Relationship Between the Subcostal and Right Lateral Ultrasound Views of Inferior Vena Cava Collapse: Implications for Clinical Use of Ultrasonography.

Background: The collapsibility index of the inferior vena cava is traditionally visualized from the subcostal region in the sagittal plane, referred to here as cIVC. Alternatively, the collapsibility index of the inferior vena cava can be visualized from the right midaxillary line in the coronal plane, referred to here as cIVC. It is unclear whether values of cIVC are comparable with values of cIVC because the inferior vena cava collapses asymmetrically into an elliptical form, quantified as the flat ratio of the inferior vena cava (F-IVC). This study aimed (1) to establish if cIVC is concordant or discordant to cIVC, and (2) to describe how this concordance or discordance is related to F-IVC.

Methods: This single-center cross-sectional study enrolled 110 spontaneously breathing patients. Values of cIVC were compared with cIVC. Performance of cIVC ≥ 42% in predicting fluid responsiveness, defined as cIVC ≥ 42%, was assessed. F-IVC was also correlated to the difference between cIVC and cIVC.

Results: cIVC ≥ 42% was 61.5% sensitive (95% CI, 31.58%-86.14%) and 67.1% specific (95% CI, 55.81%-77.06%) for predicting cIVC ≥ 42%. cIVC underestimated cIVC. The degree of discordance between cIVC and cIVC was proportional to the value of F-IVC.

Conclusions: cIVC and cIVC measures are discordant, where cIVC underestimates cIVC. The degree of discordance is directly proportional to the value of F-IVC. Therefore, we recommend that cIVC ≥ 42% be used to rule in, but not to rule out, fluid responsivity. Wherever possible, F-IVC should be assessed to understand the clinical relevance of cIVC.