Reprieve for snakebite victims
When a poisonous snake’s fangs sink into someone, the victim needs anti-venom treatment as soon as possible. The snake toxin travels from the bite’s location to the lymphatic system and then to the bloodstream, where it can, for example, cause respiratory failure and death. It might buy time when you put pressure on the bite with a bandage, slowing the venom’s journey through the body. But there is bitter disagreement among snakebite experts about whether pressure bandages help or harm.
A team of researchers at John Hunter Hospital, the University of Newcastle, and the Royal Brisbane and Women’s Hospital in Australia has tested a gel that slows the voyage of venom in a snakebite victim’s body. The gel could also heighten the effects of pressure bandages, increasing the need for consensus on this type of snakebite treatment.
Publishing their findings in the July issue of Nature Medicine, the scientists tested a commercially available gel on 15 male and female volunteers. Instead of using real snake venom on their subjects, they used a stand-in for the venom. The non-toxic substance travels just like venom from the point of injection to the lymph nodes.
The team injected the substance into the feet of their volunteers, tracking in each case the time the molecule took to travel from foot to groin lymph nodes. To be able to compare results, they smeared the ointment on the injection sites of some, but not all of their test subjects.
The gel led to a “marked slowing” of the molecule’s transit from simulated bite site to the lymph nodes. Without the ointment, the venom substitute took between 4 to 81 minutes. With the ointment it took between 6.5 to 162 minutes for it to go from foot to lymph nodes. The tested individuals show a wide range of transit times, an aspect on which the scientists do not comment in their paper.
The team also performed animal experiments using a venom replacement on the hind legs of anesthetized rats. In these cases, adding the gel increased transit time to the lymph nodes three-fold.
The gel, normally used to treat hemorrhoids, releases nitric oxide (NO), which is a chemical that is also a signaling molecule in the body. The scientists believe that NO-release brakes the spread of venom after a snake bite by stopping smooth muscle contractions that are a part of the body’s lymphatic pump. These contractions push the toxin onward in the body. The authors write that delaying venom transportation also lowers venom effects because it lowers the peak venom concentration in blood.
The scientists also applied real venom, from the Eastern Brown snake, on anesthetized rats. The Eastern Brown snake has “extremely potent venom” and causes more snakebites in Australia than any other, according to a snake site at the University of Sydney.
The researchers found that the gel “significantly” increased the lymph transit time by 6 minutes and staved off respiratory system collapse by around half an hour. As the results sicker through the scientific community, it is sure to stir up plenty of disagreement about pressure bandages.
Speed is the first priority with snakebites. The University of Sydney site has the tale of Theodore the dog who died after being bitten by the Eastern Brown snake. His owner is upset to not have recognized the symptoms quick enough. The symptoms include vomiting green bile, frothing at the mouth, swollen gums, and rapid heartbeat.
Pressure bandages must be placed skillfully to work well. The University of Melbourne’s department of pharmacology website has an explanation and illustration.
Here is a Youtube video of someone bandaging a cat’s leg to illustrate a firm bandage. (I do not think the kittie has been hurt, it is just calm enough to be a bandage show-kitty.)
Some bites are unlike others
The World Health Organization’s Regional Office for South-East Asia also mentions pressure bandages on its site about snakebites in Southeast Asia. It states that pressure immobilization is “recommended for bites by neurotoxic elapid snakes, including sea snakes but should not be used for viper bites because of the danger of increasing the local effects of the necrotic venom.” For those kinds of bites, a local compression pad is better, according to the site.
New York Search and Rescue, a private group that works in search and rescue missions, highlights the difference of opinion about pressure bandages for snakebites by the elapid snakes such as cobras, mambas and many Australian species. According to the site, pressure bandaging is a method that “remains controversial in the U.S,” and the authors note it can increase the risk of local tissue damage, which can be disfiguring and require rehabilitation or plastic surgery.
The authors of the Nature Medicine paper point out that pressure bandaging is recommended in Australia but not in other countries. According to the researchers, while pressure bandages may risk increasing damage to local tissue, they believe these bandages “need to be considered for use against a wider range of snakes.”
One drawback of the pressure bandage is that when a victim moves, the bandage loses its effect at hindering venom movement. The University of Melbourne’s site explicitly states that it is “very important to keep the bitten limb still.”
Although the Nature Medicine study does not end the debate, it adds a new perspective to the pressure bandage discussion. When ointment is applied, venom movement is slowed even if the victim moves.
The scientists write that their NO-ointment approach offers a new type of snakebite first aid and could be used in combination with the pressure bandage. Foes of the pressure bandage will not agree, but the ointment might offer common ground for both sides.
References and links: Saul, Megan et. al. A pharmacological approach to first aid treatment for snakebite. Nature Medicine (17) 7, p. 809-811. DOI: http://dx.doi.org/10.1038/nm.2382
Image: Peter Woodard, photographer.
Posted on October 10, 2011, in First aid, Medicine, Snakes and tagged John Hunter Hospital, nitric oxide, Royal Brisbane and Women’s Hospital, snakebites, snakes, University of Newcastle. Bookmark the permalink. 4 Comments.