Episode 20 – Emergency Department Management of North American Snake Envenomations

Jeff:  Welcome back to Emplify, the podcast corollary to EB Medicine’s Emergency Medicine Practice. I’m Jeff Nusbaum, and I’m back with my co-host, Nachi Gupta and we’ll be taking you through the September 2018 issue of Emergency Medicine Practice – Emergency Department Management of North American Snake envenomations.

Nachi: Although this isn’t something we encountered too frequently – it does seem like I’ve been hearing more about snake bites in the recent months.

Jeff: I actually flew someone just the other day because the local ED ran out of CroFab after an envenomation in Western PA.

Nachi: Yeah, this is definitely more than “just a boards topic,” and it’s really important to know about in those rare circumstances. In terms of incidence, there are actually about 10,000 ED visits in the US for snake bites each year, and 1/3 of these involve venomous species.

Jeff:  That’s a good teaser, so let’s start by recognizing this month’s team – the two authors, Dr. Sheikh, a medical toxicologist, and Patrick Leffers, a pharmD, and emergency medicine and clinical toxicology fellow. Both are at the University of Florida Jacksonville, and they reviewed a total of 120 articles from 2006-2017, in addition to reviews from both Cochrane and Dare.

Nachi: And don’t forget our peer reviewers this month, Dr. Daniel Sessions, a medical toxicologist working at the South Texas Poison Center, and our very own editor-in-chief, Dr. Andy Jagoda, who is also Chair of the Department of Emergency Medicine at Mount Sinai in New York City.

Jeff: What a team! But, let’s get back to the snakes. As some background, from 2006-2015 there were almost 66,000 reported snake exposures and 31 deaths from snake envenomation in the US.  Of course, this number likely underestimates the true total.

Nachi: And there are two key subfamilies of venomous snakes to be aware of – the Crotalinae – or pit vipers – which includes rattlesnakes, copperheads, and water moccasins; and the Elapidae – of which you really only need to know about the coral snake.

Jeff:  And while those are the only two NATIVE snake subfamilies to be acutely aware of, don’t forget that exotic snakes, which are shockingly popular pets — they can also cause significant morbidity and mortality.

Nachi:  Oh, and one other quick note before we get into the epidemiology – most of the recommendations this month come from expert opinion, as high quality RCTs are obviously difficult.  In addition, many of the studies were based in other countries, where the snakes, the anti-venoms and their availability, and the general healthcare systems are different from those that most of us work in.

Jeff:  Unless we have listeners abroad? Do we have listeners in other countries?

Nachi: Oh we definitely do… but we are going to be a bit biased towards US envenomation today. In any case, venomous snake bites occur most frequently in men aged 18 to 49 during warmer months with provoked bites occurring more frequently in the upper extremities and unprovoked bites in the lower extremities.

Jeff:  In one study of poison center data from the last decade, nearly half of all victims of snake bites were victims of unknown type snakes.  However, of those that were known, copperheads were the most common, while rattlesnakes caused the most fatalities – 19 of 31 in this dataset.

Nachi:  In a separate study of snake bites in the early 2000s, 32% of exposures were from venomous snakes and 59% of those resulted in admission. That’s remarkably high.

Jeff:  Snake bite severity depends on several key factors: the amount of venom, the composition of the venom, the body size of the bite victim, the victim’s clothing, the size of the bite, comorbid conditions, and the timing and quality of medical care the victim receives.

Nachi:  To be a bit more specific – First, the amount of venom will depend on the species of snake, with variations even occurring within the same species.  Secondly, while there is a correlation between rattlesnake size and bite severity, there is much more at play.  Some snakes can even vary the amount of venom based on threat risk – with defensive bites having different profiles than bites to strike prey.

Jeff: I found it pretty interesting that  an estimated 10-25% of pit viper bites are considered dry bites, that is, ones in which no venom is released.

Nachi:  Right, this is just one reason why all victims shouldn’t immediately get anti-venom, but we’ll get there.

Jeff:  We definitely will.  As we already stated – venom composition varies greatly.  Pit vipers produce a predominantly hemotoxic venom.  Systemic effects include tachycardia, tachypnea, hypotension, nausea, vomiting, weakness, and diaphoresis.  Neurotoxicity is rare and is usually due to inter-breeding between species.

