotic antivenoms not ordinarily stored at local hospitals through the Miami-Dade Fire Rescue Antivenin Bank, the largest supplier of antivenom in the United States.
Newest Antivenoms
The newest antivenom, approved by the US Food and Drug Administration in October 2000, is Crotalidae Polyvalent Immune Fab Ovine (CroFab). “CroFab appears more specific against certain types of venom and may cause less hypersensitivity than Antivenin Crotalidae Polyvalent (ACP), available since 1954. The usual starting dose of CroFab is 4 to 6 vials,” Liebelt says.
“CroFab reduces rates of anaphylaxis and hypersensitivity reactions compared with ACP. Postmarketing research and UAB physicians report favorable initial results,” she says. CroFab, produced by immunizing sheep with crotaline snake venoms, is more potent and effective than ACP in reducing venom-induced abnormalities. Prospective trials using CroFab report only a 14% incidence of acute reaction, and nearly all events were mild to moderate (Ann Emerg Med. 2001;37: 181-188).
Adverse Effects
Prior to treatment with CroFab, physicians should carefully evaluate patients with a history of certain medical conditions, such as allergies to sheep or wool products, but in most cases, Liebelt says, benefits of treating serious envenomation with antivenom far outweigh risks. Pretreating with antihistamines and steroids reduces risk of an adverse reaction to antivenom.
“Older antivenom products risked built-in immunity, so victims were able to receive specific antivenoms only once. Newer products can be taken multiple times, and their early and aggressive introduction is strongly associated with reversal or attenuation of systemic venom effects and prevents progression of local symptoms,” she says.
Serum sickness occurs far less often with newer antivenoms that are more purified than older products. Still, Liebelt says, the small amount of protein in anti-venoms can lead to joint swelling or a localized rash 7 to 10 days following antivenom administration, although this is rare. The condition is easily treated with systemic corticosteroids.
One rare but potentially serious complication of snakebite envenomation is compartment syndrome. “Venom-induced compartment syndrome presents with pathophysiology different from compartment syndrome secondary to vascular insufficiency,” Liebelt explains. Bites from rattlesnakes may result in signs and symptoms that mimic compartment syndrome, but capillary refill is normal and compartmental pressures are not elevated. “Edema is subcutaneous with venom-induced compartment syndrome, so fasciotomies should never be performed without documenting elevated compartment pressures. In fact, the procedure rarely improves wounds, and animal studies have shown fasciotomy actually worsens outcomes compared with administering antivenom.”
“Remember, snake envenomation is a dynamic process,” Liebelt says. “Promptly calling a regional poison control center and the nearest medical toxicology service are key to effectively managing snakebite victims and producing optimal outcomes.”
For more information
UAB Division of Medical Toxicology
1.205.975.2363
Regional Poison Control Center
1.205.939.9201 or 1.800.222.1222
For more information
Dr. Erica Liebelt
Dr. Ziad Kazzi
1.800.UAB.MIST
mist@uabmc.edu