Time-Dependent Changes in Extracellular-to-Intracellular Water Ratios and Risk of All-Cause Mortality in Peritoneal Dialysis Patients: A Single-Center Retrospective Cohort Study.

RATIONALE &

OBJECTIVE

Bioelectrical impedance spectroscopy (BIS) is a valuable tool for assessing body composition in patients on peritoneal dialysis (PD), as body composition can significantly change during long-term PD treatment. We aimed to clarify the relationship between time-dependent changes in the extracellular-to-intracellular water ratio (EIR) and all-cause mortality in patients undergoing long-term PD.

STUDY

DESIGN

A single-center, retrospective cohort study.

SETTING &

PARTICIPANTS

This study enrolled adult PD patients who underwent body composition measurements from our bioelectrical impedance spectroscopy-aided fluid management program from May 1, 2012, to April 30, 2023. Patients were followed up until death, withdrawal from PD, or the end of the study.

EXPOSURE: EIR and its covariates.

OUTCOMES: All-cause mortality.

ANALYTICAL APPROACH: Time-dependent Cox proportional hazards, restricted cubic splines, and propensity score matching analyzed risk factors and mortality.

RESULTS

Among the 468 PD patients, the median follow-up period was 2.0 (interquartile range [IQR] 0.6-4.3) years. Three distinct temporal EIR trajectories are found after grouping baseline EIR (bEIR) into quartiles (P interaction < 0.001). Additionally, the optimal cutoff value of bEIR for predicting survival was 0.87. A high bEIR (≥0.87) was associated with a greater risk of mortality than a low bEIR (<0.87, crude hazard ratio, 6.095; P < 0.001). The multivariable time-dependent Cox model showed that the risk of mortality increased by nearly 50% for every 0.1 increase in the EIR (P < 0.001), without significant nonlinearity (P = 0.07). After propensity score matching, the EIR remained an important predictor of the risk of mortality.

LIMITATIONS: The study had a retrospective design.

CONCLUSIONS

The EIR, regarded as either a time-independent or time-dependent variable, is a crucial predictor of mortality in PD patients under regular monitoring of fluid status. Our results also suggest that an EIR of ≥0.87 would be a useful target for predicting the long-term mortality of PD patients in clinical practice.