What are the management strategies for an asthmatic patient on a ventilator?

Management Strategies for Asthmatic Patients on Mechanical Ventilation

For asthmatic patients requiring mechanical ventilation, implement a ventilation strategy with slower respiratory rates (10-14 breaths/min), smaller tidal volumes (6-8 mL/kg), shorter inspiratory times, and longer expiratory times to minimize air trapping and auto-PEEP. 1

Initial Ventilator Settings

• Use the largest endotracheal tube available (usually 8 or 9 mm) to decrease airway resistance 1, 2
• Set tidal volume to 6-8 mL/kg of ideal body weight to minimize barotrauma 1
• Use slower respiratory rates of 10-14 breaths/min 1
• Set shorter inspiratory times (inspiratory flow rate 80-100 L/min) and longer expiratory times (I:E ratio 1:4 or 1:5) 1
• Implement "permissive hypercapnia" or "controlled hypoventilation" to provide adequate oxygenation while minimizing airway pressures and the possibility of barotrauma 3, 1

Monitoring and Managing Auto-PEEP

• Regularly assess for signs of auto-PEEP (breath stacking) which can lead to complications such as hyperinflation, tension pneumothorax, and hypotension 1, 2
• Monitor ventilator flow and pressure curves for evidence of incomplete exhalation 1
• 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 3, 1
• Consider assisting with exhalation by pressing on the chest wall after disconnection of the ventilator circuit to allow active exhalation and immediate resolution of hypotension 3

Sedation and Paralysis Management

• Provide adequate sedation to optimize ventilation and decrease ventilator dyssynchrony 1, 2
• Consider paralytic agents if auto-PEEP persists and the patient displays ventilator dyssynchrony despite adequate sedation 3, 1

Volume Management

• Maintain or replace intravascular volume as hypotension commonly accompanies the initiation of positive pressure ventilation 3, 2

Pharmacological Management

• Continue aggressive bronchodilator therapy with continuous nebulized beta-agonists 4
• Administer albuterol 2.5 mg via nebulization, with more frequent administration for acute severe asthma 5
• Continue anti-inflammatory therapy throughout the period of mechanical ventilation 4

Special Considerations

• Obtain consultation with or comanagement by a physician expert in ventilator management as ventilation of patients with severe asthma is complicated and risky 3, 1
• Consider extracorporeal membrane oxygenation (ECMO) in exceedingly rare circumstances when aggressive treatment fails to provide adequate gas exchange 3, 1
• For persistent hypercapnia, consider a strategy of mechanical ventilation combined with bicarbonate infusion to maintain physiologic pH while allowing pCO2 to remain elevated 6

Complications to Monitor For

• Hypotension, especially during initiation of positive pressure ventilation 3, 2
• Barotrauma (pneumothorax, pneumomediastinum, subcutaneous emphysema) 2, 4
• Nosocomial pneumonia 4
• Cardiac dysrhythmias due to hypoxia, dehydration, acidosis, and hypokalaemia 4

Pitfalls to Avoid

• Never use conventional ventilator settings designed for non-asthmatic patients, as these can worsen air trapping 1, 2
• Avoid high respiratory rates and large tidal volumes which can lead to incomplete exhalation and auto-PEEP 1, 2
• Do not delay intubation in patients with persistent or increasing hypercapnia, exhaustion, and depressed mental status 3, 2
• Avoid inadequate sedation which can lead to patient-ventilator dyssynchrony and worsen air trapping 2

When to Consider Intubation

• Patients presenting with apnea or coma should be intubated immediately 3, 2
• Persistent or increasing hypercapnia, exhaustion, and depressed mental status strongly suggest the need for ventilatory support 3, 2
• Intubation should be done semielectively and before respiratory arrest occurs 3