Asthma

Chronic inflammatory condition of the airways that causes episodic exacerbations of bronchoconstriction

Aetiology

  • Extrinsic - atopy, genetic links
  • Intrinsic - no trigger identified, late onset
  • Exacerbating factors - smoking, allergen exposure, ABPA

Pathophysiology

Control of bronchial calibre

Bronchial calibre is controlled by a balance between:
  • The sympathetic nervous system which causes bronchodilation and decreases mucous secretion via β2-adrenoceptors
  • The parasympathetic nervous system which causes bronchoconstriction and increases mucus secretion via M3-receptors

Non-atopic asthma

  • Low level TH1 response to antigen
  • Typical triggers include infection, night time/early morning, exercise, animal dander, cold/damp, dust, and strong emotions
  • IgG and macrophages

Atopic asthma

  • Strong TH2 response to antigen
  • Mast cells (initial asthma attack), eosinophil accumulation (late phase)

Key characteristics of asthma

  • Reversible airflow obstruction via M3 receptors (parasympathetic) → bronchoconstriction and mucus secretion
  • Bronchial inflammation
  • Bronchial hyperresponsiveness - caused by damage to epithelium
  • Over time - airway remodeling (increased goblet cells and smooth muscle)

Clinical presentation

Asthma should be suspected when all are present:

Typical Symptoms

  • Wheeze
  • Shortness of breath
  • Chest tightness
  • Cough (especially nocturnal / early morning)

Characteristic Pattern

  • Symptoms vary over time
  • Symptoms worse at night or early morning
  • Triggered by exercise, allergens, cold air, infections
  • Symptoms improve with bronchodilator
⚠️ Symptoms alone are not diagnostic → objective testing required.

Asthma Severity Classification

Severity
Daytime Symptoms
Night Symptoms
Reliever Use
Exacerbations / Year
Intermittent
≤ 2 days / week (monthly)
≤ 2 nights / month
≤ 2 days / week
0–1
Mild Persistent
> 2 days / week (not daily — weekly)
3–4 nights / month
> 2 days / week
≥ 2
Moderate Persistent
Daily
> 1 night / week
Daily
≥ 2
Severe Persistent
Throughout the day
Frequent (often nightly)
Several times daily
Frequent / ≥ 2 (often severe)

Acute Exacerbation Severity Classification

Feature
Mild–Moderate
Severe
Life-Threatening
Speech
Sentences
Words only
Unable
RR
<25/min
≥25/min
Exhaustion
HR
<110/min
≥110/min
Bradycardia
SpO₂
≥94%
<94%
<90%
PEF
≥50%
<50%
<33%
Chest
Wheeze
Loud wheeze
Silent chest

Investigations

Spirometry (Gold Standard)

Baseline findings
  • Obstructive pattern:
      • FEV₁/FVC < 0.75–0.80 (adults)
Bronchodilator reversibility test
  • Measure FEV₁ before and 10–15 min after SABA
  • Positive test:
    • ↑ FEV₁ ≥ 12% AND ≥ 200 mL
✔ Confirms asthma if clinical features are compatible

Peak Expiratory Flow (PEF) Monitoring

Used when spirometry unavailable or normal.
Diagnostic criteria
  • Diurnal variability >10% (adults)
  • Improvement after bronchodilator
Formula
notion image

Bronchial Provocation Testing

(When spirometry is normal but suspicion remains high)
Test
Positive Result
Methacholine
FEV₁ ↓ ≥20%
Mannitol / exercise
Significant fall in FEV₁
 

Management

Immediate Assessment (ABCDE)

A – Airway
  • Ensure patency
  • Look for inability to speak, altered consciousness
B – Breathing
  • RR, use of accessory muscles
  • SpO₂
    • High flow O₂
    • Target SpO₂ 94–98%
  • Auscultation (wheeze / silent chest)
  • Peak Expiratory Flow (PEF) if possible
C – Circulation
  • HR, BP
  • Capillary refill

Acute Exacerbation Therapy

Bronchodilator Therapy
  • Short-Acting β₂-Agonist (SABA)
    • Salbutamol
      • 2.5–5 mg nebulized every 20 min × 3
      • 4–10 puffs via spacer every 20 min
  • Short-Acting Muscarinic Antagonist (SAMA) → Severe/Life-Threathening
    • Ipratropium bromide
      • 0.5 mg nebulized every 20 min × 3
Systemic Corticosteroids (Early – Within 1 Hour)
  • Prednisolone (oral) 40-50 mg daily x 5-7 days
  • Hydrocortisone (IV) 100 mg/6-8hr
Reassessment (After 1 Hour)
Good Response
  • PEF >50%
  • Improved symptoms
      • ➡️ Continue bronchodilators, consider discharge
Poor / Incomplete Response
  • Persistent dyspnea
      • ➡️ Continue SABA, steroids, escalate therapy
Escalation Therapy (Severe / Life-Threatening)
IV Magnesium Sulfate
  • 2 g IV over 20 minutes
  • Indicated if:
    • PEF <25–30%
    • No response to initial therapy

