What is the difference between pressure support ventilation (PSV) and pressure control ventilation (PCV) in mechanical ventilation?

Pressure Support vs Pressure Control Ventilation: Key Differences

Fundamental Distinction

Pressure Support Ventilation (PSV) requires patient-initiated breaths and is used for awake, spontaneously breathing patients during weaning, while Pressure Control Ventilation (PCV) delivers mandatory breaths at preset intervals regardless of patient effort and is used for patients requiring complete ventilatory control. 1

Mechanical Differences

Pressure Control Ventilation (PCV)

• Delivers mandatory breaths at preset intervals with a set inspiratory pressure, regardless of whether the patient initiates a breath 1
• Provides complete ventilatory support with no requirement for patient effort 1
• The ventilator controls the respiratory rate, inspiratory time, and pressure level 2
• Tidal volume varies based on lung compliance, chest wall mechanics, and airway resistance 3
• Patient- or time-triggered, pressure-limited, and time-cycled 2

Pressure Support Ventilation (PSV)

• Requires the patient to initiate every breath—the ventilator will not deliver a breath without patient effort 1
• Augments the patient's spontaneous inspiratory efforts with a clinician-selected level of positive airway pressure 4
• Allows patients greater control over breathing pattern, respiratory rate, and inspiratory time 1
• Each breath is patient-triggered, pressure-limited, and flow-cycled 2
• Improves patient comfort and reduces ventilatory work 4

Clinical Application Algorithm

When to Use PCV

• Heavily sedated or paralyzed patients who cannot trigger breaths 1
• Patients with no spontaneous respiratory drive 1
• Acute respiratory failure requiring full ventilatory control 2
• Patients requiring guaranteed minute ventilation with pressure limitation 3

When to Use PSV

• Awake, spontaneously breathing patients during the weaning process 1
• Patients with adequate respiratory drive but requiring reduced work of breathing 4
• Patients transitioning from full support to spontaneous breathing 5
• When patient-ventilator synchrony and comfort are priorities 6

Clinical Performance Differences

Advantages of PSV

• In mild-to-moderate ARDS, PSV maintained lung-protective ventilation while improving patient-ventilator interaction compared to PCV 1
• Reduces respiratory rate and improves tidal volume in patients with respiratory muscle fatigue 5
• Normalizes lung volumes and improves ventilation efficiency 5
• Provides better patient comfort and synchrony with variable respiratory demands 3
• Improves oxygenation compared to assist-control modes in acute respiratory failure 6

Advantages of PCV

• Limits maximum airway pressure delivered to the lung, potentially reducing barotrauma risk 3
• Provides guaranteed minute ventilation regardless of patient effort 1
• May improve sleep quality compared to low-level PSV in patients with severe COPD by allowing complete respiratory muscle rest 7
• Prevents central apneas during sleep due to backup mandatory rate 8

Critical Pitfalls and Management

PSV-Specific Pitfalls

• High levels of PSV can cause central apneas during sleep, particularly in heart failure patients, leading to major sleep fragmentation 1
• Inadequate pressure support causes increased respiratory rate and patient distress—titrate upward while monitoring comfort 9
• Avoid excessive pressure support that causes hyperventilation (PaCO₂ <35 mmHg), especially during sleep 1
• PSV cannot be used in patients without spontaneous respiratory drive—they will not receive any breaths 1

PCV-Specific Pitfalls

• Tidal volumes can become dangerously high if pressure settings are not adjusted for improving lung compliance 7
• High pressure control (resulting in tidal volumes >876 mL) increases risk of barotrauma, ventilator-associated injury, and respiratory muscle atrophy 7
• Continuously monitor delivered tidal volumes and adjust pressure settings to prevent volutrauma 1
• Variable tidal volumes require vigilant monitoring as compliance changes 3

Monitoring Requirements

During PSV

• Monitor for central apneas, especially during sleep 1
• Adjust pressure support to maintain normocapnia 1
• Check respiratory rate immediately after adjustments—if rate falls, support was inadequate 9
• Assess patient comfort and work of breathing continuously 4

During PCV

• Monitor delivered tidal volumes continuously and adjust pressure to maintain lung-protective ventilation (6-8 mL/kg ideal body weight in ARDS) 1, 9
• Ensure adequate minute ventilation is maintained 3
• Watch for signs of over-assistance leading to respiratory muscle atrophy 7

Special Population Considerations

Difficult-to-Wean Patients

• In tracheostomized patients with prolonged weaning, low-level PSV increased total sleep time and sleep efficiency compared to spontaneous breathing 7
• PSV reduces work of breathing while maintaining respiratory muscle activity 1

COPD Patients

• Pressure control improved sleep efficiency, slow-wave sleep, and REM sleep compared to low-level PSV 7
• However, the high tidal volumes associated with pressure control pose significant risks 7
• Use modest pressure support with prolonged expiratory time and PEEP (3-5 cmH₂O) to offset intrinsic PEEP 9