While TBI may be managed without surgery, surgical repair of the tear is considered standard in the treatment of most TBI.[3][27] It is required if a tear interferes with ventilation; if mediastinitis (inflammation of the tissues in the mid-chest) occurs; or if subcutaneous or mediastinal emphysema progresses rapidly;[3] or if air leak or large pneumothorax is persistent despite chest tube placement.[19] Other indications for surgery are a tear more than one third the circumference of the airway, tears with loss of tissue, and a need for positive pressure ventilation.[26] Damaged tissue around a rupture (e.g. torn or scarred tissue) may be removed in order to obtain clean edges that can be surgically repaired.[15] Debridement of damaged tissue can shorten the trachea by as much as 50%.[28] Repair of extensive tears can include sewing a flap of tissue taken from the membranes surrounding the heart or lungs (the pericardium and pleura, respectively) over the sutures to protect them.[2] When lung tissue is destroyed as a result of TBI complications, pneumonectomy or lobectomy (removal of a lung or of one lobe, respectively) may be required.[29] Pneumonectomy is avoided whenever possible due to the high rate of death associated with the procedure.[3] Surgery to repair a tear in the tracheobronchial tree can be successful even when it is performed months after the trauma, as can occur if the diagnosis of TBI is delayed.[3] When airway stenosis results after delayed diagnosis, surgery is similar to that performed after early diagnosis: the stenotic section is removed and the cut airway is repaired.[28]