Efficacy of a Pressure-Immobilization bandage in delaying the onset of systemic toxicity in a porcine model of eastern coral snake (Micrurus fulvius) envenomation

Abstract

Study objectives: Pressure-immobilization bandages (PIBs) are first-aid devices that are used in foreign regions where neurotoxic elapid envenomations are common. These devices are theorized to impede lymphatic return to the central circulation, thereby sequestering venom at the bite site and delaying systemic toxicity, which allows additional time to provide the victim with definitive care in the form of antivenom and advanced airway management. Coral snakes are New World elapids with primarily neurotoxic venoms. PIB use has never been formally examined in coral snake envenomations. We evaluate the efficacy of these devices in delaying the onset of systemic toxicity in a porcine model of Micrurus fulvius envenomation. Methods: The study design was a randomized, controlled trial of PIBs in a porcine model of M fulvius envenomation. The setting was a university animal laboratory. Subjects were 12 pigs, ranging from 9.1 to 11.4 kg. The animals were sedated, intubated, and anesthetized. Volatile anesthesia was maintained by animal care technicians at a level to ensure animal comfort and that all pigs were breathing spontaneously. Lyophilized venom was obtained from Natural Toxins Research Center (Kingsville, TX) and resuspended in pure water at a concentration of 10 mg/mL. The lethal dose of M fulvius venom in a human has been estimated at 5 mg, and the venom yield of a large snake can be 20 mg. We chose a 10-mg dose to ensure that all animals would develop severe toxicity during the study. The subjects were injected with 10 mg of M fulvius venom in the subcutaneous tissue of the left distal foreleg. Immediately after injection, the subjects were randomized to either receive a PIB 1 minute after envenomation or to have no treatment. The PIB consisted of an elastic bandage applied to the entire extremity at a pressure such that a finger could be easily passed under. The same operator applied all bandages. Aluminum and foam splints were then loosely taped on either side to immobilize the extremity. Pulse rate, respiratory rate, pulse oximetry, and quality of respirations were recorded at 10-minute intervals. The primary endpoint was survival to 8 hours, and groups were compared using χ 2 analysis. Groups were also compared with respect to time to onset of systemic toxicity in the form of respiratory compromise, and total time of survival. A veterinary pathologist performed necropsies on all animals, and the histology of the envenomation site was examined. One animal from each group was removed because of the discovery of preexisting respiratory pathology. Results: Four of 5 pigs in the treatment group survived to 8 hours, but none in the control group did ( P =.0036). Time to onset of signs of respiratory compromise was 170±33.3 minutes in the control group. Two pigs in the treatment group showed signs of respiratory compromise before 8 hours, 1 at 310 minutes and 1 at 460 minutes. One of these subjects did survive to 8 hours. None of the pigs had histologic changes at the envenomation site consistent with ischemic or pressure-related injury. Conclusion: Pressure immobilization bandages were effective in delaying the onset of systemic venom toxicity in this model of M fulvius envenomation. According to this study, the use of PIBs can be recommended as initial treatment in human envenomations by coral snakes.