What is the difference between BiPAP (Bilevel Positive Airway Pressure) and CPAP (Continuous Positive Airway Pressure) for non-invasive ventilation support?

BiPAP vs CPAP: Key Differences and Clinical Selection

BiPAP is superior to CPAP for hypercapnic respiratory failure (particularly COPD exacerbations with respiratory acidosis), while CPAP is the preferred choice for hypoxemic respiratory failure (cardiogenic pulmonary edema, pneumonia) and obstructive sleep apnea. 1

Fundamental Mechanical Differences

BiPAP delivers two distinct pressure levels:

• IPAP (inspiratory positive airway pressure) provides higher pressure during inspiration to assist ventilation 2, 1
• EPAP (expiratory positive airway pressure) provides lower pressure during expiration to recruit underventilated lung and offset intrinsic PEEP 2, 1
• The pressure differential between IPAP and EPAP generates tidal volume and reduces work of breathing 1

CPAP delivers a single constant pressure:

• Maintains the same positive pressure throughout the entire respiratory cycle 2, 1
• Recruits collapsed alveoli and increases mean airway pressure to improve oxygenation 2
• Unloads inspiratory muscles and offsets intrinsic PEEP in COPD patients 2, 1
• Does not provide active ventilatory assistance—conventionally not considered respiratory support 2

Clinical Indications: When to Choose Each

Use BiPAP for:

• Acute COPD exacerbations with respiratory acidosis (pH <7.35) 1, 3
• Patients who develop hypercapnia during CPAP treatment for pneumonia 1
• Weaning from invasive ventilation when conventional strategies fail 1
• Patients with inspiratory muscle fatigue requiring ventilatory assistance 4
• OSA patients who cannot tolerate high CPAP pressures or have persistent central apneas 5, 6

Use CPAP for:

• Cardiogenic pulmonary edema with hypoxemia despite maximal medical treatment 1
• Chest wall trauma with persistent hypoxemia despite adequate analgesia and high-flow oxygen 1
• Diffuse pneumonia with hypoxemia 1, 3
• Obstructive sleep apnea as first-line therapy 6

Practical Implementation Considerations

BiPAP advantages:

• More effective for hypercapnic respiratory failure, with 46% mortality reduction and 65% reduction in intubation rates 3
• Simpler to use, cheaper, and more flexible than ICU ventilators 1
• Used in the majority of randomized controlled trials of NIV 1

BiPAP disadvantages and critical pitfalls:

• Risk of increased work of breathing in COPD patients if settings are not optimized 7
• Rebreathing can occur if exhaust ports become occluded 1
• Normal EPAP levels may not completely eliminate rebreathing, especially with increased respiratory frequency 1
• More complex setup requiring ventilator experience 4

CPAP advantages:

• Simpler technique with fewer variables to adjust 4
• Reduces preload and afterload, potentially increasing cardiac output in heart failure 4
• Demonstrated reduction in intubation rate and mortality in acute pulmonary edema over 30 years of use 4
• Typical pressure setting of 10 cmH₂O is well-established 4

Absolute Contraindications (Both Modalities)

Do not use CPAP or BiPAP in patients with: 1, 3

• Recent facial or upper airway surgery
• Facial abnormalities, burns, or trauma
• Fixed upper airway obstruction
• Active vomiting or recent upper gastrointestinal surgery
• Inability to protect airway
• Copious respiratory secretions

Monitoring and Failure Recognition

Check arterial blood gases at 1-2 hours after initiating either modality 3, 8

Discontinue and consider intubation if: 8

• No improvement in oxygenation or clinical status after 4-6 hours
• Deteriorating conscious level
• Respiratory arrest or peri-arrest
• Persistent or worsening hypoxemia despite optimal settings
• Development of complications (pneumothorax)

Critical warning: Delaying intubation when NIV is clearly failing may result in respiratory deterioration and/or cardiac arrest 3, 8

Location of Care Requirements

• pH 7.30-7.35: Respiratory ward with appropriate monitoring 3
• pH <7.30: HDU/ICU setting 3
• Severe hypoxemic respiratory failure requiring NIV: HDU/ICU with immediate availability of invasive mechanical ventilation 8

Alternative Consideration

High-flow nasal oxygen may be superior to conventional NIV (including both CPAP and BiPAP) for de novo acute hypoxemic respiratory failure, with significant mortality reduction 3, 8