Nachi:  While rattlesnake bites are associated with higher morbidity and mortality, the more common copperhead bites typically only cause local tissue effects.  More serious systemic findings such as coagulopathy and respiratory failure have been reported though.

Jeff:  So that’s a solid background to get us started.  Let’s talk about the individual snakes.  Why don’t you start with the crotalinae family – aka the pit vipers.

Nachi:  Sure – the crotalinae includes rattlesnakes, cottonmouths (also known as water moccasins), and copperheads.  These make up the vast majority of reports to the poison centers.  They can be identified by their heat sensing pits located behind their nostrils (hence pit vipers).  As a general rule, you can also identify the venomous snakes by their triangular or spade-like head, elliptical pupils, and hollow retractable fangs.

Jeff:  wait, so you want me to walk up to the snake and ask to see if their fangs retract… yea, no thanks.

Nachi: Haha, of course not, I’m just giving you some of the general principles here. In contrast, non-venomous pit vipers have rounded heads, round pupils, a double row of vertical scales, and they lack fangs.

Jeff: In terms of location, rattlesnakes are found in all states but Hawaii, and cottonmouths and copperheads are distributed mostly throughout the southern and southeastern states, with copperheads also extending further north, even into Massachusetts.

Nachi: Moving on to the Elapidae –  there are 3 species of coral snakes, only two of which you need to know about, Micrurus fulvius fulvius or the eastern coral snake and Micrurus tener or the Texas coral snake.  Of the two, the eastern or Micrurus fulvius fulvius produces more potent venom.

Jeff:  As you may have guessed by their names, the eastern coral snake is found in the southeastern united states, specifically, east of the Mississippi — whereas the Texas coral snake lives west of the Mississippi.

Nachi:  Venomous North American coral snakes can be recognized by the red and yellow bands around their bodies whereas their nonvenomous counterparts can be recognized by their characteristic black band between the red and yellow bands. I’m sure you’ve heard the popular mnemonic for this… Red touch yellow kill a fellow, red touch black, venom lack.

Jeff:  I have heard that one, and it’s not a bad mnemonic. Just remember that this is more of a guideline than a rule, as it doesn’t always hold true.

Nachi: Coral snakes also tend to chew rather than bite thanks to their short, fixed, hollow fangs.  Locally, bites can lead to muscle destruction thanks to a certain myotoxin.  Systemic signs of infection include nausea, vomiting, abdominal pain, and dizziness. 

Jeff: The venom also contains a neurotoxin which can lead to diplopia, difficulty swallowing and speaking and generalized weakness.

Nachi: Complicating matters even further, the onset of these symptoms may be delayed for many hours.

Jeff:  Alright, so I think that about wraps up the background.  Let’s move on to the meat and potatoes of this article, starting with the differential.

Nachi:  For differential this month, we are really focusing on differentiating a venomous snake from a non-venomous one.

Jeff: Oh yeah, this is where you want us to ask the snake if it can retract its fangs, right?

Nachi: Ha very funny – Although the type of snake may be obvious if the patient owns the snake, for most cases you see in the ED, the type of snake won’t be clear. Try to get a description of the snake and consider your local geography. Some patients may even bring the snake in with them.

Jeff: yea, no thanks. As for prehospital care, it’s actually pretty interesting stuff as recommendations have changed many times.  You may have heard of the recommendations for incision / excision, use of venom extraction devices, tourniquets, chill methods and even electroshock therapy – well these methods are all OUT.

Nachi:  Not only are they out, they actually worsen outcomes, so definitely don’t pursue any of them.  Instead,  since no treatment has been shown to improve outcome, you should prioritize prompt transport.

Jeff: And while we definitely don’t want to encourage ill-advised attempts at capturing the snake, taking pictures at a distance may be helpful in identifying it.  Oh and the authors do note- pretty terrifying stuff coming up here so brace yourself – even if the snake is dead the bite reflex is still intact…

Nachi: And that’s why I work in city hospitals…

Jeff:  There’s also a bit of controversy here with regards to pressure immobilization, which is definitely something I thought we were supposed to do in the prehospital setting. Apparently in other countries, like Australia, prehospital providers frequently employ pressure immobilization – that is, wrapping bandages proximally up a splinted limb to impede lymphatic toxin spread.

