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 (IVCmax and IVCmin) were significantly lower than baseline in severe blood loss. The optimal cut point for IVCmax 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 IVCmin 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 IVCmax of ≤ 0.8 cm may be useful in identifying moderate and severe hemorrhage before vital sign abnormalities are evident.

Inferior Vena Cava Diameter is an Early Marker of Central Hypovolemia during Simulated Blood Loss.

INTRODUCTION: Inferior vena cava (IVC) diameter decreases under conditions of hypovolemia. Point-of-care ultrasound (POCUS) may be useful to emergently assess IVC diameter. This study tested the hypothesis that ultrasound measurements of IVC diameter decreases during severe simulated blood loss. METHODS: Blood loss was simulated in 14 healthy men (22 ± 2 years) using lower body negative pressure (LBNP). Pressure within the LBNP chamber was reduced 10 mmHg of LBNP every four minutes until participants experienced pre-syncopal symptoms or until 80 mmHg of LBNP was completed. IVC diameter was imaged with POCUS using B-mode in the long and short axis views between minutes two and four of each stage. RESULTS: Maximum IVC diameter in the long axis view was lower than baseline (1.5 ± 0.4 cm) starting at -20 mmHg of LBNP (1.0 ± 0.3 cm; p < 0.01) and throughout LBNP (p < 0.01). The minimum IVC diameter in the long axis view was lower than baseline (0.9 ± 0.3 cm) at -20 mmHg of LBNP (0.5 ± 0.3 cm; p < 0.01) and throughout LBNP (p < 0.01). Maximum IVC diameter in the short axis view was lower than baseline (0.9 ± 0.2 cm) at 40 mmHg of LBNP (0.6 ± 0.2; p = 0.01) and the final LBNP stage (0.6 ± 0.2 cm; p < 0.01). IVC minimum diameter in the short axis view was lower than baseline (0.5 ± 0.2 cm) at the final LBNP stage (0.3 ± 0.2 cm; p = 0.01). CONCLUSION: These data demonstrate that IVC diameter decreases prior to changes in traditional vital signs during simulated blood loss. Further study is needed to determine the view and diameter threshold that most accurate for identifying hemorrhage requiring emergent intervention.