What is BiPAP (Bilevel Positive Airway Pressure)?

What is BiPAP (Bilevel Positive Airway Pressure)?

BiPAP is a non-invasive ventilatory therapy that delivers two distinct pressure levels—a higher inspiratory positive airway pressure (IPAP) during inhalation and a lower expiratory positive airway pressure (EPAP) during exhalation—to provide ventilatory support while maintaining airway patency. 1

Core Mechanism of Action

BiPAP operates fundamentally differently from continuous positive airway pressure (CPAP) by utilizing two independently adjustable pressure levels rather than a single continuous pressure throughout the respiratory cycle. 1

Key functional components include:

• IPAP (Inspiratory Positive Airway Pressure): Provides active ventilatory support during inspiration, augmenting tidal volume and reducing work of breathing 2, 1
• EPAP (Expiratory Positive Airway Pressure): Maintains airway patency during expiration, recruits underventilated lung tissue, and offsets intrinsic PEEP in conditions like COPD 2, 1
• Pressure Support: The difference between IPAP and EPAP creates the pressure support that increases tidal volume and improves ventilation 1

Operational Modes

The American Academy of Sleep Medicine describes three distinct operational modes: 1

• Spontaneous (S) Mode: The patient controls respiratory timing and frequency; the machine responds to the patient's own respiratory efforts 1
• Spontaneous-Timed (ST) Mode: Provides backup respiratory frequency to ensure minimal ventilation if the patient fails to initiate sufficient breaths 1
• Timed (T) Mode: Delivers IPAP/EPAP cycles at a preset respiratory frequency with fixed inspiratory time 1

System Components

A complete BiPAP system consists of: 1

• A pressure generator (air pump) supplying pressurized airflow
• An interface (nasal, oral, or oronasal mask) secured with a harness
• Flexible tubing connecting the device to the interface
• Control systems for adjusting pressure levels and monitoring therapy

Typical Initial Settings

Standard starting pressures are IPAP of 8 cm H₂O and EPAP of 4 cm H₂O, which are then titrated upward during polysomnography to eliminate apneas, hypopneas, and respiratory effort-related arousals. 1

Primary Clinical Indications

The American Academy of Sleep Medicine recommends BiPAP for: 1

• Obstructive sleep apnea patients who cannot tolerate CPAP therapy
• Chronic alveolar hypoventilation
• Central sleep apnea unresponsive to CPAP
• Patients requiring high CPAP pressures (≥15 cm H₂O) who experience discomfort 1

Critical Distinction from CPAP

CPAP delivers a single continuous pressure throughout the entire respiratory cycle, while BiPAP alternates between two pressure levels, making it more comfortable for patients who struggle with high continuous pressures or who require ventilatory assistance beyond simple airway stenting. 1, 3

Important Clinical Considerations

Proper mask fitting and a period of acclimatization to low pressures before full titration are essential for treatment success. 1 The ramp feature—which allows patients to fall asleep at lower pressures before therapeutic pressures are delivered—improves tolerance and adherence, though it is a comfort feature rather than a therapeutic setting. 4

Polysomnography titration remains the preferred method for determining effective nocturnal ventilatory support levels, with monitoring of airflow, tidal volume, leaks, and delivered pressure to evaluate treatment efficacy. 1

Mechanism in Acute Respiratory Failure

In acute settings, bi-level pressure support combines the ventilatory assistance of IPAP with the lung recruitment and intrinsic PEEP offset provided by EPAP. 2 The EPAP also serves the critical function of venting exhaled gas through the exhaust port, reducing rebreathing potential. 2 Bi-level pressure support ventilators have been used in the majority of randomized controlled trials of non-invasive ventilation in acute hypercapnic respiratory failure and are recommended when establishing an acute NIV service. 2

Common Pitfalls

Occlusion of the exhaust port by secretions can exacerbate hypercapnia through rebreathing—always verify proper exhaust port function. 2 Additionally, some air leak is inevitable with non-invasive ventilation, either from the mask or through the mouth, which must be accounted for during pressure adjustments. 2