Bites, stings, and envenomations

Chapter 38
Bites, stings, and envenomations


Adam Frisch, Andrew King, and Stephanie Outterson


Introduction


Animal bites are estimated to account for 1 million physician visits each year and for 1% of emergency department (ED) visits [1]. The actual number of animal-related injuries is impossible to calculate because many injuries go unreported [1,2]. The infrequent nature of animal-related calls, coupled with the excitement and emotion often found on scene, can lead to poor provider judgment or errors in proper care. This chapter focuses on prehospital management of animal bites, stings, and envenomations and reviews injuries likely to be encountered, with specific prehospital treatments and interventions where appropriate.


Animal bites


Scene safety and preplanning


As with any EMS response, scene safety is a primary concern. When responding to a call involving animals, all personnel should prevent interaction with the offending animal. Prehospital providers and medical directors should be aware of animal control resources available in their coverage areas. Protocols for responding to animal-related calls should include these resources when appropriate. The primary responsibility of EMS personnel is for their own safety and the safety of the patient. Providers should not be primarily responsible for dealing with the animals. While identification of the offending animal may be helpful for treatment, attempting to catch or quarantine the animal exposes the EMS provider to undue risk [3]. For related reasons, transportation of animals, dead or alive, to the hospital for identification is not advised.


Refusal concerns


As many animal-related injuries initially appear benign, both patients and providers often underestimate their potential seriousness, resulting in inappropriate refusal of treatment or transport. Agencies should consider mandatory medical oversight contact for refusal of care in animal encounter situations, as serious risks exist.


Animal-specific concerns


Mammals


Domesticated animals account for the vast majority of mammalian bite wounds, with dogs and cats representing 93–96% of mammalian bites [2]. Bites by both types of animals occur most frequently to the upper extremity, followed by the lower extremity, and finally the face and neck [1]. Acutely lethal wounds tend to occur in young children [1]. Children are often familiar with the offending animal and are more prone to attacks to the face and neck [1,4]. In both cats and dogs, unique oral flora contributes to considerable infection risk. While most wounds do not become infected, those that do often require in-hospital therapy and potential operative management. Two-thirds of hand bites in one study required hospitalization for IV antibiotics, and one-third required at least one surgical procedure [5]. Systemic complications including endocarditis, meningitis, brain abscess, and sepsis must also be considered by providers and medical directors when determining protocols and transport decisions [6].


Human bites carry risks of complications similar to those of other mammalian bites. Hand wounds involving the metacarpal-phalangeal joint and overlying extensor tendons are often “fight bites” (injuries to the hand from striking teeth during an altercation) and are especially prone to infection. More than 30% of fight bites become infected, resulting in decreased functional capacity. Fight bites often coincide with intoxication and/or criminal activity that may act as a barrier to prehospital care through reluctance to disclose the true mechanism, patient refusal, or law enforcement custody.


Very few poisonous mammals exist in North America. Only the short-tailed shrew, found in central and eastern sections of North America, poses a toxic threat. Several non-indigenous mammals have poisonous reputations. The shrew-like solenodon, found in Central America, induces toxins in its saliva through grooved incisors. The platypus, found in Australia, has venomous glands introduced by spurs at the base of its hind feet. In all of these animals, the toxins serve to kill prey and defend from predators [7]. Bites to humans result in unusually painful wounds with local edema, but typically lack serious or systemic effects.


Accounting for less than 10% of animal bites [2], attacks by wild or undomesticated mammalians are rare and usually require only supportive care and basic wound management in the prehospital setting. In general, most bite victims should be transported to the emergency department for wound evaluation, tetanus shots, and possibly antibiotics.


Rabies


Mammalian bites carry the unique risk of rabies virus transmission which is almost universally fatal [8,9]. Current Centers for Disease Control and Prevention (CDC) guidelines recommend postexposure prophylaxis (PEP) including immunoglobulin administration and vaccination series for high-risk bites in vaccine-naive individuals, and a modified vaccination series for those previously vaccinated [10]. Bites from skunks, foxes, raccoons, bats, and some other carnivorous animals are considered at risk and should receive PEP promptly. For domestic animals that appear healthy and can be quarantined for 10 days, PEP can be withheld pending development of symptoms. Patients with bites from other animals should be transported to the hospital so that the need for PEP can be determined [10].


Bats require special consideration because rabies transmission has occurred outside of recognized bites. Although data are conflicting and perhaps viewed as controversial [10], PEP “can be considered for persons who were in the same room as the bat and who might be unaware that a bite or direct contact had occurred (e.g. a sleeping person awakens to find a bat in the room or an adult witnesses a bat in the room with a previously unattended child, mentally disabled person, or intoxicated person) and rabies cannot be ruled out by testing the bat Thus, EMS providers should have a very low threshold to transport potential victims to the ED for evaluation whether an obvious bite exists or not [10].


Reptiles


Venomous snakes


Of the estimated 45,000 annual snake bites in the United States, roughly 8,000 are reportedly from venomous snakes. There are 25 venomous species of snakes in the United States. The majority of these are in the subfamily of Crotalids (rattlesnakes, cottonmouths, and copperheads), and the remainder in the Elapid subfamily (coral snake) [11]. This division also represents a difference in their respective toxins and clinical manifestations of envenomation.


Crotalid venom is a primarily a hemotoxin (with some cytotoxic and neurotoxic properties) and produces symptoms ranging from local swelling and ecchymosis to systemic coagulopathy, altered consciousness, and shock. The constellation of effects begins within minutes and steadily progresses to its maximal extent over a number of hours (up to 24 hours with leg bites).


Elapid envenomations can remain relatively asymptomatic for up to 12 hours and then manifest neurotoxicity ranging in severity from paresthesia to complete paralysis requiring ventilatory support.


In either case, it is important to avoid underestimating bite severity based on initial patient assessment at the scene. Although “dry bites” occur with relative frequency, the lack of clinical swelling should not lead the provider to assume that no envenomation has occurred. A period of observation of varying lengths depending on the bite site is recommended by toxicologists and should prompt any and all patients with suspected bites to be transported to the emergency department for evaluation.


Much of EMS provider education about snake bites should focus on dispelling common myths. Providers may encounter well-meaning citizens attempting to render “first aid” to snake bite victims. Cold therapy, arterial tourniquets, electricity (from TASERs or car batteries), incision of the wound, and suction (via commercially available device or oral) are popular lay therapies for snake bite that are without scientific backing and may lead to more local tissue damage [3,11–14].


While some of the literature has suggested treatments such as compression immobilization [12–14], all of the major toxicological societies of North America advocate against this technique for US crotalid envenomations [15]. Keeping the patient calm and immobilizing the affected extremity in a neutral position is the best course of action in the prehospital setting.


Insufficient evidence exists for compression immobilization in hemodynamically unstable patients. Effectiveness of pressure immobilization has been suggested in the setting of Australian elapid snake bites and thus, as a corollary, compression immobilization for confirmed North American elapid envenomation may be considered for those with anticipated long transport times [16,17]. Furthermore, if longer transport times are anticipated after elapid envenomation, EMS should be prepared to intervene on the airway and assist with ventilation. Routine use of antivenin therapy is not generally recommended in the prehospital setting, as it requires a significant amount of time and resources to prepare and administer [3].


Adequate analgesia is a significant concern after crotalid envenomation. In the acute phase, toxicologists recommend the use of intravenous fentanyl as opposed to other opioids so as not to confuse the crotalid envenomation symptoms with morphine-induced histamine release, both of which can cause anaphylaxis, hypotension, and local swelling [16].


Nonvenomous snakes

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Jun 14, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Bites, stings, and envenomations

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