Renal Resistive Index Responsiveness to a Mean Arterial Pressure Test As a Guide for Mean Arterial Pressure Target in the Early Phase of Septic Shock: A Physiological Study.

OBJECTIVES

Guidelines recommend targeting a mean arterial pressure (MAP) greater than or equal to 65 mm Hg in septic shock. Although experts advocate for individualized targets, no validated bedside tool exists. An increased renal resistive index (RRI) is associated with acute kidney injury, and increasing MAP can reduce RRI. This study investigated the physiologic impact of a higher MAP on renal function based on RRI evolution during a transient high MAP target test.

DESIGN

Prospective physiologic and randomized study.

SETTING

Medical ICU of a university hospital.

PATIENTS: Patients in the early phase of septic shock (norepinephrine ≥ 0.05 µg/kg/min base within 9 hr of initiation, with or without lactate > 2 mmol/L) without chronic kidney disease or immediate need for renal replacement therapy.

INTERVENTIONS: None.

MEASUREMENTS AND MAIN

RESULTS

All patients underwent a standardized 2-hour MAP test (65-70 followed by 80-85 mm Hg) with RRI measured at each period. RRI responders were defined by an RRI decrease greater than or equal to 0.05 during the MAP test. Following the MAP test, patients were randomized according to the "low" (65-70) or "high" (80-85 mm Hg) MAP target for 5 days, stratified by RRI response during the MAP test. Eighty patients were randomized; 23 (29%) were RRI responders. Among RRI responders, the higher MAP target was not associated with improved renal outcomes (i.e., diuresis, Kidney Disease: Improving Global Outcomes stage, need for renal replacement therapy, or serum creatinine). RRI nonresponders had higher urine output with a high MAP target, whereas no other renal parameter differed significantly; these findings should be considered exploratory.

CONCLUSIONS

In early septic shock, a decrease in RRI during a MAP test did not identify patients who would benefit from higher MAP targets to improve renal function. Conversely, the absence of an RRI decrease during the MAP test may help identify patients in whom increasing MAP is associated with increased urine output.