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

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.