Modes of high frequency ventilation

Modes of high frequency ventilation. With high frequency positive pressure ventilation (top), high-pressure conditioned gas (a) is delivered during inhalation and flows predominantly through an endotracheal tube (b) to the patient with partial escape to the atmosphere. During exhalation, the gas exits through an optional one-way valve (c). With high frequency jet ventilation (middle), conditioned high-pressure gas enters from a cannula (a) at a selected level along the endotracheal tube or trachea (c). This gas entrains additional conditioned gas (b) by the Venturi effect. During exhalation the gas exits passively through an optional one-way valve (d). With high frequency oscillation (bottom), the piston or diaphragm (a) oscillates while fresh conditioned gas (bias flow) enters (b) and exhaust gas exits (c) at a balanced constant rate. The bias flow ports can be positioned anywhere along the path from the external tip of the endotracheal tube to within the trachea itself.