Nachi:  Right, but in Australia, not only are the snakes more venomous but the hospital transport distances are much longer, so, basically they sacrifice the limb to potentially save a life.  In the US, with our current indigenous snake population and the relatively short transport distances, this isn’t justified at all!

Jeff:  Take home: based on the current literature, the American College of Medical Toxicology, other experts, and Drs. Sheikh and Leffers recommend against pressure immobilization in lieu of prompt patient transport to definitive treatment.

Nachi:  Good to know – alright so now we have the patient in the emergency department, let’s begin ED care.  As always – IV, O2, Monitor including end tidal CO2 if you suspect a neurotoxic or exotic snake bite.  Of course, avoid using the affected limbs for vitals…

Jeff: If not done already, remove any constrictive clothing or jewelry and mark the leading edge of pain, edema, and erythema both above and below the bite.  If EMS has placed bandages, leave them in place until antivenom and resuscitative equipment is ready.

Nachi:  And definitely involve the poison control center or a medical toxicology service early as they are an amazing resource. It’s an easy number to remember.. 1-800-222-1222. If you just type “poison control center” into google, that number will come up immediately.

Jeff: Hypotension should be treated with isotonic fluids and, as usual, anaphylaxis should be treated with the usual cocktail of antihistamines and epinephrine at first IM and then via infusion if refractory. Note that antivenom will NOT reverse anaphylaxis on its own.

Nachi:  When eliciting a history, there are a number of important factors to look out for, including – time and location of the bite, description of the snake, tetanus status, comorbid conditions, medications and allergies, any systemic or neurologic symptoms, muscle cramps, perioral tingling or numbness, metallic taste, history of previous snakebites and any reactions to previous envenomation or antivenom treatment.

Jeff: Moving on to the physical exam, when examining the wound, look specifically for local tissue effects which occur in over 90% of patients after pit viper envenomations.  In such cases, you would expect pain, erythema, swelling, tenderness, and myonecrosis beginning at the wound site and then spreading via the lymphatic system.

Nachi:  In addition, specifically with pit viper envenomations, monitor the patient for possible compartment syndrome as the venom can lead to local tissue destruction, increased cell permeability, third spacing of fluids, and bleeding.  And remember that while the local compartment may be hypertensive, the patient may also have systemic hypotension.

Jeff: Just to reiterate what I said before – hypotension may indicate severe anaphylaxis and its not necessarily just due to third spacing.  Regardless, the treatment is the same – epinephrine.

Nachi:  Good point, but let’s focus on compartment syndrome for a minute.  True compartment syndrome is actually quite rare — its really subcutaneous hypertension with preservation of otherwise normal compartment pressures that you’re most likely to see.  Compartment syndrome should therefore only be diagnosed by actual compartment measurements and not just the exam.  However, if you are dealing with compartments that can’t be measured, like in the fingers, you’re only choice is to be guided by the exam…

Jeff:  Risk factors for compartment syndrome in the setting of a snake bite include envenomations in small children, involvement of digits, application of ice or cold packs, and delayed or inadequate antivenom administration.

Nachi: In terms of respiratory effects of envenomations – they aren’t common.  Both bites to the head or neck and neurotoxin containing venom are potential causes. In the setting of respiratory failure, be prepared with advanced airway maneuvers like nasotracheal intubation or cricothyroidotomy. Antivenom will not reverse respiratory failure.

Jeff: Neurologic effects may be present upon arrival but may also be delayed up to 12 hours in the case of eastern coral snake bites.

Nachi: It’s noteworthy that in one study of almost 400 eastern coral snake exposures, the onset of systemic symptoms occurred on average 5.6 hours after the bite.  So definitely remember that repeat exams and observation will be tremendously important.

Jeff:  The actual neurologic symptoms to look for depend on the snake.  Coral snake venom can produce a descending flaccid paralysis characterized by motor weakness, especially of the cranial nerves.  Similarly pit vipers, especially the Mojave rattlesnake, have also been associated with muscular weakness of the cranial nerves and even respiratory insufficiency.

Nachi:  Pit viper envenomation can also lead to myokymia which is repetitive small muscle fasciculations.  Unfortunately, this myokymia may not respond to antivenom administration and myokymia of the chest well and torso can necessitate intubation in extreme cases.  Both myokymia and myonecrosis may lead to rhabdo in the case of significant envenomations.

