PSV stands for Pressure Support Ventilation, a common type of mechanical breathing support used in hospital settings, particularly in intensive care units. This mode of ventilation is designed to assist a patient’s own breathing efforts rather than completely taking over the work of respiration. It falls under the category of positive pressure ventilation, meaning the machine delivers air into the lungs under pressure to help the patient inhale. The primary purpose of this mode is to provide comfortable and adjustable support for patients who still have a functional respiratory drive.
Pressure Support Ventilation Defined
Pressure Support Ventilation (PSV) is distinct from other modes, such as Volume Control, because it delivers a set pressure rather than a fixed volume of air with each breath. The amount of pressure support, measured in centimeters of water (cmH₂O), is pre-set by a clinician to boost the patient’s inhalation. This means the total volume of air the patient receives, known as the tidal volume, can vary depending on their own effort and the condition of their lungs.
By providing a consistent pressure boost, PSV helps the patient draw in enough air without having to strain their respiratory muscles. This patient-driven nature is fundamental, allowing the individual to maintain control over two critical aspects of breathing: the respiratory rate and the timing of each breath.
The ventilator works as a pressurized demand-flow system, instantly supplying air when the patient initiates a breath. The actual flow of air is regulated so that it decelerates as the pressure target is reached.
How PSV Facilitates Breathing
The mechanism of Pressure Support Ventilation is a three-step cycle that involves constant interaction between the patient and the machine. The process begins with patient triggering, where the patient’s natural attempt to inhale generates a small drop in pressure or a slight flow of air inside the breathing circuit. The ventilator immediately senses this effort, recognizing it as a signal for a new breath.
Once triggered, the machine moves to pressure delivery, rapidly supplying air to the patient’s airway to reach the set pressure level. This positive pressure assists the patient’s inspiratory muscles, making it easier to expand the lungs and draw in a sufficient tidal volume. The pressure is maintained throughout the inhalation phase, supporting the patient’s effort until the ventilator determines the breath should end.
The final step is flow cycling, which terminates the assisted inhalation and allows the patient to exhale passively. Instead of ending the breath after a set time, the ventilator monitors the flow rate of air moving into the lungs. When this inspiratory flow drops to a pre-determined fraction of its peak rate, the machine cycles into the expiratory phase, signifying that the patient’s demand for air has been met. This flow-based termination ensures the duration of the breath is naturally controlled by the patient’s lung mechanics and effort, promoting better synchrony between the person and the ventilator.
When PSV is Used in Patient Care
Pressure Support Ventilation is one of the most frequently used modes in intensive care because it effectively supports spontaneous breathing. Its primary application is in the process of weaning, which refers to the gradual removal of a patient from mechanical ventilation. PSV allows clinicians to reduce the level of support incrementally, requiring the patient’s respiratory muscles to take on a progressively greater share of the work.
This gradual reduction in pressure support is a form of respiratory muscle training, helping to prevent disuse atrophy and strengthen the muscles needed for independent breathing. Once the pressure support is lowered to a minimal level, often between 5 and 8 cmH₂O, the patient is essentially undergoing a Spontaneous Breathing Trial (SBT). Passing this trial, which demonstrates the ability to maintain adequate breathing with minimal assistance, is a strong indicator that the patient is ready to be taken off the ventilator entirely.
Beyond weaning, PSV is also used to provide general respiratory support for patients who are breathing on their own but require assistance to manage their condition. This includes patients with chronic obstructive pulmonary disease (COPD) or those recovering from acute respiratory failure who need help decreasing their overall work of breathing. It is often considered the most comfortable mode of ventilation for patients because it aligns closely with their natural breathing patterns, often reducing the need for heavy sedation.