Adjusting BiPAP Settings to Reduce Work of Breathing
To reduce work of breathing on BiPAP, increase the pressure support (PS) - the difference between IPAP and EPAP - which directly augments tidal volume and offloads respiratory muscles. 1
Primary Adjustment: Pressure Support (PS)
Increase PS (IPAP-EPAP differential) every 5 minutes when:
- Tidal volume is low (<6-8 mL/kg ideal body weight) 1
- Respiratory muscle rest has not been achieved after 10 minutes at current settings 1
- PCO₂ remains ≥10 mmHg above goal (target ≤ awake PCO₂) for ≥10 minutes 1
- SpO₂ remains <90% for ≥5 minutes AND tidal volume is low 1
Recommended PS range: Minimum 4 cm H₂O, maximum 20 cm H₂O 1
The pressure differential between IPAP and EPAP is the primary determinant of ventilatory support - higher PS directly increases tidal volume and reduces intrinsic respiratory muscle effort 2. This is fundamentally different from treating obstructive sleep apnea, where the goal is airway patency rather than ventilatory support.
Starting Parameters
Initial settings: 1
- IPAP: 8 cm H₂O minimum
- EPAP: 4 cm H₂O minimum
- PS: 4 cm H₂O minimum (IPAP minus EPAP)
Maximum limits: 1
- IPAP: 30 cm H₂O (patients ≥12 years), 20 cm H₂O (patients <12 years)
- PS: 20 cm H₂O
EPAP Adjustments for Specific Conditions
For obstructive airway disease (COPD):
- EPAP counteracts intrinsic PEEP, reducing the threshold load to trigger inspiration 2
- Typical EPAP range: 3-5 cm H₂O 2
- Critical pitfall: EPAP >5 cm H₂O is rarely tolerated despite intrinsic PEEP potentially reaching 10-15 cm H₂O 2
- Use lower %IPAP time (approximately 30%) to allow adequate expiratory time 1
For restrictive disease (neuromuscular/chest wall):
- EPAP prevents alveolar collapse and improves functional residual capacity 2
- Use higher %IPAP time (approximately 40%) to allow longer inspiratory time 1
- EPAP addition improved oxygenation (SaO₂ min increased from 77% to 84%) in neuromuscular patients 3
Backup Rate and Mode Selection
Use Spontaneous-Timed (ST) mode with backup rate when: 1
- Central hypoventilation is present
- Significant central apneas or inappropriately low respiratory rate occurs
- Patient unreliably triggers IPAP/EPAP cycles due to muscle weakness
- Maximum tolerated PS in spontaneous mode fails to achieve adequate ventilation
Backup rate settings: 1
- Starting rate: Equal to or slightly less than spontaneous sleeping respiratory rate (minimum 10 bpm)
- Increase in 1-2 bpm increments every 10 minutes if goals not met
- Inspiratory time (IPAP time): 30-40% of cycle time (typically 1.2-1.6 seconds at 15 bpm) 1, 2
Monitoring Parameters for Adequate Support
Indicators that work of breathing is adequately reduced:
- Tidal volume: 6-8 mL/kg ideal body weight 1
- SpO₂: ≥90% sustained 1
- PCO₂: ≤ awake baseline 1
- Respiratory rate: Decreased from baseline 4
- Clinical: Respiratory comfort achieved, reduced accessory muscle use 4
Critical Pitfalls to Avoid
Excessively high EPAP:
- Can paradoxically increase work of breathing 2
- May cause gastric distension 2
- Reduces venous return in cardiovascular compromise 2
Inadequate pressure support:
- Research demonstrates that BiPAP can actually increase work of breathing compared to pressure support ventilation if PS is insufficient 5
- One study found BiPAP increased pressure-time product, work of breathing, and intrinsic PEEP compared to pressure support in COPD patients 5
Poor patient-ventilator synchrony:
- Adjust rise time, pressure relief, and IPAP/EPAP durations for comfort 1
- Ensure proper mask fit to minimize unintentional leak 1
- If patient complains pressures are too high, lower to comfortable level to allow sleep 1
Inadequate inspiratory time at higher respiratory rates:
- As backup rate increases, inspiratory time must decrease to maintain adequate I:E ratio 1, 2
- Default maximum IPAP duration (often 3 seconds) may delay IPAP-to-EPAP transition 2
Supplemental Oxygen Considerations
Add oxygen when: 1
- Awake SpO₂ <88%, OR
- PS and respiratory rate optimized but SpO₂ remains <90% for ≥5 minutes
Oxygen delivery: 2