Lung function test
A preoperative evaluation of lung function was performed, and the results were classified according to lung function test guidelines issued by the Chinese Society of Respiratory Medicine.[16]Values were determined for the percentage of predicted value of the forced expiratory volume in the first second (FEV1% pre), percentage of predicted value of the ratio of forced expiratory volume in the first second (FEV1) to forced vital capacity (FVC) (FEV1/FVC% pre), percentage of predicted value of maximal mid-expiratory flow (MMEF% pre), and the percentage of predicted value of maximal mid-expiratory flow mid-expiratory flow (MEF% pre). The FVC% pre is the main indicator of restrictive ventilatory dysfunction. The criterion for obstructive ventilation disorder was a FEV1/FVC% pre value ≥ 92% or a FEV1% pre < 80%, and the criterion for small airway dysfunction was at least two values of MMEF% pre, MEF50% pre, and MEF25% being lower than the lower limit of normal (LLN, 65%). The severity of ventilatory dysfunction was based on FEV1% pre: mild (70%-79%), moderate (60-69%), moderate-severe (50%-59%), and severe (35%-49%), and very severe (< 35%).[17]