What are the recommended tidal volumes for an ALS patient on Bi-Level Positive Airway Pressure (BIPAP)?

Recommended Tidal Volumes for ALS Patients on BiPAP

For ALS patients on BiPAP, tidal volumes should be targeted at 6-8 mL/kg of ideal body weight to optimize respiratory support and improve outcomes. 1

Tidal Volume Targets for ALS Patients

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

• Target tidal volume range: 6-8 mL/kg of ideal body weight 1
• This recommendation is based on expert consensus (Level A) for patients with chronic alveolar hypoventilation syndromes, which includes ALS patients

Adjusting Pressure Support to Achieve Target Tidal Volumes

1. Initial pressure support settings:

   • Begin with minimum pressure support of 4 cmH2O (difference between IPAP and EPAP) 1
   • Maximum pressure support should not exceed 20 cmH2O 1
   • Maximum IPAP should not exceed 30 cmH2O for adult patients 1

2. Titration protocol:

   • Increase pressure support in 1-2 cmH2O increments every 5 minutes if tidal volume remains below target 1
   • Monitor for mask leaks which may reduce effectiveness of pressure increases 1
   • Continue adjustments until target tidal volume of 6-8 mL/kg is achieved 1

Monitoring and Adjustment Parameters

When to Increase Pressure Support:

• Tidal volume below 6 mL/kg for 5 minutes or more 1
• PCO2 remains 10 mmHg above goal for 10 minutes or more 1
• SpO2 remains below 90% for 5 minutes or more with low tidal volume 1
• Respiratory muscle rest has not been achieved (persistent tachypnea or excessive inspiratory effort) 1

Signs of Adequate Ventilation:

• Achievement of target tidal volume (6-8 mL/kg)
• Resolution of tachypnea
• Reduction in inspiratory effort
• Normalization of SpO2 and PCO2 values

Special Considerations for ALS Patients

ALS patients have unique ventilatory needs due to progressive respiratory muscle weakness:

• Use ST mode (spontaneous/timed) with backup rate if the patient has frequent central apneas or fails to reliably trigger the device due to muscle weakness 1
• Consider slightly lower tidal volumes with higher respiratory rates if better tolerated by the patient 1
• Monitor for bulbar involvement which may increase risk of aspiration and affect mask fit

Clinical Impact of BiPAP in ALS

Research has shown that effective BiPAP use (>4 hours/day) in ALS patients:

• Significantly prolongs survival (14.2 months vs. 4.6 months in non-users) 2
• Slows the decline in forced vital capacity (-3.5% change/month vs. -8.3% change/month) 2

Common Pitfalls to Avoid

1. Inadequate pressure support:

   • Failure to increase pressure support when tidal volumes remain below target
   • Not accounting for mask leaks that reduce effective pressure delivery

2. Excessive pressure support:

   • Using pressure support >20 cmH2O which may cause discomfort and reduce compliance
   • Increasing pressure too rapidly (>2 cmH2O at a time) which may cause intolerance 1

3. Poor mask fit:

   • Excessive leaks can compromise ventilation effectiveness
   • Refit or change mask if leaks persist despite appropriate pressure adjustments 1

4. Inadequate monitoring:

   • Failure to regularly assess tidal volumes, respiratory rate, and patient comfort
   • Not recognizing when to switch to ST mode for patients with inadequate respiratory drive

By following these evidence-based guidelines for tidal volume targets and pressure support adjustments, clinicians can optimize BiPAP therapy for ALS patients, potentially improving survival and slowing respiratory decline.