Limited agreement between two noninvasive measurements of blood volume during fluid removal: ultrasound of inferior vena cava and finger-clip spectrophotometry of hemoglobin concentration

Abstract

Objective: Plots of blood volume measurements over time (profiles) may identify euvolemia during fluid removal for acute heart failure. We assessed agreement between two noninvasive measurements of blood volume profiles during mechanical fluid removal, which exemplifies the interstitial fluid shifts that occur during diuretic-induced fluid removal. Approach: During hemodialysis we compared change in maximum diameter of the inferior vena cava by ultrasound () to change in relative blood volume derived from capillary hemoglobin concentration from finger-clip spectrophotometry (RBVSpHb). We grouped profiles of these measurements into three distinct shapes using an unbiased, data-driven modeling technique. Methods: Fifty patients who were not in acute heart failure underwent a mean of five paired measurements while an average of 1.3 liters of fluid was removed over 2 h during single hemodialysis sessions. changed −1.0 mm (95% CI −1.9 to −0.2 mm) and the RBVSpHb changed −1.1% (95% CI −2.7 to +0.5%), but these changes were not correlated (r −0.04, 95% CI −0.32 to +0.24). Nor was there agreement between categorization of profiles of change in the two measurements (kappa −0.1, 95% CI −0.3 to +0.1). Significance: and RBVSpHb estimates of blood volume do not agree during mechanical fluid removal, likely because regional changes in blood flow and pressure modify IVC dimensions as well as changes total blood volume.