Measurement of right atrial oxygen saturation by fiberoptic oximetry accurately reflects mixed venous oxygen saturation in swine

Continuous fiberoptic measurement of mixed venous oxygen saturation (SvO₂) via a pulmonary artery catheter is a useful, though invasive, monitoring technique. Continuous right atrial venous oxygen saturation measurement by oximetry offers the potential of a significantly less invasive SvO₂ measurement. However, catheter motion, character of the vessel, chamber wall reflection, the filtering technique involved in calculating oxygen saturation, and the streaming of venous blood prior to ventricular mixing may influence the feasibility of continuous right atrial (RA) SvO₂ measurement. This study investigated the performance of fiberoptically measured RA SvO₂, at a position 2 cm from the tricuspid valve, relative to simultaneously measured pulmonary artery (PA) SvO₂. Ten pigs were subjected to circulatory shock or chemically induced lung damage. Over a total monitoring period of approximately 40 hours, 464 paired data points were sampled at 5-minute intervals. The difference between the overall means of RA and PA SvO₂ was 0.91% with a standard error of the estimate of 4.7%, a regression equation of RA SvO₂=PA SvO₂ (0.94 + 2.1) PA So₂, and a correlation coefficient of 0.94. Our conclusion, although extrapolated from a pig model, is that fiberoptic SvO₂ monitoring may be accomplished less invasively and at a lower cost with a right atrial catheter.