I learned from a speaker at this years Wilderness Medical Society conference that while we as clinicians mostly know about venom extractors and why they don’t work, this hasn’t trickled down to the lay public unfortunately. All you have to do is look at their ratings on their respective Walmart pages for the Sawyer and Coghlan devices. Even more frightening, there are still some wilderness providers out there that use and recommend these devices.
Seriously though, this is one of those things in medicine that got started because it’s a good idea, made logical sense, had plenty of anecdotal evidence, and one apocryphal article that showed some success. Due to this, it was recommended by many agencies. This success was short-lived, as future research showed that it didn’t actually remove much venom, and might actually cause harm.
Based on the plurality of case reports that were all over the map, Sean Bush (of Venom ER fame), decided to study this using pig models. His was the first RCT looking at outcomes for this device. Because actual snake venom varies by each bite, they used a simulated model by injecting a standardized amount (25mg) of venom. Of note, this was because 50mg resulted in mortality, and as the pigs were used as their own control, they needed a non-lethal dose.
They of course found no difference in local tissue swelling using the extractor, and did have two instances of necrosis in the extractor group. Thus, based on their paper, no benefit, possible harm, so don’t use them.
Bush SP, Hegewald KG, Green SM, Cardwell MD, Hayes WK. Effects of a negative pressure venom extraction device (Extractor) on local tissue injury after artificial rattlesnake envenomation in a porcine model. Wilderness Environ Med. 2000 Fall;11(3):180-8. [PMID 11055564]
This wasn’t enough for many people, as people clearly report seeing fluid in the pump after using it. It had to be doing something, so later a group from UCSF led by Michael Alberts set out to determine what actually is sucked out using the extractor. Deciding that pigs weren’t suitable for this, they instead injected a proteinaceous fluid tagged with radioactive technetium, as they would be able to measure exactly what was removed, and what was left. This was injected using a curved needle into people’s legs.
They of course succeeded in obtaining serosanguinous fluid into the pump. Even with applying the extraction device a scant 3 minutes post injection, as recommended by the instructions, when they put the counter on that fluid, they found it contained a whopping ~0.04% of the total load. Counting what was left in the body found that, on average, most people had ~98% of their venom load still present, with the maximum of 7% in one. Comically, the radioactive counts of the fluid that spontaneously “oozed” from the fluid actually measured higher than that in the extractor, with an average of 0.7%.
Thus, what it removes isn’t venom, it’s interstitial fluid.
Alberts MB, Shalit M, LoGalbo F. Suction for venomous snakebite: a study of “mock venom” extraction in a human model. Ann Emerg Med. 2004 Feb;43(2):181-6. [PMID 14747805]
So really, just don’t do it. Tell everyone you can to get rid of the kit. It doesn’t help, and probably hurts, and will likely delay what medical treatments actually would do anything.
Also, feel free to review any website that sells this device. Write the editors of websites that offer medical advice (see here) and tell them to correct their errors. We have a duty to protect the public, and preventing them from buying harmful devices is included in this.
EBM Gone Wild