PSV is a flow-limited mode of ventilation that delivers inspiratory pressure until the inspiratory flow decreases to a predetermined percentage of its peak value. This is usually 25%.
During PSV, each breath is augmented by inspiratory pressure.
The clinician sets the pressure support level (inspiratory pressure level), applied PEEP, and FiO2
There is no set respiratory rate, thus, the patient triggers each inspiration, which continues until the inspiratory flow decreases to a system-specific minimal level.
Exhalation follows.
The tidal volume is determined by the pressure support level, effort, and mechanics.
Minute volume is variable and dependent upon tidal volume and patient initiated respiratory rate, and thus does not guarantee an adequate minute volume.
increasing the level of pressure support decreases the work of breathing provided that inspiratory flow is sufficient to meet patient demand.
PSV seems particularly well suited for weaning from mechanical ventilation because it tends to be a comfortable mode, giving the patient greater control over the inspiratory flow rate and respiratory rate.
PSV is frequently combined with
SIMV. The ventilator delivers the set respiratory rate using SIMV, but patient-initiated breaths beyond the set respiratory rate are delivered using PSV. The purpose of adding PSV for patient-initiated breaths is to overcome the resistance of the endotracheal tube and ventilator circuit.
in general, PSV is poorly suited to provide full or nearly full ventilatory support, it is a particularly poor choice for patients who also have increased airway resistance (eg,
chronic obstructive pulmonary disease (COPD) or asthma exacerbation).