Continuous Arterial PO(2) and PCO(2) Measurements in Swine during Nitrous Oxide and Xenon Elimination: Prevention of Diffusion Hypoxia

Background: During nitrous oxide (N2 O) elimination, arterial oxygen tension (PaO(2)) decreases because of the phenomenon commonly called diffusive hypoxia. The authors questioned whether similar effects occur during xenon elimination.

Methods: Nineteen anesthetized paralyzed pigs were mechanically ventilated randomly for 30 min using inspiratory gas mixtures of 30% oxygen and either 70% N2 O or xenon. The inspiratory gas was replaced by a mixture of 70% nitrogen and 30% oxygen. PaO(2) and carbon dioxide tensions were recorded continuously using an indwelling arterial sensor.

Results: The PaO(2) decreased from 119 +/- 10 mmHg to 102 +/- 12 mmHg (mean +/- SD) during N2 O washout (P < 0.01) and from 116 +/- 9 mmHg to 110 +/- 8 mmHg during xenon elimination (P < 0.01), with a significant difference (P < 0.01) between baseline and minimum PaO(2) values (Delta PaO(2), 17 +/- 6 mmHg during N2 O washout and 6 +/- 3 mmHg during xenon washout). The PaCO(2) value also decreased (from 39.3 +/- 6.3 mmHg to 37.6 +/- 5.8 mmHg) during N2 O washout (P < 0.01) and during xenon elimination (from 35.4 +/- 1.6 mmHg to 34.9 +/- 1.6 mmHg; P < 0.01). The Delta PaCO(2) was 1.7 +/- 0.9 mmHg in the N2 O group and 0.5 +/- 0.3 mmHg in the xenon group (P < 0.01).