Measurement of renal congestion and compliance following intravenous fluid administration using shear wave elastography.

OBJECTIVE: Ultrasound shear wave elastography (SWE) is a novel technique that may provide non-invasive measurements of renal compliance. We aimed to investigate the relationship between intravenous (IV) fluid administration and change in SWE measurements. We hypothesised that following IV fluid administration in healthy volunteers, global kidney stiffness would increase and that this increase in stiffness could be quantified using SWE. Our second hypothesis was that graduated doses of IV fluids would result in a dose-dependent increase in global kidney stiffness measured by SWE.

DESIGN: Randomised prospective study.

SETTING: Intensive Care Unit.

PARTICIPANTS: Healthy volunteers aged 18-40 years.

INTERVENTIONS: Participants were randomised to receive 20 ml/kg, 30 ml/kg, or 40 ml/kg of normal saline. The volume of fluid infused was based on the actual body weight recorded.

MAIN OUTCOME MEASURES: We recorded average SWE stiffness (kPa with standard deviation of the mean), median SWE stiffness (kPa), and the interquartile range.

RESULTS: Ninety-eight percent of participants (44/45) demonstrated an increase in global kidney stiffness following administration of IV fluids. The average SWE pre fluid administration was 7.572 kPa ± 2.38 versus 14.9 kPa ± 4.81 post fluid administration ( p < 0.001). In subgroup analysis, there were significant changes in global kidney stiffness pre and post fluid administration with each volume (ml/kg) of fluid administered. Average percentage change in global kidney stiffness from baseline was compared between the three groups. There was no significant difference when comparing groups 1 and 2 (197.1% increase ± 49.5 vs 216.1% ± 72.0, p ¼ 0.398), groups 2 and 3 (216.1% increase ± 72.0 vs 197.8% ± 59.9, p ¼ 0.455), or groups 1 and 3 (197.1% increase ± 49.5 vs 197.8% ± 59.9, p ¼ 0.972).

CONCLUSIONS: Fluid administration results in immediately visible and quantifiable changes in global kidney stiffness across all infused volumes of fluid.