Renal Doppler ultrasound: a new tool to assess renal perfusion in critical illness

Despite our increasing ability to support vital organs and resuscitate patients, the morbidity and mortality of acute kidney injury (AKI) remain high in the intensive care unit (ICU). The ability to predict the occurrence of AKI is crucial for the development of preventive strategies. Early diagnosis of AKI requires markers that are sensitive and easily applicable in clinical practice. The use of Doppler ultrasonography to assess renal perfusion is increasing in many kidney diseases and in the ICU. The Doppler-based renal resistive index, which is a simple, rapid, noninvasive, and repeatable marker, could be a promising tool to prematurely detect the patients most at risk of developing AKI in the ICU and to distinguish transient from persistent AKI. Moreover, the resistive index could also be useful to adjust preventive or therapeutic modalities for the kidney perfusion at the bedside. The recent progress in ultrasound with contrast-enhanced ultrasound gives the opportunity to assess not only the kidney macrocirculation but also the kidney microcirculation in the ICU.