What are the appropriate BiPAP settings for a patient with type 2 respiratory failure, pH 7.291, PCO2 of 8.1, and PO2 of 8.51?

BiPAP Settings for Type 2 Respiratory Failure

For a patient with type 2 respiratory failure (pH 7.291, PCO2 8.1 kPa, PO2 8.51 kPa) weighing 108kg, the initial BiPAP settings should be IPAP 16-18 cmH2O and EPAP 6-8 cmH2O with target oxygen saturation of 88-92%.

Initial BiPAP Settings

Based on the most recent guidelines, the following initial settings are recommended:

• IPAP (Inspiratory Positive Airway Pressure): 16-18 cmH2O
• EPAP (Expiratory Positive Airway Pressure): 6-8 cmH2O
• Pressure Support Differential: 10 cmH2O (difference between IPAP and EPAP)
• Mode: Spontaneous-Timed (ST) mode
• Backup Rate: 12-14 breaths/minute
• FiO2: Titrate to maintain SpO2 88-92%

The American Academy of Sleep Medicine recommends a minimum starting IPAP of 8 cmH2O and minimum EPAP of 4 cmH2O 1, but for acute type 2 respiratory failure with significant hypercapnia (PCO2 8.1 kPa), higher initial pressures are warranted.

Rationale for Settings

1. Higher Initial IPAP: The patient has significant hypercapnia (PCO2 8.1 kPa) and acidosis (pH 7.291), indicating the need for more ventilatory support. Starting with IPAP 16-18 cmH2O provides adequate ventilatory assistance for CO2 removal 2.

2. EPAP Selection: The EPAP of 6-8 cmH2O helps maintain airway patency and provides a baseline pressure to prevent alveolar collapse 2.

3. Pressure Support Differential: A differential of 10 cmH2O (maximum recommended) is appropriate for this patient with significant respiratory acidosis to maximize ventilatory support 1.

4. Oxygen Target: The BTS guidelines specifically recommend targeting SpO2 88-92% in patients with type 2 respiratory failure to prevent worsening hypercapnia 2.

Monitoring and Adjustment Algorithm

First 30-60 minutes:

• Check arterial blood gases after 30-60 minutes of BiPAP initiation
• If pH improves and PCO2 decreases, continue with current settings
• If no improvement in pH or PCO2 remains elevated:
  • Increase IPAP by 2 cmH2O (up to maximum 30 cmH2O)
  • Consider increasing backup rate by 2 breaths/minute

Adjustments based on specific issues:

• For persistent hypercapnia: Increase IPAP by 2 cmH2O every 30 minutes until improvement 1
• For patient discomfort with high pressure: Consider reducing IPAP by 1-2 cmH2O to improve tolerance 2
• For inadequate oxygenation: Adjust FiO2 to maintain SpO2 88-92%, avoid exceeding 92% 2

Important Considerations

• Mask Selection: For this acute presentation, a full face mask is often better tolerated and more effective
• Monitoring: Continuous monitoring of SpO2, respiratory rate, and work of breathing is essential
• Reassessment: Repeat ABG after 1 hour to assess response to therapy 2
• Intubation Criteria: Be prepared for intubation if:
  • Respiratory acidosis worsens (pH continues to fall)
  • Patient becomes obtunded or unable to protect airway
  • Significant respiratory distress persists despite optimal BiPAP settings

Pitfalls to Avoid

1. Excessive oxygen: Avoid SpO2 >92% as this may worsen hypercapnia in type 2 respiratory failure 2

2. Inadequate pressure support: Starting with too low IPAP may fail to adequately reduce work of breathing and CO2 retention 1

3. Delayed reassessment: Failure to check ABGs within 30-60 minutes may miss deterioration requiring escalation of care 2

4. Mask leaks: Significant mask leaks can compromise ventilation effectiveness; ensure proper mask fitting

5. Overlooking patient comfort: Discomfort may lead to poor compliance; adjust settings if the patient cannot tolerate the prescribed pressures 2