Fluid Overload and Precision Net Ultrafiltration in Critically Ill Patients

<b><i>Background:</i></b> Fluid overload is present in two-thirds of critically ill patients with acute kidney injury and is associated with morbidity, mortality, and increased healthcare resource utilization. Kidney replacement therapy (KRT) is frequently used for net fluid removal (i.e., net ultrafiltration [UF_NET]) in patients with severe oliguric acute kidney injury. However, ultrafiltration has considerable risks associated with it, and there is a need for newer technology to perform ultrafiltration safely and to improve outcomes. <b><i>Summary:</i></b> Caring for a critically ill patient with oliguric acute kidney injury and fluid overload is one of the most challenging problems. Although diuretics are the first-line treatment for management of fluid overload, diuretic resistance is common. Various clinical practice guidelines support fluid removal using ultrafiltration during KRT. Emerging evidence from observational studies in critically ill patients suggests that both slow and fast rates of net fluid removal during continuous kidney replacement therapy are associated with increased mortality compared with moderate UF_NET rates. In addition, fast UF_NET rates are associated with an increased risk of cardiac arrhythmias. Randomized trials are required to examine whether moderate UF_NET rates are associated with a reduced risk of hemodynamic instability, organ injury, and improved outcomes in critically ill patients. There is a need for newer technology for fluid removal in patients who do not meet traditional criteria for initiation of KRT. Emerging newer and miniaturized ultrafiltration devices may address an unmet clinical need. <b><i>Key Messages:</i></b> Among critically ill patients with acute kidney injury and fluid overload requiring continuous kidney replacement therapy, use of higher and slower UF_NET rates compared with moderate UF_NET rates might be associated with poor outcomes. Newer minimally invasive technologies may allow for safe and efficient UF_NET in patients with acute kidney injury who do not meet criteria for initiation of KRT.