Oliveira RAG, et al. - In this prospective observational study, researchers assessed the variables that could influence renal Doppler resistive index (renal RI) in 83 consecutive critically ill patients in a 14-bed medical–surgical adult intensive care unit (ICU), including 65% male and 50.6% medical admissions. They performed renal RI until the third day after ICU admission, death, or renal replacement therapy (RRT) requirement. They classified acute kidney injury (AKI) reversibility as transient (normalization of renal function within 3 days of AKI onset) or persistent (non-resolution of AKI within 3 days of onset or need for RRT). The assessment of the factors that could impact renal RI was carried out using a linear mixed model. Mean SAPS 3 (Simplified Acute Physiology Score 3) was 47 ± 16. They noted remarkably different renal RI between no-AKI, transient AKI, and persistent AKI groups. In critically ill patients, renal RI might be impacted by mean arterial pressure, lactate, age, and type of AKI.