What is the best ventilator mode for permissive tachypnea?

Best Ventilator Mode for Permissive Tachypnea

Bi-level pressure support ventilation is the recommended mode for permissive tachypnea, as it provides better patient comfort, adequate ventilation, and better leak compensation compared to volume-controlled modes. 1

Understanding Permissive Tachypnea

• Permissive tachypnea is a ventilation strategy that allows for an elevated respiratory rate while maintaining adequate minute ventilation and preventing ventilator-associated lung injury 1
• This approach is similar to permissive hypercapnia strategies used in acute lung injury, where pressure-limited small volume ventilation is preferred 1
• The goal is to minimize ventilator-induced lung injury while allowing the patient to maintain their own respiratory drive 1

Recommended Ventilator Mode

Bi-level Pressure Support Ventilation

• Bi-level pressure support ventilators using IPAP (inspiratory positive airway pressure) and EPAP (expiratory positive airway pressure) are recommended as first-line for permissive tachypnea 1
• These ventilators are simpler to use, more flexible, and provide better leak compensation compared to volume-controlled ventilators 1
• The de-accelerating flow profile of pressure-controlled breaths results in better distribution of ventilation 1

Key Settings for Bi-level Pressure Support

• Initial IPAP should be 8-15 cmH2O and EPAP 4-8 cmH2O 1
• Pressure support (difference between IPAP and EPAP) should be at least 5 cmH2O 1
• Increase pressure support if tidal volume is low (<6-8 mL/kg) 1
• For patients with COPD or obstructive disease, use shorter inspiratory time (approximately 30% of cycle time) to allow adequate time for exhalation 1

When to Use Spontaneous/Timed (ST) Mode

• Add a backup rate (ST mode) if the patient has an inappropriately low respiratory rate or fails to trigger the ventilator reliably 1
• Set the backup rate equal to or slightly less than the patient's spontaneous sleeping respiratory rate (minimum 10 breaths/min) 1
• Adjust inspiratory time based on respiratory rate to provide an I:E ratio of approximately 1:2 for patients with obstructive disease 1

Alternative Options

Volume-Controlled Ventilation

• Consider volume-controlled ventilation for difficult-to-manage patients where ensuring consistent alveolar ventilation is crucial 1
• Some patients who fail on pressure support may be successfully treated with volume control 1
• However, volume-controlled ventilation is associated with greater patient discomfort compared to pressure support 2

Pressure-Limited Small Volume Ventilation

• For acute lung injury, pressure-limited small volume ventilation with permissive hypercapnia is recommended 1, 3
• Limit peak inspiratory pressure to less than 40 cmH2O while decreasing tidal volume as needed 3
• Increase respiratory rate to maintain pH above 7.25 if hypercapnia becomes severe 3

Monitoring and Adjustments

• Monitor work of breathing - higher values indicate increased patient effort and potential need for ventilator adjustment 4
• Assess patient-ventilator synchrony - dyssynchrony may occur if flow termination doesn't coincide with the end of neural inspiration 5
• Adjust flow-termination criteria on newer ventilators to improve synchrony 5
• If rebreathing is suspected (especially with increasing respiratory rate), ensure proper function of exhalation valves and consider increasing EPAP 1

Common Pitfalls to Avoid

• Inadequate expiratory time for tachypneic patients can lead to air trapping and auto-PEEP 1
• Excessive pressure support may cause patient discomfort and worsen patient-ventilator synchrony 6, 2
• Rebreathing can occur during bi-level pressure support, especially with increasing respiratory frequency, if EPAP is too low 1
• Occlusion of exhaust ports by secretions can exacerbate hypercapnia through rebreathing 1

Patient Comfort Considerations

• Pressure support ventilation is significantly more comfortable than volume-controlled ventilation for most patients 6, 2
• If the patient complains that pressures are too high, lower them to a level comfortable enough to allow continued ventilation 1
• Adjust ventilator parameters such as pressure relief, rise time, and IPAP duration to optimize patient comfort and synchrony 1