Preoxygenation in parturients: a comparison of 4, 6 and 8 vital capacity breaths to 5 minutes of tidal volume breathing.

We compared the difference in denitrogenation (by intermittent measurement of arterial tension, PaO2) in 45 parturients at term when preoxygenated with 4, 6 or 8 rapid vital capacity breaths and 5 minutes of tidal volume breathing. Oxygen, at 8 litres min-1, was delivered through a facemask via a circle absorber with a 2 litre reservoir bag. Higher PaO2 was produced with 5 minutes of tidal volume breathing. This differed significantly from the PaO2 produced by 4, 6 or 8 rapid vital capacity breaths (p less than 0.01).