Inferior vena cava displacement during respirophasic ultrasound imaging

Patients were enrolled from a single urban academic emergency department with ultrasound examinations performed by sonographers experienced in IVC ultrasound. The IVC was imaged from the level of the diaphragm along its entire course to its bifurcation with diameter measurements and respiratory collapse measured at a single point inferior to the confluence of the hepatic veins. While imaging the vessel in its long axis, movement in a craniocaudal direction during respiration was measured by tracking the movement of a fixed point across the field of view. Likewise, imaging the short axis of the IVC allowed for measurement of mediolateral displacement as well as the vessel's angle of collapse relative to vertical.Seventy patients were enrolled over a 6-month period. The average diameter of the IVC was 13.8？mm (95% CI 8.41 to 19.2？mm), with a mean respiratory collapse of 34.8% (95% CI 19.5% to 50.2%). Movement of the vessel relative to the transducer occurred in both mediolateral and craniocaudal directions. Movement was greater in the craniocaudal direction at 21.7？mm compared to the mediolateral movement at 3.9？mm (p？<？0.001). Angle of collapse assessed in the transverse plane averaged 115° (95% CI 112° to 118°).Movement of the IVC occurs in both mediolateral and craniocaudal directions during respirophasic ultrasound imaging. Further, collapse of the vessel occurs not at true vertical (90°) but 25° off this axis. Technical approach to IVC assessment needs to be tailored to account for these factors.The increased presence of point-of-care ultrasound machines in the critical care setting has fueled attempts to use ultrasound as a noninvasive means of assessing volume status. Studies focusing on the sonographic measurement of the inferior vena cava (IVC) and its respirophasic change in diameter have demonstrated mixed results, but findings suggest that increase in respiratory variation of IVC correlates with low central venous pressure [1-4] as well as volume responsiv