EMERGENCIES
August 11, 2010

Snakebite! What to Do If You're Bitten and How Treatments Work

Thomas C. Arnold, M.D., and Robert A. Barish, M.D., M.B.A.
Snake bites are rare, but some bites are lethal. Know what to look for and do -- and how to avoid bites completely.
Dr. Arnold is Professor and Chairman, Department of Emergency Medicine, and Dr. Barish is Chancellor, the LSU Health Sciences Center, Shreveport, LA.

Now that summer is in full swing, many of us have vacation on the brain. For some people, this may mean traveling to new places, hiking, camping, and enjoying the scenery. But sometimes lurking in these exotic (or not so exotic) environments is a sneaky little critter: the snake. Though their bites are often not deadly – or even dangerous – some bites can be lethal.

We’ve all seen the Hollywood version of snakebite rescue, in which one person furiously sucks the venom out of the leg of the quickly fading victim. But this is absolutely the wrong thing to do. Though snake bites are fairly rare in this country, they do occur, so it’s a good idea to know a little bit about the different kinds of poisonous snakes and what to do if you or someone you’re with is bitten.

We’ve all seen the Hollywood version of snakebite rescue, in which one person furiously sucks the venom out of the leg of the quickly fading victim. But this is absolutely the wrong thing to do.

It is estimated that five million people worldwide are bitten by snakes every year. Of these, as many as 125,000 bites are fatal. However, in the United States, only 7,000 to 8,000 people are bitten by venomous snakes each year, and here are even better odds: only five to six of those bites lead to death. Throughout the world, most bites are associated with farming and food production. Not surprisingly, most bites in the United States are the result of intentional contact with a snake, whether captive (pet snakes) or in the wild.

Snake bites can be frightening events, and tend to evoke strong emotions both in the victim and the doctor who is treating him or her. In recent years, there have been many advances in the techniques that hospitals use to treat snake bites, particularly in antivenom methods, and the snakebite is now recognized as a tropical disease worldwide.

The North American pit vipers include the well-known rattlesnake, as well as the cottonmouth, and copperhead. All of these snakes have hollow fangs; slit-like pupils; and a heat-seeking “pit” between each eye and nostril.

While many doctors are becoming more familiar with how to treat snakebite emergencies, it’s also a good idea for all of us to have a working knowledge of which snakes are poisonous, what happens in the body when one is bitten, and what kinds of treatment options, including antivenoms, are available these days.

Which Snakes Are Poisonous?

Pit vipers (from the Crotalinae subfamily) and coral snakes (Elapidae family),are the only poisonous snakes native to North America. There are many other types of poisonous snakes, however, that now live on the continent because they have been imported. Mostly these importers are collectors and zoos, but obviously not all snakes come here in legitimate trade. When exotic snakes such as cobras and vipers are brought over illegally it is particularly dangerous because antivenoms may be difficult – or impossible – to obtain.

The North American pit vipers include the well-known rattlesnake, as well as the cottonmouth, and copperhead. All of these snakes have hollow fangs; slit-like pupils; and a heat-seeking “pit” between each eye and nostril. They also have different scale patterns from non-poisonous snakes. Since most people aren’t going to be able to bring the snake that bit them to the hospital with them, it’s important for doctors to know what kinds of snakes are in their area.

In contrast to the pit viper, the coral snake has grooved teeth instead of hollow fangs, round pupils, and no heat-seeking pit.

Why Venom is Dangerous

Snake venoms are made up of various types of proteins that work in different ways throughout the body. The North American pit vipers’ venom damages the lining of blood vessels and lymphatic system (which includes the lymph nodes, spleen, and bone marrow). But venom varies quite a lot among species. And even within a species, venom can be very different depending on where the snake is located geographically, how old the snake is, what season of the year it is, and other factors like genes.

When the walls of red blood cells break down, a critical cascade of events occur throughout the body, particularly in the cardiovascular system. Ultimately the situation, if left untreated, could be fatal.

Almost every type of organ in the snake bite victim is affected by some component of the venom. Though some venoms can be categorized as mainly effecting the heart, nervous system, muscle, etc., it’s not terribly accurate to say that a particular venom falls into just one of these categories because there is so much overlap.

