BACKGROUND While permissive hypercapnia is commonly practised in critical care, it remains unclear if the comparable manoeuvres are clinically acceptable during anaesthesia. This retrospective study aimed at describing the anaesthetic implications of hypercapnia associated with deliberate hypoventilation during thoracic surgery in patients with severe emphysema. METHODS Thirteen patients with emphysema who required thoracic surgery under similar anaesthesia were reviewed: 3 patients were managed to maintain normocapnia (normocapnia group) whereas 10 patients developed hypercapnia (PaCO2 >70 mmHg) as a result of restricting peak airway pressures (hypercapnia group). RESULTS In the normocapnia group (PaCO2: 45+/-1 mmHg, mean+/-SD), no event which required therapeutic intervention during the surgery was seen, whereas 2 of 3 patients showed postoperative air leakage which persisted over 5 days. In the hypercapnia group, the maximum PaCO2 during anaesthesia ranged between 70 mmHg and 135 mmHg (98-21 mmHg). During anaesthesia, all 10 patients required inotropic support to prevent hypotension, 4 patients required tracheal gas insufflation of oxygen to the operated lung to avoid hypoxaemia and 3 patients required lidocaine to treat ventricular arrhythmia. However, the trachea was extubated in the operation theatre in 9 of 10 patients and no organ dysfunction was observed postoperatively. Four patients showed postoperative air leak on the first postoperative day, one of which persisted over 5 days. CONCLUSION Although there are some limitations, this preliminary study indicates that hypercapnia around 100 mmHg during anaesthesia for thoracic surgery may not be associated with serious consequences.