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.