Rattlesnake Envenomation: Tourniquet or Not?
ABSTRACT & COMMENTARY
Source: Amaral CF, et al. Tourniquet ineffectiveness to reduce the severity of envenomating after Crotalus durissus snake bite in Belo Horizonte, Minas Gerais, Brazil. Toxicon 1998;36:805-808.
A recent article attempted to compare the outcomes of patients who applied tourniquets prior to antivenom therapy with those who received antivenom alone. All patients were envenomated by Crotalus durissus (the neotropical rattlesnake), which has both neurologic and tissue toxic effects. The 45 patients who applied tourniquets were similar to the 52 who did not with regard to age, sex, time since bite, and degree of early neurologic findings. In addition, the two groups had rates of coagulopathy, rhabdomyolysis, and fatality that were not statistically different.
Comment by Robert Hoffman, MD
Despite common beliefs, fatalities following envenomation by North American pit vipers are quite uncommon. This probably results from several factors including the predominant tissue toxicity of the snake venom, the easy accessibility of health care, and the proven benefits of antivenom. Although fatalities are rare, life-threatening, systemic symptoms such as coagulopathy and shock do occur, and the envenomated patient has no way of knowing whether he or she will develop these symptoms prior to obtaining definitive health care. Thus, the search for simple, safe, and effective first aid measures continues.
Arterial or venous tourniquets, or lymphatic constrictors seem sensible in that venom will remain concentrated in that extremity, thereby preventing systemic toxicity. In fact, when primarily dealing with neurotoxic snakes (such as cobras), constricting bandages of varying degrees have been shown to limit weakness and respiratory arrest.1,2 Unfortunately, when released, systemic symptoms often rapidly develop. However, when envenomated by a snake with primarily local effects, the debate becomes one of sacrificing a limb or exacerbating local toxicity in order to prevent systemic effects. Under those circumstances, the ischemic damage produced by the tourniquet may be worse than those expected from the original snake bite.3 Although selection bias (why some people applied tourniquets and others did not) prevents any firm conclusions from this study, it appears that tourniquets offer little advantage. For the present time, and especially with North American rattlesnakes, it seems unlikely that application of a tourniquet will significantly improve outcome; it may potentially exacerbate local toxicity. If traveling abroad, or if bitten many hours from health care, a loose-fitting lymphatic constriction bandage may be reasonable. Venous and arterial occlusion are never advisable. If you receive a patient who has a tourniquet applied, it is essential to have antivenom and resuscitation equipment ready prior to releasing the tourniquet.
References
1. Pearn J, et al. First-aid for snake bite: Efficacy of a constrictive bandage with limb immobilization in the management of human envenomation. Med J Aust 1981;2:293-295.
2. Watt G, et al. Tourniquet application after cobra bite: Delay in the onset of neurotoxicity and the dangers of sudden release. Am J Trop Med Hyg 1988;38:618-622.
3. Trevett AJ, et al. Tourniquet injury in a Papuan snakebite victim. Trop Geogr Med 1993;45:305-307.
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