What are the differences between Pressure Control Ventilation (PCV) and Pressure Support Ventilation (PSV) in mechanical ventilation?

Pressure Control Ventilation (PCV) vs. Pressure Support Ventilation (PSV)

PCV and PSV are fundamentally different modes: PCV is a fully controlled mode that delivers mandatory breaths regardless of patient effort, while PSV is a spontaneous mode that requires patient triggering and provides variable support based on patient demand. 1

Key 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
• The clinician sets the inspiratory pressure, and resulting tidal volume depends on lung compliance, resistance, and chest wall mechanics 1, 2
• Limits maximum airway pressure but may result in variable tidal volumes 2
• Provides complete ventilatory support with no requirement for patient effort 1

Pressure Support Ventilation (PSV)

• Requires patient-initiated breaths; the ventilator only responds to patient triggering 3
• Each breath is patient-triggered, with the ventilator delivering a preset pressure support level 3
• Allows patients greater control over breathing pattern, respiratory rate, and inspiratory time 4
• Reduces work of breathing while maintaining some respiratory muscle activity 3

Clinical Performance and Outcomes

Perioperative Setting

• In surgical patients, volume-controlled ventilation (VCV) appears superior to PCV for preventing postoperative pulmonary complications 3
• An observational study found higher risk of postoperative pulmonary complications with PCV compared to VCV, particularly when PEEP <5 cmH₂O 3
• A meta-analysis in obese surgical patients demonstrated VCV superiority over PCV 3

Critical Care Setting

• In acute lung injury, pressure-controlled assisted ventilation (P-ACV) preserves oxygenation and hemodynamic function with less respiratory effort compared to PSV in some contexts 5
• PSV with appropriate PEEP (5 cmH₂O) reduced lung damage and inflammatory markers in experimental mild ARDS 6
• In patients with mild-to-moderate ARDS, PSV maintained lung-protective ventilation while improving patient-ventilator interaction compared to PCV 4

Non-Invasive Ventilation

• PSV mode was significantly associated with NIV success compared to PCV mode (OR 2.303,95% CI 1.216-4.360) in acute respiratory failure 7
• PSV required lower inspiratory pressures than PCV (15.0 vs 18.0 cmH₂O) with similar outcomes 7

Critical Pitfalls and Complications

PSV-Specific Risks

• High levels of PSV can cause central apneas during sleep, particularly in patients with heart failure, leading to major sleep fragmentation (53 ± 8 events/hour) 3
• Excessive pressure support causes hyperventilation, dropping PaCO₂ below the apneic threshold, triggering central apneas 3
• Sleep quality was poorest during PSV compared to assist-control modes due to central apnea development 3
• The level of pressure support must be carefully titrated to prevent hyperventilation while avoiding under-assistance 3

PCV-Specific Risks

• Variable tidal volumes may occur with changes in lung mechanics 2
• Requires vigilant monitoring of delivered tidal volume to prevent volutrauma 2
• May deliver excessive tidal volumes (876 ± 179 mL) if pressure settings are too high, risking barotrauma 3

Practical Clinical Algorithm

When to Choose PCV:

• Patients requiring complete ventilatory control (heavily sedated, paralyzed, or unable to trigger) 1
• Need for guaranteed minute ventilation with backup rate 3, 1
• Patients at risk for central apneas (heart failure, during sleep periods) 3
• When airway pressure limitation is the primary concern 2

When to Choose PSV:

• Awake, spontaneously breathing patients during weaning 3, 4
• Patients requiring reduced work of breathing while maintaining respiratory muscle activity 3, 5
• Non-invasive ventilation for acute respiratory failure 7
• When improved patient-ventilator synchrony is needed 4

Critical Monitoring Requirements:

• During PSV: Monitor for central apneas, adjust pressure support to maintain normocapnia (avoid PaCO₂ <35 mmHg), especially during sleep 3
• During PCV: Continuously monitor delivered tidal volumes (target 6-8 mL/kg ideal body weight) and adjust pressure settings accordingly 3, 2
• Both modes require PEEP optimization (typically 5-10 cmH₂O) for lung protection 3, 6

Avoiding Common Errors:

• Never use high PSV levels during sleep without backup ventilation—this causes severe central apneas and sleep disruption 3
• Do not assume PCV provides lung protection—excessive pressure settings can deliver harmful tidal volumes 3
• Recognize that PSV requires adequate respiratory drive; it will fail in patients with depressed central drive 1
• In heart failure patients on PSV, be especially vigilant for central apneas and consider modes with backup rates 3