A medical ventilator is a device designed to provide mechanical ventilation to a patient. Ventilators are chiefly used in intensive care medicine and emergency medicine (as standalone units) and in anesthesia (as a component of an anesthesia machine).
In its simplest form, a ventilator consists of a compressible air reservoir, air and oxygen supplies, a set of valves and tubes, and a disposable or reusable "patient set". The air reservoir is pneumatically compressed several times a minute to deliver an air/oxygen mixture to the patient; when overpressure is released, the patient will exhale passively due to the lungs' elasticity. The oxygen content of the inspired gas can be set from 21 percent (ambient air) to 100 percent (pure oxygen). Pressure and flow characteristics can be set mechanically or electronically.
Ventilators may also be equipped with monitoring and alarm systems for patient-related parameters (e.g. pressure and flow) and ventilator function (e.g. air leakage, power failure), backup batteries, air and oxygen tanks, and remote control and alarms. The pneumatic system is nowadays often replaced by a computer-controlled turbopump.
Modern ventilators are electronically controlled by a small embedded system to allow exact adaptation of pressure and flow characteristics to an individual patient's needs. Fine-tuned ventilator settings also serve to make ventilation more tolerable for the patient. In Canada, respiratory therapists are responsible for tuning these settings.
Because the failure of a mechanical ventilation system may result in death, it is classed as a life-critical system, and precautions must be taken to ensure that mechanical ventilation systems are highly reliable. This includes their power-supply provision.
Mechanical ventilators are therefore carefully designed so that no single point of failure can endanger the patient. They usually have manual backup mechanisms to enable hand-driven respiration in the absence of power. Some systems are also equipped with compressed-gas tanks and backup batteries to provide ventilation in case of power failure or defective gas supplies, and methods to operate or call for help if their mechanisms or software fails.