What is the target tidal volume in an Amyotrophic Lateral Sclerosis (ALS) patient?

Target Tidal Volume in ALS Patients

The target tidal volume for ALS patients should be 6 mL/kg predicted body weight (PBW), with plateau pressures maintained below 30 cmH2O. 1

Rationale for Low Tidal Volume Ventilation

Low tidal volume ventilation has become the standard of care for mechanical ventilation in critically ill patients, particularly those with respiratory compromise. This approach is based on substantial evidence showing that:

• Lower tidal volumes (4-8 mL/kg PBW) reduce the risk of ventilator-induced lung injury 1
• Maintaining plateau pressures ≤30 cmH2O prevents alveolar overdistension 2, 1
• Driving pressure (plateau pressure - PEEP) should be targeted to <15 cmH2O 1

Implementation in ALS Patients

For ALS patients requiring mechanical ventilation:

1. Calculate predicted body weight:

   • Men: 50 + 2.3 (height in inches - 60) kg
   • Women: 45.5 + 2.3 (height in inches - 60) kg 2

2. Initial ventilator settings:

   • Set tidal volume at 6 mL/kg PBW 1
   • Use volume-cycled ventilation in assist-control mode initially 2
   • Monitor plateau pressure to ensure it remains ≤30 cmH2O 2, 1

3. Adjust based on patient response:

   • If plateau pressure exceeds 30 cmH2O, consider further reducing tidal volume to 4-5 mL/kg PBW 1
   • If hypercapnia occurs, permissive hypercapnia is generally acceptable as long as pH remains above 7.15-7.2 2

Special Considerations for ALS Patients

ALS patients have unique respiratory challenges that must be considered:

• Progressive respiratory muscle weakness leads to decreased vital capacity
• Reduced ability to clear secretions increases risk of atelectasis
• Bulbar dysfunction may increase aspiration risk

These factors may necessitate adjustments to the standard approach:

• Higher PEEP levels (5-10 cmH2O) may help prevent atelectasis
• Careful monitoring of respiratory mechanics is essential as disease progresses
• More frequent assessment of plateau pressures may be needed

Potential Pitfalls and Caveats

• Avoid excessive tidal volumes: Traditional tidal volumes of 10-15 mL/kg can cause stretch-induced lung injury 3
• Monitor for auto-PEEP: As respiratory rate increases to maintain minute ventilation with lower tidal volumes, the risk of air trapping increases 4
• Balance gas exchange goals: Target PaO2 between 70-90 mmHg or SpO2 between 92-97% 1
• Consider driving pressure: This may be a better target than tidal volume alone for assessing and preventing alveolar overdistension 5

By adhering to lung-protective ventilation strategies with appropriate tidal volumes, clinicians can optimize respiratory support for ALS patients while minimizing the risk of ventilator-induced lung injury.