If a low tidal volume (VTi) is observed in a patient on BiPAP, which ventilator settings should be adjusted?

Adjusting BiPAP Settings for Low Tidal Volume

When a patient on BiPAP demonstrates low tidal volume (VTi), increase the pressure support (PS) by raising IPAP while keeping EPAP constant, targeting a tidal volume of 6-8 mL/kg ideal body weight. 1

Primary Adjustment: Increase Pressure Support

The pressure support (difference between IPAP and EPAP) should be increased in 1-2 cm H₂O increments every 5 minutes if tidal volume remains below 6-8 mL/kg ideal body weight. 1 This is the most direct and evidence-based intervention for low VTi on BiPAP.

Specific Titration Protocol:

• Target tidal volume: 6-8 mL/kg using ideal body weight 1
• Increment size: 1-2 cm H₂O increases in PS 1
• Timing: Adjust every 5 minutes if VTi remains low 1
• Maximum PS: Up to 20 cm H₂O 1
• Maximum IPAP: 30 cm H₂O for patients ≥12 years; 20 cm H₂O for patients <12 years 1

Critical Pitfall: Check for Leak First

Before increasing pressure support, always assess for excessive mask leak, as leak degrades flow signal accuracy and prevents effective pressure delivery. 1 If PS increases fail to raise tidal volume, this strongly suggests significant leak rather than inadequate pressure. 1

Leak Management:

• Refit or change the mask interface 1
• Consider switching from nasal to full-face mask if mouth leak is present 1
• Reduction in leak may improve PS effectiveness without further pressure increases 1

Secondary Considerations

When PS Alone Is Insufficient:

If maximum tolerated PS fails to achieve adequate ventilation, switch to spontaneous-timed (ST) mode with a backup rate. 1 This ensures a minimum respiratory rate and guarantees ventilatory support even if patient effort is inadequate.

ST Mode Settings:

• Backup rate: Set equal to or slightly below spontaneous sleeping respiratory rate (minimum 10 bpm) 1
• IPAP time: 30-40% of cycle time (e.g., 1.2-1.6 seconds at 15 breaths/min) 1
• I:E ratio: Minimum 1:2, with longer expiratory time for obstructive lung disease 1

Alternative: Volume-Targeted BiPAP

Volume-targeted BiPAP (AVAPS) automatically adjusts IPAP to deliver a set tidal volume and may be considered if manual titration is challenging. 1 This mode showed faster recovery in COPD patients with hypercapnic encephalopathy compared to standard BiPAP. 2

Initial AVAPS settings:

• Target VT: 8 mL/kg ideal body weight 1
• EPAP: 4 cm H₂O 1
• IPAP min: EPAP + 4 cm H₂O 1
• IPAP max: 25-30 cm H₂O 1

Additional Indications for PS Increase

Beyond low tidal volume, pressure support should also be increased if: 1

• PCO₂ remains ≥10 mmHg above goal for >10 minutes
• **SpO₂ <90%** for >5 minutes with concurrent low VTi (<6-8 mL/kg)
• Respiratory muscle rest not achieved after 10 minutes (evidenced by persistent tachypnea or excessive inspiratory effort)

Practical Algorithm

1. Verify adequate mask fit and minimize leak 1
2. Increase PS by 1-2 cm H₂O every 5 minutes until VTi reaches 6-8 mL/kg 1
3. If PS increases fail to improve VTi, reassess for leak 1
4. If maximum PS reached without adequate ventilation, add backup rate (ST mode) 1
5. Consider volume-targeted mode if manual titration unsuccessful 1