AAPA: Only One Way to Take the Poison Out of Snakebites

PHILADELPHIA, May 31 -- In the frantic moments after being bitten by a poisonous snake, many people try first aid that does more harm than good, according to an emergency medicine specialist here.

Patients should be cautioned against using the so-called "extractor devices" commonly carried by campers and hikers, said Paul S. Auerbach, M.D., of the Stanford University School of Medicine, told attendees at the American Academy of Physician Assistants meeting.

"No one has ever shown that these are effective first aid," said Dr. Auerbach, who has more than 30 years experience treating snakebites, including a stint on a Montana Indian reservation where rattlesnake bites were common.

The extractor devices are designed to make an incision at the bite site and then suck the venom out of the wound. But, Dr. Auerbach said, recent evidence suggests that the suction probably only keeps the venom localized to the wound site and increases the chance of tissue necrosis there.

In addition, the incision increases the risk of infection and probably worsens any necrosis that occurs, he added.

Another popular first-aid strategy that patients should be advised against is the tourniquet, Dr. Auerbach said. Tourniquets are often applied to a leg or an arm in hopes of stopping the venom from traveling into the core of the body and damaging vital organs.

While tourniquets slow the spread of venom, they vastly increase the chances of local complications and necrosis and loss of the limb, Dr. Auerbach said. Clinicians should tell patients that the risk simply isn't worth it for a treatment that has not been shown to save lives, he added.

Applying ice to the bite or immersing the victim in ice-cold water to slow the spread of venom is another oft-tried method of on-site bite treatment. But these strategies could drive some venom components deeper into tissues and could worsen any ischemia, Dr. Auerbach said. They have even been known to result in frostbite, he said.

So what should patients do after being bitten by a poisonous snake?

"The best first-aid is a cell phone and a set of car keys-you want to get to anti-venom as soon as possible," Dr. Auerbach advised. Clinicians should stress to patients that nothing should delay getting the victim to a medical facility for anti-venom treatment, he said, because that's the only therapy proven to save lives.

Before anti-venom became widely available, the mortality rate from poisonous snakebites in the United States was as high as 35%, and there were about 200 deaths each year, said Dr. Auerbach. Today, he noted, the mortality rate for those treated with anti-venom is about one-quarter of one percent. About 8,000 people are bitten annually, but only 10 to 20 die as a result.

A chief cause of snakebite death is delay in receiving anti-venom. If a victim has received a high dose of snake venom and is not given anti-venom, 4% will die within the hour, 17% within about six hours, and 68% within the next 48 hours, Dr. Auerbach said.

Snake venom contains a mixture of cardiotoxins, neurotoxins, myotoxins, and hemotoxins, and the cause of snakebite death is usually multiple organ failure, Dr. Auerbach said. In the United States, the Mojave rattlesnake and the coral snake have the most potent venom, he said.

Death is also more likely if the venom is injected intravascularly or if the bite is to the head or neck, he said. More than half of all bites are to the feet and legs (68%). Upper extremity bites account for 38%, and the rest are to the head, face, neck and other areas.

In the U.S., venomous snakes can be divided into two groups, Dr. Auerbach said. The pit vipers-which include rattlesnakes, water moccasins, and copperheads-account for 98% of bites. The elapsids, which include coral snakes, account for the rest.

Patients planning a camping trip or outdoor expedition should be told to think ahead about the possibility of poisonous snakebite, urged Dr. Auerbach, and plan for how they would quickly get to the nearest medical facility if bitten.