Abstract
IntroductionIn this cohort study, we explored the relationship between fluid balance, intradialytic hypotension and outcomes in critically ill patients with acute kidney injury (AKI) who received renal replacement therapy (RRT).MethodsWe analysed prospectively collected registry data on patients older than 16 years who received RRT for at least two days in an intensive care unit at two university-affiliated hospitals. We used multivariable logistic regression to determine the relationship between mean daily fluid balance and intradialytic hypotension, both over seven days following RRT initiation, and the outcomes of hospital mortality and RRT dependence in survivors.ResultsIn total, 492 patients were included (299 male (60.8%), mean (standard deviation (SD)) age 62.9 (16.3) years); 251 (51.0%) died in hospital. Independent risk factors for mortality were mean daily fluid balance (odds ratio (OR) 1.36 per 1000 mL positive (95% confidence interval (CI) 1.18 to 1.57), intradialytic hypotension (OR 1.14 per 10% increase in days with intradialytic hypotension (95% CI 1.06 to 1.23)), age (OR 1.15 per five-year increase (95% CI 1.07 to 1.25)), maximum sequential organ failure assessment score on days 1 to 7 (OR 1.21 (95% CI 1.13 to 1.29)), and Charlson comorbidity index (OR 1.28 (95% CI 1.14 to 1.44)); higher baseline creatinine (OR 0.98 per 10 μmol/L (95% CI 0.97 to 0.996)) was associated with lower risk of death. Of 241 hospital survivors, 61 (25.3%) were RRT dependent at discharge. The only independent risk factor for RRT dependence was pre-existing heart failure (OR 3.13 (95% CI 1.46 to 6.74)). Neither mean daily fluid balance nor intradialytic hypotension was associated with RRT dependence in survivors. Associations between these exposures and mortality were similar in sensitivity analyses accounting for immortal time bias and dichotomising mean daily fluid balance as positive or negative. In the subgroup of patients with data on pre-RRT fluid balance, fluid overload at RRT initiation did not modify the association of mean daily fluid balance with mortality.ConclusionsIn this cohort of patients with AKI requiring RRT, a more positive mean daily fluid balance and intradialytic hypotension were associated with hospital mortality but not with RRT dependence at hospital discharge in survivors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-014-0624-8) contains supplementary material, which is available to authorized users.
Highlights
In this cohort study, we explored the relationship between fluid balance, intradialytic hypotension and outcomes in critically ill patients with acute kidney injury (AKI) who received renal replacement therapy (RRT)
Variation in the timing of RRT initiation is unlikely to be the sole explanation for the association between fluid overload and mortality, since it has been demonstrated in cohorts that included AKI patients managed without RRT [9,10] and has been noted at time points other than at RRT initiation [10]
The mean (SD) age was 62.9 (16.3) years, the mean (SD) sequential organ failure assessment (SOFA) score at intensive care unit (ICU) admission was 12.1 (4.2), and 251 (51.0%) patients died in hospital
Summary
We explored the relationship between fluid balance, intradialytic hypotension and outcomes in critically ill patients with acute kidney injury (AKI) who received renal replacement therapy (RRT). In sepsis-related AKI, to treat possible hypovolaemia, improve cardiac output, and maximise renal blood flow [5] This practice is largely unsupported by evidence and has been challenged by observations that renal blood flow in sepsis may be normal, elevated or decreased [1,4,6], that the renal resistive index, a measure of renal vascular tone, is unchanged in response to fluid challenge in septic patients [5,7], and by numerous observational studies demonstrating an association between fluid overload and mortality in critically ill adults and children with AKI [1,2,3,4,8,9,10,11,12]. It is unclear whether treatment with diuretics or ultrafiltration is effective in modifying this relationship
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