Utilisation de l'index de résistance vasculaire rénal mesuré par échographie Doppler au cours du choc septique

Detection of kidney function alteration through serum creatinine is delayed compared to the onset of renal injury. A tool directly allowing detecting patients with or at risk of such injury is missing notably in septic shock patients. Animal studies on acute tubular necrosis showed that renal vascular Resistive Index (RI) as measured by renal Doppler ((peak systolic flow velocity - minimum diastolic flow velocity)/peak systolic flow velocity) increased earlier than serum creatinine after injury. RI has been studied in several renal diseases: ureteral obstruction, acute and chronic allograft dysfunction, diabetic nephropathy, renovascular disease… and was found to correlate with severity or risk of renal dysfunction although data are not unequivocal. Studies in patients with acute renal failure showed that elevated RI could discriminate prerenal failure from parenchymatous renal injury. These data prompted to test whether RI elevation could be an early marker of acute renal failure in septic shock patients. On a cohort of 35 patients with septic shock and studied at ICU admission, an RI above 0.74 was associated with acute renal failure by day 5 [Intensive Care Med 32 (2006) 1553-1559]. Importantly, RI values overlapped markedly between patients precluding its direct applicability in individual patients. Renal RI has many determinants. Some of them can probably be linked to renal injury (renal vascular resistance, vascular compliance) but others are not related to kidney damage and are therefore confounding factors when RI is used to diagnose acute renal injury: arterial pressure modification, systemic pulse pressure, oxygenation… Finally, the published results show that Doppler-derived RI may be a potentially interesting tool to explore the kidney in the intensive care setting but additional researches are needed to clarify its condition of measurement before it could be used in clinical routine practice.