Ventilators are machines that help patients breathe and are used for patients who are unable to compensate for their respiratory function and have lost their own breathing. There are no absolute contraindications to ventilators. The relative contraindications are as follows: 1. Patients with pneumothorax and mediastinal emphysema who have not been drained should first have their pneumothorax or mediastinal emphysema drained and punctured to reduce the pneumothorax before mechanical ventilation is performed; patients with large amounts of pleural effusion should also have their effusion drained before mechanical ventilation is performed. 2. In addition, patients with hemoptysis should have their airway kept open after intubation.