RE-EXPANSION OF ATELECTASIS DURING GENERAL ANAESTHESIA: A COMPUTED TOMOGRAPHY STUDY

Formation of atelectasis is one mechanism of impaired gas exchangeduring general anaesthesia. We have studied manoeuvres to re-expandsuch atelectasis in 16 consecutive, anaesthetized adults withhealthy lungs. In group 1 (10 patients), the lungs were inflatedstepwise to an airway pressure (Paw) of 10, 20, 30 and 40 cmH₂O In group 2 (six patients), three repeated inflations upto Paw = 30 cm H₂O were followed by one inflation to 40 cm H₂O.Atelectasis was assessed by analysis of computed x-ray tomography(CT). In group 1 the mean area of atelectasis in the CT scanat the level of the right diaphragm was 6.4 cm² at Paw = 0 cmH₂O, 5.9 cm² at 20 cm H₂O, 3.5 cm ² at 30 cm H₂O and 0.8 cm²at 40 cm H₂O, A Paw of 20 cm H₂O corresponds approximately toinflation with twice the tidal volume. In group 2 the mean areaof atelectasis was 9.0 cm² at Paw = 0 cm H₂O and 4.2 cm² afterthe first inflation to 30 cm H₂O. Repeated inflations did notadd to re-expansion of atelectasis. The final inflation (Paw= 40 cm H₂O) virtually eliminated the atelectasis. We concludethat, after induction of anaesthesia, the amount of atelectasiswas not reduced by inflation of the lungs with a conventionaltidal volume or with a double tidal volume ("sigh"). An inflationto vital capacity (Paw = 40 cm H₂O, however, re-expanded virtuallyall atelectatic lung tissue. (Br. J. Anaesth. 1993; 71: 788–795)