Is BiPAP (Bilevel Positive Airway Pressure) preferred over CPAP (Continuous Positive Airway Pressure) for patients requiring pressure support?

PS Mode in CPAP: BiPAP vs CPAP for Pressure Support

BiPAP (bilevel positive airway pressure) is the appropriate modality when pressure support is needed, as CPAP by definition does not provide pressure support—it maintains constant pressure throughout the respiratory cycle and is primarily indicated for correcting hypoxemia, not for ventilatory assistance. 1

Understanding the Fundamental Difference

CPAP is not considered respiratory support in the conventional sense—it maintains a single continuous pressure level throughout inspiration and expiration, primarily recruiting underventilated lung and offsetting intrinsic PEEP, but does not actively assist ventilation. 1 While CPAP can unload inspiratory muscles and reduce work of breathing in certain contexts (particularly in COPD by offsetting intrinsic PEEP), its main indication remains correction of hypoxemia. 1

BiPAP provides true pressure support through its dual-level system: the inspiratory positive airway pressure (IPAP) actively produces ventilation by assisting the patient's inspiratory effort, while the expiratory positive airway pressure (EPAP) recruits underventilated lung, offsets intrinsic PEEP, and facilitates triggering. 1 This pressure differential between IPAP and EPAP (the pressure support) directly increases tidal volume and reduces the patient's intrinsic respiratory muscle effort. 2

Clinical Algorithm for Mode Selection

Choose BiPAP When:

• Hypercapnic respiratory failure is present (elevated PaCO₂ with respiratory acidosis)—BiPAP is specifically indicated for type 2 respiratory failure. 3, 4

• Active ventilatory assistance is required—when the patient needs help moving air in and out, not just maintaining airway patency. 4, 2

• COPD exacerbations with respiratory acidosis—BiPAP reduces intubation rates and improves gas exchange by offsetting intrinsic PEEP and providing inspiratory assistance. 3, 4

• Neuromuscular disorders affecting respiratory function—particularly when poor respiratory drive requires backup rate support. 3, 4

• Obesity hypoventilation syndrome (BMI >30 kg/m² with daytime hypercapnia). 3

• CPAP intolerance due to high pressures (>15 cm H₂O) or significant pressure-related discomfort—BiPAP allows lower mean airway pressure while maintaining therapeutic effect. 3, 5

Choose CPAP When:

• Pure hypoxemic (type 1) respiratory failure without hypercapnia—CPAP is more appropriate, as BiPAP has 2.6 times higher failure rates in this setting. 4

• Obstructive sleep apnea as first-line therapy—CPAP/APAP should be the initial approach before considering BiPAP. 3

• Acute heart failure—CPAP is preferred over BiPAP, as some evidence suggests BiPAP may increase myocardial infarction risk (71% vs 31% in one study). 4

Practical Implementation of BiPAP for Pressure Support

Initial Settings:

• Minimum starting IPAP: 8 cm H₂O 3, 2
• Minimum starting EPAP: 4 cm H₂O 3, 2
• Typical pressure differential (pressure support): 4-6 cm H₂O initially, with adjustments based on response 3
• For reducing work of breathing: IPAP 14-20 cm H₂O, EPAP 4-8 cm H₂O 4

Titration Strategy:

• Increase pressure support (IPAP-EPAP differential) every 5 minutes when tidal volume remains low (<6-8 mL/kg ideal body weight) or respiratory muscle rest has not been achieved after 10 minutes at current settings. 2

• Target tidal volume: 6-8 mL/kg ideal body weight 2

• Target SpO₂: ≥90% sustained, with some guidelines recommending ≥92-94% 4, 2

• Target PCO₂: ≤ awake baseline 2

• Maximum pressure support: 20 cm H₂O 2

• Maximum IPAP: 30 cm H₂O for adults (≥12 years), 20 cm H₂O for children 2

Mode Selection:

• Use Spontaneous (S) mode when the patient has adequate respiratory drive and reliably triggers breaths. 2

• Use Spontaneous-Timed (ST) mode with backup rate when central hypoventilation is present, significant central apneas occur, inappropriately low respiratory rate exists, or the patient unreliably triggers cycles due to muscle weakness. 2

• Starting backup rate: equal to or slightly less than spontaneous sleeping respiratory rate (minimum 10 bpm), increasing in 1-2 bpm increments every 10 minutes if goals are not met. 2

Critical Pitfalls and How to Avoid Them

Equipment-Related Issues:

• Ensure proper mask fitting—air leaks reduce effectiveness and increase aerophagia likelihood regardless of device type. 3, 2

• Verify exhalation ports are functioning properly—occlusion can exacerbate hypercapnia, particularly problematic in tachypneic patients. 1

• Monitor for rebreathing—normally used EPAP levels (3-5 cm H₂O) do not completely eliminate rebreathing during bilevel pressure support, especially when respiratory frequency increases. 1

Physiological Complications:

• Excessive EPAP can paradoxically increase work of breathing or cause gastric distension. 4, 2

• In COPD patients with hyperinflation, further increases in lung volume from excessive positive pressure may adversely affect inspiratory muscle function. 1

• Use caution in hypotensive patients—positive intrathoracic pressure reduces venous return and can further decrease blood pressure. 3, 2

Clinical Decision Errors:

• Do not delay intubation—if no improvement or worsening occurs after 1-2 hours of BiPAP trial, persistent or worsening hypercapnia with pH <7.25, worsening mental status, hemodynamic deterioration, inability to manage secretions, or patient exhaustion despite BiPAP support, proceed to intubation immediately. 4

• Avoid BiPAP in type 1 respiratory failure—it has lower success rates compared to CPAP with higher risk of failure. 4

• Recognize absolute contraindications: apnea or impending respiratory arrest requires immediate intubation, not BiPAP trial. 4

Evidence Quality Considerations

The guideline evidence consistently supports BiPAP as the appropriate modality when pressure support is needed. 1, 3, 4, 2 The American Academy of Sleep Medicine provides the most detailed titration protocols. 3, 2 However, one research study from 2000 found that BiPAP carried risk of increased work of breathing in spontaneously breathing COPD patients compared to pressure support ventilation, suggesting pressure support mode may be superior for reducing respiratory muscle effort in this specific population. 6 This highlights the importance of close monitoring during BiPAP initiation and proper titration of settings.