Association between intradialytic central venous oxygen saturation and ultrafiltration volume in chronic hemodialysis patients

BACKGROUND: Cardiac disease is highly prevalent in hemodialysis (HD) patients. Decreased tissue perfusion, including cardiac, due to high ultrafiltration volumes (UFVs) is considered to be one of the drivers of cardiac dysfunction. While central venous oxygen saturation (ScvO(2)) is frequently used as an indicator of cardiac output in non-uremic populations, the relationship of ScvO(2) and UFV in HD patients remains unclear. Our aim was to determine how intradialytic ScvO(2) changes associate with UFV. METHODS: We conducted a 6-month retrospective cohort study in maintenance HD patients with central venous catheters as vascular access. Intradialytic ScvO(2) was measured with the Critline monitor. We computed treatment-level slopes of intradialytic ScvO(2) over time (ScvO(2) trend) and applied linear mixed effects models to assess the association between patient-level ScvO(2) trends and UFV corrected for body weight (cUFV). RESULTS: We studied 6042 dialysis sessions in 232 patients. In about 62.4% of treatments, ScvO(2) decreased. We observed in nearly 80% of patients an inverse relationship between cUFV and ScvO(2) trend, indicating that higher cUFV is associated with steeper decline in ScvO(2) during dialysis. CONCLUSIONS: In most patients, higher cUFV volumes are associated with steeper intradialytic ScvO(2) drops. We hypothesize that in a majority of patients the intradialytic cardiac function is fluid dependent, so that in the face of high ultrafiltration rates or volume, cardiac pre-load and consequently cardiac output decreases. Direct measurements of cardiac hemodynamics are warranted to further test this hypothesis.