The percentage of inspired oxygen at different flow rates during nebulisation

The aim of this study was to determine the mean value for the fraction of inspired oxygen (FiO2) in normal subjects at oxygen flow rates of 2L/min, 4L/min and 6L/min during mouthpiece nebulisation. The FiO2 was defined as the fractional extraction of oxygen at the mouth. The variation in the FiO2 during normal and deep breathing was also studied in order to assess whether a significant difference in the FiO2 occurred. Breathing at a normal tidal volume, the values of the FiO2 were 27.5 per cent, 30.8 per cent and 34.9 per cent respectively. The values during deep breathing were 24.4 per cent, 27.9 per cent and 31.3 per cent respectively. It was clearly evident that the FiO2 during deep breathing was approximately 3 per cent less than that during normal tidal breathing.