Asthma in Infants and Children

Asthma in infants and children shares the same underlying pathophysiology as adult asthma — chronic airway inflammation producing variable, often reversible airflow obstruction with recurrent cough, wheeze, chest tightness, and shortness of breath^[1] — but the practical challenge in this age group is fundamentally different: a confident, spirometry-confirmed diagnosis is rarely possible under 6 years of age, because most preschool-age children cannot reliably perform the reproducible forced-exhalation maneuvers spirometry requires.^[2] Diagnosis in young children instead depends on a structured clinical pattern — recurrent wheezing episodes, exclusion of alternative causes, and a documented, timely response to a trial of asthma therapy — rather than a single confirmatory test.^[1]

This chapter covers asthma from infancy through 11 years of age, organized around the two age bands current guidelines treat differently: children 5 years of age and younger, in whom diagnosis, device technique, and approved dosing all differ substantially from older patients, and children 6 to 11 years of age, who are closer to the adult/adolescent framework but still require pediatric-specific dosing, devices, and product approvals. Asthma in patients 12 years of age and older follows a different treatment-track structure and is addressed separately in Asthma in Adults and Adolescents.

Typical presentation

Recurrent episodes of wheeze, cough, and difficulty breathing, often triggered or worsened by viral upper respiratory infections but also occurring with exercise, laughing, crying, cold air, or allergen exposure. A cough that is paroxysmal, worse at night, or longer or more severe than a typical viral illness is a clue to airway hyperreactivity rather than a simple cold. A true acute wheezing episode, as distinct from other noisy breathing, typically lasts more than 24 hours.^[1]

Wheeze phenotypes — useful for framing, not for individual prediction

Recurrent wheeze is common in children 5 years of age and younger, and several classification schemes have historically been used to describe it. A symptom-based classification distinguishes episodic wheeze (occurring only during discrete illness-associated periods, absent between episodes) from multiple-trigger wheeze (episodic wheeze plus symptoms between episodes, e.g., during sleep or with activity, laughing, or crying). A time-trend classification, applicable only retrospectively, describes transient wheeze (beginning and resolving before 3 years of age), persistent wheeze (beginning before 3 years and continuing past 6 years), and late-onset wheeze (beginning after 3 years of age). Neither classification has good predictive value for an individual child, and neither should be used to withhold a therapeutic trial from a child with a compatible clinical pattern — they are useful only for framing the discussion, not for making the diagnosis.^[1]

History clues that support airway hyperreactivity

Ask caregivers specifically about: wheeze (a high-pitched whistling sound on breathing out, distinguished from other noisy breathing by direct observation or a video/audio recording whenever possible), dry cough or coughing spells, symptoms worse during sleep or after laughing, crying, or activity, chest retractions or laboured breathing during episodes, and how quickly symptoms improved after any reliever or corticosteroid already given.^[1] A personal history of atopic dermatitis, food allergy, or allergic rhinitis, or a family history of asthma or allergic disease in a parent or sibling, supports the diagnosis but is neither required nor specific for it. A previous hospital admission for bronchiolitis, particularly RSV bronchiolitis, is a recognized risk factor for later asthma.

Examination findings

Look for intercostal or suprasternal retractions, hyperexpansion of the chest, wheeze on normal or forced breathing, and signs of comorbid atopic disease (atopic dermatitis, pale or boggy nasal turbinates). Findings that point away from asthma toward an alternative diagnosis include nasal polyps or digital clubbing at any age (consider cystic fibrosis), localized or unilateral wheeze (consider an inhaled foreign body or a congenital airway anomaly), and stridor or a weak voice that is absent at night (consider vocal cord dysfunction, typically in older children and adolescents).

