[Determination of pulmonary diffusing capacity during artificial ventilation (author's transl)]

Pulmonary diffusing capacity may be determined by rebreathing techniques using various test gases. The errors caused by functional inhomogenities are smaller with the rebreathing method than those found in the single-breath technique. However, until now there have been some disadvantages to the clinical application of the rebreathing technique. In the present paper, a modification of the rebreathing technique suggested by Piiper, Scheid, Meyer and Adaro (1975 and 1976), in which pulmonary diffusing capacity for carbon monoxide, DCO(RB), is measured, has been applied to intubated and anesthetised patients. Measurements were performed in 39 surgical patients with healthy lungs during artificial ventilation and narcosis. Under these conditions all patients had a DCO(RB) greater than or equal to 75 ml/min . kPa (10 ml/min.torr). The coefficient of variation for duplicate measurements was +/- 4.2%. In the same patients DCO-single-breath-measurements, DCO(SB), were also made. There was a significant (p less than 0.0001) correlation between DCO(RB) in artificially ventilated, anaesthetised patients in a supine position and DCO(SB) for spontaneously breathing, awake patients in a sitting position. A linear regression analysis of the data showed the DCO(SB) was related to DCO(RB) in the following manner: DCO(SB) = 1.62DCO(RB) = 4.44 (ml/min.torr) (r = 0.71, n = 39). The mean value of DCO(RB) was 53.4% of the mean value of DCO(SB). This difference may be due to the combination of different techniques used and different conditions during the measurements (reduced FRC, difference in F1O2 etc.). The histogramm of the distribution of DCO(RB) had a similar form to that of DCO(SB). The modified method has a high reproducibility and can easily be performed as a bed-side test without disturbance to patients with an endotracheal tube.