Clinical predictors of tissue necrosis following rattlesnake envenomation

Background: Rattlesnake envenomation (RSE) causes edema, hemotoxicity and tissue necrosis. Necrosis may result in permanent disability. Objective: To study patient-related factors associated with tissue necrosis after Crotalus envenomation. Methods: Prospective cohort study of patients admitted to the Medical Toxicology service with diagnosis of RSE between April 2011 and November 2014. Inclusion criteria were age ≥18 years and upper extremity (UE) envenomation site. Primary outcome was tissue necrosis, including dermonecrosis, manifesting as bullae. Secondary outcome was amputation. Results: 77 subjects, age 18 to 88 years, met inclusion criteria. Rattlesnake species was unknown in most cases. All received Fab antivenom. 62 (82%) had a digital envenomation. 31 (40.3%) had necrosis. Necrotic area ranged from 0.1 cm² to 14 cm². Procedural interventions, (superficial debridement, dermotomy, surgical exploration, and operative debridement of devitalized tissue) occurred in 25 (32.5%). Five (6.5%) underwent dermotomy and 6 (7.8%) operative debridement. No amputations were performed. Patients with cyanosis on presentation had increased risk of developing necrosis (11/12; RR 2.98 95% CI 1.99–4.46). Ecchymosis on presentation was also associated with increased risk of necrosis (24/32; RR 4.04 95% CI 2.08–7.86). Patients with social or regular ethanol use were more likely to develop necrosis than those without (28/53; RR 4.23 95% CI 1.42–12.6). Regular cocaine use was associated with increased risk of operative debridement (4/6; RR 9.13 95% CI 2.33–35.8). A nonsignificant risk of operative debridement occurred with tobacco use (RR 1.14 95%CI 0.99–1.31 p = 0.09). Time to antivenom did not correlate with risk of necrosis. Conclusion: UE RSE patients who presented with cyanosis, ecchymosis or history of ethanol use were at increased risk of developing necrosis. Cocaine use was associated with increased risk of operative debridement.