• Family history of asthma or atopic disease (eczema, allergic rhinitis, food allergy) in a parent or sibling.
• Personal history of atopic dermatitis, food allergy, or allergic rhinitis.
• Allergen-specific sensitization, particularly multiple early-life sensitizations.
• Previous hospital admission for bronchiolitis, particularly RSV bronchiolitis, in infancy.
• First- or second-hand exposure to tobacco smoke, vaping, or cannabis smoke.
• Recurrent viral upper respiratory infections and daycare attendance.
• Male sex — asthma onset is typically earlier in males than females in childhood.
• Prematurity or bronchopulmonary dysplasia.
• Obesity.
• Low socioeconomic status or low parental education level.
• Vitamin D deficiency.
• Environmental allergen exposure (house dust mite, pet dander, mould, seasonal pollen).

Differentiating asthma from its common childhood mimics

Diagnosis in children 5 years of age and younger — the 3-criteria approach

Formal spirometry is not feasible in most children under 6 years of age, since it requires a reproducible forced-exhalation maneuver most preschoolers cannot perform reliably.^[2] Diagnosis instead relies on a structured, 3-criteria clinical approach; all three must be met to confirm a diagnosis of asthma — if only 1 or 2 are met, record the working diagnosis as "suspected asthma" and reassess.^[1]

Criterion 1, recurrent acute wheezing episodes: at least 2 acute wheezing episodes in the past 12 months, OR at least 1 acute wheezing episode plus asthma-like symptoms between episodes (interval symptoms, e.g., dry cough, coughing spells, or symptoms worse during sleep or after laughing, crying, or activity). Because parents may use the word "wheeze" for any noisy breathing, at least one episode should be confirmed as true expiratory wheeze by a trained health care provider directly observing the child, reviewing a recording, or by a caregiver convincingly describing or imitating the sound.^[1]

Criterion 2, no likely alternative cause: based on a thorough history and examination, no other condition (aside from a concurrent viral respiratory infection) is likely to explain the symptoms — see the differential diagnosis table above.^[1]

Criterion 3, timely clinical response to asthma treatment: confirmed improvement within 20-60 minutes of a SABA, or within 3-4 hours after SABA plus oral corticosteroids for a more severe episode; or a documented decrease in the frequency or severity of episodes and interval symptoms during a 2-3 month trial of daily inhaled corticosteroid (ICS) (e.g., fluticasone propionate 100-250 mcg/day or equivalent by pressurized metered-dose inhaler via spacer) plus as-needed SABA. Reduce the ICS dose to the minimum effective dose immediately once the trial has confirmed the diagnosis.^[1]

Asthma is less likely when the child is younger than 12 months and this is a first wheezing episode (bronchiolitis is far more likely, and the younger the child, the higher the likelihood of an alternative diagnosis); when the only symptom is a productive cough; when there is no response to a SABA or ICS trial; or when the respiratory signs and symptoms are otherwise atypical.^[1] Refer an infant younger than 12 months with 2 or more wheezing episodes for expert assessment, and refer whenever an alternative diagnosis is suspected or symptoms fail to respond to, or worsen during, an appropriately conducted treatment trial.

Diagnosis in children 6 to 11 years of age

Spirometry showing reversible airflow obstruction is the preferred method of confirming the diagnosis at this age, using the same principle as in adults — an increase in FEV1 of at least 12% after a bronchodilator or after a course of controller therapy.^[2] Peak flow is an insensitive indicator in children, and a normal value does not exclude significant airflow limitation; where spirometry is unavailable or non-diagnostic, a positive bronchoprovocation challenge (methacholine) or a convincing symptomatic response to a treatment trial can support the diagnosis. Perform spirometry at least annually in every child 6 years of age and older who is using regular asthma medication, to track lung function over time and confirm ongoing control.^[2]

Objective testing across the pediatric age spectrum

• Impulse oscillometry — an effort-independent test performed during quiet tidal breathing, usable from about 3 years of age, that can provide supportive evidence of reversible airway obstruction when spirometry is not feasible.
• Skin prick testing or allergen-specific IgE — to identify allergic sensitization contributing to symptoms; most useful in children with persistent or poorly controlled symptoms being considered for environmental control measures or, in older children, biologic therapy.
• Blood eosinophil count — to help guide treatment decisions in children with difficult-to-control asthma being considered for biologic therapy.
• Chest x-ray — not routine, but useful when the diagnosis is in doubt, to exclude a structural abnormality, an inhaled foreign body, or chronic infection.

