Each manufacturer supplied the saturation computer, optical module, and oximetry PA catheters that were used in the study. Representatives from each company instructed two of the authors (P.E.S. and L.C.H.) in the proper use of the instruments. Several catheters from each manufacturer were placed in patients before initiation of the comparative study. Proper insertion technique and use of the equipment were confirmed by the company representatives during these prestudy trials.
The performance of the three instruments was evaluated by comparing the SvOa obtained using the PA oximetry system (in vivo SvOj) with that from a blood sample drawn from the distal port of the catheter (in vitro SvOJ analyzed using an Instrumentation Laboratory IL-282 CO-oximeter (Lexington, Mass) as the criterion standard. This device determines the relative concentrations of oxyhemoglobin, deoxyhemoglobin, methemoglobin, and carboxy-hemoglobin using a four-reference wavelength spectrophotometric technique. The instrument was maintained and calibrated according to the manufacturers specifications. Yearly maintenance was performed by a factory representative before the start of the study.