Generally, negative pressure is used to aspirate sputum in the respiratory tract, and the pressure of the negative pressure device is 250-300 mmHg for adults and adjusted to about 200-250 mmHg for children, which can be slightly adjusted according to the different conditions of patients. When doing negative pressure aspiration, mainly through oral, nasal and artificial tracheotomy and airway establishment, secretions caused by various reasons in the respiratory tract are sucked out in order to keep the whole passage of the respiratory tract open and prevent the emergence of infections especially aspiration pneumonia, pulmonary atelectasis and even asphyxia caused by the obstruction of the airway by sputum clots.