Assessment of fluid and nutritional status using bioelectrical impedance methods in acute kidney injury patients requiring continuous renal replacement therapy

Abstract

Objective To investigate the predictive value of nutritional and fluid status measured by bioelectrical impedance methods for the prognosis of acute kidney injury (AKI) patients undergoing continuous renal replacement therapy (CRRT). Methods Patients with severe AKI received CRRT in the First Affiliated Hospital of Nanjing Medical University from September 2016 to September 2018 were enrolled, and divided into death group and survival group according to 28-day survival. Cox regression was used to analyze the association between 28-day survival and lean tissue index (LTI), fat tissue index (FTI), the ratio of extracellular water (ECW) and body cell mass (BCM) (ECW/BCM), and overhydration (OH), respectively. Results A total of 156 patients were included, including 101 males and 55 females. The age was (62.7±15.4) years, with sequential organ failure assessment (SOFA) score of 9.9±3.9. The 28-day mortality rate was 46.2%. The pre-CRRT OH values in the 28-day survival group and death group were 2.95(1.80, 5.50) L and 4.20(2.95, 5.70) L(P=0.016), and ECW/BCM values were 1.00(0.76, 1.18) and 1.07(0.88, 1.25) (P=0.033), respectively. Univariate Cox regression analysis showed that pre-CRRT high OH values (HR=1.08, 95%CI 1.00-1.17, P=0.040) and high ECW/BCM values (HR=3.02, 95%CI 1.46-6.22, P=0.003) were associated with 28-day death. The changes of OH values (HR=0.83, 95% CI 0.72-0.95, P=0.008) and ECW/BCM values (HR=6.79, 95% CI 1.72-26.82, P=0.006) between pre-CRRT and the 7th day after CRRT initiation were significantly associated with 28-day mortality in patients who survived 7 days after CRRT initiation. After adjusting for age, gender, and SOFA scores, multivariate Cox regression analysis showed that the high OH value (HR=1.16, 95%CI 1.06-1.27, P=0.002) and the high ECW/BCM value (HR=2.80, 95% CI 1.30-6.06, P=0.003) before CRRT, the change of OH value (HR=0.82, 95%CI 0.72-0.95, P=0.008) and ECW/BCM value (HR=2.79, 95% CI 1.30-5.98, P=0.009) between the 7th day after CRRT initiation and pre-CRRT, were independently associated with 28-day death, while LTI (HR=0.93, 95% CI 0.86-1.02, P=0.113) and FTI (HR=0.98, 95% CI 0.92-1.04, P=0.475) before CRRT were uncorrelated with 28-day death. Conclusions In bioelectrical impedance analysis, the high OH value and high ECW/BCM value before CRRT are associated with 28-day mortality in patients with AKI, while the nutritional indicators LTI and FTI before CRRT are not significantly related. The correction of fluid overload by CRRT within 7 days may reduce the risk of 28-day mortality. Key words: Acute kidney injury; Renal replacement therapy; Body composition; Electric impedance; Nutritional status; Organism hydration status; Prognosis