Continuous Measurement of Intraarterial pHa, Paco2, and Pao2, in the Operating Room

Miniaturized sensors based upon the principles of optical fluorescence can measure the pH, Pco2, and Po2 of liquid or gas media. A prototype of a three-component fiberoptic sensor has been developed for intraarterial application by CDI, 3M Health Care, Irvine, California. We report the first study of this continuous intraarterial monitor in patients undergoing surgical procedures under general anesthesia. Fourteen patients participated in the study. The fiberoptic sensor was calibrated before insertion and then passed through an existing 18-gauge radial artery cannula. Blood samples were drawn at frequent intervals through the same cannula for in vitro blood gas analysis. For each of the 87 arterial blood gas samples obtained, the in vitro values of pHa, Paco2, and Pao2 were compared with simultaneous readings from the fiberoptic sensor. For pHa, the mean error (error = fiberoptic value minus in vitro value) or “bias” of the fiberoptic data was −0.032 and the standard deviation of error or “precision” was 0.042. For Paco2, the bias was −3.8 mm Hg and the precision was 4.7 mm Hg. For Pao2, the bias was −9.0 mm Hg and the precision was 23.3 mm Hg. For Pao, values less than 175 mm Hg, the bias was −8.5 mm Hg and the precision was 8.3 mm Hg. Expressed in terms of percentage errors, the bias ± precision values were −11.5% ± 13.3% for Paco2, and −6.2% ± 10.0% for Pao2. The duration of the surgical procedures ranged from 1.6 to 8 h with an average of 4.2 h. Although further refinements in accuracy are needed, particularly for Paco2, this study demonstrates both the feasibility and clinical utility of continuous intraoperative three-component blood gas monitoring.