When not to test: imaging and laboratory tests are not usually required to diagnose straightforward asthma in a young child with a classic history. A normal spirometry result performed between symptomatic episodes does not exclude asthma in an older child — repeat testing when symptomatic, or proceed to a bronchoprovocation challenge, rather than concluding the diagnosis is excluded.

Assessing exacerbation severity — the Pediatric Respiratory Assessment Measure (PRAM)

The PRAM score is a validated, 5-item clinical severity score for children 2-17 years of age presenting with acute wheeze or an asthma exacerbation, and is recommended to help standardize severity assessment and guide the intensity of treatment.^[3]

Total score out of 12: 0-3 is mild, 4-7 is moderate, 8-12 is severe. Use the score alongside, never in place of, direct clinical assessment.^[3]

• Prevent cough, wheeze, or shortness of breath that interferes with daytime activity, exercise, school or daycare attendance, growth and development, or sleep.
• Prevent exacerbations requiring emergency department visits, hospitalization, or courses of systemic corticosteroids.
• Limit reliever (SABA) use to 2 or fewer doses per week outside of pre-exercise dosing.
• Achieve normal or near-normal lung function where measurable (spirometry, 6 years of age and older).
• Maintain normal growth velocity while on inhaled corticosteroid therapy.
• Minimize medication adverse effects by using the lowest inhaled corticosteroid dose that maintains control.
• Support normal participation in play, sport, and school or daycare activities.
• Avoid unscheduled emergency care and repeated oral corticosteroid courses.

• Advise caregivers to eliminate the child's exposure to tobacco smoke, vaping, and cannabis smoke — one of the highest-yield interventions in pediatric asthma.^[2]
• Identify and reduce exposure to specific environmental allergens or irritants the child is sensitized to or reacts to; multi-component environmental interventions are more effective than a single measure alone.
• Educate caregivers, and the child when developmentally able, that asthma is a chronic condition requiring ongoing management even between symptomatic episodes, not just treatment of flare-ups.
• Device technique is a critical, ongoing adherence and efficacy factor at this age. Always use a pressurized metered-dose inhaler (pMDI) with a valved holding chamber or spacer, never a pMDI alone, in children of any age. Use a facemask for children younger than 3-4 years of age and switch to a mouthpiece as soon as the child can reliably form a seal and cooperate (typically 4-6 years of age) — a mouthpiece delivers more drug to the lower airway than a facemask.^[1]
• Teach tidal-breathing technique: after each single actuation into the spacer, have the child take 5-6 normal breaths in and out through the mask or mouthpiece; only 1 puff should be actuated into the spacer at a time, and inhalation should start as soon as possible after actuation.^[1]
• Shake any suspension-formulation inhaler (e.g., salbutamol) immediately before each actuation.
• If a facemask is used, fit it snugly around the mouth and nose to prevent drug loss and eye exposure, and clean the skin around the mouth and nose after each use.
• Wash plastic spacers periodically with detergent, without rinsing, and air dry, to reduce static charge that can reduce lung drug delivery; anti-static or metal spacers are less prone to this problem.
• Reserve nebulizers for the minority of children who genuinely cannot be taught effective spacer technique — a pMDI with spacer delivers medication at least as effectively as a nebulizer for both maintenance and exacerbation treatment, with faster administration and lower infection-transmission risk.^[1]
• Provide caregivers with a written, individualized asthma action plan describing daily preventive therapy, how to recognize worsening control, how to use a reliever, and specific instructions for when to seek urgent medical care.
• Share the action plan and device instructions with daycare or school staff, and confirm a reliever inhaler is accessible during school or daycare hours.
• Oral bronchodilator syrups are not recommended — they have a slower onset of action and a higher rate of side effects than inhaled SABA and should not be substituted for an inhaled device.^[1]
• Advise on current, locally recommended vaccinations for children with asthma — annual influenza vaccination, routine childhood immunizations, pertussis vaccination, and RSV immunoprophylaxis for eligible infants.

