Changes in Central Venous Oxygen Saturation During Inpatient Hemodialysis

Background: Established tools to guide fluid removal during hemodialysis (HD) are lacking, particularly in the inpatient setting, where lingering effects of acute illness and impaired cardiovascular compensatory mechanisms render patients particularly susceptible to hemodynamic instability. Central venous oxygen saturation (ScvO2) is a commonly used surrogate for cardiac output in the critical care setting. We sought to evaluate whether intradialytic ScvO2 is associated with ultrafiltration (UF) and blood pressure during HD in hospitalized patients. Methods: We conducted a prospective observational study of patients receiving inpatient HD through a central venous catheter at an academic university hospital between March 2022-April 2025. Patients had continuous hematocrit and central oxygen monitoring throughout HD (using CritLine-IV®). Data from continuous monitoring was not provided to clinical teams who made decisions about HD prescriptions and interventions. Linear mixed effects models were used to examine trends in ScvO2 throughout HD. To compare patients, we indexed the ratio of the change in ScvO2 to UF volume. Mixed effects models were used to examine the relationship between ScvO2, UF, blood pressure, and the need for interventions during HD. Results: We analyzed data from 186 HD sessions among 127 patients (55% with end-stage kidney disease and 45% with acute kidney failure). Mean (SD) age was 56.8±14.7 years, 56.7% were men, and mean (SD) ultrafiltration rate was 7.75±3.51 ml/kg/h. The mean (SD) starting ScvO2 was 65.2±7.7% and decreased in 58.6% of HD sessions, with a population average decline of 0.3±0.2%/h. Using the ratio of ScvO2 to UF, each 0.1%/h drop in ScvO2 per ml/kg UF was associated with a 5 mmHg lower nadir systolic blood pressure during HD. Moreover, each 1%/h drop in ScvO2 per ml/kg UF was associated with increased risk of subsequent intervention (unadjusted OR 1.22, 95% CI 1.06, 1.40), which was accentuated in the acute kidney injury group (unadjusted OR 1.63, 95% CI 1.01, 2.65) even after adjustment for age, sex, pre-HD blood pressure, and heart failure diagnosis (adjusted OR 1.63, 95% CI 1.07, 2.48). Conclusion: Routine blood pressure and heart rate monitoring are often inadequate to guide fluid removal decisions during HD. Intradialytic change in ScvO2 may be a useful adjuvant tool, particularly for acute kidney failure requiring HD. Funding: NIDDK Support