Ventilator-Integrated Cough-Assist Modes
Ventilators offer two primary cough-assist modes: breath-stacking (air stacking/AS) and volumetric cough mode (VCM), both of which effectively increase peak cough flow and lung volumes in neuromuscular patients, with VCM typically producing superior results when it achieves greater inspiratory capacity.
Primary Ventilator-Based Cough Modes
Breath-Stacking (Air Stacking)
- Mechanism: Patient takes 2 or more consecutive ventilator insufflations without exhaling between breaths, accumulating volume progressively
- Settings: Use existing volume-control continuous mandatory ventilation settings; no special programming required
- Advantages:
- Effectiveness: Significantly increases both peak cough flow and vital capacity compared to baseline 3
Volumetric Cough Mode (VCM)
- Mechanism: Programmable intermittent deep breath set to a specific percentage above baseline tidal volume (typically 150-200% of baseline)
- Settings: Program the ventilator to deliver periodic large insufflations equal to a predetermined percentage of tidal volume
- Advantages:
- Key Finding: The technique that produces the greatest inspiratory capacity typically yields the highest peak cough flow 1
Optimizing Ventilator Settings for Cough Assistance
Standard NIV Settings
- Baseline approach: Using NIV at usual home settings increases peak cough flow compared to unassisted cough 3
- Enhanced pressure: Increasing inspiratory positive airway pressure to 30 cmH₂O further improves cough effectiveness 3
- Both approaches significantly increase vital capacity 3
Selection Algorithm
- Measure baseline inspiratory capacity with both breath-stacking and VCM
- Select the mode that achieves greater inspiratory capacity - this will typically produce higher peak cough flow 1
- Monitor displayed volumes on the ventilator screen to verify adequate insufflation 1
- Combine with manually assisted cough (MAC) for additional peak cough flow gains - all techniques show further improvement when MAC is added 3
Critical Considerations
When Ventilator Modes Are Sufficient
- If peak cough flow exceeds 270 L/min with ventilator-based techniques alone, mechanical insufflation-exsufflation (MI-E) may be unnecessary 1
- Important caveat: When peak cough flow with insufflation + MAC exceeds 500 L/min (5 L/s), adding MI-E becomes counterproductive because the expiratory flow exceeds the device's vacuum capacity, creating a transient load against cough 4
Limitations by Patient Factors
- Bulbar dysfunction: Reduces effectiveness of all insufflation techniques due to upper airway collapse 2
- Compliance issues: Chest wall and lung compliance affect volume delivery and technique effectiveness 2
- Glossopharyngeal breathing (GPB) showed no significant improvement in this context and requires specialized training that not all patients can master 2, 3
Artificial Airways
- Endotracheal tubes and tracheostomy tubes significantly reduce peak expiratory flow during cough assistance 5
- The narrower the inner diameter, the greater the reduction in effectiveness 5
- Higher pressures (40-50 cmH₂O) may be needed to compensate for this resistance 5
Practical Implementation
The guideline consensus indicates no single airway clearance technique is superior to another 2, but the research evidence shows VCM and breath-stacking are both effective, with VCM having a slight edge when it achieves greater lung volumes 1. The choice should be based on:
- Available ventilator capabilities (does it have VCM programming?)
- Real-time monitoring of achieved inspiratory volumes
- Individual patient response measured by peak cough flow
- Always consider adding MAC for synergistic benefit 3
The 2023 American College of Chest Physicians guidelines emphasize that decisions should be based on local resources and patient-specific conditions rather than rigid protocols 2, but when both modes are available, start with the one that displays volumes and allows you to verify which achieves greater inspiratory capacity 1.