Optimal Ventilator Settings for Severe Asthma
Initial Ventilator Settings
- The American Heart Association recommends using a ventilation strategy with slower respiratory rates (10-14 breaths/min), smaller tidal volumes (6-8 mL/kg), shorter inspiratory times (inspiratory flow rate 80-100 L/min), and longer expiratory times (I:E ratio 1:4 or 1:5) to minimize air trapping and auto-PEEP in patients with severe asthma requiring mechanical ventilation 1, 2, 3
- Use the largest endotracheal tube available (usually 8 or 9 mm) to decrease airway resistance in patients with severe asthma 1, 2
- Set tidal volume to 6-8 mL/kg of ideal body weight to minimize barotrauma in patients with severe asthma 1, 2, 3
- Implement permissive hypercapnia (mild hypoventilation) to reduce the risk of barotrauma in patients with severe asthma 1, 2, 3
Monitoring for Auto-PEEP
- Regularly assess for signs of auto-PEEP (breath stacking) which can lead to complications such as hyperinflation, tension pneumothorax, and hypotension in patients with severe asthma 1, 2, 3
- Monitor ventilator flow and pressure curves for evidence of incomplete exhalation in patients with severe asthma 1, 2
Managing Auto-PEEP
- If auto-PEEP develops, quickly reduce high-end expiratory pressure by briefly disconnecting the patient from the ventilator circuit to allow PEEP to dissipate during passive exhalation in patients with severe asthma 2, 3
- Consider paralytic agents if auto-PEEP persists and the patient displays ventilator dyssynchrony despite adequate sedation in patients with severe asthma 2, 3
Sedation Management
- Provide adequate sedation to optimize ventilation, decrease ventilator dyssynchrony, and minimize barotrauma in patients with severe asthma 1, 2
Special Considerations
- Obtain expert consultation for management of mechanical ventilation in severe asthma 1, 2
- Consider extracorporeal membrane oxygenation (ECMO) in exceedingly rare circumstances when aggressive treatment fails to provide adequate gas exchange in patients with severe asthma 2, 3