Jeff:  Pit viper envenomation can also cause hematologic effects.  Fibrinolysis and platelet consumption at the bit site can lead to decreased fibrinogen and thrombocytopenia.  In severe cases this can lead to systemic bleeding and even hemorrhagic shock.  Those on anticoagulants and anti-platelet agents are at increased risk.

Nachi:  Dermal effects such as edema, ecchymosis, bullae, and bleeding are not uncommon, but up to 50% of coral snake bite victims may have none of these.

Jeff:  And to round out this section – just be aware that rare effects such as osteonecrosis, ischemic stroke, massive PE, and septic shock have all been reported.

Nachi: Let’s move on to diagnostic studies.  Most patients require a CBC, coags, and a fibrinogen concentration.  Those with systemic toxicity should also have their electroyltes, CPK, creatinine, glucose, and urine tested.

Jeff:  And while the data is somewhat mixed, one study suggests that all patients with pit viper envenomations need their coags checked, not just those with severe symptoms as in one series nearly 90% of patients had missed coagulation abnormalities.  The clinical consequences of this aren’t clearly explained, so the authors don’t make a specific recommendation.

Nachi:  In terms of imaging, a chest x-ray should be obtained in those with respiratory symptoms and ultrasound may even have an expanding role here for tracking edema, looking for fluid collections, and assessing deep muscle compartments and vascular flow.

Jeff: I feel like we should get some entry music for every ultrasound reference because it seems to make its way into just about every episode.

Nachi: What would it sound like? You bring this up every month. I’ll look into something for a future episode. If any of our listeners have a suggestion, shoot us an e-mail at emplify@ebmedicine.net. In terms of monitoring and observation, this is important, ALL patients with suspected pit viper envenomations should be observed for 8-12 hours with the leading edge marked every 15-30 minutes.

Jeff:  In addition, serial diagnostic testing may also be needed as such changes will be used to guide treatment.  In those with systemic symptoms, lab testing will be required every 4-6 hours prior to discharge.

Nachi:  Before we move onto treatment – let me quickly mention grading.  There is no universal grading system.  The snakebite severity score, the minimum-moderate-severe score, and grade 1-4 score which consider symptoms, exam findings, and lab abnormalities have all been studied.  None have been validated and none track changes, so the authors recommend relying on severity of symptoms and progression of symptoms to guide treatment.

Jeff:  The crux of treatment for pit viper envenomations is with supportive care and anti-venom.

Nachi:  FabAV or CroFab is the antivenom of choice for pit viper envenomations.  This antivenom is made from extracting the Fab portion of anti-venom antibodies from envenomated sheep and processing them with papain.

Jeff:  Since the sheep are injected with venom from the western diamondback, eastern diamondback and Mojave rattlesnake as well as the cottonmouth, the FabAV is most effective against venom from these snakes, however it does have cross reactivity to other immunologically similar venoms.

Nachi:  Indications for FabAV include a more than minimal local swelling, rapid progression of swelling, swelling crossing a major joint, evidence of hemotoxicity, signs of systemic toxicity including hemodynamic compromise, neuromuscular toxicity, and late or recurrent new-onset coagulopathy.

Jeff:  Initially, dose FabAV as a bolus of 4-6 vials, IV.  With life threatening envenomations or those with cardiovascular collapse, double the starting dose to 8-12 vials.  The goal is arresting progression, improvement in coagulation abnormalities, and resolution of systemic symptoms.

Nachi: Although FabAV will reduce the duration and severity of symptoms and lab abnormalities, it will not reverse tissue necrosis and may not reverse neurologic effects.

Jeff:  Once the symptoms have been controlled after the bolus dose or a second bolus dose, maintenance dosing of 2 vials every 6 hours for 3 doses is recommended to prevent recurrence.

Nachi:  So to reiterate.  4-6 vial bolus to start, doubled in severe cases and then 2 vials every 6 hours for 18 hours after that.

Jeff:  You got it.

Nachi:  And like most, maybe all medicines, there are side effects and contraindications to be aware of.  Hypersensitivity reactions and serum sickness to FabAV have been reported as 8% and 13% respectively.   Most are mild and can be treated with your standard bundle of steroids, antihistamines, fluids and epi.

Jeff:  Risk factors for developing allergic reactions to FabAV include  a known allergy to papaya, papain, chymopapin, pineapple enzyme bromelain, and previous allergic reaction to FabAV.