Infants younger than 12 months

A first episode of wheeze in an infant under 12 months of age is usually bronchiolitis, not asthma — the younger the infant, the higher the likelihood of an alternative diagnosis, and a confirmed asthma diagnosis is rarely made at this age.^[1] Refer any infant with 2 or more wheezing episodes for expert assessment rather than committing to a long-term asthma diagnosis and controller therapy in primary care.

Pregnancy and breastfeeding

Not directly applicable — this chapter addresses infants and children with asthma. For asthma management specific to pregnancy and breastfeeding, see Asthma in Adults and Adolescents.

Renal and hepatic impairment

Inhaled therapy has minimal systemic absorption and generally requires no renal or hepatic dose adjustment in children. Montelukast requires no dose adjustment in mild-to-moderate hepatic impairment; data in severe hepatic impairment are limited.

Neurodevelopmental or cognitive conditions affecting device use

A child with a neurodevelopmental condition, motor impairment, or significant behavioural difficulty may need extra time, a caregiver-administered facemask-and-spacer technique well beyond the age at which peers switch to a mouthpiece, or occupational therapy input to achieve reliable drug delivery — do not assume poor control in this population reflects true refractory asthma before device technique has been directly observed and optimized.

Transition to adolescent and adult care

As a child approaches 12 years of age, anticipate the shift to the adult/adolescent treatment-track framework and product approvals (e.g., budesonide-formoterol becomes available as both a reliever and maintenance option at this age) — see Asthma in Adults and Adolescents. Use the transition period to reinforce self-management skills and independent device technique before the child takes over primary responsibility for their own therapy.

Reassess symptom control and exacerbation risk factors at every visit, and formally at least every 3-6 months once therapy is established. Measure and plot height at every visit, or at least annually, in any child on regular inhaled corticosteroid therapy — an initial reduction in growth velocity is a recognized, usually non-progressive effect in the first 1-2 years of treatment, but persistent poor growth velocity should prompt reassessment of the dose, the diagnosis, and adherence/technique rather than being accepted as an unavoidable cost of treatment. Reassess inhaler and spacer technique at every visit, and reassess whether the child is developmentally ready to move from a facemask to a mouthpiece. Perform spirometry at least annually in children 6 years of age and older using regular controller therapy. Check adherence, including refill patterns, at every visit. Confirm the written asthma action plan is current, matches the child's current medications, and has been shared with school or daycare. Reassess vaccination status annually. Track the cumulative number of oral corticosteroid courses and emergency or urgent care visits over the past year — frequent courses warrant specialist referral and, over time, consideration of adrenal function and bone health.

1. Confirm the diagnosis is genuinely asthma — reconsider the differential diagnosis table above, particularly in a child 5 years of age or younger who has never met all 3 diagnostic criteria.
2. Check inhaler and spacer technique directly rather than relying on the caregiver's self-report, and confirm the device matches the child's developmental stage (facemask versus mouthpiece).
3. Confirm adherence, including refill patterns, before escalating therapy.
4. Address modifiable comorbidities and triggers — allergen exposure, tobacco or vape smoke exposure, and, in an older child, undertreated allergic rhinitis or gastroesophageal reflux.
5. For a child on maintenance controller therapy with a self-managed loss of control at home: it is not recommended to double or quadruple the inhaled corticosteroid dose in a child with acute loss of control — unlike the specific higher-risk adult scenario, pediatric trial evidence (fluticasone 200 mcg/day versus 1000 mcg/day in 5-11 year olds) found no reduction in exacerbations with this strategy.^[2] Instead, for a child with a history of a severe exacerbation in the past year who fails to respond adequately to SABA at home, start prednisone or prednisolone 1 mg/kg/day PO (maximum 50 mg/day) for at least 3-5 days, and seek medical review.^[2]
6. If steps 1-4 do not identify a correctable cause, step up therapy per the age-appropriate sequence above, or refer to a pediatric asthma/respirology specialist.
7. Refer for diagnostic uncertainty, an alternative diagnosis suspected on the differential above, poor growth velocity on inhaled corticosteroid therapy, frequent oral corticosteroid courses, 2 or more emergency department visits, any hospitalization, or lack of control on medium-dose inhaled corticosteroid therapy with confirmed technique and adherence.

