The changes in the oxygen saturations in the superior vena cava and the pulmonary artery are not the same during cardiac surgery

Abstract Objective To evaluate the changes over time (trend) in sign and magnitude for S SV O 2 and S V O 2 during and after cardiac surgery. Patients and methods A prospective and observational study was conducted on 34 cardiac surgery patients. Venous blood samples were taken simultaneously from the introductory (S VC O 2 ) and distal (S V O 2 ) port of the pulmonary artery catheter at predefined intervals. Systemic and pulmonary hemodynamic variables were measured at the same time. The trend was calculated as the difference between 2 consecutive measurements (tSO 2 ). Data were processed with ANOVA for multiple comparisons, Pearson correlation coefficient and Bland–Altman analysis. Results There was a significant correlation between S VC O 2 and tS V O 2 ( R 2  = 0.55), the mean of the differences was 0.36 ± 7.75%, and the limits of agreement ranged from −15.1 to 15.9%. The sign of the trend was similar in 85.1% of the paired data. However, the magnitude of the changes in tS VC O 2 and tS V O 2 were not always equivalent. Between 0 and 5% of the change in the tS VC O 2 was coincident with only 44.7% of the tS V O 2 . A wide variation was found between both trends when the signs and magnitudes of the changes were taken into account. Conclusions When considering the sign and magnitude, the change over time of central venous O 2 saturations were not interchangeable in cardiac surgery patients. Clinical decisions based exclusively on tS VC O 2 monitoring should be taken with caution.