Bioimpedance-defined overhydration predicts survival in end stage kidney failure (ESKF): systematic review and subgroup meta-analysis

Abstract

Both overhydration and comorbidity predict mortality in end-stage kidney failure (ESKF) but it is not clear whether these are independent of one another. We undertook a systematic review of studies reporting outcomes in adult dialysis patients in which comorbidity and overhydration, quantified by whole body bioimpedance (BI), were reported. PubMed, EMBASE, PsychInfo and the Cochrane trial database were searched (1990-2017). Independent reviewers appraised studies including methodological quality (assessed using QUIPS). Primary outcome was mortality, with secondary outcomes including hospitalisation and cardiovascular events. Of 4028 citations identified, 46 matched inclusion criteria (42 cohorts; 60790 patients; 8187 deaths; 95% haemodialysis/5% peritoneal dialysis). BI measures included phase angle/BI vector (41%), overhydration index (39%) and extra:intracellular water ratio (20%). 38 of 42 cohorts had multivariable survival analyses (MVSA) adjusting for age (92%), gender (66%), diabetes (63%), albumin (58%), inflammation (CRP/IL6-37%), non-BI nutritional markers (24%) and echocardiographic data (8%). BI-defined overhydration (BI-OH) independently predicted mortality in 32 observational cohorts. Meta-analysis revealed overhydration >15% (HR 2.28, 95% CI 1.56-3.34, P < 0.001) and a 1-degree decrease in phase angle (HR 1.74, 95% CI 1.37-2.21, P < 0.001) predicted mortality. BI-OH predicts mortality in dialysis patients independent of the influence of comorbidity.

Figure 1

PRISMA flow diagram. The flow diagram summarises the systematic search, citation screening, exclusion and inclusion processes undertaken within this review.

Figure 2

The temporal change in the reporting of BI-OH measures within studies according to year of publication. PA = phase angle, BIVA = Bioimpedance Vector Analysis, ECWR = Extracellular water expressed as a ratio (e.g. intracellular or total body water, OHI = overhydration index.

Figure 3

Summary of subgroup meta-analysis. The pooled summary of the effect of OH > 15% and a 1-degree decrease in PA on mortality in the dialysis population. 95% CI = 95% confidence interval, IV = inverse variance method.

Figure 4

Summary of the QUIPS analysis from all cohorts included within the systematic review. SP = study participation, SA = study attrition, PFM = prognostic factor measurement, OM = outcome measure, SC = study confounding and STR = statistical analysis reporting.