Severe toxicity from crotalid envenomation after early resolution of symptoms

A case report of mis-snaken identity: When misdiagnosis really bites

When patients present with an unknown puncture wound, emergency physicians need to consider regional hazards, in addition to standard mechanical injury etiologies. In the Southwestern United States, one such hazard is the rattlesnake. In this report, we present a case in which a rattlesnake envenomation was not considered as a possible cause for a puncture wound of unknown origin, which resulted in an envenomation left untreated for 7 days. A full dry bite observation period of 12 h with serial physical exams and laboratory analysis with guidance from the region poison control center might have led to earlier recognition of an envenomation and antivenom administration. A male patient in his late 70's felt a painon his right ankle while in his backyard in southern Arizona. He did not see the cause and assumed he had sustained an insect bite. He went to the ED that day with minor pain and swelling and was discharged home. One week later, he re-presented severely anemic with edema and ecchymosis to the entire right lower extremity that developed over several days after his first ED visit. He was admitted for antivenom and blood transfusion and discharged on hospital day three. For as long as humans continue to interact with the natural world, venomous creature encounters are going to continue to happen. Rattlesnake envenomation should be included in a physician's differential diagnosis even if one is not witnessed, especially in regions with high rattlesnake activity. In addition to assessing for other potential causes of undifferentiated puncture wounds, serial physical examinations and laboratory testing (with guidance of the regional poison center) are necessary to rule out rattlesnake envenomation.

North American poisonous bites and stings

Critters and creatures can strike fear into anyone who thinks about dangerous animals. This article focuses on the management of the most common North American scorpion, arachnid, hymenoptera, and snake envenomations that cause clinically significant problems. Water creatures and less common animal envenomations are not covered in this article. Critical care management of envenomed patients can be challenging for unfamiliar clinicians. Although the animals are located in specific geographic areas, patients envenomed on passenger airliners and those who travel to endemic areas may present to health care facilities distant from the exposure.

Snake Bite: Pit Vipers

Pit vipers are the largest group of venomous snakes in the United States and are involved in an estimated 150,000 bites annually of dogs and cats. The severity of any pit viper bite is related to the volume and toxicity of the venom injected as well as the location of the bite, which may influence the rate of venom uptake. The toxicity of rattlesnake venom varies widely. It is possible for pit vipers' venom to be strictly neurotoxic with virtually no local signs of envenomation. Venom consists of 90% water and has a minimum of 10 enzymes and 3 to 12 nonenzymatic proteins and peptides in any individual snake. The onset of clinical signs after envenomation may be delayed for several hours. The presence of fang marks does not indicate that envenomation has occurred, only that a bite has taken place. Systemic clinical manifestations encompass a wide variety of problems including pain, weakness, dizziness, nausea, severe hypotension, and thrombocytopenia. The victim's clotting abnormalities largely depend upon the species of snake involved. Venom induced thrombocytopenia occurs in approximately 30% of envenomations. Many first aid measures have been advocated for pit viper bite victims, none has been shown to prevent morbidity or mortality. Current recommendations for first aid in the field are to keep the victim calm, keep the bite site below heart level if possible, and transport the victim to a veterinary medical facility for primary medical intervention. The patient should be hospitalized and monitored closely for a minimum of 8 hours for the onset of signs of envenomation. The only proven specific therapy against pit viper envenomation is the administration of antivenin. The dosage of antivenin needed is calculated relative to the amount of venom injected, the body mass of the victim, and the bite site. The average dosage in dogs and cats is 1 to 2 vials of antivenin.

Envenomations

Numerous types of envenomations may be encountered by health care workers depending on where in North America they work. Clinicians should be familiar with the animals in their region that may lead to envenomation.A rational approach with use of poison center or medical toxicology consultation services ensures that cases are managed appropriately.

Effectiveness of Delayed Use of Crotalidae Polyvalent Immune Fab (Ovine) Antivenom

Traditionally, horse-serum-based antivenom has been used in the United States for North American crotaline snake evenomation. Crotalidae polyvalent immune Fab (ovine) was approved in 2000 for use in mild to moderate envenomations. The manufacture recommends use within 6 h of envenomation. Published postmarketing retrospective reports describe its use up to 9 h after envenomation. We describe a case of effective use of FabAV 52 h after envenomation with resultant correction of coagulopathy and mild improvement of local symptoms.

Snakebite envenomation in children: a 10-year retrospective review

OBJECTIVE

To describe the epidemiology, short-term outcomes, and clinical characteristics of rattlesnake bites (RSB) in children.

METHODS

This was a 10-year retrospective chart review of all patients who were <13 years old admitted to a medical toxicology referral service in a major metropolitan area of the southwestern United States with a diagnosis of RSB.