For example, the venom of the pit vipers presents a particularly grim situation. Their venom makes the walls of body’s blood vessels permeable, or leaky, so that red blood cells and other particles leach out where they shouldn’t. This usually begins in the tissues around the bite itself, but then spreads further to the body’s organs, affecting the lungs, heart, kidneys, and nervous system. Clearly this is not a good situation. When the walls of red blood cells break down, a critical cascade of events occur throughout the body, particularly in the cardiovascular system. Ultimately the situation, if left untreated, could be fatal. This is why it’s so important to get medical help as soon as the bite occurs, so that one may have the best odds of preventing tissue damage before it becomes severe.

Immediately After A Bite
In case you were wondering, yes, there is a certain amount of pain involved in a poisonous snake bite. Pain from the bite of a pit viper is almost immediate and is often described as an intense stinging sensation or a blow from a hammer. Up to 25% of pit viper bites are “dry” (no appreciable venom is injected into the victim). The effects of venom vary depending on the specific situation, and can range from minimal to severe. The effects can remain local, spread throughout the body and/or present themselves as problems with the way the blood clots (which are dubbed “coagulation abnormalities”; see Table 1).



Table 1
Guidelines for Determining the Severity of North American Pit Viper Bites
Type of Signs or Symptoms Severity of Envenomation
Minimal Moderate Severe
Local Swelling, skin reddening, and/or bruising confined to the bite site Evidence of progression of swelling, skin reddening and/or bruising beyond the bite site Rapid swelling, skin reddening and/or bruising involving the entire extremity
Systemic No bodily signs or symptoms Non-life-threatening signs/symptoms nausea, vomiting, lack of sensation around eyes; mild hypotension (low blood pressure) Markedly severe signs/symptoms systolic blood pressure (upper number) <80 mm Hg, quivering eyelids;
fast heart rate, respiratory distress
Coagulation No coagulation abnormalities or other important laboratory abnormalities Mildly abnormal coagulation profile without clinically significant bleeding; mild abnormalities in other laboratory tests Markedly abnormal coagulation profile with evidence of bleeding or threat of spontaneous hemorrhage;
results of laboratory tests may be severely abnormal

The ultimate grade of severity of any snakebite is determined on the basis of the most severe sign, symptom, or laboratory abnormality (for example, systolic blood pressure <70 mm Hg in the absence of local swelling should be graded as a severe envenomation).

SBP, systolic blood pressure; INR, international normalized ratio; APTT, activated partial thromoboplastin time.

From Gold BS, Dart RC, Barish RA. Bites of venomous snakes. N Engl J Med 2002; 347(5):347-356. Copyright © 2002 Massachusetts Medical Society. All rights reserved.

It is usually possible for the snakebite victim and the doctor to see the fang marks on the victim’s skin: usually they look like puncture wounds, but can also appear as scratches. Continued oozing of blood from the fang marks is usually good evidence that a snake bite has taken place and that the problems with blood coagulation mentioned above are beginning to occur around the bite mark. Venom spreads from the bite to other organs through the lymphatic system. Doctors can measure this “lymphatic spread” and use it to track how severe the bite is. Some of the other signs that a doctor will look for are bruising and tender lymph nodes around the area. Signs that the effects have spread include a patient feeling very fatigued, having low blood pressure, a racing heart, and having trouble breathing.

Treating Snakebite Before and At the Hospital

What Should You Do Before You Get to the Hospital?
If you or someone you’re with has been bitten, it’s important to get away from the snake as soon as possible so that it does not bite again. Don’t try to capture the snake to help officials identify it: not only is this not necessary, but it can often lead to more bite wounds or more victims.It is important to try to stay as calm as possible while making arrangements to get to medical help.

Outdated first-aid measures like we’ve seen in old movies, such as incision and suction, applying a tourniquet, immersing the bite area in ice, or electric shock, have all been shown to be of no value and obviously they can be quite dangerous.

Although no science exists to confirm this, it makes sense to keep the body part that has been bitten in a neutral position or just slightly below the level of the heart. Any constricting clothing or jewelry should be removed immediately to prevent swelling (edema) from developing.

Outdated first-aid measures like we’ve seen in old movies, such as incision and suction, applying a tourniquet, immersing the bite area in ice, or electric shock, have all been shown to be of no value and obviously they can be quite dangerous. So please abandon all thoughts of using one of these measures, even in the heat of the moment. First responders or EMTs will focus on supporting the victim’s airway, breathing, and circulation (the “ABC”s of first aid), and putting in an IV catheter while transporting the patient to a treatment facility as quickly as possible.

What Happens in the ER
The two main goals in treatment of snakebite victims are the ABCs of first aid and quick administration of antivenom when it is needed.

