What are the methods and precautions of mechanical sputum aspiration?

Mechanical sputum aspiration is suitable for those who cannot cough up phlegm, are unconscious or have difficulty in expectoration. Negative pressure sputum aspiration can be performed through the patient's mouth, nasal cavity, tracheal intubation or tracheotomy. Each suction time is less than 15 second, and the interval between two suction times is more than 3 minutes. And appropriately increase the oxygen concentration before, during and after sputum aspiration to avoid hypoxemia caused by sputum aspiration.