Dry Powder Inhalers in Acute Asthma
Dry powder inhalers (DPIs) containing short-acting beta-agonists (SABAs) are as effective as pressurized metered-dose inhalers (pMDIs) with spacers or nebulizers for treating acute asthma exacerbations, and should be considered a first-line alternative when patients can generate adequate inspiratory flow. 1
Evidence for DPI Efficacy in Acute Asthma
A comprehensive review of 23 clinical studies concluded that SABAs delivered by DPIs were as effective as MDI + spacer or nebulizers in acute asthma settings 1. This finding is supported by multiple randomized controlled trials:
- Salbutamol DPIs achieve equivalent bronchodilation to pMDIs when comparing specific devices like the Clickhaler DPI versus Ventolin pMDI, with a relative potency ratio of 1.29 (90% CI 1.04-1.63) 2
- Clinical outcomes are comparable across delivery methods, with studies showing approximately 11% improvement in peak expiratory flow rate (PEFR) and 2% increase in oxygen saturation regardless of whether salbutamol was delivered via MDI-spacer or DPI 3
- Pediatric studies confirm equivalence in children aged 5-18 years with mild to moderate acute exacerbations, showing no significant differences in asthma scores, oxygen saturation, or vital signs between DPI (Easyhaler), MDI with spacer, and nebulization 4
Critical Limitation: Inspiratory Flow Requirements
The primary caveat is that DPIs require adequate inspiratory flow rates to be effective, typically around 60 L/min with rapid (1-2 second) deep inhalation 1. This creates an important clinical decision point:
- Most children under 4 years cannot generate sufficient inspiratory flow to activate DPIs effectively 1
- During severe acute exacerbations with significant respiratory distress, some patients may lack the inspiratory capacity needed for optimal DPI use 1
- However, the majority of patients with severe acute asthma can achieve sufficient peak inspiratory flow to inhale bronchodilators from DPIs like the Turbuhaler 5
Practical Algorithm for Device Selection in Acute Asthma
When inspiratory flow is adequate (patient can take a rapid, deep breath):
- Use DPI with salbutamol 200-400 mcg, which can be repeated every 20 minutes up to 3 times 3, 4
- DPIs have the advantage of requiring no coordination between actuation and inhalation, unlike standard pMDIs 1
When inspiratory flow is questionable or patient is severely distressed:
- Consider "rescue packs" of MDI with spacer as suggested by some guidelines 1
- Alternatively, proceed directly to nebulization for doses exceeding 1 mg salbutamol 6
When patient cannot use any hand-held device correctly after instruction:
Additional Clinical Considerations
DPIs offer several practical advantages that may improve real-world outcomes:
- Substantially lower error rates (10-40%) compared to MDIs (76%) 6
- No need for spacers, which are often unpopular with adolescents and adults 1
- Most patients prefer multi-dose DPIs when offered a choice of devices 1
Common pitfall to avoid: Never assume adequate inspiratory flow without assessment, particularly in young children or during severe exacerbations 1, 7. If there is any doubt about the patient's ability to generate adequate flow, default to MDI with spacer or nebulization rather than risk inadequate drug delivery.
Environmental consideration: DPIs have a substantially lower carbon footprint than pMDIs, which may be relevant for shared decision-making with patients 6