What is Pressure Support Ventilation (PSV)?

What is Pressure Support Ventilation (PSV)?

Pressure Support Ventilation (PSV) is a patient-triggered, pressure-limited, and flow-cycled mode of mechanical ventilation where the patient controls respiratory rate, inspiratory time, and tidal volume while the ventilator augments each spontaneous breath with a clinician-selected level of positive airway pressure. 1

Core Mechanism

In PSV, the patient's respiratory effort triggers the ventilator both on and off, with respiratory frequency and timing of each breath entirely determined by the patient. 1 The ventilator delivers a preset positive pressure (typically called pressure support or PS) to assist each spontaneous inspiratory effort. 1

Key Operational Characteristics:

• Patient-initiated: Each breath must be triggered by the patient's own inspiratory effort 2
• Pressure-targeted: The clinician sets a specific pressure level (e.g., 5-20 cm H₂O) that augments each breath 3, 4
• Flow-cycled termination: The breath ends when inspiratory flow decelerates to a predetermined percentage of peak flow (typically 20-80% depending on ventilator) 1, 2
• No mandatory backup rate (on basic PSV): If the patient stops breathing, no ventilatory support occurs, though many modern ventilators incorporate a backup rate of 6-8 breaths per minute 1

Physiological Effects

PSV produces several beneficial respiratory changes:

• Reduces work of breathing by providing positive pressure assistance that unloads respiratory muscles 3, 4
• Normalizes breathing pattern: Decreases respiratory rate while increasing tidal volume 4
• Improves gas exchange through increased alveolar ventilation, typically lowering PaCO₂ 4
• Enhances patient comfort compared to controlled modes by allowing patient control of breathing pattern 3

Clinical Application in Bi-Level Systems

In non-invasive ventilation (NIV), PSV is typically delivered using bi-level positive airway pressure with two pressure settings: 1

• IPAP (Inspiratory Positive Airway Pressure): The higher pressure during inspiration that provides the pressure support 1
• EPAP (Expiratory Positive Airway Pressure): The lower baseline pressure during expiration that prevents alveolar collapse, eliminates CO₂ rebreathing, and counteracts intrinsic PEEP in COPD patients 1, 5

The actual pressure support level equals IPAP minus EPAP. 1

Critical Pitfall: PSV-Induced Central Apneas

A major hazard of PSV during sleep is the development of central apneas from excessive ventilatory support. 1 When pressure support is set too high, it causes hyperventilation and hypocapnia, dropping PaCO₂ below the apneic threshold, which triggers central apneas (up to 53 ± 8 events/hour in one study). 1 This leads to severe sleep fragmentation, arousals, and poor sleep quality. 1

Prevention Strategy:

• Adjust pressure support to prevent hyperventilation by monitoring tidal volume and avoiding excessive minute ventilation 1
• Use modes with backup ventilation (assist-control or SIMV) in patients at risk for central apneas, particularly those with heart failure 1
• Consider adding dead space if central apneas develop, which can reduce events from 53 to 4 per hour 1

Patient Selection Considerations

PSV is appropriate for stable patients with intact respiratory drive but is contraindicated in critically ill patients with abnormal central respiratory drive. 6 The patient must be able to consistently trigger breaths, as no mandatory ventilation occurs in basic PSV mode. 1

Ideal Candidates:

• Patients weaning from mechanical ventilation with respiratory muscle fatigue 4
• Stable patients requiring partial ventilatory support 6
• Patients with COPD exacerbations when combined with EPAP to offset intrinsic PEEP 1

Poor Candidates:

• Patients with unreliable respiratory drive 6
• Heavily sedated patients unable to trigger breaths 1
• Patients requiring guaranteed minute ventilation 1

Ventilator Settings and Adjustments

The primary clinician-adjustable parameter is the pressure support level, typically starting at 5-10 cm H₂O and titrated based on patient response. 4 Modern ventilators also allow adjustment of:

• Pressure rise time (pressurization rate): Controls how quickly the set pressure is reached 2
• Flow termination criteria: Adjusts when the breath cycles to exhalation (percentage of peak flow) 2
• Backup rate: Safety feature providing mandatory breaths if patient effort ceases 1

Titration should target tidal volumes of 4-8 mL/kg, respiratory rates <30 breaths/minute, and adequate gas exchange without hyperventilation. 4