Ventilator circuits

(A) In this configuration, the leak port is always open to atmosphere. Pressure is generated as the result of flow in the circuit and resistance through the leak port. Thus, with higher pressure, the ventilator must deliver more flow into the circuit. It is important to appreciate that, with this design, leak is integral to the function of the device. Thus, the leak should not be occluded. This circuit type is commonly used in ventilators designed for noninvasive ventilation. It is also the typical design for positive airway pressure devices used for the treatment of obstructive sleep apnea. (B) Single limb circuit with active exhalation valve near the patient. This circuit type is typically used with portable ventilators, such as those used for transport or in the home. During inspiration, the exhalation valve is closed via the pressurization line from the ventilator. (C) Dual limb ventilator circuit commonly used with critical care ventilators. In this design, the valves are within the ventilator.