Renal Resistive Index is Unsusceptible to Systemic Hemodynamics in Fluid Responsive Critically Ill Patients

INTRODUCTION: In critically ill patients, the primary goal for fluid resuscitation is to improve oxygen delivery to ensure adequate organ perfusion. Little evidence is known about renal response to fluids in the acute phase, so renal monitoring after the fluid challenge is fundamental during critical care stay. This study aims to evaluate the changes in the renal resistive index(RRI) and to compare these changes with the hemodynamic parameters after fluid challenge in fluid responsive critically ill patients.
METHODS: Thirty patients older than 18 years who sedated and receiving mechanical ventilation were prospectively studied.20 patients were fluid responsive and included to study.An increase of cardiac output by 10% or more after PLR which is measured by the Ultrasonic Cardiac Output Monitor(USCOM) suspected fluid responsiveness. 500ml of isotonic solution was administered intravenously over 30min.Cardiac output (CO) measurements were done at 0th,1st and 30th minutes. RRI and mean arterial pressure (MAP) were measured by Doppler ultrasonography at 0th and 30th minutes.Repeated measures ANOVA method was used for statistical analysis and p <0.05 was considered significant.
RESULTS: The CO increased significantly after fluid challenge when compared to baseline (from 3.48±1.14 to 4.34±1.43 L/min,P< 0.001).MAP increased significantly after fluid administration when compared to baseline (80±19 to 86±17,P=0.002).RRI didn't differ significantly from the baseline after fluid challenge (62±9 to 60±10,P=0.11).There was a negative correlation between RRI and MAP at the baseline and after fluid challenge.
DISCUSSION AND CONCLUSION: The effect of hemodynamic changes on renal perfusion after the fluid challenge is controversial. In our study, 500ml of crystalloid treatment for 30 minutes increased MAP and CO while not contributed to the improvement of RRI in patients who represented fluid responsive.We found that fluid challenge did not improve RRI in the early phase of the fluid resuscitation in fluid responsive critically ill patients and RRI is unsusceptible to systemic hemodynamic changes during this period.