What initial BiPAP settings should be used in an adult with an acute asthma exacerbation who is a candidate for non‑invasive ventilation?

Initial BiPAP Settings for Adult Asthma Exacerbation

Start with IPAP 8 cm H₂O and EPAP 4 cm H₂O, maintaining a minimum pressure differential of 4 cm H₂O, though evidence for BiPAP in acute asthma remains insufficient to make a strong recommendation for its routine use. 1, 2

Critical Context: Limited Evidence Base

The 2017 ERS/ATS guidelines explicitly state they are unable to offer a recommendation on the use of NIV for acute respiratory failure due to asthma due to uncertainty of evidence. 3 Similarly, the 2002 Thorax guidelines recommend that NIV should not be used routinely in acute asthma. 3 This reflects the reality that acute asthma requiring ICU admission is uncommon, and published research in this field is limited. 3

When to Consider BiPAP in Asthma

If you proceed with BiPAP despite limited evidence, consider it only for:

• Patients with respiratory acidosis (pH <7.35) who have failed maximal medical therapy 3
• Selected patients not responding well to standard treatment but not requiring emergency intubation 3
• Never use in patients with ongoing aspiration risk, inability to protect airway, vomiting, copious secretions, or confusion/agitation 3

Initial Pressure Settings

Start with IPAP 8 cm H₂O and EPAP 4 cm H₂O as recommended by the American Academy of Sleep Medicine for all adult patients. 1, 2

• Maintain minimum pressure support (IPAP-EPAP differential) of 4 cm H₂O 1, 2
• Maximum IPAP should not exceed 30 cm H₂O in adults ≥12 years 1, 2
• Maximum pressure differential should not exceed 10 cm H₂O 1

Mode Selection

Use spontaneous-timed (ST) mode with backup rate of 10-12 breaths/minute rather than spontaneous mode alone, as asthma patients may develop respiratory muscle fatigue. 4, 2

• Set inspiratory time to achieve I:E ratio of approximately 1:2 to prevent air trapping 4
• This is critical in asthma where hyperinflation is already a problem 3

Titration Algorithm

Wait at least 5 minutes between pressure adjustments. 1, 2

• Increase pressures by 1-2 cm H₂O increments 1, 2
• If patient awakens complaining pressure is too high, restart at lower comfortable pressure 1, 2
• Target elimination of respiratory distress, not specific pressure thresholds 1

Research studies have used varying pressures: one study used IPAP 15 cm H₂O with EPAP 5-10 cm H₂O 5, another reported mean IPAP 11.9 cm H₂O and EPAP 5.8 cm H₂O 6, and a third used 12/7 cm H₂O 7. These studies showed physiological improvements but were small and uncontrolled.

Oxygen Titration

• Target SpO₂ 92-96% in most patients 4
• Start with FiO₂ 0.6 and adjust based on response 4

Critical Monitoring and Failure Criteria

Evaluate response within 1-2 hours of initiating BiPAP. 1, 4, 2 This narrow window is essential because delayed intubation due to failed NIV can cause harm. Nearly half of clinical guidelines emphasize close monitoring to prevent delayed intubation. 4

Signs of BiPAP failure requiring immediate intubation:

• Inability to maintain SpO₂ >90% despite FiO₂ escalation 1, 4, 2
• Worsening mental status or exhaustion 3
• Persistent or increasing hypercapnia 3
• Apnea or coma (intubate immediately) 3

Common Pitfalls to Avoid

• Do not delay intubation if patient shows deterioration or fails to improve within 1-2 hours 4, 2
• Avoid BiPAP in patients with pneumothorax unless chest tube already placed 3
• Do not use after recent upper airway surgery or with facial trauma 3
• Ensure adequate mask fit to minimize leaks that reduce effectiveness 1, 2
• Monitor for excessive secretions which limit BiPAP effectiveness in asthma 3

Alternative Considerations

The 2009 NAEPP guidelines note that there is insufficient evidence to recommend noninvasive ventilation in acute asthma treatment. 3 Standard therapy remains:

• Inhaled β2-agonists and anticholinergics
• Systemic corticosteroids
• Oxygen to maintain saturation
• Consider heliox-driven nebulization in severe cases 3

If intubation becomes necessary, use permissive hypercapnia strategy to avoid barotrauma, and perform intubation semielectively before respiratory arrest. 3