Variations in lung volume and compliance during pulmonary surgery

Many factors affect pulmonary function during surgery on the lung. The consequences on lung volume, ventilatory mechanics and the distri-bution of ventilation between the lungs when turning the patient to his side are well docu-mented. Thus, the FRC of the upper lung increases markedly, while that of the dependent lung decreases somewhat. If intermittent positive pressure ventilation is used, the greater fraction of tidal volume is directed to the upper side, the compliance of which is greater than that of the dependent side (Rehder et al., 1972). Less is known about the changes in lung volume which occur during the operative procedure—those brought about by opening the pleura or by one-lung ventilation. As regards postoperative changes, Lambert, Willauer and Dasch (1955) obtained chest x-rays shortly after lung surgery and found marked signs of impared aeration in the dependent lung, suggesting a reduction in volume. However, to our knowledge, lung volume has not been measured directly at this stage. We measured functional residual capacity (FRC), compliance of the ventilatory system and the distribution of ventilation between the lungs during various phases before, during and after thoracic surgery. Interest was focused primarily on the dependent lung, that is, the lung not undergoing surgery. PATIENTS AND METHODS Ten patients undergoing elective pulmonary surgery were studied (table I). Any patient with marked impairment of lung function or cardiac decompensation was not included. Patients gave informed consent and the project was approved b