• Assuming spirometry is required to diagnose asthma in a child under 6 years of age — use the 3-criteria clinical approach (recurrent wheeze, exclusion of alternatives, timely treatment response) instead.
• Doubling or quadrupling the inhaled corticosteroid dose for a viral upper respiratory infection or a mild loss of control — pediatric trial evidence does not support this strategy, unlike the specific higher-risk adult scenario where it is sometimes used.
• Leaving a young child on a facemask well past the age they could switch to a mouthpiece, reducing lung drug delivery.
• Actuating more than one puff into a spacer before the child inhales, or delaying inhalation after actuation — both markedly reduce the dose actually delivered.
• Prescribing budesonide-formoterol, or any ICS-formoterol combination, as a reliever or maintenance-and-reliever regimen in a child under 12 years of age — not Health Canada-approved at this age.
• Withholding daily inhaled corticosteroid therapy from a child who is currently well controlled on as-needed SABA alone but has a genuine risk factor for a severe exacerbation — risk status, not only current symptom frequency, should drive the decision to start a controller.
• Missing an alternative diagnosis (foreign body aspiration, gastroesophageal reflux, cystic fibrosis, vocal cord dysfunction, primary ciliary dyskinesia) in a child not responding to correctly administered asthma therapy.
• Using an oral bronchodilator syrup instead of an inhaled short-acting beta2-agonist.
• Not measuring or tracking growth velocity in a child on long-term inhaled corticosteroid therapy.
• Adding routine oral corticosteroids to a self-management action plan for a child without a history of a severe exacerbation who is responding adequately to inhaled SABA at home.
• Skipping montelukast's neuropsychiatric boxed-warning counselling at first dispensing because the drug feels gentler than an inhaler.
• Continuing an ICS-LABA combination product that is not actually approved for the child's specific age.
• Not confirming inhaler/spacer technique and adherence before assuming a child has treatment-resistant or difficult-to-control asthma.

How to use this table: Every dose below is a pediatric, weight- or age-banded dose specific to infants and children through 11 years of age. Confirm each weight-based calculation against the child's current weight and the product monograph maximum before dispensing. For patients 12 years of age and older, follow the adult/adolescent dosing framework in Asthma in Adults and Adolescents. Drug pricing is intentionally omitted.

Short-acting beta2-agonists (SABAs)

Short-acting muscarinic antagonist (SAMA) — acute exacerbation adjunct only

Not for routine daily maintenance in children.

Inhaled corticosteroids (ICS), by age band

Low/medium/high categories are Canadian-approved pediatric dosing tiers, sourced from CTS 2021 Table 8. "n/a" means the molecule does not have an approved indication in that age band in Canada.

ICS-LABA combination — the only option approved under 12 years of age in Canada

Health Canada has not approved budesonide-formoterol, fluticasone furoate/vilanterol, formoterol/mometasone, or indacaterol/mometasone for use under 12 years of age — do not substitute any of these for the product below in a child 6-11 years of age.

Long-acting muscarinic antagonist (LAMA) add-on

Specialist-initiated only, for a child not controlled on Step 3 therapy.

Leukotriene receptor antagonist

Systemic corticosteroids — acute exacerbation

A short course used occasionally for an exacerbation generally does not require a taper. Repeated or prolonged courses can affect adrenal function, bone health, and growth — track cumulative courses.

Additional adjunct therapy — severe acute exacerbation, emergency department setting

Biologics — specialist-initiated, 6 years of age and older

Reserved for children with a confirmed asthma diagnosis whose disease is not controlled by the therapies above; initiate and monitor under specialist supervision, with expertise in managing anaphylaxis.