EMReports | Rattlesnake Bites and Systemic Hypotension

Rattlesnake Bites and Systemic Hypotension

Larry Mellick, MD, MS, FAAP, FACEP
Professor of Emergency Medicine
Medical College of Georgia

Pearl: Rattlesnakes bites can rapidly cause hypotension from the systemic effects of the venom. Management of the hypotension benefits from understanding the potential mechanisms.

HPI: The emergency communications center received a request for EMS medical direction for a patient who had sustained a rattlesnake bite to the chest. The paramedic reported that their patient was a 25-year-old male who was combative, hypotensive (80s systolic), and tachycardic (160s). The patient had been bitten in the chest by a large diamond back rattlesnake that he had recently found in the woods and was keeping as a pet. Assuming that this rapid deterioration could be an anaphylactic response to the venom, the EMS crew was instructed to give intravenous epinephrine and 50 mg of diphenhydramine. The ambulance was delayed by a train for 15-20 minutes and, on arrival, the patient continued to be hypotensive and have a heart rate in the 160s. On his right upper chest was an area of ecchymosis, and blood was oozing from two fang marks. The rattlesnake was estimated to be at least five feet in length, and the fang marks were measured at 3 cm apart. The patient's skin was dusky and mottled. The combative patient was intubated with an endotracheal tube, and central venous and arterial lines were placed. The patient briefly underwent chest compressions when his blood pressure was briefly unattainable. An infusion of 4 vials of CroFab® [Crotalidae Polyvalent Immune Fab (Ovine)] was started, 125 mg of solumedrol and 300 mg of cimetidine were administered, and 5-6 liters of normal saline were rapidly infused. The patient's first arterial blood gas showed a pH of 7.03, PCO2 52, PO₂ 619, and HCO₃ 15. The protime (PT) was 19.1, the APTT was 57, and his INR was 2.2. His blood alcohol level (ETOH) level was 176. At approximately an hour of the start of the CroFab, the patient's skin became pink, the vital signs stabilized to a normal heart rate, and his blood pressure was 138/77. The patient was admitted to the trauma service where additional doses of CroFab were administered. After being intubated for several days, he was subsequently discharged from the hospital with no apparent long-term sequelae.

Four months later, this same patient returned to the emergency department in a combative, intoxicated state, and the pet rattlesnake was again a central player. This time the snake was dead, and the patient was threatening suicide. The lifeless rattlesnake had bite wounds on the head and tail. (See Figure 1.) Examination of the patient demonstrated no evidence that he had been bitten by the snake. He was admitted to the psychiatry service.

Discussion: Hypotension that occurs rapidly after a rattlesnake bite is uncommon. A significant number of bites have no evidence of envenomation (25%) or are "dry" bites, and the majority of rattlesnake bites are local reactions. A smaller percentage, however, demonstrate systemic signs and symptoms. Terror or extreme fear is a very common reaction to a snake bite. Subsequently, nausea, vomiting, diarrhea, syncope, tachycardia, and cold, clammy skin can result. These autonomic reactions related to terror must be differentiated from systemic manifestations of envenomation.^1,2 Besides fainting, early collapse may be due to cardiac toxins or anaphylactic or anaphylactoid reactions. Most commonly, the etiology is not anaphylactic, but this should also be a consideration.^3,4,5 Rattlesnake venom is also thought to increase the permeability of the capillary membranes, resulting in pooling of blood and fluids in the microcirculation. This contributes to hypovolemic shock and lactic acidosis.¹ Finally, there is some evidence that the observed hypotension and cardiovascular collapse are due to impaired left ventricular filling rather than myocardial depression or cardiac arrhythmias.⁶

References:

Gold BS, Dart RC, Barish R. Bites of Venomous Snakes. N Engl J Med. 2002; 347(5):347-56.
Norris RL, Wilkerson JA, Feldman J. Syncope, massive aspiration, and sudden death following rattlesnake bite. Wilderness Environ Med. 2007 Fall;18(3):206-8.
Tanen DA, Ruha AM, Graeme KA, Curry SC, Fischione MA. Rattlesnake envenomations: unusual case presentations. Arch Intern Med. 2001 Feb 12;161(3):474-9
Hogan DE, Dire DJ: Anaphylactic shock secondary to rattlesnake bite. Ann Emerg Med 1990;19:814-816.
Klotz JH, Klotz SA, Pinnas JL. Animal Bites and Stings with Anaphylactic Potential. J Emerg Med. 2007 Nov 8. Epub ahead of print.
Fish LR, O'Rourke D, Lust R, Brewer KL, Hack JB, Meggs WJ. Cardiovascular Effects of Intravenous Rattlesnake. Ann Emerg Med, October 2008; 52(4): S140 Abstract

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