Agreement of IVC Diameter Measurements via Subcostal and Transhepatic POCUS Views.

Background: Inferior vena cava (IVC) point of care ultrasound (POCUS) is essential for hemodynamic evaluation, with the subcostal view (SCV) being the gold standard. However, in situations where this view is inaccessible, the transhepatic view (THV) is a viable alternative. This study evaluates the concordance between these two views in ventilated and non-ventilated patients, categorizing the IVC as small, intermediate, or large. Methods: This prospective observational study included 99 patients; healthy volunteers, ventilated patients, and non-ventilated patients. We measured end-expiratory IVC diameter, classified as small (<10 mm), intermediate (10-20 mm) or large (>20 mm), via SVC and THV. We then assessed agreement by categorical concordance, using Bland-Altman (mean bias ± 95% limits) and Pearson's correlation (r). Results: The overall concordance between both views was 83.8% (83/99; 95% CI: 76.4-90%). By IVC diameter category, concordance was 93.8% (15/16; 95% CI: 69.8-99.8) for small, 84% (42/50; 95% CI: 70-90 %) for intermediate, and 82% (27/33; 95% CI: 77-95%) for large. Concordance was unaffected by ventilation status (p = 0.83), but patients with Body Mass Index (BMI) ≥ 30 had lower concordance than those with BMI < 30 (73.9% vs. 89.5%; p = 0.086). The Bland-Altman analysis showed a mean bias of +0.22 mm with 95% limits of agreement from -6.99 to +7.43 mm. Pearson's correlation coefficient for the 99 paired measurements was r = 0.86 (p < 0.001), overall, and when stratified by category was r = 0.81 (small), r = 0.78 (intermediate) and r = 0.74 (large) (all p < 0.001). The sensitivity and specificity of THV for identifying "responders" (CI > 42%) were 28% and 93%, respectively. Conclusion: The THV is a reliable alternative for categorical evaluation of the IVC, particularly when the SCV is inaccessible. This method supports rapid and accurate clinical decision, especially for dichotomous POCUS decisions but should be used cautiously in patients with elevated BMI.