Position of the catheter tip to the left of the zero point was defined as positive and to the right as negative. Distances were recorded in centimeters. After proper location of the catheter was confirmed, the SAT-2 oximetry system was calibrated to CO-oximetry (in vitro SvO,) and the current hematocrit (Hct) and hemoglobin (Hgb) values were entered into the saturation computer. The HEMOPRO, system also had the current Hct and Hgb values entered into its saturation computer as recommended by the manufacturer. The Oximetrix 3 system does not require entry of Hgb or Hct values into the saturation computer.
The study began immediately after calibration of each catheter. Blood samples for comparison were obtained every 15 min for 3 h, and hourly for an additional 9 h, with a final sample obtained at 24 h. The in vivo SvO was recorded immediately before and after each sample was drawn. This pair of in vivo values was then averaged and compared with the corresponding in vitro SvO. The blood samples were withdrawn from the distal port of the PA catheter after an initial volume of approximately 10 ml was withdrawn to clear the flush solution from the lumen of the PA catheter and stopcock. The sample for analysis was then collected anaerobically into a 3-ml heparinized syringe. Each sample was withdrawn over approximately 1 min to minimize the possibility of obtaining a retrograde, arterialized sample.