Clinical comparison of two- and three-wavelength systems for continuous measurement of venous oxygen saturation

OBJECTIVE: To evaluate clinically the accuracy of continuous SvO2 systems to reflect reference SvO2 values over a 24-hour period. DESIGN: Randomized clinical trial. SETTING: Six-bed cardiac surgical intensive care unit of a 540-bed federal facility. POPULATION: Sixty postoperative cardiac patients. INTERVENTIONS: Random assignment to a two- or three-wavelength continuous SvO2 catheter for postoperative SvO2 monitoring. At 4-hour intervals over a 24-hour period, mixed venous blood samples were analyzed with a reference cooximeter and compared with the monitor value of the SvO2 catheter. MAIN OUTCOME MEASURES: A reference cooximeter method to measure SvO2 in mixed venous blood; SvO2 as measured by the in-line, SvO2 catheter system. RESULTS: SvO2 measured by the three-wavelength system did not differ significantly from the reference SvO2 measurement. In contrast, SvO2 measured by the two-wavelength system was significantly lower than the reference SvO2 measurement within 4 hours of admission to the critical care unit and remained significantly lower throughout the 24-hour study period. CONCLUSIONS: The results of this clinical study confirmed a previous study in dogs, showing that SvO2 is measured more accurately by the three-wavelength continuous monitoring system.