Positive pressure ventilation (PPV) is a form of artificial respiration in which a mechanical ventilator is used to force air into a patient who is not breathing. Unlike negative pressure ventilation, in which the body is encased in an iron lung that forces the chest to expand and draw in air, PPV forces air directly into the lungs. This is accomplished by attaching an artificial endotracheal or tracheostomy tube to the patient. The most common types of PPV machines are volume cycle fans, pressure cycle fans, flow cycle fans, and time cycle fans.
Volume-cycled positive-pressure ventilation is used in patients with acute respiratory distress syndrome (ARDS) or bronchospasm. A certain predetermined volume of airflow is pumped into the lungs, after which passive exhalation is allowed. It is most commonly applied in critical situations where the patient requires a previously calculated amount of air, and is one of the most widely used forms of this treatment.
Pressure-cycled PVP provides oxygen during inhalation until a certain predetermined pressure level is reached, after which passive exhalation is allowed. Generally less powerful than the volume-cycling type, pressure-cycling positive-pressure ventilation is most commonly used as a short-term solution to provide a pressure-assisted breath. It is also sometimes used for critical situations, but this is rare. It is most often applied in health centers and mobile intensive care units.
Flow-cycled positive pressure ventilation provides an increased supply of oxygen. At least, that is until the resistance is reduced enough to allow a preset flow rate. When this has been achieved, the oxygen rate is gradually reduced until it exactly matches the desired flow rate.
Time-cycled positive pressure ventilation relies on a timer to deliver artificial respiration until a preset time has been reached. The patient can then passively exhale. The amount of time is based on the volume required. If the current oxygen flow rate is higher than desired, then less time should be used. However, if flow is impeded, the time must be extended until the correct volume is delivered to the patient's lungs.
All methods of this treatment rely on a self-inflating bag and face mask attached to a tube that is inserted into the patient's mouth (endotracheal) or through a hole in the neck (tracheostomy) to deliver oxygen. Unlike negative pressure ventilation, positive pressure ventilation is much less invasive and therefore the most preferred solution. It has become an integral tool in the treatment of respiratory failure since the 1990s.