Pulmonary physiology in the postoperative period

After upper abdominal or thoracic surgery, loss of lung volume, manifested most importantly by reduced FRC, and abnormal gas exchange, manifested by postoperative reduction in PaO2, are the rule rather than the exception. These physiologic alterations in lung function occur in the absence of superimposed complications such as pneumonia and/or lobar atelectasis; the usual physiologic alterations do, in fact, predispose to pulmonary complications (approximate 20 per cent incidence) which, when present, further compromise lung function. The mechanisms of postoperative impairment in lung function are multiple, interactive, and at the present, incompletely understood. An attempt to summarize the more important causes of impaired postoperative lung function is shown in Figure 6.