Controller Therapy

Preferred Track (Track 1 – ICS–Formoterol Based) ⭐
GINA Step
Controller & Reliever Strategy
Step 1
As-needed low-dose ICS–formoterol
Step 2
As-needed low-dose ICS–formoterol
Step 3
Low-dose ICS–formoterol maintenance + reliever (MART)
Step 4
Medium-dose ICS–formoterol MART
Step 5
High-dose ICS–LABA ± add-ons
ICS–Formoterol Dosage 💨
👽 Budesonide–Formoterol 160/4.5 µg/inhalation → (Most commonly used worldwide)
ICS Dose Level
Maintenance Dose
Total Daily Budesonide
GINA Step
Low dose
1 x 1 puff/day
160–320 µg/day
Step 2–3
Medium dose
2 x 1 puff/day
320 µg/day
Step 4
High dose
2 x 2 puff/day
640 µg/day
Step 5
Reliever (MART)
  • 1 puff as needed
  • Maximum total: 12 inhalations/day (maintenance + reliever)
 
👽 Beclomethasone–Formoterol 100/6 µg/inhalation
ICS Dose Level
Maintenance Dose
Total Daily Beclomethasone
GINA Step
Low dose
1 x 1 puff/day
100–200 µg/day
Step 2–3
Medium dose
2 x 1 puff/day
200 µg/day
Step 4
High dose
2 x 2 puff/day
400 µg/day
Step 5
Reliever (MART)
  • 1 puff PRN
  • Maximum: 8 inhalations/day
 
Alternative Track (Track 2 – SABA Reliever)
(Only if Track 1 not feasible)
GINA Step
Controller
Step 1 (Intermittent)
Low-dose ICS taken whenever SABA used
Step 2 (Mild Persistent)
Daily low-dose ICS
Step 3 (Moderate Persistent)
Low-dose ICS–LABA
Step 4 (Severe Persistent)
Medium/high-dose ICS–LABA
Step 5
High-dose ICS–LABA ± add-ons
ICS Dose Categories (Adults) 💨
ICS
Low Dose (µg/day)
Medium Dose
High Dose
Budesonide
200–400
>400–800
>800
Beclomethasone
200–400
>400–800
>800
Fluticasone propionate
100–250
>250–500
>500
LABA (Maintenance Only – Never Alone) 💨
Drug
Dose
Formoterol
4.5–9 µg 2x1
Salmeterol
50 µg 2x1
Add-On Therapies (Step 5 – Severe Asthma)
Therapy
Indication
LAMA (Tiotropium)
Persistent symptoms despite ICS–LABA
Anti-IgE (Omalizumab)
Allergic asthma
Anti-IL-5 / IL-5R
Eosinophilic asthma
Anti-IL-4R (Dupilumab)
Type 2 inflammation
Oral corticosteroids
Last resort (lowest dose)
Step-Up Therapy (When?)
  • Symptoms uncontrolled
  • ≥ 1 severe exacerbation/year
  • After checking:
    • Inhaler technique
    • Adherence
    • Comorbidities
Step-Down Therapy (When?)
  • Well controlled ≥ 3 months
  • Reduce ICS dose by 25–50%
  • Never stop ICS completely

Asthma Control & Risk Classification

Symptom-Based Asthma Control (Past 4 Weeks)
Parameter
Cut-off Features
Daytime symptoms
> 2 days/week
Night waking
Any
Reliever use
> 2 days/week
Activity limitation
Any
Lung function (FEV₁ / PEF)
↓
Interpretation
  • 0 features → Well controlled
  • 1–2 features → Partly controlled
  • ≥3 features → Uncontrolled
 
Exacerbation-Based Risk Classification (Past 12 Months)
Risk Category
Exacerbations Requiring Systemic Steroids
Low risk
0–1 / year
High risk
≥ 2 / year
Very high risk
≥ 1 ICU admission / intubation
Combined Clinical Classification (Decision-Making Table)
Symptom Control
Exacerbation Risk
Overall Interpretation
Management Implication
Well controlled
Low
Stable asthma
Continue current therapy
Well controlled
High
Controlled but high risk
Step-up / review adherence
Partly controlled
Low
Suboptimal control
Optimize controller therapy
Partly controlled
High
Poor control + high risk
Step-up + close follow-up
Uncontrolled
Any
High risk asthma
Escalate therapy urgently

Complications

Acute (Exacerbation-Related)

  • Status asthmaticus
      • Severe, refractory bronchospasm → hypoxemia, hypercapnia, respiratory failure
  • Respiratory failure
      • From exhaustion, air trapping, and V/Q mismatch
  • Pneumothorax / pneumomediastinum
      • Due to alveolar rupture from severe air trapping

Chronic (Disease-Related)

  • Airway remodeling
      • Subepithelial fibrosis, smooth muscle hypertrophy → fixed airflow limitation
  • Chronic airflow obstruction
      • Asthma–COPD overlap–like physiology in long-standing disease
  • Reduced quality of life
      • Activity limitation, sleep disturbance, absenteeism

Treatment-Related

  • Inhaled corticosteroids (high dose)
      • Oral candidiasis, dysphonia, adrenal suppression (rare)
  • Systemic corticosteroids
      • Osteoporosis, diabetes, hypertension, infection risk
  • β₂-agonists (overuse)
      • Tachycardia, hypokalemia, masking of worsening inflammation