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

IntroductionIn maintenance hemodialysis (HD) patients, low central venous oxygen saturation (ScvO(2)) and small decline in relative blood volume (RBV) have been associated with adverse outcomes. Here we explore the joint association between ScvO(2) and RBV change in relation to all-cause mortality. MethodsWe 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(2) and hematocrit-based RBV. We defined four groups per median change of RBV and median ScvO(2). Patients with ScvO(2) 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(2) and RBV and all-cause mortality during follow-up. FindingsBaseline comprised 5231 dialysis sessions in 216 patients. The median RBV change was -5.5% and median ScvO(2) was 58.8%. During follow-up, 44 patients (20.4%) died. In the adjusted model, all-cause mortality was highest in patients with ScvO(2) below median and RBV change above median (HR 6.32; 95% confidence interval [CI] 1.37-29.06), followed by patients with ScvO(2) below median and RBV change below median (HR 5.04; 95% CI 1.14-22.35), and ScvO(2) above median and RBV change above median (HR 4.52; 95% CI 0.95-21.36). DiscussionConcurrent combined monitoring of intradialytic ScvO(2) and RBV change may provide additional insights into a patient's circulatory status. Patients with low ScvO(2) 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.