Pressure Support Ventilation (PSV) is a type of breathing assistance provided by a mechanical ventilator. This mode is described as patient-driven, meaning the machine only delivers support when the patient initiates a breath. PSV is considered a partial support mode that supports the patient’s own respiratory effort. It is frequently employed when a patient is awake and stable enough to maintain a spontaneous respiratory drive.
How Pressure Support Ventilation Works
PSV operates via a three-step cycle: patient-triggering, pressure-limiting, and flow-cycling. The process begins when the ventilator senses the patient’s attempt to inhale (triggering the breath). This trigger is typically detected by a slight drop in air pressure or a change in air flow within the breathing circuit.
Once triggered, the ventilator immediately delivers a set, constant positive pressure boost to the patient’s airway throughout the inspiration phase. This programmed pressure helps overcome the natural resistance of the breathing tube and reduces the effort required to draw a breath. Because the ventilator maintains a fixed pressure level, the breath volume the patient receives can vary based on their lung condition and how hard they pull against the machine.
The breath is terminated, or “cycled off,” not after a set amount of time, but when the patient’s inspiratory flow rate significantly decreases. As the patient’s lungs fill and their inspiratory muscles begin to relax, the speed of the air moving into the lungs naturally slows down. When this inspiratory flow drops to a specific percentage of its peak, the ventilator recognizes that the patient is ready to exhale and stops providing the positive pressure boost. This flow-cycling mechanism allows the patient to largely control the duration of their breath, which promotes better comfort and synchronization with the machine.
Clinical Reasons for Using PSV
The primary goal of using PSV is to reduce the patient’s work of breathing (WOB) while ensuring their respiratory muscles remain active. By providing a constant pressure boost during inhalation, the ventilator acts as an immediate assist, making each spontaneous breath easier for the patient. This supportive environment helps prevent the excessive fatigue that can occur when patients with underlying lung issues or muscle weakness try to breathe unassisted.
PSV is utilized to facilitate the weaning process, which is the transition from full mechanical support back to independent breathing. Since the patient retains control over their breathing rate and effort, PSV allows for a gradual “re-conditioning” of the respiratory muscles, particularly the diaphragm. Clinicians slowly lower the amount of pressure support over time, effectively serving as a controlled exercise program for the patient’s lungs until they are strong enough to be extubated.
This patient-driven mode significantly improves patient-ventilator synchrony, which contributes to greater comfort and less need for sedating medications. Since the breath timing is determined by the patient’s own respiratory drive, the ventilator matches the patient’s natural breathing pattern. This improved coordination helps reduce events where the patient fights the ventilator, which can lead to complications like lung injury and prolonged ventilation.
PSV Versus Full Mechanical Control
The difference between PSV and full mechanical control modes lies in which party dictates the breath: the patient or the machine. In full control modes, such as Assist-Control Ventilation, the ventilator delivers a set number of breaths at a predetermined volume or pressure, regardless of the patient’s desire to breathe. These modes are time-triggered, meaning the ventilator initiates the breath based on a set rate, and are used when a patient is heavily sedated, paralyzed, or has a severely suppressed respiratory drive.
Conversely, PSV is purely a spontaneous mode that is entirely patient-triggered, providing support only when the patient makes an effort to inhale. This is vital for respiratory muscle function; full control modes can lead to disuse atrophy of the diaphragm because the machine does all the work. PSV requires and supports the patient’s effort, helping maintain muscle strength and endurance crucial for successful liberation from the ventilator.
The patient on PSV also controls their breath duration and volume, whereas full control modes predetermine these parameters. Because PSV is flow-cycled, the patient ultimately determines when the inspiratory phase ends by the natural decay of their inspiratory flow. This allows for a more physiologic breathing pattern, unlike controlled modes which deliver breaths with fixed timing that may not align with the patient’s true needs.