Fluid Overload and Precision Net Ultrafiltration in Critically Ill Patients

Abstract

Background: 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 [UFNET]) 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.

Summary: 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 UFNET rates. In addition, fast UFNET rates are associated with an increased risk of cardiac arrhythmias. Randomized trials are required to examine whether moderate UFNET 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.

Key messages: Among critically ill patients with acute kidney injury and fluid overload requiring continuous kidney replacement therapy, use of higher and slower UFNET rates compared with moderate UFNET rates might be associated with poor outcomes. Newer minimally invasive technologies may allow for safe and efficient UFNET in patients with acute kidney injury who do not meet criteria for initiation of KRT.

Keywords: Fluid overload; Kidney replacement therapy; Mortality; Net ultrafiltration.

Fig. 1.. Association of net ultrafiltration rate with mortality in critically ill patients.

The association between net ultrafiltration (UF_NET) rate and mortality in critically ill patients receiving continuous kidney replacement therapy is ‘J’ shaped. An observational study showed that slow UF_NET rates <1.01 mL/kg/h and fast UF_NET rates >1.75 mL/kg/h are associated with increased mortality. Moderate UF_NET rates of 1.01–1.75 mL/kg/h are associated with the lowest risk of death [40]. High UF_NET rates are associated with organ ischemia, and low U_FNET rates are associated with organ oedema [1]. Figure adapted from Murugan R et. al. [1] and with permission.

Fig. 2.. Potential organ dysfunction associated with faster and slower net ultrafiltration rates

Slower ultrafiltration rates will increase exposure to fluid overload in critically ill patients and may be associated with organ edema in heart, kidney, liver, brain, and the gut. Faster ultrafiltration rates have been associated with organ ischemia in kidney, liver, brain, and the gut in patients with kidney failure [1]. Whether such associations exist in critically ill patients with acute kidney injury needs to be evaluated further.