Intravascular volume status is an important clinical consideration in the management of the critically ill. Point of care ultrasonography (POCUS) has gained popularity as a non-invasive means of intravascular volume assessment via examination of the inferior vena cava (IVC). However, there is limited data comparing different acquisition techniques for IVC measurement by POCUS.
The goal of this evaluation is to determine the reliability of three IVC acquisition techniques for volume assessment: sub-xiphoid transabdominal long axis (LA), transabdominal short axis (SA), and right lateral transabdominal coronal long axis (CLA) (aka “rescue view”).
Volunteers were evaluated by three experienced emergency physician sonographers (EP). Gray scale (B-mode) and Motion-mode (M-mode) diameters were measured and IVC collapsibility index (IVCCI) calculated for three anatomic views (LA, SA, CLA). For each IVC measurement, descriptive statistics, intra-class correlation coefficients (ICC), and 2-Way Univariate Analyses of Variance (ANOVA) were calculated.
Thirty-nine volunteers were evaluated yielding 351 total US measurements. Measurements of the three views had similar means (LA 1.9 ± 0.4cm; SA 1.9 ± 0.4cm; CLA 2.0 ± 0.5cm). For B-Mode, LA had the highest ICC (0.86, 95% CI = 0.76 to 0.92) while CLA had the poorest ICC (0.74, 95% CI = 0.56 to 0.85). ICCs for all M-mode IVCCI were low. Significant interaction effects between anatomical view and EP were observed for B-mode and M-mode measurements. Post-hoc analyses reveal difficulty in consistent view acquisition between EPs.
Inter rater reliability of the IVC by EPs was highest for B-mode LA and poorest for all M-Mode IVC collapsibility indices (IVCCI). These results suggest that B-mode LA holds the most promise to deliver reliable measures of IVC diameter. Future studies may focus on validation in a clinical setting as well as comparison to a reference standard.