Fluid overload in the ICU: evaluation and management

Abstract

Background: Fluid overload is frequently found in acute kidney injury patients in critical care units. Recent studies have shown the relationship of fluid overload with adverse outcomes; hence, manage and optimization of fluid balance becomes a central component of the management of critically ill patients.

Discussion: In critically ill patients, in order to restore cardiac output, systemic blood pressure and renal perfusion an adequate fluid resuscitation is essential. Achieving an appropriate level of volume management requires knowledge of the underlying pathophysiology, evaluation of volume status, and selection of appropriate solution for volume repletion, and maintenance and modulation of the tissue perfusion. Numerous recent studies have established a correlation between fluid overload and mortality in critically ill patients. Fluid overload recognition and assessment requires an accurate documentation of intakes and outputs; yet, there is a wide difference in how it is evaluated, reviewed and utilized. Accurate volume status evaluation is essential for appropriate therapy since errors of volume evaluation can result in either in lack of essential treatment or unnecessary fluid administration, and both scenarios are associated with increased mortality. There are several methods to evaluate fluid status; however, most of the tests currently used are fairly inaccurate. Diuretics, especially loop diuretics, remain a valid therapeutic alternative. Fluid overload refractory to medical therapy requires the application of extracorporeal therapies. In critically ill patients, fluid overload is related to increased mortality and also lead to several complications like pulmonary edema, cardiac failure, delayed wound healing, tissue breakdown, and impaired bowel function. Therefore, the evaluation of volume status is crucial in the early management of critically ill patients. Diuretics are frequently used as an initial therapy; however, due to their limited effectiveness the use of continuous renal replacement techniques are often required for fluid overload treatment. Successful fluid overload treatment depends on precise assessment of individual volume status, understanding the principles of fluid management with ultrafiltration, and clear treatment goals.

Keywords: Acute kidney injury; Continuous renal replacement therapies; Diuretics; Fluid overload.

Fig. 1

Lung comet tail image. ‘B lines’ also known as comet-tail images are a marker of pulmonary edema. In the presence of extravascular lung water the reflection of the ultrasound beam on the sub-pleural interlobular septa thickened by edema creates comet-tail reverberation artifacts. The ultrasound appearance is of a vertical, discrete, hyperechogenic image that arises from the pleural line and extends to the bottom of the screen moving synchronously with the respiration (white arrows)

Fig. 2

Circuit set up at University of California San Diego, Medical Center. The mean infusion rate of tri-sodium citrate was 180 ml/h and blood flow rate (Qb) was set at 100 ml/min. Tri-sodium citrate was added at the arterial catheter port with ionized calcium levels been measured post-filter. Post-filter ionized calcium levels were used to adjust tri-sodium citrate flow rates. Pre-filter BUN value was measured after the infusion of tri-sodium citrate and after pre-dilution replacement fluid (Qr), thus accounting for the pre-dilutional effect. A fixed ultrafiltration rate (Quf) was used (set at 1000 ml/h) for achieving fluid balance. A target effluent volume was adjusted by hourly modifying substitution fluid rate (Qs) to achieve a negative, zero, or positive fluid balance. Qb, blood flow rate; Qd, dialysate flow rate; Qr, replacement fluid rate; Quf, total ultrafiltration rate; Qnet, net fluid removal rate