Mechanisms of postoperative pulmonary dysfunction.

Postoperative pulmonary complications are not uncommon, and the factors that contribute to lung dysfunction are well documented. Postoperative pain, spasm, and paralysis are all known to reduce lung function, although relief of pain does not completely restore function. Rather, diaphragmatic dysfunction has been found to persist even with adequate pain relief. Functional residual capacity is reduced both by the supine position and anesthesia. During anesthesia, the reduced FRC can contribute to airway closure during expiration and to a compression atelectasis that in turn precipitates hypoxemia and infection. Muscle paralysis can also create or contribute to atelectasis. Microthromboembolism impedes perfusion distribution, adding to the other causes of a ventilation-perfusion mismatch. Different anesthetic techniques and intraoperative management may help prevent or reduce the incidence of postoperative lung complications.