What is the criteria for determining a safe peak expiratory flow (PEF) value for a patient with a recent asthma exacerbation, treated for the first time, who wants to fly?

Safe Peak Expiratory Flow Criteria for Air Travel After First Asthma Exacerbation

A patient who has been treated for their first asthma exacerbation should not fly until their peak expiratory flow (PEF) is above 75% of predicted value or personal best, with diurnal variability below 25%, and they are free of nocturnal symptoms. 1

Objective Criteria Before Clearing for Air Travel

The British Thoracic Society establishes clear discharge criteria that must be met before a patient can be considered stable enough for activities like air travel:

• PEF must exceed 75% of predicted or personal best value - this is the minimum threshold for considering symptoms controlled and function restored 1
• Diurnal variability must be below 25% - calculated as the day's highest PEF minus lowest PEF, divided by mean PEF, averaged over one week 1
• Complete absence of nocturnal symptoms - nighttime awakening indicates inadequate control and is a critical warning sign 2
• Patient must be stable for at least 30-60 minutes after the last bronchodilator dose without deterioration 3

Determining the Patient's Predicted or Personal Best PEF

For a first-time exacerbation where no personal best is established, use predicted values based on the patient's height, age, and sex 1. The British Thoracic Society provides normative charts showing that predicted PEF varies significantly by these factors 1.

For ongoing monitoring, the patient should record PEF twice daily (morning and evening) over several weeks to establish their true personal best, as this is more accurate than predicted values alone 1.

Critical Timeline Considerations

• Systemic corticosteroids require 1-3 weeks for post-viral asthma, not the shorter 5-10 day courses used for typical exacerbations 2
• Morning PEF continues to improve for 2-3 months with inhaled corticosteroid treatment, meaning early measurements may underestimate true recovery 1
• The patient must complete their full course of oral prednisolone (30-60 mg daily) before considering air travel 1, 2

Practical Assessment Algorithm

1. Measure PEF at the same time each day (ideally morning and evening) using proper technique - standing position, best of three attempts 1, 4
2. Calculate the percentage of predicted or personal best - if <75%, the patient is not ready for air travel 1
3. Track diurnal variability over one week - if amplitude percent mean exceeds 25%, control is inadequate 1
4. Specifically ask about nocturnal symptoms - any nighttime awakening, cough, or wheeze disqualifies the patient 2
5. Verify the patient can perform normal activities without dyspnea and has minimal or absent symptoms 3

Common Pitfalls to Avoid

Never rely on the patient's subjective assessment alone - physicians' and patients' subjective assessments of airway obstruction are frequently inaccurate, which is why objective PEF measurement is essential 1, 5. The severity of asthma is often underestimated by patients, relatives, and doctors due to failure to make objective measurements 1.

Do not clear for travel based on a single PEF measurement - asthma is characterized by fluctuations in airway caliber, requiring serial measurements over days to weeks 1, 6. A single normal reading may miss significant variability that indicates inadequate control.

Ensure the patient has been taught proper peak flow technique - incorrect technique yields inaccurate results that may falsely reassure 4, 7. The patient should blow as hard as possible from full inspiration, and the best of three attempts should be recorded 1, 4.

Additional Safety Requirements Before Air Travel

• The patient must have a written asthma action plan with clear instructions for recognizing deterioration and escalating treatment 2
• Ensure adequate supply of rescue bronchodilator (albuterol/salbutamol) and continuation of inhaled corticosteroids 2, 3
• The patient should carry oral prednisolone tablets with instructions to self-initiate if symptoms worsen during travel 2
• Verify inhaler technique before travel to ensure the patient can effectively self-treat if needed 3

Lower Threshold for Delaying Travel

Consider postponing air travel even if PEF criteria are met in patients with:

• Recent onset or worsening of nocturnal symptoms - this indicates unstable disease 1
• Afternoon or evening presentation of the original exacerbation - these patients have higher risk 1
• Previous severe attacks, especially with rapid onset - history predicts future risk 1
• Poor assessment of their own symptom severity - these patients may not recognize deterioration in flight 1