Continuous, in vivo pulmonary venous admixture from fiberoptically measured hemoglobin saturations

In six anesthetized swine, pulmonary venous admixture ( sp/ t) was calculated by four methodsa) sp/ t 1, fiberoptically measured arterial and mixed venous Hgb saturation (Sao2 and Svo2), Pao2 and Pvo2 derived from saturations; b) sp/ t 2, fiberoptically measured Sao2 and Svo2, Pao2 and Pvo2 measured by blood gas analysis; c) sp/ t 3, Pao2 and Pvo2 measured by blood gas analysis, Sao2 and Svo2 derived from tensions; d) sp/ t 4, Sao2 and Svo2 measured by bench oximetry, Pao2 and Pvo2 derived from saturations. Input from the fiberoptic catheters was fed into a computer programmed to calculate sp/ t 1 every 20 sec. Fifty-eight of these values were compared with simultaneously calculated sp/ t 2, 3, and 4. There was no difference between fiberoptic and derived Sao2 or fiberoptic and cooximetric Svo2. Correlations and slopes for sp/ t 1 with sp/ t 2, 3, and 4 were significant (p < .05). Comparing mean differences, sp/ t 1 was significantly different only from sp/ t 3 (p < .01). We conclude that dual oximetry reliably tracks sp/ t.