The impact of fluid balance on diagnosis, staging and prediction of mortality in critically ill patients with acute kidney injury

Charat Thongprayoon, Wisit Cheungpasitporn, Narat Srivali, Patompong Ungprasert, Wonngarm Kittanamongkolchai, Kianoush Kashani

Fluid accumulation may delay recognition of acute kidney injury (AKI) in intensive care unit (ICU) patients. This study aims to evaluate the impact of fluid balance on the incidence, time of AKI diagnosis and predictive performance for outcomes of critically ill patients. This study included a cohort of 7696 adult ICU patients at Mayo Clinic Hospital in year 2011 with at least one serum creatinine (SCr) measured in ICU. AKI was defined based on SCr criterion for stage I of KDIGO definition. The AKI incidence and predictive performance for 60-day mortality was compared before and after SCr adjustment for fluid balance. AKI was detected in 1860 (24.2 %) before and 1947 (25.3 %) after fluid balance adjustment (P < 0.001). Patients with AKI both before and after SCr adjustment had significantly higher 60-day mortality in comparison with patients who did not develop AKI (OR 3.38; 95 % CI 2.84-4.02). The risk of 60-day mortality in patients who met AKI criteria after but not before SCr adjustment was significantly higher than patients without AKI (OR 2.00; 95 % CI 1.25-3.11). In contrast, the risk of 60-day mortality in patients who met AKI criteria before but not after SCr adjustment was similar to patients without AKI (OR 1.19; 95 % CI 0.48-2.50). The C-statistic for unadjusted and adjusted SCr to predict 60-day mortality were 0.68 and 0.70, respectively (P = 0.001). Our study found that SCr adjustment for fluid balance could result in a more accurate detection of AKI cases. We suggest using fluid balance adjustment for volume overload critically ill patients.