What is the target tidal volume for ALS patients on BiPAP (Bilevel Positive Airway Pressure)?

Target Tidal Volume for ALS Patients on BiPAP

The target tidal volume for ALS patients on BiPAP should be 6-8 mL/kg of ideal body weight, with 8 mL/kg being the recommended target for volume-targeted BiPAP therapy. 1

Rationale for Tidal Volume Targets

The American Academy of Sleep Medicine provides clear guidance on tidal volume targets for patients requiring non-invasive positive pressure ventilation (NPPV), including BiPAP:

• An acceptable tidal volume goal ranges from 6-8 mL/kg using ideal body weight 1
• For volume-targeted BiPAP specifically, 8 mL/kg using ideal body weight is the recommended target 1
• Pressure support should be increased every 5 minutes if tidal volume falls below this acceptable goal 1

Adjusting BiPAP Settings to Achieve Target Tidal Volume

When tidal volumes are inadequate, the following algorithm should be followed:

1. Increase pressure support (PS) if tidal volume is below 6-8 mL/kg for 5 minutes 1
2. Check for mask leaks if increases in pressure support fail to raise tidal volume, as leaks can significantly impact delivered volumes 1
3. Consider ST mode (backup rate) if the patient fails to reliably trigger the BiPAP device due to muscle weakness, which is common in ALS 1
4. Monitor for respiratory muscle rest, indicated by resolution of tachypnea and reduced inspiratory effort 1

Special Considerations for ALS Patients

ALS patients have unique considerations that affect BiPAP management:

• Respiratory muscle weakness is a hallmark of disease progression, requiring careful monitoring of tidal volumes
• BiPAP use >4 hours/day has been shown to significantly prolong survival and slow vital capacity decline in ALS patients 2
• Backup rate (ST mode) is particularly important as ALS patients may have an inappropriately low respiratory rate or fail to trigger the device due to muscle weakness 1

Monitoring Parameters

When managing BiPAP in ALS patients, monitor:

• Tidal volume: Maintain 6-8 mL/kg of ideal body weight 1
• SpO2: Increase pressure support if SpO2 remains below 90% for 5+ minutes with low tidal volume 1
• PCO2: Increase pressure support if PCO2 remains 10 mmHg above goal for 10+ minutes 1
• Respiratory muscle rest: Look for resolution of tachypnea and excessive inspiratory effort 1

Common Pitfalls to Avoid

• Inaccurate height estimation: Visual estimation of height leads to incorrect tidal volume calculations. Always measure actual height to ensure appropriate tidal volume targets 3
• Ignoring mask leaks: Excessive leaks can make tidal volume measurements unreliable and reduce effective ventilation 1
• Inadequate pressure support: Failure to increase pressure support when tidal volumes are low can result in hypoventilation 1
• Overlooking backup rate needs: ALS patients often require ST mode due to muscle weakness 1

By maintaining appropriate tidal volumes through careful BiPAP management, clinicians can help improve survival and slow functional decline in ALS patients requiring respiratory support.