RESULTS

Sixty-six children (mean age, 6.33 years) presented to or were transferred to our center with a diagnosis of RSB. Sixty-three percent were male, and the majority of bites (71.93%) occurred on the lower extremities. Forty-nine children (85.96%) developed coagulopathies, and 50 children (87.72%) received Antivenin (Crotalidae) Polyvalent (ACP) administration. Of the 50 children receiving ACP, 19 developed an immediate hypersensitivity reaction. Five cases of morbidity resulted, but no deaths were recorded.

CONCLUSIONS

Serious morbidity is infrequent in children following RSB.

Effects of a negative pressure venom extraction device (Extractor) on local tissue injury after artificial rattlesnake envenomation in a porcine model

OBJECTIVES

To determine if a commercially available negative-pressure venom extraction device (Extractor) reduces local tissue injury after artificial rattlesnake envenomation in a porcine model.

METHODS

We prospectively studied 10 pigs using a crossover design. After the pigs were anesthetized, 25 mg Crotalus atrox venom was injected obliquely with a 22-gauge needle 7 mm deep into subcutaneous tissues proximal to the ventral hind hoof. Pigs were randomized to receive either the Extractor (applied 3 minutes following envenomation and left in place for 30 minutes) or no Extractor. The protocol was repeated 14 days later by using the alternate treatment group and opposite hind leg for each animal. We measured leg circumference at standardized locations on the hoof, foreleg, and thigh at baseline and then 1, 2, 3, 4, 5, 6, 24, 48, 72, and 96 hours following venom injection. Maximal changes in circumference at 6 hours were compared using the paired t test. Minimum residual swelling at up to 96 hours was similarly compared.

RESULTS

Maximal 6-hour swelling was similar with and without the Extractor: the hoof difference with the Extractor was -0.1% (95% CI = -3.4% to 3.2%, P = .95), foreleg difference was 0.3% (95% CI = -4.1% to 4.7%, P = .88), and thigh difference was -2.8% (95% CI = -10.0% to 4.4%, P = .40). Minimum residual swelling at up to 96 hours was also similar with and without the Extractor: hoof difference with the Extractor was 1.2% (95% CI = -5.6% to 8.0%, P = .70), foreleg difference was 0.6% (95% CI = -3.7% to 4.9%, P = .76), and thigh difference was 0.3% (95% CI = -2.4% to 3.0%, P = .81). A circular lesion identical in size and shape to the Extractor suction cup, which later necrosed and resulted in tissue loss, developed where the device had been applied in 2 animals. No such lesions occurred in legs not treated with the Extractor.

CONCLUSION

No benefit was demonstrated from Extractor use for artificial rattlesnake envenomation in our animal study. The skin necrosis noted in 2 Extractor-treated extremities suggests that an injury pattern may be associated with the device.

Antivenom therapy in the Americas

Envenomations are an important cause of injury in the Americas. While supportive care alone may result in an acceptable outcome, antivenom offers a specific therapy that can significantly reduce the injury and symptoms of the envenomation. Antivenoms are hyperimmune sera collected from animals immunised with venom. The antibodies contained in the serum bind and inactive venom components. This leads to cessation or reversal of the toxic effects of the venom. The serum is often processed to increase the level of antibodies directed against venom components and decrease the amount of inactive proteins that may cause allergic reactions. The processing may include precipitation of inactive proteins, chromatographic methods and cleavage of the immunoglobulins to form antibody fragments known as Fab or F(ab)2. In the Americas, antivenoms are produced to treat crotalid and Micrurus snake envenomations. Latrodectus and Loxosceles spider envenomations and Centruroides and Tityus scorpion envenomations. The indications, method of administration and incidence of adverse reactions differ greatly for each antivenom. The adverse effects encountered when using antivenoms are primarily allergic in nature. Anaphylaxis, which may be life threatening, is a major concern. Preparations to treat anaphylaxis must be made before initiating antivenom therapy. Serum sickness is also common with many of the antivenom preparations.

Envenomations

Envenomations are uncommon, challenging causes of critical care admissions. This article describes the diagnosis and treatment of envenomations that cause the most critical care admissions in the United States. Most are caused by the following animals: rattlesnakes, copperheads, cottonmouths, coral snakes, brown recluse spiders, and bark scorpions.

Crotalid snake envenomation

Over 5000 Americans suffer from snake bites annually, and of these, nearly one quarter are from poisonous species. Although these cases are undeniably reported, death appears to occur in only a few cases each year, and often reflects delay in obtaining medical care. Two families of venomous snake indigenous to the United States account for most envenomations: Crotalidae (pit vipers or new world vipers) and Elapidae. This article focuses on the snakes of the Crotalidae family.