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Charles J. Gerardo, MD, MHS, discusses the clinical examination for severe envenomation after snakebite.
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Charles J. Gerardo, MD, MHS, discusses the clinical examination for severe envenomation after snakebite.
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[ Music ] >> Hello, and welcome to JAMAevidence, our monthly podcast focused on core issues in evidence-based medicine. I'm David Simel, the Editor of the Rational Clinical Examination series, and Professor of Medicine at the Durham Veterans Affairs Medical Center and Duke University.
Today we're discussing the clinical evaluation of patients who have the misfortune of being bitten by a snake. Joining me to talk about this topic is my colleague, Dr. Chuck Gerardo, Chief of Emergency Medicine at Duke University. Well, hello, Chuck. And before we get into the content of your recently published Rational Clinical Examination article, "Does this Patient have a Severe Snake Envenomation?" I'd like a little background.
I expect that most people like me see a snake and our instincts are to immediately run away. You've run towards snakes in your clinical research career. So just how did that happen? >> Well, Dr. Simel, like you, I run away from snakes, too. I only run towards the patients and towards the research. During my training I saw numerous snakebites and some of those patients had severe bites, so that clinical exposure, combined with the opportunity to engage in the research, kind of led me down this path of scholarly work.
>> Well, most people don't think of North Carolina as a place for snakes. Do we have a lot of snakes in our backyards? >> Oh, absolutely. North Carolina is one of the states that consistently has a high number of snakebites per capita, and they're often in the backyard, which is one of the reasons that we have so many bites here. >> Okay. Well, then let's talk about the unfortunate person who has been bitten by a snake, and we'll constrain our discussion to a location in the Americas. What's the chance that they've been severely bitten and will develop real tissue injury?
>> So, we should start with the exclusion of coral snakes, which we did not cover in our article, as well as dry bites. So we're talking about pit vipers and those that have a real envenomation, or venom in the tissue. So their chance of any tissue injury actually approaches 100%. However, the chance of severe tissue injury is about 14%, so not high. >> So the good news then is that more likely than not a person's going to be okay, but if you are that person or that person's companion, what are the circumstances and features of the immediate situation that are going to help you predict the chance of severe envenomation?
>> Well, I think it's important to know that snakebite venom effects can be broadly grouped into a few domains. That includes tissue injury, systemic venom effects, and hematologic venom effects. So a patient can have a severe envenomation, any single venom effect domain, or in any combination. For tissue injury, for example, things like a bite to the digit or a large snake species increase the likelihood of having a severe bite, and that makes sense.
If you think about a bite to the finger or the toe, that's a smaller space, with the same venom load, so that would increase the likelihood that that tissue injury could lead to necrosis or a more severe outcome. And for large snakes within any given species, they tend to have worse bites as well, and that's counter to the prevailing wisdom that these juvenile snakes will lead to worse bites, and in actuality, the larger the snake, the larger amount of venom they can deposit in your tissue, and the worse tissue injury you can have.
If you extend beyond that to severe systemic effects, delays in care, so time from the bite to care of greater than six hours increases the likelihood of a severe bite, as does bite from a large snake, once again. And then also, a young age, so patients less than 12 years old tend to have more severe bites; and that also makes sense because that same amount of venom goes into a smaller volume of distribution in a smaller patient. >> Well, I think some of that leads into my next question, which is if you can get to a hospital, should everyone go for an evaluation?
And the parallel question to that would be are there some features of snakebites that create so low a risk that you can stay in the field or at home? >> Current recommendations are that all venomous snakebites need to be evaluated if the patient has any signs or symptoms, even if those signs or symptoms are mild. Unfortunately, in our work we could not find a single factor that could adequately exclude a severe envenomation, and that was even with starting with the baseline prevalence of severe bites at about 14%.
So it would be impossible to adequately exclude a severe bite based on their initial presentation, so all patients should be seen. >> Well, let's say the snakebite victim is out hiking, but they can get to the hospital. I'm sure you've got some wonderful stories about the snakes that came in with their victim. So should a victim or companion invite the snake to come with them to the emergency room? >> No, they shouldn't. Personally, I was always like to see the snake, but you shouldn't bring in the snake just so I can take a look at it.
