Pressure immobilization delays mortality and increases intracompartmental pressure after artificial intramuscular rattlesnake envenomation in a porcine model

Abstract

We determine the effect of pressure immobilization on mortality and intracompartmental pressure after artificial intramuscular Crotalus atrox envenomation in a porcine model. We prospectively studied 20 pigs using a randomized, controlled design. After anesthesia, C atrox venom (20 mg/kg) was injected with a 22-gauge needle 10 mm deep into the tibialis anterior muscle of the hind leg. Pigs were randomized to receive either pressure immobilization (applied 1 minute after envenomation and maintained throughout the duration of the experiment) or no pressure immobilization. We measured time to death, intracompartmental pressure before venom injection and at 2 hours after injection, and leg circumference at a standardized location before injection and immediately postmortem. Duration of survival was compared using Kaplan-Meier survival analysis. The dose of venom resulted in 100% mortality. The median survival was longer in the pressure immobilization group (191 minutes, range 140 to 240 minutes) than in the control group (median 155 minutes, range 119 to 187 minutes). The difference between the groups was 36 minutes (95% confidence interval [CI] 2 to 64 minutes; P =.0122). The mean intracompartmental pressures were 67+/-13 mm Hg+/-SD with pressure immobilization and 24+/-5 mm Hg without pressure immobilization. The difference between groups was 43 mm Hg (95% CI 32 to 53 mm Hg). The mean circumferences were 14.3 cm in the pressure immobilization group and 19.1 cm in the control group. The difference between groups was -4.8 cm (95% CI -5.7 to -3.9 cm). Compared with control animals without treatment, the pressure immobilization group had longer survival, less swelling, and higher intracompartmental pressures after artificial, intramuscular C atrox envenomation in our porcine model.