Variations in lung volume and compliance during pulmonary surgery.

Functional residual capacity (FRC) and breath-by-breath compliance of the ventilatory system (Crs) were measured in 10 mechanically ventilated patients during anaesthesia for lung surgery (pneumonectomy, lobectomy, lung or pleural resections or exploratory thoracotomy). In eight patients not requiring pneumonectomy, FRC of the lower lung decreased by 8 +/- 9% (mean +/- 1 SD) (P less than 0.05) while that of the upper lung increased by 75 +/- 24% (P less than 0.001) when the patient was turned to the lateral position. When the pleura was opened, FRC of the lower lung decreased by a further 10 +/- 10% (P less than 0.01). One-lung ventilation (OLV), however, increased FRC of the lower lung back to the value found in the supine position before surgery. When two-lung ventilation was re-established, FRC of the lower lung was about the same as during corresponding stages before OLV. In the two patients who underwent pneumonectomy, FRC of the remaining lung was about 30% greater after OLV than at corresponding stages before surgery. In the patients not requiring pneumonectomy, Crs decreased from 29 +/- 6 ml/cm H2O to 23 +/- 6 ml/cm H2O (P less than 0.05) on the lower side when the patient was turned on his side. The corresponding figures on the upper side were 24 +/- 8 ml/cm H2O and 30 +/- 5 ml/cm H2O respectively (P less than 0.05). There was no further significant change when the pleura was opened. After surgery when the patient was turned to the supine position, Crs of the lung not operated on was almost the same as before surgery.