Pressure Support Ventilation

Introduction

• PSV is a spontaneous mode of mechanical ventilation where each breath is initiated by the patient and assisted by a preset positive pressure delivered during inspiration. PSV can be used both invasively (via endotracheal tube) and non-invasively (via mask). Because patients control both the timing and volume of breaths, PSV provides a more physiologic and comfortable breathing pattern, compared to other ventilator modes, and is considered the ideal mode for weaning patients from mechanical ventilation once they have regained sufficient respiratory drive.^1,2
• Unlike more traditional volume-controlled ventilation (VCV) or pressure-controlled ventilation (Figure 1), PSV does not deliver mandatory breaths or ensure a minimum minute ventilation. Instead, the patient controls the timing and rate of breaths, while the ventilator assists by delivering a fixed driving pressure.
• Several factors determine the inspiratory flow delivered by the ventilator:
  • Driving pressure (set by a clinician)
  • Airway resistance
  • Lung compliance
  • Patient’s inspiratory effort
• In PSV, breaths are flow-cycled, so the ventilator ends inspiratory support when the inspiratory flow decreases to a preset threshold (typically 25% of the peak inspiratory flow).³ During expiration, positive end-expiratory pressure (PEEP) is typically added to maintain alveolar recruitment, improve V/Q matching, and enhance oxygenation.⁴

Benefits of PSV

Benefits of PSV include:^6,7,8

• Improves patient comfort and reduces the work of breathing
• Provides respiratory muscle reconditioning during weaning
• Reduces sedative requirements compared to controlled modes
• Facilitates synchrony and reduces dyssynchrony events such as double triggering

Uses and Contraindications

PSV is used in several scenarios:

• Delivers oxygen (O₂) and ventilatory support in patients with hypoxemic, hypercapnic, or mixed respiratory failure
• Weaning and spontaneous breathing trials (SBTs): PSV supports spontaneous breathing while assessing readiness for extubation.
• Enhances carbon dioxide (CO₂) elimination by increasing minute ventilation when necessary
• Improves ventilation-perfusion matching with PEEP, reduces shunt, and maintains alveolar patency during expiration
• Reduces the work of breathing and O₂ consumption by assisting the respiratory muscles during inspiration

PSV is not appropriate for:

• Patients with depressed respiratory drive (e.g., sedative use, neurologic impairment) because PSV does not deliver mandatory breaths
• Conditions with elevated airway resistance (e.g., chronic obstructive pulmonary disease or asthma), where intrinsic PEEP and airway obstruction reduce the tidal volume delivery
• Central apnea or critical illness encephalopathy, where mandatory ventilation is required^4,6,7
• Patients in shock or with low cardiac output states requiring full ventilatory support⁴
• These limitations occur primarily because PSV does not guarantee a minimum minute ventilation, placing the responsibility for adequate ventilation on the patient’s respiratory drive and mechanics.^4,6,7

Advantages and Disadvantages

Advantages of PSV

• Earlier liberation from mechanical ventilation compared to VCV by delivering lower peak airway pressures, reducing the risk of barotrauma²
• The patient’s spontaneous breathing effort is supported, improving patient-ventilator synchrony (Figure 2).⁷
• Facilitates respiratory muscle reconditioning by allowing patients to sustain spontaneous breathing efforts with supportive assistance⁷
• The flow-cycled breath termination, tailored to patient effort, minimizes dyssynchrony events such as delayed cycling or double triggering.³
• Automatic tube compensation can offset additional resistance imposed by the endotracheal tube.⁴

Disadvantages of PSV

• PSV does not guarantee consistent tidal volumes or minute ventilation (Figure 2), so it is unsuitable for patients lacking adequate respiratory drive (apnea, sedation).⁴
• It is associated with poorer sleep quality than assist-control ventilation modes due to increased sleep fragmentation.^3,4
• Increased risk of ventilator-induced lung injury and atelectasis at high pressure support levels (>20 cm H₂O)¹
• Requires close monitoring to detect patient dyssynchrony and inadequate ventilation⁸

Weaning Strategy

PSV is important in weaning due to its ability to provide graduated support, allowing patients to gradually regain respiratory muscle strength.

• Readiness Testing for weaning is assessed through clinical criteria:10
  • Improved underlying disease, stable hemodynamics
  • Adequate oxygenation (FiO₂ ≤ 0.4, PEEP ≤ 5 cm H₂O)
  • Intact respiratory drive
• SBTs at preferred low-level PSV (5–8 cm H₂O, with PEEP 5 cm H₂O)
  • PSV offsets the work of breathing imposed by the endotracheal tube and circuit, improving accurate assessment of respiratory ability.^3,7,10
  • Categories:
    • Simple wean: Pass first SBT
    • Difficult wean: Fail initially, succeed in 3-7 days
    • Prolonged wean: Require more than 7 days and multiple SBTs
• Automated Weaning
  • Automated, computer-driven PSV weaning protocols have emerged, dynamically adjusting pressure support based on respiratory rate, tidal volume, and exhaled CO₂.¹⁰
  • Evidence shows similar MV duration compared to clinician-driven weaning, but adoption is limited by variability in systems¹⁰
• PSV vs. Other Methods
  • Randomized trials show PSV improves weaning success compared to T-piece and synchronized intermittent mandatory ventilation trials.⁶
  • Meta-analyses suggest no clear superiority between SBT-based protocols and gradual PSV, though both outperform usual care.¹⁰
  • PSV-SBTs are likely superior to continuous positive airway pressure (CPAP)-SBTs, especially in obstructive lung disease, as CPAP may cause mask fatigue.¹⁰
  • PSV’s patient-driven support promotes better synchrony and reduces respiratory muscle fatigue, key to successful weaning.⁴