Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for artificial ventilation where mechanical means are used to assist or replace spontaneous breathing. This may involve a machine called a ventilator, or the breathing may be assisted manually by a suitably qualified professional, such as an anesthesiologist, paramedic or other first responder, or in some parts of the United States, by a respiratory therapist (RT), by compressing a bag valve mask device.
Mechanical ventilation is termed "invasive" if it involves any instrument inside the trachea through the mouth, such as an endotracheal tube, or the skin, such as a tracheostomy tube.
Face or nasal masks are used for non-invasive ventilation in appropriately selected conscious patients.
The two main types of mechanical ventilation include positive pressure ventilation where air (or another gas mix) is pushed into the lungs through the airways, and negative pressure ventilation where air is usually, in essence, sucked into the lungs by stimulating movement of the chest. Apart from these two main types, there are many specific modes of mechanical ventilation, and their nomenclature has been revised over the decades as the technology has continually developed.