Discrimination between transient and persistent AKI is of clinical relevance but currently often based on urinary indices which are not very reliable in critically ill patients. Darmon et al. [5] used a different approach by determining Doppler resistive indices in 51 patients. They found that a RI [0.795 predicted persistent AKI with an OR of 1.85 (95% CI 1.2-2.85) upon applying logistic regression analysis. Considering the large influence of interobserver variability on this method, larger multicentre trials are required to prove the utility of this method in daily clinical practice.