What is pressure support mode in Non-Invasive Ventilation (NIV)?

Pressure Support Mode in Non-Invasive Ventilation

Pressure support mode in NIV is a patient-triggered, pressure-controlled ventilation method that delivers a preset inspiratory positive airway pressure (IPAP) to assist each spontaneous breath, combined with a lower expiratory positive airway pressure (EPAP), making it the most commonly used and recommended mode for acute NIV services due to its simplicity, flexibility, and superior patient comfort. 1

Core Mechanism and Function

Pressure support ventilation operates as a bi-level system using two distinct pressure levels 1:

• IPAP (Inspiratory Positive Airway Pressure): Provides pressure assistance during inspiration when the patient triggers a breath 1
• EPAP (Expiratory Positive Airway Pressure): Maintains positive pressure during expiration, typically 3-5 cm H₂O 1

The ventilator compensates automatically for air leakage, which is inevitable with non-invasive interfaces 1. Flow sensors detect changes in machine-produced bias flow to trigger breaths, allowing the ventilator to synchronize with patient effort 1.

Physiological Benefits

Respiratory Mechanics

• Reduces work of breathing by augmenting spontaneous inspiratory efforts with preset positive pressure 2, 3
• Overcomes intrinsic PEEP in COPD patients through EPAP, which offsets the recoil pressure of overinflated lungs and helps trigger breaths 1
• Normalizes lung volumes and improves ventilation efficiency, particularly in patients with respiratory muscle fatigue 2

Gas Exchange and Comfort

• Improves oxygenation through lung recruitment encouraged by EPAP 1
• Reduces PaCO₂ by increasing effective tidal volumes without increasing minute ventilation 2
• Superior patient comfort compared to volume-controlled modes because it does not limit inspiratory flow, allowing the ventilator to match variable patient demand 4, 5

Clinical Application and Settings

Recommended Initial Settings

• IPAP: Start at 8-12 cm H₂O and titrate up to 12-25 cm H₂O based on patient response 6
• EPAP: Typically 3-5 cm H₂O, though levels >5 cm H₂O are rarely tolerated despite intrinsic PEEP potentially reaching 10-15 cm H₂O in severe COPD 1
• Target: Augment spontaneous tidal volumes to >4 mL/kg 2

Evidence-Based Recommendations

Bi-level pressure support ventilators are simpler to use, cheaper, and more flexible than other types of ventilators currently available; they have been used in the majority of randomised controlled trials of NIV and are recommended when setting up an acute NIV service. 1

Critical Nuances and Common Pitfalls

Rebreathing Risk

• Significant rebreathing potential exists with bi-level systems, especially at low EPAP levels (3-5 cm H₂O) and high respiratory rates 1, 4
• This can paradoxically worsen hypercapnia in tachypneic, anxious patients who fail to improve 1
• Ensure exhalation ports are functioning properly; occlusion by sputum can exacerbate hypercapnia 1, 4

Patient-Ventilator Asynchrony

Patient-ventilator asynchrony may result from 1:

• Undetected inspiratory effort
• Delayed response to start of inspiration
• Delayed detection of breath termination
• Excessive air leakage

When asynchrony cannot be resolved, consider switching to timed or assist-control mode, which provides mandatory breaths and is particularly important for 1:

• Patients with advanced acute respiratory failure who may cease spontaneous effort
• Patients dependent on hypoxic respiratory drive
• Neuromuscular disease patients with insufficient respiratory effort to trigger breaths

Mode Selection Algorithm

1. Start with pressure support for most acute NIV applications due to comfort and proven efficacy 1
2. Switch to volume control if ensuring consistent alveolar ventilation is crucial when compliance or airway resistance changes acutely 1, 4
3. Add timed backup rate for patients at risk of central apneas or inadequate spontaneous drive 1

Comparison with Other Modes

Pressure support has been compared to volume control in acute COPD with no significant outcome differences when both are properly applied 1. However, pressure support offers better respiratory comfort during assisted breathing because it allows variable inspiratory flow to match patient demand 4, 5. Some patients who fail pressure support may respond to volume control, possibly because volume control better ensures alveolar ventilation when lung mechanics change 1, 4.