It doesn't really impact the medical care, and there's a lot of risk of bringing the snake in. Even when the snake has been killed, they often aren't dead, and even a dead, severed snake head retains its bite reflex, so we've seen quite a number of patients who were bitten by the dead head or the dead snake, or the presumed dead snake that was actually alive. So there's really no need for that. At most, you could get a photo of the snake from a safe distance, and then you won't run into any troubles that way.
>> Safe distance sounds good there. What are the features that tell you right away you've got a serious snakebite victim when you're in the emergency room? >> If they already have any of the outcome that defines severe envenomation from the beginning, such as hemodynamic or respiratory instability, any bleeding that's remote to the site or significant bleeding into the local tissue, or any early signs of severe tissue injury, those bad outcomes, if they're already present on presentation, of course, are a bad sign.
And then, of course, any combination of the factors that we discussed earlier that increase the likelihood of severe bites. For example, if you had a symptomatic young child less than 12 years old that was bitten on the finger by a large snake, and had an anticipated delay in care or there was a delay in care before presenting to the emergency department, those would all be signs that the patient was at risk of having a severe bite. >> Okay. Well, suppose your triage nurse calls you and they tell you they've got a patient in triage who's been bitten by the dead snake they have in a bag, and the patient looks okay, but the snake is quite dead.
So aside from your general emergency assessment, what are the most useful clinical features and what lab tests do you send? >> Even perceived dry bites can develop symptoms and progress. The current recommendations are to observe for a minimum of eight hours, so even an asymptomatic patient should be observed. On examination you should look at the vital signs, looking for signs of systemic toxicity. You should also evaluate the extent of the local tissue injury, and then evaluate if there's any bleeding remote from the site.
In addition to that kind of history and physical exam evaluation, there are some labs that you should get. Most importantly, you should get platelets and fibrinogen levels. They are important to assess the coagulation status of the patient at the time of evaluation, but they also, when abnormal, increase the likelihood of having a severe envenomation. PT and PTT are also important to assess their degree of coagulopathy, but based on the evidence that we found in our study, they couldn't be demonstrated to be very predictive of a severe envenomation down the road.
>> While you're observing them for the eight hours, do you repeat any labs or give them any medication? >> Yeah. I think if they're having pain, you should treat the symptoms, you should address tetanus. There's no need for prophylactic antibiotics. You should elevate the extremity. And often, they will be receiving anti-venom or another therapy, even if the symptoms are mild or moderate and not severe yet. But as far as the dry bites, you really just repeat the physical exam, if the initial laboratory tests are totally normal and your exam and history is totally normal.
You just watch for any derangement in that area. >> Most of our listeners are not going to have your expertise or a facility where frequent snakebites are handled. Is there a central place they call for information to get advice when they have a snakebite victim? >> A great place to look for additional expertise when caring for a patient with a snakebite is the local Poison Center and the practitioner can simply call 1-800-222-1222 to get expert assistance in the management of their snakebite.
>> And that's good anywhere in the United States, Chuck? >> Yes. In addition to that, often there'll be a person locally who has expertise in envenomation and often you can contact that person. Sometimes it will require a referral to a higher level of care, depending upon the ability of the local institution to care for the patient. >> Well, thanks, Chuck. Now is your chance to tell our listeners anything else you'd like them to know should they themselves get bitten by a snake or their role in evaluating a snakebite victim.
>> So I think it's important to know that most snakebites can actually be avoided by some simple measures, such as not handling wild snakes, but also clearing out wood or debris piles at the home and then using appropriate clothing, such as boots or gloves, pants, when doing any activity that puts someone at risk for a snakebite. If you are unfortunate enough to be bitten, then patients should seek medical care immediately, and most patients who receive care rapidly will do well.
>> Thank you very much for talking to us today. More information about this topic is available in the Rational Clinical Exam, and on our website, JAMAevidence.com, where you can listen to our entire roster of podcasts. I'm David Simel and I'll be back with you soon for another edition of JAMAevidence. [ Music ]
Segment:0 .
