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There are approximately 10,000 emergency department visits in the United States for snakebites every year, and one-third of those involve venomous species. Venomous North American indigenous snakes include species from the Crotalinae (pit vipers) and Elapidae (coral snakes) subfamilies. Treatment relies on supportive care, plus antivenom for select cases. While certain principles of management are widely accepted, controversies exist with regard to prehospital use of pressure immobilization, antivenom use, coagulation testing after copperhead envenomation, and fasciotomy. An evidence-based approach to management of North American venomous snakes will be discussed, along with a review of the current controversies.
A 4-year-old boy is brought to your ED by his distraught parents. An hour ago, he was in the backyard by the pool, playing with what they thought was a toy. He started screaming, and when the mother moved closer, she saw a foot-long black, yellow, and red snake in his hand. She frantically pulled it off him and threw it into the bushes. She reports that she had to pull quite hard before it would release. The child has several small marks on the palm of his left hand. There is minimal redness, and no swelling is apparent. The dad took a picture of the snake with his phone and you can tell quickly that it was a coral snake. The child is asymptomatic currently, but the nearest pediatric ICU is over an hour away. You wonder: should you transfer this patient to the ICU or can you observe him in the ED—and should you start antivenom?
A 26-year-old man arrives to the ED via private vehicle with his arm in a makeshift sling. He reports that his pet rattlesnake bit him on his right index finger about 45 minutes ago. His hand and wrist are swollen. He reports that he has no past medical history besides his 3 previous visits for snakebites. He reports having a “reaction” to the snakebite antidote during his last visit. You wonder whether the patient is immune . . . or should you give antivenom again?
A 51-year-old man with a history of a rattlesnake bite approximately 4 days ago presents from his primary care physician's office for abnormal lab test results. He reports easy bruising and some bleeding when he brushes his teeth, but is otherwise asymptomatic. You wonder how you should manage this patient.
According to the American Association of Poison Control Centers (AAPCC) 2006-2015 annual reports, there were 65,695 reported exposures and 31 deaths from snakes in the United States in that time period.1 There are 2 subfamilies of venomous snakes that are native to the United States: (1) the Crotalinae (pit vipers, subfamily of family Viperidae), which includes rattlesnakes, copperheads, and water moccasins (also called cottonmouths), and (2) the subfamily Elapidae (subfamily of family Colubridae) of which only the coral snake is native to the United States. Bites from snakes from these native subfamilies can produce significant morbidity and, rarely, death, so prompt clinical evaluation and management is essential. In addition, exotic snakes are popular as pets, and bites from these snakes may cause rapid death, depending on the species, so expertise is required to manage them expeditiously.
Patients with snake envenomations generally access healthcare either through the emergency department (ED) or through first-aid providers who generally turn to the emergency clinician for direction. Management of envenomations is considered a core competency of emergency clinicians, and along with Poison Control Centers, they often serve as community resources for snakebite emergencies. Not all envenomations require antivenom; however, delayed administration may lead to significant morbidity and even death, in some cases. This issue of Emergency Medicine Practice provides a comprehensive update on the principles of clinical evaluation of envenomations from pit vipers and coral snakes native to the United States as well as current management recommendations and controversies. Resources are also provided to assist in the management of envenomation from exotic species.
A literature search was performed on PubMed using the search terms snake bites, snake envenomation, Agkistrodon, cottonmouth, copperhead, rattlesnake, Crotalinae, Elapidae, Colubridae, water moccasin, coral snake, and pit viper. A total of 120 relevant articles from 2006 to 2017 were reviewed.
A search of literature published from 2006 to 2017 using key terms snake bite or snake envenomation of the Cochrane Database of Systematic Reviews, Evidence Based Medicine Reviews: Best Evidence (ACP), Database of Abstracts of Reviews of Effectiveness (DARE), and Evidence-Based Medicine Reviews Multifile (EBMZ) identified 11 articles. Of these, 3 were not relevant to indigenous North American snakes, 3 were randomized controlled trials, 1 was a poststudy subanalysis, and 2 were reviews (Cochrane and DARE).
As is the case with most of the toxicology literature, evidence on the management of snake envenomations from high-quality prospective randomized controlled trials is limited. The few published studies in the past 10 years are mostly from other countries where the snake species, the level of supportive care, and antivenom availability and effectiveness are different from that in North America. The literature is comprised primarily of case reports/series, retrospective chart reviews, animal model studies, expert consensus panels, and review articles.
The current relevant literature is comprised of case reports/series describing novel or known but not well-characterized clinical effects after a snake envenomation; observational studies using data from hospital charts, Internet search, Poison Control Centers, and national databases; animal model studies; in vitro venom and antivenom studies; conclusions from expert consensus panels; a position statement; and 3 randomized controlled trials. Many of the retrospective observation studies utilized Poison Control Center data (Texas Poison Control Center Network, Florida Poison Information Center Network, AAPCC database, and the American College of Medical Toxicology ToxIC North American Snakebite Registry). Poison Control Centers collect self-reported, unverified information provided by the public or healthcare workers on potential or actual exposures, but they may not be true envenomations and may not reflect the true incidence of snakebites. Furthermore, reported clinical effects and outcomes may be incomplete or inaccurate. For example, according to a compilation of data reported to United States Poison Control Centers, there were no deaths from coral snakes from 2006 to 2015; however, a confirmed death after a coral snake envenomation was published in 2009 (the first and only confirmed death in the literature).2 The ToxIC Registry contains prospectively collected verified clinical information, and it also relies on voluntary reporting.
