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Arterial oxygen partial pressures during nitrous oxide and xenon elimination


A fall in arterial oxygen partial pressure (PaO2) during nitrous oxide (N2O) elimination is a well known phenomenon denominated as diffusive hypoxia that is caused by the relatively fast N2O-elimination compared with the slower simultaneous N2-uptake. On the one hand, the occurence of diffusive hypoxia during Xenon (Xe) elimination could be supposed because of the rapid recovery from an inhalational (Xe)-anesthesia that can be explained by the low blood/gas partition coefficient (λXe = 0.l4, λN20 = 0.47). On the other hand, since diffusion of gas molecules is highly dependent on molecular weight (MWN2 = 28, MWN2O = 44, MWXe = 133), the velocity of Xe-elimination should not exceed N2-uptake very much. Therefore we compared PaO2 during the course of Xe- and N2O elimination.


After approval by the institutional animal ethics committee 11 pigs (Xe group=6, N2O=5) were anestethized and paralyzed. The animals were ventilated using a standard semiclosed anesthesia circuit (Cicero EM, Drägerwerk AG, Germany) with a fresh gas flow (70% Xe + 30% O2 or 70% N2O + 30% O2) corresponding to the minute ventilation. Ventilatory parameters were: tidal volume (Vt) = 12 ml/kg BW, respiratory time (f) = 12/min, inspiration rate (Ti) = 1.5 s, inspiratory breath hold = 1.0 s. After equilibration (45 min) fresh gas composition was switched from Xe or N2O respectively to nitrogen (N2) keeping FiO2 as well as the ventilatory parameters constant. PaO2 was measured continuously throughout the equilibration period and up to 15 min after switching to N2 by the continuous blood gas monitoring device Paratrend 7 (Biomedical Sensors, New York, NY).


Data are mean ± SD, *P < 0.05 RS Mann Whitney.

figure 1

Data are mean ± SD, *P < 0.05 RS Mann Whitney.


Since PaO2 decreased to a much lesser degree during Xe-elimination compared with N2O. Diffusive hypoxia during recovery from Xe-anesthesia seems to be unlikely to occur.


We thank Drägerwerk AG, Germany for kindly providing us the Cicero-Xenon EM.

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Stahl, W., Handschuh, T., Calzia, E. et al. Arterial oxygen partial pressures during nitrous oxide and xenon elimination. Crit Care 2 (Suppl 1), P108 (1998).

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