Utility of ABI and API Versus CTA to Identify Surgically Significant Arterial Injury After Lower Extremity Trauma in a LMIC.

Background: South Africa faces a high burden of trauma-related vascular injury. Prompt diagnosis and management are crucial to limit morbidity and mortality. Literature recommends a thorough vascular examination of at-risk patients. Ankle brachial index (ABI) and arterial pressure index (API) are considered reliable screening tools for lower extremity vascular injury (LEVI) in the correct clinical scenario. Patients with an abnormal ABI/API warrant diagnostic imaging with computed tomography angiography (CTA). However, recent international literature demonstrates a trend toward potential CTA overuse in the work up for LEVI, when the internationally recommended vascular injury work-up guidelines are not followed correctly.

Objective: To assess the reliability of ABI/API in trauma patients with suspected LEVI as a screening tool to safely avoid unnecessary CTA.

Methods: A retrospective cohort study of all lower extremity trauma patients with soft signs of LEVI who presented to Charlotte Maxeke Johannesburg Academic Hospital from February 1, 2018 to January 31, 2020 was undertaken. Sensitivity, specificity, NPV, and PPV were calculated for ABI/API versus CTA and ABI/API/CTA versus surgically significant arterial injury. A p-value < 0.05 indicated statistical significance (confidence level = 95%).

Results: Four hundred and thirty-three CTAs were performed for suspected traumatic LEVI. Two hundred and eighty-two were excluded due to missing data (precluding retrospective calculation of ABI/API) and 151 patients were included. To detect surgically significant injury, CTA had a 100% sensitivity, 97.2% specificity, 100% NPV, and 69.2% PPV; ABI and API had a 100% sensitivity, 83.8%-85.9% specificity, 100% NPV, and 28.1%-35.9% PPV, respectively. Neither ABI nor API missed surgically significant arterial injuries.

Conclusions: This affirms the reliability of ABI/API as a screening tool to identify patients at risk of LEVI from penetrating trauma. Findings supported international data demonstrating CTA overuse in this subset of patients.