Ultrasonographic Inferior Vena Cava Measurement is More Sensitive Than Vital Sign Abnormalities for Identifying Moderate and Severe Hemorrhage

Background: Ultrasound inferior vena cava (IVC) diameter has been shown to decrease in response to hemorrhage. IVC diameter cut points to identify moderate and severe blood loss have not been established. Objectives: This study sought to find ultrasound IVC diameter cut points to identify moderate and severe hemorrhage and assess the performance of these cut points vs. vital sign abnormalities. Methods: This is a secondary analysis of data from a study that described changes in vital signs and sonographic measurements of the IVC during a lower body negative pressure model of hemorrhage. Using receiver operator curve analyses, optimal cut points for identifying moderate and severe hemorrhage were identified. The ability of these cut points to identify hemorrhage in patients with no vital sign abnormalities was then assessed. Results: In both long- and short-axis views, maximum and minimum IVC diameters (IVC_max and IVC_min) were significantly lower than baseline in severe blood loss. The optimal cut point for IVC_max in both axes was found to be ≤ 0.8 cm. This cut point is able to distinguish between no blood loss vs. moderate blood loss, and no blood loss vs. severe blood loss. The optimal cut point for IVC_min was variable between axes and blood loss severity. IVC diameter cut points obtained were able to identify hemorrhage in patients with no vital sign abnormalities. Conclusion: An ultrasound IVC_max of ≤ 0.8 cm may be useful in identifying moderate and severe hemorrhage before vital sign abnormalities are evident.