End-tidal oxygraphy during pre-oxygenation in patients with severe diffuse emphysema

We hypothetised that the rate of pre-oxygenation could be altered by the increase in lung volume and airflow obstruction observed in emphysema. End-tidal oxygen concentration was monitored, using a paramagnetic oxygen analyser, during 10-min pre-oxygenation (tidal breathing of 100% oxygen) in 10 normal patients and in 10 patients with severe diffuse emphysema documented by computerised tomography. Emphysema was characterised by an important increase in functional residual capacity of the lungs [190 (23)% of predicted values] and a decrease in expiratory flow. The increase in end-tidal oxygen concentration was slower in the emphysema group than in the control group (p = 0.0024). After 3 and 5 min of pre-oxygenation, the end-tidal fractional oxygen concentration was significantly lower in the emphysema group than the control group [mean (SD); value at 3 min: emphysema: 0.83 (0.06) vs. control: 0.91 (0.02), p = 0.0005]. Individual values of end-tidal oxygen concentration measured after 3, 5 and 10 min of pre-oxygenation were negatively correlated with functional residual capacity in the emphysema group, whereas no such correlation was found in the control group. These results suggest that pre-oxygenation should be monitored in patients with diffuse emphysema to ensure that adequate pre-oxygenation is achieved.