Asthma

Guidelines on the Aeromedical Assessment of Asthma

• Preamble
• Aeromedical Significance
• Protocol for the Assessment of Risk
• Medications Available for Asthma Treatment
• Recommendations
• References

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Preamble

Asthma is a disorder characterized by increased responsiveness of the small airways to various allergens and non-specific stimuli resulting in widespread airways inflammation and reflex narrowing of the airways. It has a wide clinical spectrum varying from a single short-lived episode, requiring little or no medication to that of a constant, disabling condition requiring a combination of therapeutic agents. It's course and severity can be quite predictable in most, albeit less predictable in some. Sudden incapacitation is not a rare phenomenon and may pose a threat to aviation safety.

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AeromedicalSignificance

• Acute asthma attacks may cause partial (or complete) incapacitation in the cockpit (or air traffic control workplace).
• Acute asthmatic attacks may be precipitated in flight by the inhalation of fumes such as might occur in engine or electrical fires or from other agents which could act as bronchial irritants.
• In severe asthmatics, particularly after a recent attack , actual pulmonary function may be worse than that determined from simple clinical examination. Consequently, hypoxia, as measured by oximetry, may develop at lower altitudes than normal. A humid environment and high pollen counts that may be encountered during low altitude flight can exaggerate airway responsiveness and predispose to more severe asthma attacks. Air trapping in chronic asthma can present an increased risk of barotrauma in high altitude flight, particularly if sudden decompression should occur.

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Protocol for the Assessment of Risk

The applicant who discloses a diagnosis of asthma should be assessed against the subjective and objective criteria outlined below, and, when necessary, such applicants should be referred to a respirologist or specialist in internal medicine with an interest in respiratory medicine, for a more precise determination of the diagnosis, severity, treatment, and prognosis.

Subjective Criteria

• age of onset;
• nature of symptoms, past and present;
• present medication regime, any recent change, and reason for change;
• duration of present therapy;
• compliance with therapy;
• side effects of therapy (if any);
• active smoking history;
• and reaction to passive smoke.

Critical Criteria

• number of emergency room visits in the last five years;
• number of hospitalizations in the preceding five years;
• ataia in childhood;
• use of steroids, oral or IV;
• severity of exacerbations: ICU admission, intubation requirement;
• and length of recovery following exacerbation.

Objective Criteria

• evidence of bronchospasm, dyspnea, chest hyperinflation;
• other ancillary features of asthma: nasal polyps, rhinitis, eczema pulmonary function tests.

1. The most sensitive tests are the FEV1 (Forced Expiratory Volume in one second ) and MMFR (Maximum Midexpiratory Flow Rate).
2. Results below predicted normal for age should be questioned.
3. Results below 70% predicted, indicates a more serious problem.
4. Response to ß-adrenergic challenge - better or equal to 12%, and more than a 200cc change in FEV1.

Note: The decision to refer to a specialist should be based on discussions with the RAMO/AMO. Decisions concerning the use of the methacholine challenge tests should be made by the attending specialist.

Table 1 - Levels of Asthma Severity Based on Treatment Needed to Obtain Control

Asthma Severity	Symptoms	Therapy Required
Very Mild	Well controlled	None, or inhaled SABA
Mild	Well controlled	Inhaled SABA + low dose ICS SABA + ICS +
Moderate	Well controlled	LABA or other Rx additions
Severe	May or may not be well controlled	As above + oral steroids

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Medications Available for Asthma Treatment

Short acting ß2 agonists (SABA): (terbutaline, salbu-tamol, albuterol)

• drugs of choice for relief of acute symptoms and for short-term duration.
• used for prevention of exercise induced bronchospasm.
• side effects may include tremor, nervousness and tachycardia.

Long acting ß2 agonists (LABA): (formoterol, salmeterol)

• Add-on therapy to inhaled steroids (see Canadian Asthma Consensus Report).
• Or can be used as a SABA (particularly formoterol) for PRN use.

Methylxanthines (aminahylline)

• rarely used these days for asthma. If used, question its use.
• have a narrow therapeutic range.
• potential for severe side-effects including cardiac arrhythmias, tremor and may induce convulsive disorders. Leukotriene receptor antagonists (zafirlukast, montelukast)
• anti-inflammatory agent as "add-on" to steroid therapy in asthma.
• no side effects.
• their role in asthma is limited and response rate not predictable (30% of patients will do well on
  these agents).

Inhaled gluco-corticosteroids: (ICS) (fluticasone, budesonide, beclomethasone)

• highly effective and predictable asthma stabilizers.
• infrequent clinically important side-effects (most often taical).
• used in all stages of asthma.
• combination therapy with a LABA now available.

Table 2 - Measures of Asthma Severity

	Severity of Asthma
Event or Measurement	Mild	Moderate	Severe
FEV1, or PEF, % of predicted	>80%	60-80%	<60%
Need for inhaled SABA	Every 8 or more h	Every 4-8 h	Every 2-4 h
Probability of:
Previous near fatal episode	0	0	0+
Recent admission to hospital	0	0	0+
Night time symptoms	0 to +	+	+++
Limitation of daily activities	0 to +	++	+++
Note: FEV1 = forced expiratory volume in 1 second;  PEF = peak expiratory flow

Figure 1 - Continuum of Asthma Management

Severity of asthma is ideally assessed by medication required to maintain asthma control.  Environmental control and education should be instituted for all asthma patients.  Very mild asthma is treated with short-acting ß₂-agonists are needed more than 3 times/week (excluding 1 dose/day before exercise), then inhaled glucocorticosteroids should be added at the minimum daily dose required to control the asthma.  If asthma is not adequately controlled by moderate doses (500-1000 µg/d of beclomethasone or equivalent), additional therapy (including long-acting ß2-agonists, leukotriene antagonists or, less often, other medications) should be considered.  Severe asthma may require additional treatment with prednisone.

The above diagram is from the Canadian Asthma Consensus Report, 1999.

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Recommendations

1. All Categories-Initial Applicants

When there is a significant history of asthma (emergency room visits within the past two years) or when medication usage to prevent/treat airways inflammation and bronchospasm is in excess of the "mild" criteria in the Tables above), the applicant should be referred to a specialist for clinical assessment including an objective appraisal of asthma through pulmonary function tests (usually spirometry, flow-volume loop, bronchial challenge and at times a study of residual volume, oximetry, etc).

2. Initial or Renewal Applicants

1. Very mild and mild asthma by clinical or 'challenge' * definition may be acceptable for Category 1, 2 , 3 or 4 if symptoms are well controlled by daily inhaled steroids or occasional aerosol bronchodilators.
2. Moderate asthma should be referred to the Aviation Medical Review Board (AMRB ) for a recommendation. All cases referred to the AMRB should have the appropriate specialist's report. A "restricted" category may be considered for renewal candidates only.
3. Severe asthma is disqualyifing for all categories of medical certification

* Methacholine challenge of 2.0 mg/ml or higher

3. Follow-up for all but "mild" applicants

An annual specialist report to include PFTs at the discretion of the specialist.

Note: Any increase in the severity of the asthma will necessitate reevaluation.

4. The use of SABA /LABA should be restricted to eight hours or more prior to flying, but may be used in an unusual asthmatic attack in flight to allow the safe completion of the flight.

References

Canadian Asthma Consensus Report, 1999.
Supplement to CMAJ 1999; 161 (11 Suppl)

Special Thanks to Drs Jocelyn Deneault and André Peloquin