Serial evaluation of local changes in snakebite envenomation using infrared thermal imaging

Abstract

Background There is a lack of objective tools to assess the local changes following snakebite envenomation. We aimed to describe the progression of local changes in envenomed patients using serial infrared thermal imaging. Methods In a prospective sample of patients with snakebite envenomation, clinical assessment and infrared imaging of local changes were done at enrolment and 6 h and 24 h later, followed by once daily until hospital discharge or day 7, whichever was earlier. Infrared images were interpreted by an investigator masked to clinical findings. Results We studied 39 patients with snakebite envenomation. Their mean age was 44.6±12.7 y and 25 (64%) were men. The median time to stability of local changes was 24.6 h (interquartile range [IQR] 17.0–30.1) on clinical examination and 28.0 h (IQR 13.7–55.2) on infrared imaging. At 24 h there was simple agreement between the two methods on whether the local changes were progressing or not in 31 of 39 patients (80%; Cohen's κ=0.59, p<0.001). The maximum proximal extent of local changes assessed using the two methods had a good correlation (Spearman's ρ=0.713, p<0.001). However, the extent of thermal changes on infrared images often exceeded the upper limit of swelling detected clinically. Conclusions Infrared imaging could be used to objectively document the local changes caused by snakebite envenomation.