Denitrogenation in pregnancy.

This study measured nitrogen washout in ten pregnant and nine non-pregnant women to understand better how pregnancy effects denitrogenation. Nitrogen concentration was monitored continuously while the women breathed 100 per cent O2 for three minutes and took four deep breaths of 100 per cent O2 using a circle anaesthesia system and 8 L.min-1 fresh gas flow. Parturients achieved 95 per cent denitrogenation significantly (P less than 0.0005) faster than non-pregnant women (54.5 +/- 17.8 vs 110.8 +/- 35.7 sec). In parturients, denitrogenation for three minutes lowered expired N2 concentration to 1.0 +/- 0.2 per cent while four deep breaths lowered it to 5.1 +/- 1.7 per cent (P less than 0.0001). This difference, while statistically significant, is predicted to supply only 10-15 sec of extra protection against hypoxaemia, and thus is probably not clinically significant. The authors conclude that either two minutes of tidal breathing or four deep breaths of 100 per cent O2 provide adequate denitrogenation and similar protection against apnoeic hypoxaemia in normal parturients.