The effect of weight-based volume loading on the inferior vena cava in fasting subjects: a prospective randomized double-blinded trial.

OBJECTIVES Inferior vena cava ultrasound (IVC-US) assessment has been proposed as a noninvasive method of assessing volume status. Current literature is divided on its ability to do so. The primary objective was to compare IVC-US changes in healthy fasting subjects randomized to either 10 or 30 mL/kg of intravenous (IV) fluid administration versus a control group that received only 2 mL/kg. METHODS This was a prospective randomized double-blinded trial set in emergency department (ED) clinical care rooms. Volunteer subjects with no history of cardiac disease or hypertension fasted for 12 hours. Subjects were randomly assigned to receive IV 0.9% saline bolus of 2 (control group), 10, or 30 mL/kg over 30 minutes. IVC-US was performed before and 15 minutes after each fluid bolus. RESULTS Forty-two fasting subjects were enrolled. Analysis of variance (ANOVA) comparison showed that IVC-US was unable to detect any significant difference between the control group and those given either 10 or 30 mL/kg fluid, whether using maximum or minimum IVC diameter or caval index (IVC-CI). The groups receiving 10 and 30 mL/kg each had a statistically significant change in IVC-CI; however, the 30 mL/kg group had no significant change in either of the mean IVC diameters. CONCLUSIONS Overall, there were statistically significant differences in mean IVC-US measurements before and after fluid loading, but not between groups. Fasting asymptomatic subjects had a wide intersubject variation in both baseline IVC-US measurements and fluid-related changes. The degree of IVC-US change in association with graded acute volume loading was not predictably proportional between our subjects.