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Ventilators designed for use in critical care settings; most use positive pressure to deliver gas to the lungs at normal breathing rates and tidal volumes through an endotracheal tube or tracheostomy. These ventilators typically consist of a flexible breathing circuit, a control system, monitors, and alarms. The gas is typically delivered to the patient using a double-limb breathing circuit. The inhalation limb provides sites where the gas may be heated or humidified using appropriate devices, and the exhalation limb includes an exhaust valve to release the gas to the ambient air. Intensive care ventilators are usually connected to a wall gas (e.g., oxygen, air) supply. Intensive care ventilators are frequently classified according to the variable used to terminate inspiration (e.g., volume, flow, pressure, time-cycled); they can be operated using several modes, such as assist/control or synchronized patient triggered. Some intensive care ventilators can provide gases to the lungs at frequencies much higher than the normal breathing rates (100 or more times per minute is typical); negative-pressure ventilators are also used in intensive care as an alternative to positive-pressure ventilators for some selected patients.
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