Table 3: Spirometric classification of chronic obstructive pulmonary disease severity based on postbronchodilator FEV1 [4, 11].

Stage I: mildFEV1/FVC < 0.70 FEV1 80% predicted
Stage II: moderateFEV1/FVC < 0.70 50% FEV1 < 80% predicted
Stage III: severeFEV1/FVC < 0.70 30% FEV1 <50% predicted
Stage IV: very severeFEV1/FVC < 0.70 FEV1 < 30% predicted or FEV1 < 50% predicted plus chronic respiratory failure*

FEV1: forced expiratory volume in 1 second; FVC: forced vital capacity
*Respiratory failure: arterial partial pressure of oxygen ( P a o 2 ) <8.0 kPa (60 mm Hg) with or without arterial partial pressure of CO2 ( P a c o 2 ) >6.7 kPa (50 mm Hg) while breathing air at sea level.