[Relationship between mixed venous saturation and cardiac index, hemoglobin and oxygen consumption in aortic surgery]

Mixed venous oxygen saturation (SvO2) depends mainly on four variables: cardiac index (CI), hemoglobin concentration (Hb), arterial oxygen saturation (SpO2) and oxygen consumption (VO2). Our aim was to study the correlation between each of these variables and SvO2 during abdominal aortic surgery, a situation which is of special interest because of associated hemodynamic and metabolic variations and the high risk of cardiovascular events.

Twelve patients undergoing intrarenal aortic surgery were monitored by pulmonary artery catheter (Opticath), pulse oximetry and indirect calorimetry (Deltatrac Metabolic Monitor). SvO2, CI (measured by thermodilution), SpO2 and VO2 at six moments: post-induction (baseline), 1 min before and 1 min after clamping (pre-C, post-C), 1 min (post-D) and 10 min after declamping and at the end of the surgery. Hemoglobin concentration was measured at all moments except 10 min after declamping.

All variables except SpO2 varied significantly (p < 0.001) during the study. SvO2 was associated with CI at all moments except post-D and at the end of surgery. Hemoglobin concentration was related to SvO2 at baseline and post-C. We found no correlation between SvO2 and VO2 or SpO2 at any moment.

Monitoring SvO2 in patients undergoing aortic surgery is useful for detecting potentially prejudicial variations in cardiac output or hemoglobin concentration.