In medicine, mechanical ventilator is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a mechanical ventilator or the breathing may be assisted by a registered nurse,physician, respiratory therapist, paramedic, or other suitable person compressing a bagor set of bellows. Mechanical ventilator is termed "invasive" if it involves any instrument penetrating through the mouth (such as an endotracheal tube) or the skin (such as a tracheostomy tube).There are two main modes of mechanical ventilator within the two divisions: positive pressure ventilation, where air (or another gas mix) is pushed into the trachea, and negative pressure ventilation, where air is, in essence, sucked into the lungs.