Prevention and treatment of postoperative atelectasis. Can it and will it be adequately studied?

Pul monary atelectasis is the most common post-operative respiratory complication encountered today , and considerable time and resources are being directed toward its evaluation and management. Treatment modalities which are commonly employed for the prevention or treatment of atelectasis include voluntary deep breathing, incentive spirometry, intermittent positive pressure breathing (IPPB), chest physical therapy, bronchoscopy, aerosol therapy, and more recently, intermittent continuous positive airway pressure (CPAP) by mask. Studies which have attempted to compare or evaluate therapeutic techniques have generally added more confusion than enlightenment because of faulty design and failure to consider the mechanisms, clinical relevance, and natural history of the disorder. In most patients, the development of postoperative atelectasis is attributable to the absence of periodic deep breaths. This occurs in association with a reduction in lung volumes and expiratory flow rates.' Absence of periodic lung expansion also results in decreased surfactant activity which contributes to a reduction in functional residual capacity and to early airway closure.2'3 In patients undergoing open heart surgery, the frequent occurrence of left lower lobe atelectasis appears to correlate best with phrenic nerve and diaphragm dysfunction.43 Because of differences in the mechanism of atelectasis, it may be impossible to compare results of therapy in open heart surgery with other abdominal or thoracic procedures. The natural history of postoperative atelectasis is that spontaneous improvement occurs as periodic deep breathing returns and lung volumes and flow rates increase. Most postoperative atelectasis is not clinically significant and requires no specific therapy. The devotion of extension time and resources to the study of transient and clinically irrelevant postopera-tive atelectasis is not likely to serve any useful purpose. Up to 90 percent of patients undergoing open heart surgery will develop roentgenographic evidence of lower lobe atelectasis, usually on the left, but only a small fraction of these patients experience a true clinical complication that justifies specific treatment. Therefore, any study which uses patients with postop-erative atelectasis following open heart surgery as a target group must define the clinical relevance of the disease in the group or subgroup of patients studied and must be designed to distinguish the natural course of improvement from the response attributable to the treatment modality. Finally, it is very likely that favorable or unfavorable results of therapy in patients with open heart surgery cannot he translated to other surgical patients because of differences in the pathophysiology of the disease. It is critical in the design …