Nachi:  Although FabAV isn’t produced using copperhead venom, it may be effective in severe envenomations and in one study, FabAV reduced limb disability compared to placebo.

Jeff:  Therefore, the authors very reasonably advise that you should use the patient’s clinical picture and individual factors rather than the snake species to guide your treatment.

Nachi:  Interestingly, compartment syndrome should be treated with the initial 4-6 vial dose of antivenom and not necessarily a fasciotomy.  Fasciotomies have not been shown to improve outcomes and are reserved only for those failing anti-venom treatment.

Jeff:  The reason for this is that antivenom may reduce tissue pressures obviating the need for fasciotomy.  In addition, fasciotomy wouldn’t affect muscle necrosis that is occurring so fascia removal really doesn’t solve anything.

Nachi:  And just as anti-venom can be used to treat elevated compartment pressures, it can also be used to treat coagulopathy.

Jeff:  Blood products should be used for those who are actively bleeding or severely anemic as venom does not discriminate and will destroy whatever blood it comes across.

Nachi:  Recurrent and late onset coagulopathy after FabAV treatment has also been well described.   Although not exactly clear why, some speculate that it occurs for one of 4 reasons. 1) because the half life of FabAV is shorter than that of the venom, or 2) because the venom is initially stored in the soft tissues and then slowly released over time or 3) because the venom has a late onset component, or lastly, 4) there is delayed dissociation of the venom-antivenom complexes.  Regardless of the mechanism, late onset coagulopathy can be treated with FabAV.

Jeff:  Luckily, bleeding associated with coagulopathy and bleeding associated with late onset coagulopathy are both extremely rare.  

Nachi:  Moving on to coral snakes.  Coral snake bites should be treated with NACSA or North American Coral Snake anti-venom.  This antivenom halts or at least limits the progression of muscle paralysis and shortens the clinical course.

Jeff:  Most experts recommend NACSA treatment with the first signs of systemic toxicity and not for all comers.  This recommendation is backed by the literature as in one observational study those treated with prophylactic NACSA did less favorably as compared to those who got it only after symptoms onset.  This is probably because NACSA doesn’t reverse neuromuscular weakness and only limits progression.

Nachi:  And it’s not like you are just sitting by and watching while doing nothing – focus your initial treatment on wound care, pain control, and then observation for the development of systemic symptoms.  The exact length of observation will depend on the snake, but should be somewhere between 8 and 24h.

Jeff:  As for dosing – the initial NACSA dose is 3-5 vials IV for both peds and adults with a repeat dose if the initial symptoms don’t improve.

Nachi: Side effects and adverse reactions occur somewhere between 8-11% of the time with dermal reactions being most common and anaphylaxis being the most severe.

Jeff: There is also one last anti-venom to be aware of – Coralmyn, for coral snake envenomations.  Coralmyn is a polyclonal antivenom F(ab’)2 coral snake antivenom, developed because the current lot of NACSA has technically expired although the date has been extended numerous times.  It’s currently in a phase 3 trial, so keep your eyes out.

Nachi:  Other non-antivenom treatments that have been tested include acetylcholinesterase inhibitors and trypsin at the bite site – both should be considered experimental at this point.

Jeff:  To wrap up the treatment section, let’s talk exotic snakes.  You may recall from the intro that these have a higher morbidity and mortality compared to native species.

Nachi:  You will have to rely on your local poison control center or toxicologist for advice and you may even need to turn to the zoo or aquarium for antivenom, if it exists at all.  Patients with bites from exotic snakes should be monitored, likely in the ICU, for up to 24 hours as toxicity from some venom may have a delayed onset of up to 20 hours.

Jeff:  Scary stuff, hopefully the patient knows which type of exotic snake they own and you don’t have to sort through a million google images to try to get to the bottom of this.  Anyway, there are 3 special populations to discuss.  First are pregnant patients.

Nachi:  The authors cite a 1.4% incidence of snake bites in pregnant patients.  They note that this is low, but from my perspective, this seems shockingly high – why would a pregnant person ever get anywhere near a snake, seems just ill advised…

Jeff:  haha, true.   But regardless, treatment is the same with antivenom as needed for all the same indications.  With fetal demise rates as high as 30%, in addition to maternal monitoring, the fetus should also be monitored.