The attending doctor will ask for a brief history of the patient, but it will be focused on the specifics of the bite, a description of the snake, and the patient's medical conditions and allergies, particularly those to horse or sheep products because these animals are used in the production of the antivenoms. The doctor will inspect the wound closely for evidence of fang marks, swelling, and bruising.

It is common for doctors to measure the swelling around the wound and track how fast it progresses – this can serve as a guide for administering antivenom.12 Blood is usually drawn to get a baseline of certain measures like platelets as well as complete blood count (CBC) and other tests, depending on the severity of the bite and any other existing health issues the patient may have.

If a pit viper bite is suspected, the patient will probably be observed for at least 8 hours before discharge, since a delayed reaction to the snakebite venom is possible.

The doctor will make the decision to treat a patient with antivenom after carefully considering all the issues involved, like the species of snake (if known), how quickly the swelling from the bite site is progressing, and any problems with coagulation. The doctor may also consult with a toxicologist or someone from the local Poison Center, to discuss the appropriate dosage for the antivenom.

Coral snake bites will not produce the same kind of local tissue effects that are seen with the pit vipers.But with coral snake bites, there may be neurological or respiratory symptoms that don’t begin until hours later. For this reason, patients who are thought to have been bitten by a coral snake but who are not showing any symptoms will still be admitted to the hospital and closely monitored for 12 hours (antivenom will be readily available should it be needed).

Patients who are known to have been bitten by a coral snake are treated immediately with antivenom, since the outcome is much better when this is done as early as possible.

What is Antivenom and How Is It Administered?
The antivenom approved for the North American pit viper is called CroFab. It is made by immunizing sheep with venom from four different species of pit vipers, and collecting the antibodies the sheep produce to use in the antivenom

Doses of the antivenom are given in increments until the doctor can determine how much is needed to stop the symptoms from progressing.

CroFab is being used more readily today, which is a good thing for the snakebite victim. In the past there was some concern that severe allergic reactions might develop in patients who received it, but recently doctors have gotten much more familiar with it, and as its safety has been demonstrated over time, they have felt more comfortable using it.

There are two parts to antivenom treatment. First, doctors typically give a series of doses of the antivenom to treat the patient (this is termed “initial control”). The goal of the initial control is to stop symptoms from progressing: this includes local, systemic, and blood coagulation problems. Doses of the antivenom are given in increments until the doctor can determine how much is needed to stop the symptoms from progressing.

The amount of antivenom needed will be determined, in part, by the type of snake bite (e.g., rattlesnake or non-rattlesnake). After the initial control is complete, the second part of the treatment involves “scheduled maintenance” doses , which are given for about 18 hours to maintain a certain amount of the antivenom in the patient’s body.

For coral snake bites, another type of antivenom is used (Wyeth Antivenin®), which, if you were wondering, is derived from horses rather than sheep. However, plans to discontinue the product are now in effect, which is unfortunate since it was the only FDA-approved antivenom for coral snake bites. The final production batch will expire on October 31, 2010. At the time of this article, the FDA was still grappling with how to proceed in light of the potential catastrophe that could occur once coral snake antivenom is no longer available in the U.S. A coral snake antivenom available in Mexico has been shown to be effective against the North American species but, since few people in the United States are bitten by coral snakes each year (roughly 100), a clinical trial of the product would be very difficult (and financially impractical) to carry out at this stage of the game.

The Best Solution: Avoiding Bites

Though there are many fewer snake bites in the United States than there are in other parts of the world, snakebite remains a potentially serious problem if you are bitten. There are some easy steps you can take to lessen your chances of being bitten. First, never handle a snake even if you think it is dead. Reflexes in the snake are active long after death that could result in a bite. Secondly, be aware of your surroundings while outdoors and never reach into a hole or step over logs and rocks without looking first. And lastly, always wear protective foot and leg coverings when venturing into snake territory.

never handle a snake even if you think it is dead. Reflexes in the snake are active long after death that could result in a bite.

If you live in or plan to travel to the parts of the country where snake bites are more common, it’s a good idea to be aware of how to handle it if it does occur. Doctors should be up-to-date on the best methods for treatment, as well as the new developments in antivenom as they come about. Antivenom is clearly the best treatment option for poisonous bites. As even safer antivenoms are developed in the future, it is possible that deaths from snake bites in the U.S. could be eliminated completely if patients receive prompt medical attention. In the meantime, try to steer clear of any snakes that you even think may be poisonous, because not being bitten is still the best way to go!

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