A comparison of two pulmonary artery mixed venous oxygen saturation catheters during the changing conditions of cardiac surgery.

Continuous mixed venous oxygen saturation (SvO2), using modified pulmonary artery (PA) catheters, can assist in the management of cardiac surgery patients. Two FDA-approved catheters are available for SvO2 monitoring. One system uses two wavelengths of light and the other is a three-wavelength system. The present study was designed to determine the accuracy of the two catheters during cardiac surgery. Sixty-five consecutive patients were assigned to one of the two catheter groups. Data were collected pre- and post-induction, after sternotomy, and after extracorporeal circulation. An updated hematocrit was entered in the two-wavelength system preceding the last two measurements. Patient demographics, severity of preoperative cardiac disease, and intraoperative hemodynamics were comparable between groups. Two-wavelength determinations varied inconsistently from cooximeter values, while three-wavelength measurements did not differ significantly. Changes in hematocrit were responsible in part for the variability in two-wavelength measurements. In summary, three-wavelength measurements by the Shaw system were more accurate than two-wavelength measurements by the Edwards system.