Interactions between intradialytic central venous oxygen saturation, relative blood volume, and all-cause mortality in maintenance hemodialysis patients.

Introduction: In maintenance hemodialysis (HD) patients, low central venous oxygen saturation (ScvO ) and small decline in relative blood volume (RBV) have been associated with adverse outcomes. Here we explore the joint association between ScvO and RBV change in relation to all-cause mortality.

Methods: We conducted a retrospective study in maintenance HD patients with central venous catheters as vascular access. During a 6-month baseline period, Crit-Line (Fresenius Medical Care, Waltham, MA) was used to measure continuously intradialytic ScvO and hematocrit-based RBV. We defined four groups per median change of RBV and median ScvO . Patients with ScvO above median and RBV change below median were defined as reference. Follow-up period was 3 years. We constructed Cox proportional hazards model with adjustment for age, diabetes, and dialysis vintage to assess the association between ScvO and RBV and all-cause mortality during follow-up.

Findings: Baseline comprised 5231 dialysis sessions in 216 patients. The median RBV change was -5.5% and median ScvO was 58.8%. During follow-up, 44 patients (20.4%) died. In the adjusted model, all-cause mortality was highest in patients with ScvO below median and RBV change above median (HR 6.32; 95% confidence interval [CI] 1.37-29.06), followed by patients with ScvO below median and RBV change below median (HR 5.04; 95% CI 1.14-22.35), and ScvO above median and RBV change above median (HR 4.52; 95% CI 0.95-21.36).

Discussion: Concurrent combined monitoring of intradialytic ScvO and RBV change may provide additional insights into a patient's circulatory status. Patients with low ScvO and small changes in RBV may represent a specifically vulnerable group of patients at particularly high risk for adverse outcomes, possibly related to poor cardiac reserve and fluid overload.