Renal Resistive Index Calculator

Renal resistive index is an assessment of the peak systolic and end diastolic flow through the renal artery at the level of the renal cortex. In critically ill and trauma patients, it is a reliable predictor of acute kidney injury. In shock, the kidney is often the first organ that we see signs of malperfusion in, often manifesting as low urine output.

Renal arteries are typically low resistance, with continuous forward flow throughout systole and diastole. An elevated renal resistive index indicates a state of increased resistance within the renal vasculature, which may be due to systemic and intra-renal factors. Systemic factors include changes in MAP, venous congestion, and central venous pressure, while renal factors include tubular injury (ATN, glomerulonephritis) and microvascular dysfunction.

A normal value for renal resistive index is <0.7, with values >0.7 predictive of acute kidney injury.

Consider both systemic and renal factors when evaluating patients with shock and elevated resistive indices. Are systemic contributors like venous congestion, bradycardia, or wide pulse pressure (Pulse Pressure Calculator) present? Is there other evidence of renal disease?