[Comparison of oxygen saturations in mixed venous and central blood during thoracic anesthesia with selective...

To establish the ratio of oxygen saturation in mixed venous to that of central venous blood in patients undergoing thoracic surgery, in order to rationalize use of the pulmonary arterial catheter.

We compared simultaneous spectrophotometric in vivo measurements for SvO2 [Abbott Oximetrix 3/SvO2 (O)] and in vitro analysis of blood taken from the distal opening of the catheter (co-oximeter/SvO2 [CO]), with in vitro analysis of central venous blood from the superior vena cava (co-oximetry/SvcO2 [CO]) for 23 patients scheduled for lung resection by thoracotomy in lateral decubitus with single lung ventilation and the same type of monitoring and anesthesia. Measurements were taken 15 min after induction (M1), after 15 minutes in lateral decubitus (M2), 5 minutes after pleurotomy (M3), 5 min (M4) and 20 min (M5) after lung collapse, 5 min after closure of the thoracic wall (M6) and after 5 min supine (M7).

SvO2(O) was higher than SvcO2 (CO) at M1, M3, M6 and M7 and the mean difference between the two concentrations was always less than 0.9%. SvcO2 (CO) was always higher than SvO2 (CO) (M1 to M7) and the mean difference was less than 1.3%. Simple linear correlation was significant (p < 0.001) for each of the measurements as well as for the whole sample. Both bias (0.2 and 0.7%) and its standard deviation (2.7 and 2.5%) between the two techniques were small and the differences between all measurements were less than 5% in 97 and 95.6%.

For thoracic anesthesia in patients who are not good candidates for catheterization of the pulmonary artery, continuous measurement of SvO2 may be substituted for that of SvcO2 in order to monitor the balance of supply/demand.