Mixed venous versus central venous oxygen saturation in patients undergoing on pump beating coronary artery bypass grafting

Objective: To examine the validity of central venous oxygen saturation (ScvO 2 ) as a numerical substitution of mixed venous oxygen saturation (SvO 2 ) in adult patients undergoing normothermic on pump beating coronary artery bypass grafting (CABG). Materials and Methods: Prospective clinical observational study was done at King Khalid University Hospital, King Saud University, Riyadh, Kingdom of Saudi Arabia. Thirty four adult patients scheduled for coronary artery surgery were included. Patients were monitored by a pulmonary artery catheter (PAC) as a part of our routine intraoperative monitoring. SvO 2 and ScvO 2 were simultaneously measured 15 minutes ( T 1) and 30 minutes ( T 2) after induction of anesthesia, 15 and 30 minutes after initiation of cardiopulmonary bypass ( T 3 and T 4), and 15 and 30 minutes after admission to intensive care unit ( T 5 and T 6). Results: ScvO 2 showed higher reading than SvO 2 all through our study. Our results showed perfect positive statistically significant correlation between SvO 2 and ScvO 2 at all data points. Individual mean of difference (MOD) between both the readings at study time showed MOD of 1.34 and 1.44 at T 1 and T 2 simultaneously. This MOD was statistically insignificant, but after on pump beating normothermic bypass was initiated; MOD was 5.2 and 4.4 at T 3 and T 4 with high statistical significance. In ICU, MOD continues to have high statistical significance, MOD was 6.3 at T 5 and at T 6 it was 4.6. Conclusions: In on pump beating CABG patients; ScvO 2 and SvO 2 are not interchangeable numerically. ScvO 2 is useful in the meaning of trend; our data suggest that ScvO 2 is equivalent to SvO 2 , only in the course of clinical decisions as long as absolute values are not required.