REEXPANSION OF ATELECTASIS DURING GENERAL-ANESTHESIA - A COMPUTED-TOMOGRAPHY STUDY

Formation of atelectasis is one mechanism of impaired gas exchange dur ing general anaesthesia. We have studied manoeuvres to re-expand such atelectasis in 16 consecutive, anaesthetized adults with healthy lungs . In group 1 (10 patients), the lungs were inflated stepwise to an air way pressure (Paw) of 10, 20, 30 and 40 cm H2O. In group 2 (six patien ts), three repeated inflations up to Paw = 30 cm H2O were followed by one inflation to 40 cm H2O. Atelectasis was assessed by analysis of co mputed x-ray tomography (CT). In group 1 the mean area of atelectasis in the CT scan at the level of the right diaphragm was 6.4 cm2 at Paw = 0 cm H2O, 5.9 cm2 at 20 cm H2O, 3.5 cm2 at 30 cm H2O and 0.8 cm2 at 40 cm H2O. A Paw of 20 cm H2O corresponds approximately to inflation w ith twice the tidal volume. In group 2 the mean area of atelectasis wa s 9.0 cm2 at Paw = 0 cm H2O and 4.2 cm2 after the first inflation to 3 0 cm H2O. Repeated inflations did not add to re-expansion of atelectas is. The final inflation (Paw = 40 cm H2O) virtually eliminated the ate lectasis. We conclude that, after induction of anaesthesia, the amount of atelectasis was not reduced by inflation of the lungs with a conve ntional tidal volume or with a double tidal volume (''sigh''). An infl ation to vital capacity (Paw = 40 cm H2O), however, re-expanded virtua lly all atelectatic lung tissue.