Nachi:  That number may seem high, but keep in mind that that’s from studies in other countries with more venomous snakes, so it’s likely to be lower in the US.  But the point remains, that antivenom is generally recommended to be given if the mother has indications for treatment, as poor fetal outcome is tied directly to the severity of envenomation in the mother.

Jeff: Continuing right along, the next special population to discuss are pediatric patients.  Because dosing is based on the amount of venom delivered and not on patient specific factors, dosing is the same for peds and adults.

Nachi:  How rare – so few meds seem to be the same for peds and adults.  The last population to discuss are anticoagulated patients.  Patients on antiplatelet or anti-coagulants are at increased risk of bleeding after pit viper envenomations and therefore should have their coags checked every 2 days following the last dose of FabAV.

Jeff:  I think we’ve at least mentioned most of this months controversies, but it’s probably worth quickly reviewing them since they mostly dispel common myths.

Nachi:  Good idea.  Incision and suction of snake bites is nearly universally not recommended.

Jeff:  In the absence of ischemia, fasciotomy for snake bites is not recommended, even with elevated compartment pressures.  Instead treat compartment syndrome with anti-venom and save the fasciotomy for true cases of ischemia refractory to antivenom.

Nachi:  With a known or suspected coral snake envenomation, due to shortages of NACSA, wait until the patient develops symptoms instead of empirically treating all bite victims.

Jeff:  Maintenance dosing of FabAV continues to be debated.  The manufacturer recommends 2 doses every 6 hours for 3 doses while some experts recommend only maintenance dosing as needed.  It’s therefore probably safest to punt this to whatever poison control center or toxicologist you speak with.

Nachi:  I feel like we are plugging the poison center a lot, but it’s such a good free, and usually very nice consult to have on your team.

Jeff: Nice consultant – what a win!  Moving on to the cutting edge.  There is a new Crotalidae antivenom called Crotalidae Immune F(ab’)2 or, more simply, Anavip.  It should be available in the next few months.  The dosing will be 10 vials up front over 60 minutes followed by an additional 10 vials if the symptoms having been controlled.  4 more vials may be given for symptom recurrence.  Patients must be observed for a minimum of 18 hours after initial control of symptoms.

Nachi: This would be a really nice development as Anavip has a longer half life and therefore should reduce the rates of late coagulopathy and decrease the need for maintenance dosing, follow up, and repeating coags.

Jeff:  And finally, like we mentioned before, injection of the trypsin has been tried as a bridge to antivenom, as has carbon monoxide, which may mediate degradation of fibrinogen dependent coagulation.

Nachi:  Alright, so let’s talk about the disposition next. Victims of pit viper envenomations should be monitored for 8-12 hours from the time of the bite.  They will need baseline labs and repeat testing ever 4-6 hours.  IF there is no progression of the symptoms and repeat testing is normal, the patient can be discharged.

Jeff: Victims of coral snake bites should be admitted and observed for 12-24 hours regardless of symptoms.

Nachi: Victims of rattle snake envenomations who initially develop hematologic abnormalities and are treated with FabAV should have repeat testing done in 2-4 days and 5-7 days.

Jeff:  Wounds should also be closely followed to avoid complications and long term disfigurement and disability.  PT/OT may be necessary as well.

Nachi:  Perfect, let’s round this episodes out with a review of the key points and clinical pearls from this month’s issue.

