A Re-evaluation of the Current Ankle-Brachial Index Threshold in the Setting of Trauma

Abstract

INTRODUCTION: An ankle-brachial index (ABI) less than 0.9 is the current threshold for determining need for CT angiogram in a trauma patient without hard signs of vascular injury. Recent work suggests a screening threshold of 0.7 may be used without missing an injury. We hypothesized that a threshold of 0.7 would lead to missed injuries. METHODS: Retrospective review during a 44-month period identified patients 15 years and older with traumatic injury, recorded ABI, and CT angiogram of an extremity. Sensitivity and specificity were calculated for radiographic abnormality and major vascular injury requiring intervention at various ABI thresholds. Analyses were performed for all-cause traumatic injury, blunt, and penetrating mechanisms. RESULTS: A total of 319 patients met inclusion criteria. Penetrating injury was the predominant mechanism (63%). Of the patients who had a radiographic abnormality on CTA (33%), 7.6% required procedural intervention. All patients undergoing intervention had a soft sign of vascular injury at time of presentation: penetrating injury adjacent to major vascular structure (n = 7), history of arterial bleeding (n = 3), or nonexpanding hematoma (n = 3). An ABI of 0.7 had a sensitivity of 33.3% for detecting vascular injuries requiring intervention. Sensitivity was poor even for the standard ABI threshold of 0.9 (66.7%; Table). Table. - Sensitivity and Specificity Analyses for Various Ankle-Brachial Index Thresholds Outcome Ankle-Brachial Index ≤ 0.9 Ankle-Brachial Index ≤ 0.8 Ankle-Brachial Index ≤ 0.7 Major vascular injury requiring intervention All-cause Sensitivity = 66.7% Specificity = 49.5% Sensitivity = 44.4% Specificity = 78.2% Sensitivity = 33.3% Specificity = 87.8% Penetrating Sensitivity = 66.7% Specificity = 49.7% Sensitivity = 44.4% Specificity = 80.0% Sensitivity = 33.3% Specificity = 90.3% Radiographic Irregularity All-cause Sensitivity = 56.3% Specificity = 53.7% Sensitivity = 31.1% Specificity = 82.8% Sensitivity = 19.4% Specificity = 91.1% Penetrating Sensitivity = 62.9% Specificity = 54.9% Sensitivity = 32.3% Specificity = 84.4% Sensitivity = 19.4% Specificity = 93.4% Blunt Sensitivity = 46.3% Specificity = 51.9% Sensitivity = 29.3% Specificity = 80.2% Sensitivity = 19.5% Specificity = 87.7% CONCLUSION: ABI alone proved to be a poor screening test for vascular injury in this cohort of patients, which represents the highest rate of penetrating trauma in any study evaluating ABI. These results invite a re-evaluation of ABI’s usefulness in modern trauma assessments because a subset of clinically significant vascular injuries may go undetected by the current threshold.