A 28-year-old emergency physician is bitten by a diamondback rattlesnake on the right middle finger. He applies a tourniquet and arrives to the hospital approximately four hours after envenomation. On physical examination, the patient is in mild distress because of hand pain. His vital signs were as follows: temperature, 99° F; pulse, 118 and regular; blood pressure 130/75 mm Hg. Pulse oximetry on room air showed 100% saturation but not detected on the injured digit. Respiratory, cardiopulmonary, abdominal and neurological examinations were normal. No lymph node tenderness was present. Extremity exam is normal except for mild swelling of the hand that the finger is noted to be necrotic. (left).
The patient had a white blood count, hemoglobin, fibrinogen and platelet counts were normal.
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Dx: Finger Amputation
This unfortunate patient eventually had to have his finger amputated. He is angry for he feels he “adhered to the ACLS First Aid 2010 Guidelines.” His attending physician feels that a tourniquet led to ischemia and eventually amputation of the finger even though the envenomation was relatively mild. What does the literature say?
Markenson D et al., reported in First Aid Guidelines that following a snakebite one should “apply pressure immobilization bandage between 40 and 70 mm Hg in the upper and 55 mm Hg in the lower extremity around the entire length of the bitten extremity…” Unfortunately, most patients and providers are unable to measure external pressure. Even when providers are taught how to apply proper pressure, only 25% retain the skill three days after training.
The First Aid Guidelines reference a study by Bush et al., that revealed decreased mortality in a swine model. North American rattlesnake envenomations are almost never fatal and the mortality is associated with tissue necrosis and ischemia. Since the main concern with North American rattlesnake envenomation is tissue death, edema, bleeding diathesis and compartment syndrome, a more helpful study would measure these outcomes. Interestingly the application of the pressure immobilization device in the porcine was associated with an increase in compartment pressure, which would exacerbate or predispose to compartment syndrome and tissue necrosis. I believe this recommendation in a swine model has no external validity in the setting of a rattlesnake envenomation.
In Summary:
-Prehospital first aid advice following a rattlesnake envenomation after ABC’s: immobilize and elevate the extremity. Come to the hospital.
-In wilderness medicine, much like other aspects of health, interpretation of animal studies are not always able to be extrapolated to humans beings and should be interpreted with caution.
-Universal adaption of tourniquets in the setting of rattlesnake envenomations is likely to cause more harm than good and is not recommended at this time.
References
- Markenson D, Ferguson JD, Chameides L, et. al. Part 17: First Aid: 2010 American Heart Association and American Red Cross Guidelines for First Aid. Circulation. 2010; 122 (18 Suppl 3):S934-46.
- Bush SP, Green SM, Laack TA, et. al. Pressure immobilization delays mortality and increases intracompartmental pressure after artificial intramuscular rattlesnake envenomation in a porcine model. Ann Emerg Med. 2004; 44:599-604.
- Simpson ID, Tanwar PD, Andrade C, et al. The Ebbinghaus retention curve: training does not increase the ability to apply pressure immobilisation in simulated snake bite--implications for snake bite first aid in the developing world. Trans R Soc Trop Med Hyg. 2008 May;102(5):451-9.
- Norris RL, Ngo J, Nolan K, Hooker G. Physicians and lay people are unable to apply pressure immobilization properly in a simulated snakebite scenario. Wilderness Environ Med. 2005 Spring;16(1):16-21.
- Dr. Frank LoVecchio is the primary investigator on four major NIH Grants. He is an award-winning emergency medicine educator and currently practices emergency medicine in Arizona.