The Effect of Postoperative Fluid Balance on the Occurrence and Progression of Acute Kidney Injury After Cardiac Surgery

Abstract

Objectives: In addition to the association between positive fluid balance (FB) and acute kidney injury (AKI) after cardiac surgery reported by former studies, this study examined the relationship between FB and progressive AKI.

Design: A retrospective, observational study.

Setting: University teaching, grade A tertiary hospital in Shanghai, China.

Participants: Adult patients after cardiac surgery from July-December 2016.

Interventions: Perioperative data relating to postoperative fluid intake and output were collected. AKI progression was defined as a worsening of AKI stage. FB was calculated as (fluid intake [L] - fluid output [L]/body weight [kg] × 100%).

Measurements and main results: The study comprised 1,522 patients. The incidences of AKI and progressive AKI were 33.1% (n = 504) and 18.1% (n = 91), respectively. There was an exponential increase between 24-hour FB and AKI occurrence, and an approximate "U"-shape association between 48-hour FB and AKI progression. Multivariate logistic regression showed that 24-hour FB ≥5% was an independent risk factor for AKI incidence (odds ratio [OR] 3.976; p < 0.001) and 48-hour FB <-5% or ≥3% was associated with an increase of AKI progression (FB <-5%, OR 7.078 [p = 0.031]; FB 3%-5%, OR 6.598 [p = 0.020]; FB ≥5%, OR 16.453 [p < 0.001]).

Conclusions: An exponential increase was found between 24-hour FB and AKI occurrence and a "U"-shape association between 48-hour FB and AKI progression. Both excessively negative and positive accumulative 48-hour FB increased the risk of AKI progression, suggesting cautious monitoring and application of fluid load in clinical practice.

Keywords: acute kidney injury; acute kidney injury progression; cardiac surgery; fluid balance.