[ Music ] >> Hello, and welcome to JAMAevidence, our monthly podcast focused on core issues in evidence-based medicine. I'm David Simel, the Editor of the Rational Clinical Examination series, and Professor of Medicine at the Durham Veterans Affairs Medical Center and Duke University.
Today we're discussing the clinical evaluation of patients who have the misfortune of being bitten by a snake. Joining me to talk about this topic is my colleague, Dr. Chuck Gerardo, Chief of Emergency Medicine at Duke University. Well, hello, Chuck. And before we get into the content of your recently published Rational Clinical Examination article, "Does this Patient have a Severe Snake Envenomation?" I'd like a little background.
I expect that most people like me see a snake and our instincts are to immediately run away. You've run towards snakes in your clinical research career. So just how did that happen? >> Well, Dr. Simel, like you, I run away from snakes, too. I only run towards the patients and towards the research. During my training I saw numerous snakebites and some of those patients had severe bites, so that clinical exposure, combined with the opportunity to engage in the research, kind of led me down this path of scholarly work.
>> Well, most people don't think of North Carolina as a place for snakes. Do we have a lot of snakes in our backyards? >> Oh, absolutely. North Carolina is one of the states that consistently has a high number of snakebites per capita, and they're often in the backyard, which is one of the reasons that we have so many bites here. >> Okay. Well, then let's talk about the unfortunate person who has been bitten by a snake, and we'll constrain our discussion to a location in the Americas. What's the chance that they've been severely bitten and will develop real tissue injury?
>> So, we should start with the exclusion of coral snakes, which we did not cover in our article, as well as dry bites. So we're talking about pit vipers and those that have a real envenomation, or venom in the tissue. So their chance of any tissue injury actually approaches 100%. However, the chance of severe tissue injury is about 14%, so not high. >> So the good news then is that more likely than not a person's going to be okay, but if you are that person or that person's companion, what are the circumstances and features of the immediate situation that are going to help you predict the chance of severe envenomation?
>> Well, I think it's important to know that snakebite venom effects can be broadly grouped into a few domains. That includes tissue injury, systemic venom effects, and hematologic venom effects. So a patient can have a severe envenomation, any single venom effect domain, or in any combination. For tissue injury, for example, things like a bite to the digit or a large snake species increase the likelihood of having a severe bite, and that makes sense.
If you think about a bite to the finger or the toe, that's a smaller space, with the same venom load, so that would increase the likelihood that that tissue injury could lead to necrosis or a more severe outcome. And for large snakes within any given species, they tend to have worse bites as well, and that's counter to the prevailing wisdom that these juvenile snakes will lead to worse bites, and in actuality, the larger the snake, the larger amount of venom they can deposit in your tissue, and the worse tissue injury you can have.
If you extend beyond that to severe systemic effects, delays in care, so time from the bite to care of greater than six hours increases the likelihood of a severe bite, as does bite from a large snake, once again. And then also, a young age, so patients less than 12 years old tend to have more severe bites; and that also makes sense because that same amount of venom goes into a smaller volume of distribution in a smaller patient. >> Well, I think some of that leads into my next question, which is if you can get to a hospital, should everyone go for an evaluation?
And the parallel question to that would be are there some features of snakebites that create so low a risk that you can stay in the field or at home? >> Current recommendations are that all venomous snakebites need to be evaluated if the patient has any signs or symptoms, even if those signs or symptoms are mild. Unfortunately, in our work we could not find a single factor that could adequately exclude a severe envenomation, and that was even with starting with the baseline prevalence of severe bites at about 14%.
So it would be impossible to adequately exclude a severe bite based on their initial presentation, so all patients should be seen. >> Well, let's say the snakebite victim is out hiking, but they can get to the hospital. I'm sure you've got some wonderful stories about the snakes that came in with their victim. So should a victim or companion invite the snake to come with them to the emergency room? >> No, they shouldn't. Personally, I was always like to see the snake, but you shouldn't bring in the snake just so I can take a look at it.
