Prognostic impact of segmental extracellular water to total body water ratio in cardiovascular surgery patients

Abstract

Background and aims

Perioperative fluid management is a key component of care for patients undergoing cardiovascular surgery. The ratio of extracellular water to total body water (ECW/TBW) has been recognized as a valuable biomarker for perioperative assessment, as it integrates information regarding fluid retention, muscle wasting, and nutritional status. However, evidence regarding the clinical utility of ECW/TBW and its association with long-term postoperative outcomes in cardiovascular surgery remains limited. This study aimed to investigate the prognostic value of ECW/TBW for long-term mortality in patients undergoing cardiovascular surgery.

Methods

This retrospective cohort study included consecutive patients who underwent elective cardiovascular surgery between October 2016 and March 2021 at Nagoya Heart Center, Japan. ECW/TBW was assessed using bioelectrical impedance analysis before surgery and measured for the whole body, as well as each segment of the extremities. The association between ECW/TBW and all-cause mortality after discharge was assessed using Kaplan–Meier and multivariate Cox regression analyses. The cut-off value for all-cause mortality at each segmental ECW/TBW was calculated using the receiver operating characteristic curve.

Results

In total, 859 patients were included in this study (mean age = 68.4 ± 11.9 years, 67.6 % male). Whole-body ECW/TBW showed a significant positive correlation with log NT-proBNP (ρ = 0.51, p < 0.001) and age (ρ = 0.58, p < 0.001) and negative correlation with skeletal muscle mass index (ρ = −0.33, p < 0.001), body mass index (ρ = −0.22, p < 0.001), peak grip strength (ρ = −0.60, p < 0.001), knee extension isometric muscle strength (ρ = −0.51, p < 0.001), and Geriatric Nutritional Risk Index (ρ = −0.51, p < 0.001). The mean follow-up period was 907.6 ± 500.8 days, during which 46 patients (5.4 %) died. Kaplan–Meier survival curves based on ECW/TBW tertiles showed that higher ECW/TBW was associated with worse prognosis (log-rank test, p < 0.001). Cox regression analysis showed an independent association between ECW/TBW and mortality risk, even after adjusting for multiple confounding factors. The cut-off values for all-cause mortality, derived from the receiver operating characteristic curve, were 0.396 (area under the curve [AUC], 0.768) for whole-body ECW/TBW, 0.390 (AUC, 0.764) for upper-extremity ECW/TBW, and 0.398 (AUC, 0.764) for lower-extremity ECW/TBW.

Conclusions

The segmental ECW/TBW is a useful predictor of long-term mortality in patients undergoing cardiovascular surgery. Although ECW/TBW strongly correlates with muscle mass and physical function, this correlation weakens at higher ECW/TBW levels, affecting measurement accuracy. Therefore, combining these measures may achieve more accurate postoperative risk stratification.