Continuous arterial PO2 and PCO2 measurements in swine during nitrous oxide and xenon elimination -: Prevention of diffusion hypoxia

Background During nitrous oxide (N2O) elimination, arterial oxygen tension (Pa-O2) decreases because of the phenomenon commonly called diffusive hypoxia. The authors questioned whether similar effects occur during xenon elimination. Methods: Nineteen anesthetized and paralyzed pigs were mechanically ventilated randomly for 30 min using inspiratory gas mixtures of 30% oxygen and either 70% N2O or xenon. The inspiratory gas was replaced by a mixture of 70% nitrogen and 30% oxygen. Pa-O2 and carbon dioxide tensions were recorded continuously using an indwelling arterial sensor. Results: The Pa-O2 decreased from 119 +/- 10 mmHg to 102 +/- 12 mmHg (mean +/- SD) during: N2O 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 Pa,, values (Delta Pa-O2, 17 +/- 6 mmHg during N2O washout and 6 +/- 3 mmHg during xenon washout). The Pa-CO2 value also decreased (from 39.3 +/- 6.3 mmHg to 37.6 +/- 5.8 mmHg) during N2O 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 Pa-CO2 was 1.7 +/- 0.9 mmHg in the N2O group and 0.5 +/- 0.3 mmHg in the xenon group (P < 0.01). Conclusion: Diffusive hypoxia is unlikely to occur during recovery from xenon anesthesia, probably because of the low blood solubility of this gas.