It doesn't really impact the medical care, and there's a lot of risk of bringing the snake in. Even when the snake has been killed, they often aren't dead, and even a dead, severed snake head retains its bite reflex, so we've seen quite a number of patients who were bitten by the dead head or the dead snake, or the presumed dead snake that was actually alive. So there's really no need for that. At most, you could get a photo of the snake from a safe distance, and then you won't run into any troubles that way.
>> Safe distance sounds good there. What are the features that tell you right away you've got a serious snakebite victim when you're in the emergency room? >> If they already have any of the outcome that defines severe envenomation from the beginning, such as hemodynamic or respiratory instability, any bleeding that's remote to the site or significant bleeding into the local tissue, or any early signs of severe tissue injury, those bad outcomes, if they're already present on presentation, of course, are a bad sign.
And then, of course, any combination of the factors that we discussed earlier that increase the likelihood of severe bites. For example, if you had a symptomatic young child less than 12 years old that was bitten on the finger by a large snake, and had an anticipated delay in care or there was a delay in care before presenting to the emergency department, those would all be signs that the patient was at risk of having a severe bite. >> Okay. Well, suppose your triage nurse calls you and they tell you they've got a patient in triage who's been bitten by the dead snake they have in a bag, and the patient looks okay, but the snake is quite dead.
So aside from your general emergency assessment, what are the most useful clinical features and what lab tests do you send? >> Even perceived dry bites can develop symptoms and progress. The current recommendations are to observe for a minimum of eight hours, so even an asymptomatic patient should be observed. On examination you should look at the vital signs, looking for signs of systemic toxicity. You should also evaluate the extent of the local tissue injury, and then evaluate if there's any bleeding remote from the site.
In addition to that kind of history and physical exam evaluation, there are some labs that you should get. Most importantly, you should get platelets and fibrinogen levels. They are important to assess the coagulation status of the patient at the time of evaluation, but they also, when abnormal, increase the likelihood of having a severe envenomation. PT and PTT are also important to assess their degree of coagulopathy, but based on the evidence that we found in our study, they couldn't be demonstrated to be very predictive of a severe envenomation down the road.
>> While you're observing them for the eight hours, do you repeat any labs or give them any medication? >> Yeah. I think if they're having pain, you should treat the symptoms, you should address tetanus. There's no need for prophylactic antibiotics. You should elevate the extremity. And often, they will be receiving anti-venom or another therapy, even if the symptoms are mild or moderate and not severe yet. But as far as the dry bites, you really just repeat the physical exam, if the initial laboratory tests are totally normal and your exam and history is totally normal.
You just watch for any derangement in that area. >> Most of our listeners are not going to have your expertise or a facility where frequent snakebites are handled. Is there a central place they call for information to get advice when they have a snakebite victim? >> A great place to look for additional expertise when caring for a patient with a snakebite is the local Poison Center and the practitioner can simply call 1-800-222-1222 to get expert assistance in the management of their snakebite.
>> And that's good anywhere in the United States, Chuck? >> Yes. In addition to that, often there'll be a person locally who has expertise in envenomation and often you can contact that person. Sometimes it will require a referral to a higher level of care, depending upon the ability of the local institution to care for the patient. >> Well, thanks, Chuck. Now is your chance to tell our listeners anything else you'd like them to know should they themselves get bitten by a snake or their role in evaluating a snakebite victim.
>> So I think it's important to know that most snakebites can actually be avoided by some simple measures, such as not handling wild snakes, but also clearing out wood or debris piles at the home and then using appropriate clothing, such as boots or gloves, pants, when doing any activity that puts someone at risk for a snakebite. If you are unfortunate enough to be bitten, then patients should seek medical care immediately, and most patients who receive care rapidly will do well.
>> Thank you very much for talking to us today. More information about this topic is available in the Rational Clinical Exam, and on our website, JAMAevidence.com, where you can listen to our entire roster of podcasts. I'm David Simel and I'll be back with you soon for another edition of JAMAevidence. [ Music ]
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