Most of the management recommendations discussed in this article are based on expert opinion supported by low- to moderate-quality evidence. Expert consensus panel recommendations for the surgical management of snake envenomation were published in 2013.3 Clinical questions were structured in the “Patient, Intervention, Comparison, Outcome” format, and recommendations were developed using Grading of Recommendations, Assessment, Development, and Evaluation. A unified treatment algorithm for the management of Crotalinae envenomations was published in 2011.4 Experts utilized a modified Delphi methodology to develop evidence-informed recommendations. Standard evidence-level scales were not used, as only 1 randomized clinical trial involving the treatment of Crotalinae envenomation with antivenom had been published at the time.5 Since then, a randomized clinical trial comparing Crotalidae Polyvalent Immune Fab (Ovine) (FabAV, CroFab®) to F(ab’)2 immunoglobulin derivatives was published in 2015.6 Additionally, a post hoc analysis of data from this trial comparing copperhead coagulation parameters was also published.7 A position statement from leading national and international clinical toxicology associations regarding use of pressure immobilization after a North American Crotalinae snake envenomation was published in 2011.8
1. “The patient had some minor abrasions, but no visible fang marks, pain, or swelling at the bite site, so I discharged him.”
Patients can develop a coagulopathy and covert bleeding from pit viper bites without having visible tissue damage. The patient should be observed for a minimum of 8 hours, and coagulation studies repeated before discharge home. Coral snake bites may not produce any visible signs on examination. If a coral snake is the suspected culprit, the patient should be monitored for 24 hours to ensure delayed symptoms do not develop.
3. “I thought that I could wait until signs of respiratory distress developed, because the antivenom would quickly reverse the paralysis.”
Administration of antivenom does not reverse symptoms; it merely halts progression of symptoms. Patients with coral snake bites should be treated with antivenom at the first signs of neurological impairment.
7. “The patient had urticaria and wheezing that developed soon after I started administering antivenom, so I stopped the infusion. The patient continued to worsen, even though I stopped it.”
Allergic reaction to antivenom is a serious adverse effect; however, patients can also develop anaphylaxis and other allergic symptoms to snake venom. For each case, consider this possibility and weigh the risks of not treating a snakebite. Consultation with a regional Poison Control Center is recommended.
Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, randomized, and blinded trial should carry more weight than a case report.
To help the reader judge the strength of each reference, pertinent information about the study, such as the type of study and the number of patients in the study is included in bold type following the references, where available. In addition, the most informative references cited in this paper, as determined by the author, are highlighted.
Points and Pearls Excerpt
Most Important References
Why to Use
The Antivenom Dosing Algorithm is an anti-venom dosing tool for Crotalinae (pit viper, formerly known as Crotalidae) snake envenomations.
Antivenom is an extremely expensive resource that carries a risk of adverse events. Emergency clinicians should be aware of the indications for its use, as well as other steps to take in the management of patients with pit viper bites.
When to Use
Stephen A. Harding, MD
The leading edge of swelling and tenderness surrounding the envenomated area should be marked every 15 to 30 minutes. Elevate and immobilize the affected extremity, treat pain aggressively with intravenous opioids, and update the patient’s tetanus status as needed.
The following should be avoided:
Lavonas et al analyzed the medical literature regarding use of Crotalidae Polyvalent Immune Fab for pit viper envenomations. After analysis of 42 original articles, this panel of experts met and held a consensus-building meeting, which resulted in a unified treatment algorithm.
Eric J. Lavonas, MD
Copyright © MDCalc • Reprinted with permission.
Sophia Sheikh, MD; Patrick Leffers, PharmD
Daniel J. Sessions, MD; Andy Jagoda, MD, FACEP
September 1, 2018
September 30, 2021
Physician CME Information
Date of Original Release: September 1, 2018. Date of most recent review: August 10, 2018. Termination date: September 1, 2021.
Accreditation: EB Medicine is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians. This activity has been planned and implemented in accordance with the accreditation requirements and policies of the ACCME.
Credit Designation: EB Medicine designates this enduring material for a maximum of 4 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.
Specialty CME: Included as part of the 4 credits, this CME activity is eligible for 4 Trauma CME credits, subject to your state and institutional approval.
ACEP Accreditation: Emergency Medicine Practice is approved by the American College of Emergency Physicians for 48 hours of ACEP Category I credit per annual subscription.
AAFP Accreditation: This Enduring Material activity, Emergency Medicine Practice, has been reviewed and is acceptable for credit by the American Academy of Family Physicians. Term of approval begins 07/01/2018. Term of approval is for one year from this date. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Approved for 4 AAFP Prescribed credits.
AOA Accreditation: Emergency Medicine Practice is eligible for up to 48 American Osteopathic Association Category 2-A or 2-B credit hours per year.
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