Predicting postoperative pulmonary function in patients undergoing lung resection

Our aim was to determine the effect of lung resection on spirometric lung function and to evaluate the accuracy of simple calculation in predicting postoperative pulmonary function in patients undergoing lung resection.

We reviewed preoperative and postoperative pulmonary function test results on patients who were followed in the multidisciplinary lung cancer clinic between July 1991 and March 1994 and who underwent lung resection. The predicted postoperative FEV1 and FVC were calculated based on the number of segments resected and were compared with the actual postoperative FEV1 and FVC.

This study was conducted at a university, tertiary referral hospital.

All patients were evaluated at a multidisciplinary lung cancer clinic and underwent lung resection by one surgeon (L.A.L.).

Sixty patients undergoing 62 pulmonary resections were reviewed. The predicted postoperative FEV1 and FVC were calculated using the following formula: predicted postoperative FEV1 (or FVC) = preoperative FEV1 (or FVC) x (1-(S x 0.0526)); where S = number of segments resected. The actual postoperative FEV1 and FVC correlated well with the predicted postoperative FEV1 and FVC for patients undergoing lobectomy (r = 0.867 and r = 0.832, respectively); however, the predicted postoperative FEV1 consistently underestimated the actual postoperative FEV1 by approximately 250 mL. For patients undergoing pneumonectomy, the actual postoperative FEV1 and FVC did not correlate as well with the predicted postoperative FEV1 and FVC (r = 0.677 and r = 0.741, respectively). Although there was considerable variability, the predicted postoperative FEV1 consistently underestimated the actual postoperative FEV1 by nearly 500 mL. Of the patients undergoing lobectomy, eight also received postoperative radiation therapy. When analyzed separately, patients receiving combined therapy lost an average of 5.47% of FEV1 per segment resected. This contrasts with a 2.84% per segment reduction in FEV1 for patients who did not receive radiation therapy.

This simple calculation of predicted postoperative FEV1 and FVC correlates well with the actual postoperative FEV1 and FVC in patients undergoing lobectomy. The predicted postoperative FEV1 consistently underestimated the actual postoperative FEV1 by approximately 250 mL. The postoperative FEV1 and FVC for patients undergoing pneumonectomy is not accurately predicted using this equation. The predicted postoperative FEV1 for patients undergoing pneumonectomy was underestimated by an average of 500 mL and by greater than 250 mL in 12 of our 13 patients. Thus, by adding 250 mL to the above calculation of predicted postoperative FEV1, we improve our ability to we identify a minimal postoperative FEV1 for patients undergoing pneumonectomy. Finally, combined modality treatment with surgery followed by radiation therapy may result in additive lung function loss.