What is BiPap (Bilevel Positive Airway Pressure) and what are its indications?

What is BiPAP and Its Indications

BiPAP (Bilevel Positive Airway Pressure) is a non-invasive ventilatory device that delivers two distinct pressure levels—higher pressure during inspiration (IPAP) and lower pressure during expiration (EPAP)—and is primarily indicated for patients with obstructive sleep apnea who cannot tolerate CPAP, chronic alveolar hypoventilation syndromes, and acute hypercapnic respiratory failure. 1, 2, 3

Device Mechanism and Components

BiPAP operates fundamentally differently from CPAP by providing independently adjustable inspiratory and expiratory pressures rather than a single continuous pressure throughout the respiratory cycle. 1, 3 The system consists of:

• Pressure generator (air pump) that supplies pressurized airflow 3
• Interface (nasal, oral, or oronasal mask) secured with headgear 1, 3
• Flexible tubing connecting the device to the mask 1, 3
• Control systems to adjust pressure levels and monitor therapy 3

The pressure differential between IPAP and EPAP (called pressure support) increases tidal volume and improves ventilation, making BiPAP particularly effective for patients requiring ventilatory assistance. 3

Operating Modes

BiPAP devices function in three primary modes:

• Spontaneous (S) mode: Patient determines respiratory timing and frequency; machine responds to patient's respiratory efforts 3
• Spontaneous-Timed (ST) mode: Provides backup respiratory frequency to ensure minimal ventilation if patient doesn't initiate sufficient breaths 3
• Timed (T) mode: Machine delivers IPAP/EPAP cycles at set respiratory frequency with fixed inspiratory time 3

Primary Clinical Indications

Obstructive Sleep Apnea (OSA)

Switch from CPAP to BiPAP when: 2, 4

• Patient cannot tolerate CPAP pressures >15 cm H₂O 2
• Significant pressure-related discomfort occurs with CPAP 2
• Respiratory events persist at 15 cm H₂O of CPAP 3

CPAP remains first-line therapy for most OSA patients, but BiPAP serves as an effective alternative for the subset who fail or cannot tolerate CPAP. 4, 5

Chronic Alveolar Hypoventilation Syndromes

BiPAP is indicated for: 1, 2

• Obesity hypoventilation syndrome (OHS): BMI >30 kg/m² with daytime hypercapnia 2
• Neuromuscular diseases (NMD): Including ALS and muscular dystrophy affecting respiratory function 1, 2
• Restrictive thoracic cage disorders (RTCD): Such as kyphoscoliosis 1
• Central respiratory control disturbances (CRCD): Including congenital central hypoventilation 1

Studies show that 11 of 17 patients with OHS and 9 of 16 patients with COPD plus OSA required BiPAP rather than CPAP. 5

Acute Hypercapnic Respiratory Failure

BiPAP is indicated for type 2 respiratory failure with: 2, 6

• Elevated PaCO₂ 2
• Respiratory distress with SpO₂ <90% or PaO₂ <60 mmHg 2
• Hypercapnia with respiratory acidosis 2

For COPD exacerbations specifically, BiPAP reduces mortality by 46% (RR 0.54,95% CI 0.38-0.76; NNTB 12) and reduces need for intubation by 65% (RR 0.36,95% CI 0.28-0.46; NNTB 5). 6

Initial Pressure Settings

The American Academy of Sleep Medicine recommends starting with: 2, 3

• Minimum IPAP: 8 cm H₂O 2, 3
• Minimum EPAP: 4 cm H₂O 2, 3
• Typical pressure differential: 4-6 cm H₂O 2

Manual titration during attended polysomnography remains the gold standard for determining optimal pressure settings. 1, 2, 3

Important Clinical Caveats

Contraindications and Cautions

• Type 1 (hypoxemic) respiratory failure: BiPAP has lower success rates with risk ratio 2.6 times higher for failure compared to CPAP 2
• Acute heart failure: BiPAP may increase myocardial infarction risk (71% vs 31% with CPAP in one study) and has not shown clear superiority over CPAP 2
• Hypotensive patients: Use with caution as BiPAP can further reduce blood pressure 2

Monitoring Requirements

• For acute respiratory failure: Do not delay intubation if BiPAP fails to improve clinical status within 1-2 hours 2
• Target SpO₂: 90-96% during titration, with some guidelines recommending ≥92% 2
• For chronic hypoventilation: Monitor blood gases for improvement in PaCO₂ and PaO₂, assess symptom improvement and treatment adherence 2

Practical Implementation

• Ensure proper mask fitting to minimize leaks and improve comfort 2, 3
• Consider using the ramp feature (starts at lower pressures before reaching therapeutic levels) to improve tolerance and adherence 7
• Add heated humidification if patient complains of dryness or nasal congestion 1
• Close follow-up after initiation is essential to establish effective utilization patterns and remediate side effects 1

Treatment intolerance is significantly greater with BiPAP than usual care (RD 0.11,95% CI 0.04-0.17), requiring careful attention to patient comfort and device synchrony. 6