Overhydration, cardiac function and survival in hemodialysis patients

Background and objectives: Chronic subclinical volume overload occurs very frequently and may be ubiquitous in hemodialysis (HD) patients receiving the standard thrice-weekly treatment. It is directly associated with hypertension, increased arterial stiffness, left ventricular hipertrophy, heart failure, and eventually, higher mortality and morbidity. We aimed to assess for the first time if the relationship between bioimpedance assessed overhydration and survival is maintained when adjustments for echocardiographic parameters are considered. Design, setting, participants and measurements: A prospective cohort trial was conducted to investigate the impact of overhydration on all cause mortality and cardiovascular events (CVE), by using a previously reported cut-off value for overhydration and also investigating a new cut-off value derived from our analysis of this specific cohort. The body composition of 221 HD patients from a single center was assessed at baseline using bioimpedance. In 157 patients supplemental echocardiography was performed (echocardiography subgroup). Comparative survival analysis was performed using two cut-off points for relative fluid overload (RFO): 15% and 17.4%(a value determined by statistical analysis to have the best predictive value for mortality in our cohort). Results: In the entire study population, patients considered overhydrated (using both cut-offs) had a significant increased risk for all-cause mortality in both univariate (HR = 2.12, 95% CI = 1.30-3.47 for RFO> 15% and HR = 2.86, 95% CI = 1.72-4.78 for RFO> 17.4%, respectively) and multivariate (HR = 1.87, 95% CI = 1.12-3.13 for RFO> 15% and HR = 2.72, 95% CI = 1.60-4.63 for RFO> 17.4%, respectively) Cox survival analysis. In the echocardiography subgroup, only the 17.4% cut-off remained associated with the outcome after adjustment for different echocardiographic parameters in the multivariate survival analysis. The number of CVE was significantly higher in overhydrated patients in both univariate (HR = 2.46, 95% CI = 1.56-3.87 for RFO > 15% and HR = 3.67, 95% CI = 2.29-5.89 for RFO > 17.4%) and multivariate (HR = 2.31, 95% CI = 1.42-3.77 for RFO > 15% and HR = 4.17, 95% CI = 2.48-7.02 for RFO > 17.4%) Cox regression analysis. Conclusions: The study shows that the hydration status is associated with the mortality risk in a HD population, independently of cardiac morphology and function. We also describe and propose a new cut-off for RFO, in order to better define the relationship between overhydration and mortality risk. Further studies are needed to properly validate this new cut-off in other HD populations