What are the optimal BiPAP (Bilevel Positive Airway Pressure) settings for a patient with obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS)?

BiPAP Setup for OSA with OHS

For patients with both OSA and OHS, start with attended BiPAP titration using initial settings of IPAP 8 cm H₂O and EPAP 4 cm H₂O, with a minimum pressure support of 4 cm H₂O, then titrate upward to eliminate obstructive events and achieve adequate ventilation with target tidal volumes of 6-8 mL/kg ideal body weight. 1

Initial BiPAP Settings

• Start with IPAP 8 cm H₂O and EPAP 4 cm H₂O 1, 2, 3
• Maintain minimum pressure support (IPAP-EPAP difference) of 4 cm H₂O 1, 2, 3
• EPAP of 4 cm H₂O represents the lowest available setting on most devices and serves as the standard starting point 1
• Maximum IPAP should not exceed 30 cm H₂O for patients ≥12 years 1, 3
• Maximum pressure support should not exceed 20 cm H₂O 1

Titration Algorithm

Step 1: Eliminate Obstructive Events First

• Adjust IPAP and EPAP together to eliminate obstructive apneas, hypopneas, RERAs, and snoring following standard OSA titration protocols 1
• Increase pressures in 1-2 cm H₂O increments every 5 minutes minimum 1
• The majority of OHS patients have concurrent OSA that must be addressed first 1

Step 2: Optimize Ventilatory Support

• Increase pressure support (IPAP-EPAP difference) if tidal volume remains below 6-8 mL/kg ideal body weight 1
• Monitor for signs of hypoventilation including persistent oxygen desaturation despite elimination of obstructive events 1
• Increase pressure support every 5 minutes if tidal volume goals are not met 1
• Target normalization or improvement of gas exchange, particularly reduction in PaCO₂ 1

Step 3: Confirm Adequate Settings

• Verify settings eliminate obstructive events AND achieve adequate ventilation for at least 30 minutes, including supine REM sleep 3
• Document improvement in oxygen saturation and reduction in transcutaneous or end-tidal CO₂ if monitored 1
• Ensure respiratory rate decreases and tidal volume increases compared to baseline 1

Critical Pitfalls to Avoid

• Never use CPAP alone as initial therapy for patients with documented OHS and hypoventilation, as CPAP only addresses upper airway obstruction and does not provide ventilatory support 1
• Do not add supplemental oxygen without addressing the underlying ventilatory problem, as this may worsen hypercapnia 2
• Do not increase pressure support beyond what is needed for adequate ventilation, as excessive pressure may worsen patient tolerance 1
• If the patient awakens complaining pressure is too high, reduce to a comfortable level that allows return to sleep, then resume titration more gradually 3

When BiPAP May Not Be First-Line

• For stable ambulatory OHS patients with severe OSA (AHI >30), CPAP can be attempted first as it may adequately treat both the OSA and improve daytime hypercapnia over time 1, 2
• However, many OHS patients require high CPAP levels (often >15 cm H₂O) and may have persistent desaturation, making BiPAP necessary 1
• Switch from CPAP to BiPAP if obstructive events persist at CPAP ≥15 cm H₂O or if patient cannot tolerate high pressures 2, 3, 4

Monitoring Requirements

• Attended polysomnography with BiPAP titration is the standard method for determining optimal settings in OHS 1
• Monitor oxygen saturation continuously via pulse oximetry 1
• Monitor tidal volume, respiratory rate, and ideally transcutaneous or end-tidal CO₂ to document adequate ventilatory support 1
• Assess for reduction in accessory muscle use and work of breathing 1

Expected Outcomes

• BiPAP effectively reduces PaCO₂ in OHS patients, with studies showing reductions of 12-21 mmHg within days to weeks 5, 6
• Improvements in mortality, gas exchange, daytime sleepiness, sleep quality, and quality of life are documented with PAP therapy in OHS 7
• For patients failing CPAP, BiPAP achieves better adherence (7.0 vs 2.5 hours/night) and symptom control in obese patients with high pressure requirements 8