Use of the anatomical formulae for predicted postoperative (PPO) evaluation overestimates the loss of FEV1 and DLCO after minimally invasive lung resections

Background: Pulmonary function assessment is mandatory before oncological lung resection surgery. To do so, subjects undergo a pulmonary function test (PFT) and the calculation of predicted postoperative (PPO) values to estimate the residual lung function after surgery. The aim of this study is to evaluate the use of anatomical formulae in estimating postoperative pulmonary function in patients undergoing minimally invasive surgery (MIS). Methods: This is a retrospective study. Patients affected by lung cancer who underwent pulmonary lobectomy or segmentectomy with MIS or thoracotomy approach at our center from June 2020 to May 2021 were considered. Exclusion criteria were: subjects who underwent atypical pulmonary resection surgery or pneumonectomy; and patients who underwent adjuvant therapy (chemotherapy or immunotherapy). PFT data measured before and 1 year after surgery were collected. In particular, postoperative PFT data, especially forced expiratory volume in the first second (FEV1) and diffusing capacity for carbon monoxide (DLCO), and PPO values calculated by the anatomical formulae were compared. Secondary endpoints were: analysis of the postoperative pulmonary function in patients who underwent lung resection with the standard approach (thoracotomy) and evaluation of the anatomical formulae accuracy in subjects operated through thoracotomy. Results: The sample consisted of 48 patients operated on MIS (video-assisted thoracoscopic surgery and robotic-assisted thoracoscopic surgery) and 20 subjects who underwent thoracotomy for stage I-IIA and I-IIB lung cancer in both groups. The anatomical formula seemed to underestimate the postoperative FEV1% by 8.65% [interquartile range (IQR), 0.5-17.28%; P<0.001]. Furthermore, when comparing postoperative PPODLCO% and post-operative DLCO%, a significant difference was shown with an underestimation of the actual postoperative value of 2.78% (IQR, -3.63% to 10.47%; P=0.045). Conclusions: Our results confirmed that the anatomical formulae currently used to predict postoperative pulmonary function are reliable in the case of the standard approach (thoracotomy), while they tend to overestimate the loss of FEV1 and DLCO in the postoperative period in patients who were operated on MIS, thus excluding some subjects from the operation.