Breathing can be assisted mechanically for people who have spontaneous but weak breathing or for people who cannot breathe on their own. Mechanical ventilation (MV), or assisted ventilation, can be used on a short-term or long-term basis, depending on the individual's medical needs.
Short-term use of MV generally occurs in a hospital ICU, e.g., during an acute illness or during and after an operation, until an individual can breathe unassisted. In the ICU, MV can be delivered noninvasively through a face or nasal mask, but is usually delivered by an endotracheal tube placed in the mouth and down the throat (intubation).  
In some cases, short-term use of MV in the hospital turns into longer-term use. Generally, if an individual has been intubated for an extended period, such as two or three weeks, a tracheotomy is performed. This is a surgical procedure that creates an opening in the neck to the windpipe. A plastic or metal tracheostomy tube is placed into the windpipe through this opening. The individual relies on air delivered by a machine through the tracheostomy tube rather than through a tube inserted into the nose or mouth and into the windpipe. When the person becomes medically stable, but still needs to use tracheostomy ventilation, he or she is usually discharged from the hospital to a skilled nursing facility or to home care if feasible. Eventually, the individual may be able to breathe unassisted or to be converted to noninvasive ventilation.