Background Snakebites that have cytotoxic venom can cause significant soft tissue swelling. Assessing the site and degree of swelling using ultrasound as a non-invasive technique would be an important tool for instituting appropriate treatment.

Methods Forty-two patients who presented to a referral hospital in South Africa with cytotoxic swelling of the limbs from snakebite were assessed using ultrasound. The envenomed limb of each patient was scanned at the point of maximal swelling and compared with the unaffected limb at the same site. Data were presented as an expansion coefficient defined as the ratio of the thickness of tissue structure (subcutaneous tissue or muscle compartment) in the envenomed limb to that in the unaffected limb. A p value of 0.05 was regarded as significant, and 95% CIs were expressed throughout.

Results The majority of bites were in the upper limb (27/42). Twenty-five patients were children less than 12 years. Tissue expansion was noted in both the subcutaneous and muscle compartments of the envenomed limbs. The site of swelling was predominantly in the subcutaneous tissues, while swelling in muscle compartment was limited (the mean expansion coefficient for subcutaneous tissues was 2.0 (CI 1.7 to 2.3) vs 1.06 (CI 1.0 to 1.1), respectively). The difference between the groups was significant (p<001). One case, confirmed as compartment syndrome, showed marked swelling in the muscle group.

Conclusions Basic ultrasound techniques may be used to identify the site and degree of tissue swelling from cytotoxic envenomation. It is a non-invasive, painless procedure that can assist the clinician to assess the injured limb and may also be of benefit to monitor the progression of swelling.