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Wilderness Drum, Inc.
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Wilderness Emergency Care
Thoughts on Snakebite
Steve Beyer

Pit vipers      Coral snakes      Neotropical snakes

Pit Vipers

There are three genera of the Crotalidae or pit viper family in the United States. The pit vipers include the copperhead, the cottonmouth or water moccasin, and fifteen species of rattlesnakes. They are called pit vipers because they have a pit or depression between the eye and the nostril on each side of the head, which functions as an extremely sensitive infrared heat-detecting organ.

Many pit viper strikes in fact are dry and inject no venom, even when there are fang marks. Part of this may be due to the fact that humans are much bigger – and give off a lot more heat – than the snake's usual prey, and this throws off the timing of the snake's venom delivery. Additionally, Crotalids can differ significantly in the toxicity of their venom, even within a single litter.

Pit viper venom is a complex mixture of enzymes, which varies from species to species, and which is designed to immobilize, kill, and digest the snake's prey. Pit viper strikes on humans are overwhelmingly on the extremities. Crotalid venom works by destroying tissue, and is capable of causing significant, sometimes disfiguring local tissue damage; but deaths in the United States are very rare and limited almost entirely to children and the elderly.

Pit viper envenomation can be excruciatingly painful, and the discomfort can last for several days. The envenomated extremity can also become frighteningly ugly, leading to panic in both the patient and the caretaker. Greater or smaller areas of the extremity can turn blue or black, swell alarmingly, and develop large blood blisters. It is altogether an unpleasant experience.

There is no question that a Crotalid envenomation is a medical emergency requiring urgent evacuation if possible. However, the first step in treatment is to avoid panic. Death is rare; even without evacuation, most cases result in several days of serious misery and then full recovery. Remember that the fatality rate even for untreated pit viper bites is extremely low. The treatment steps are:

• Use the Sawyer Extractor. If you are in snake country, the Extractor should always be within easy reach in your pack. The Extractor can remove as much as 30% of Crotalid venom proteins if applied within three minutes. Use the Extractor as quickly as possible and then keep it on the bite for about thirty minutes. Because of the great suction it creates, no cutting is necessary.
   
• Immobilize the bitten extremity with a splint, just as you would a fracture.
   
• Have the patient rest and keep activity to a minimum.
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• Have the patient drink as much fluid as possible, in frequent small amounts, in order to maintain fluid volume and kidney flow.
   
• Remember that a snakebite is a contaminated puncture wound, and treat it as such.
   
• Get to definitive care as quickly as you can, if at all possible. Otherwise, have the patient rest and drink fluids; keep the wound clean; give lots of encouragement and support.

The following are not recommended for pit viper envenomations:

• Do not make incisions or try to suck out the venom. In wilderness conditions, cutting into an already compromised limb is asking for an infection. You absolutely do not want pit viper venom in your mouth. Conversely, your mouth is full of all kinds of bacteria. And you can't suck as hard as the Extractor can anyway.
   
• Do not use a tourniquet. Tourniquets can result in loss of the limb due to decreased blood flow. In addition, you are just keeping the venom localized where it does the most tissue damage.
   
• Do not use electric shock. It can be dangerous, and has no proven value in managing pit viper bites. It is the great urban legend of wilderness first aid.
   
• Do not use ice. There is no evidence that snake venom enzyme activity diminishes with cold. Freezing already compromised tissue can lead to frostbite, which can damage the limb more than the original bite. Packing in ice has probably resulted in more lost limbs than snakebite itself; this is particularly tragic when limbs have been lost to frostbite because of a non-envenomated bite.
   
• Do not give alcohol. It causes vessels to dilate and may speed venom absorption.

There are two questions regarding the treatment of Crotalid envenomation you should be aware of – the use of antivenom, and the use of use of an elastic bandage pressure wrap.

For many years, the only commercially available antivenom in the United States for pit viper envenomation was Wyeth Laboratories’ Antivenin (Crotalidae) Polyvalent. This antivenom was made with horse serum, and patients were at risk for severe allergic reactions, including anaphylactic shock. However, a new antivenom, Crotalidae Polyvalent Immune Fab (Ovine), marketed by Savage Laboratories as CroFab™, is made with sheep serum; now in its third season of commercial use since FDA approval, CroFab reportedly has fewer adverse reactions than the Wyeth serum, although no clinical studies have been conducted which directly compare the two products.

In an ideal world, anyone envenomated by a pit viper in the wilderness would be immediately evacuated and receive antivenom within four hours – six at the most – in a hospital setting, under sterile conditions, with constant monitoring, and with a crash cart available in case of an allergic reaction. If such an evacuation is possible, then by all means it should be done. Crotalid envenomation is nothing to fool around with.

But should you carry antivenom with you? Bear in mind that both antivenoms must be dissolved in sterile water and then diluted for intravenous administration. The initial dose is four to six vials, and as many as eighteen or twenty vials may be indicated as venom effects progress. You have to know how to set up and maintain an intravenous line under dirty and uncomfortable conditions. Most important, the patient may still have a severe allergic reaction, and you will have no facilities for endotracheal intubation, no oxygen, and probably no epinephrine. In the wilderness context, it seems to me, the risks of contamination, sepsis, and anaphylactic shock – not to mention that you have to hump the whole damn setup in your backpack – create risk-benefit questions that must be carefully considered in consultation with an experienced wilderness physician.

The use of an elastic bandage pressure wrap – recommended for use with bites from Elapidae or coral snakes and described below – has been recommended for use in cases of Crotalid envenomation as well. The argument against its use is that the pressure may actually increase the risk of disfiguring local tissue damage, which may then require skin grafts and extensive repair and treatment; and that removal of the pressure may result in sudden massive swelling and discoloration. The argument in favor of its use is that the spread of venom to vital organs can be life-threatening – in fact, some Crotalid bites can cause serious damage to limbs even when the bites were to a finger or foot – and the use of a pressure bandage can prevent this spread, even at the risk of greater localized damage. The problem is that there is no way of knowing how serious the envenomation is at the outset, when the decision must be made. There is a tradeoff between averting more serious life-threatening damage and increasing the risk of painful and disfiguring local damage. Such a decision should be considered a serious one, to be decided in full consultation with the patient.

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