• There are about 10,000 ED visits in the US for snake bites each year, and 1/3 of these involve venomous species.
• Pit vipers produce a predominantly hemotoxic venom. Both local and systemic effects can occur. Systemic effects include tachycardia, tachypnea, hypotension, nausea, vomiting, weakness, and diaphoresis.
• In general, venomous snakes have a triangular or spade-like head, elliptical pupils, and hollow retractable fangs. In contrast, non-venomous snakes have a rounded head, round pupils, lack fangs, and can have a double row of vertical scales on the tail.
• Venomous North American coral snakes often have adjacent red and yellow bands, whereas their nonvenomous counterparts usually have a characteristic black band between the red and yellow bands.
• For prehospital care in the US, the following strategies are not recommended: incision or excision, use of venom extraction devices, tourniquets, chill methods, and electroshock therapy — and they can all actually worsen outcomes.  Prehospital providers should focus on rapid transport.
• Be cognizant of compartment syndrome, but measure compartments when possible, as some envenomations present similarly but have only subcutaneous hypertension.
• Neurologic effects can be delayed up to 12 hours after coral snake envenomations. Symptoms can include a descending paralysis.
• For diagnostic testing, consider a CBC, coags, fibrinogen level, electrolytes, cpk, creatine, glucose, and urine studies.  All patients with envenomation should be observed for at least 8 hours. Mark the site of envenomation circumferentially to monitor for changes.
• Management of patients with snake bites should be treated with supportive care, pain control, and specific antivenom when indicated.
• FabAV or CroFab is the antivenom of choice for pit viper envenomations. Although FabAV will reduce the duration and severity of symptoms and lab abnormalities, it will not reverse tissue necrosis and may not reverse neurologic effects.
• Be aware of the possibility for a hypersensitivity reaction or serum sickness to FabAV. Treat with steroids, antihistamine, IV fluids, and epinephrine as appropriate.
• Coral snake envenomations can be treated with NACSA, which halts or at least limits the progression of muscle paralysis and shortens the clinical course.  Side effects to NACSA include dermal reaction as the most common — and anaphylaxis as the most severe.
• Patients with bites from exotic snakes should be monitored, likely in the ICU, for up to 24 hours as toxicity from some venom may have a delayed onset of up to 20 hours. You may have to turn to your local zoo for help with anti-venoms here.
• Management of pregnant patients is the same as nonpregnant patients with regards to snake envenomations.
• Dosing of antivenom is based on the amount of venom. Dosing is the same regardless of the age of the patient.
• All patients requiring antivenom or with suspected envenomation should be admitted.  Seek consultation with your regional poison center and local toxicologist

Jeff: So that wraps up the September 2018 episode of Emplify.

Nachi: As always – the address for this month’s credit is ebmedicine.net/E0918, so head over there right away to get your credit.  Remember that the  you heard throughout the episode corresponds to the answers to the CME questions.

Jeff: And don’t forget to grab your free issue of Synthetic Drug Intoxication in Children at ebmedicine.net/drugs specifically for emplify listeners. Feel free to share the link with your colleagues or through social media too. Next month we are talking sepsis and the ever frequently changing guidelines so it’s not something you want to miss.  Talk to you soon

Most Important References

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6. *Bush SP, Ruha AM, Seifert SA, et al. Comparison of F(ab’)2 versus Fab antivenom for pit viper envenomation: a prospec­tive, blinded, multicenter, randomized clinical trial. Clin Toxicol (Phila). 2015;53(1):37-45. (Randomized controlled trial; 121 patients)

7. *Gerardo CJ, Vissoci JR, Brown MW, et al. Coagulation parameters in copperhead compared to other Crotalinae envenomation: secondary analysis of the F(ab’)2 versus Fab antivenom trial. Clin Toxicol (Phila). 2017;55(2):109-114. (Ran­domized controlled trial; 121 patients)

8. *American College of Medical Toxicology, American Acad­emy of Clinical Toxicology, American Association of Poison Control Centers, European Association of Poison Control Centres and Clinical Toxicologists, International Society on Toxinology, Asia Pacific Association of Medical Toxicology. Pressure immobilization after North American Crotalinae snake envenomation. Clin Toxicol (Phila). 2011;49(10):881-882. (Position statement)

10. *Wood A, Schauben J, Thundiyil J, et al. Review of eastern coral snake (Micrurus fulvius fulvius) exposures managed by the Florida Poison Information Center Network: 1998-2010. Clin Toxicol (Phila). 2013;51(8):783-788. (Retrospective; 387 patients)

48. *Cumpston KL. Is there a role for fasciotomy in Crotalinae envenomations in North America? Clin Toxicol (Phila). 2011;49(5):351-365. (Review)

75. *Walker JP, Morrison RL. Current management of copper­head snakebite. J Am Coll Surg. 2011;212(4):470-474. (Retro­spective; 142 patients)

81. *Kitchens C, Eskin T. Fatality in a case of envenomation by Crotalus adamanteus initially successfully treated with polyvalent ovine antivenom followed by recurrence of defibrinogenation syndrome. J Med Toxicol. 2008;4(3):180-183. (Case report)

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Last Updated on January 25, 2023