Residency · Residency · Internal Medicine
Asthma in the Adult Patient
Pathophysiology
Asthma is a chronic airway disease driven primarily by Th2 (type 2) immune responses involving eosinophils, mast cells, and IgE. The airways become hyperresponsive to a range of triggers including allergens, exercise, cold air, irritants, and infections. The resulting airflow obstruction is reversible and arises from bronchospasm, mucosal edema, and mucus hypersecretion. Over time, prolonged disease leads to airway remodeling characterized by subepithelial fibrosis, smooth muscle hypertrophy, and goblet cell hyperplasia. Non-type 2 phenotypes also exist, particularly neutrophilic or paucigranulocytic patterns seen in obesity-related and adult-onset asthma.
Diagnosis
Spirometry
The diagnosis requires demonstration of variable airflow obstruction. Spirometry showing an FEV1/FVC ratio below 0.70 (or below the lower limit of normal) confirms obstruction, and bronchodilator reversibility is demonstrated by a 12 percent or greater improvement plus at least 200 mL increase in FEV1 after SABA administration. When spirometry is normal, bronchoprovocation testing with a methacholine challenge (PC20 below 4 mg/mL) is diagnostic. In resource-limited settings, peak expiratory flow variability exceeding 20 percent supports the diagnosis.
Assessment of Control vs. Severity
Control reflects the patient's current status and is assessed by examining daytime symptoms, nighttime awakenings, rescue inhaler use, and activity limitation. Patients are classified as well-controlled, partly controlled, or uncontrolled by GINA criteria. The "Rule of 2s" from NAEPP provides a practical framework: asthma is not well-controlled if symptoms occur more than 2 days per week, nighttime awakenings happen more than 2 times per month, SABA is used more than 2 days per week, or there is any activity interference. Severity, by contrast, is a retrospective assessment based on the treatment step required to achieve control and should not be judged from initial symptoms alone.
Differential Diagnosis
Important conditions that mimic asthma include COPD (especially in smokers over 40, and the two may coexist as asthma-COPD overlap), vocal cord dysfunction or inducible laryngeal obstruction (characterized by inspiratory stridor and a flattened inspiratory loop), heart failure (cardiac asthma), GERD, post-nasal drip, anxiety with hyperventilation, eosinophilic bronchitis, and allergic bronchopulmonary aspergillosis.
Stepwise Chronic Management (GINA 2023+)
Track 1 (Preferred) -- ICS-Formoterol Maintenance and Reliever
At Steps 1 and 2, low-dose ICS-formoterol is used as needed (PRN) for both maintenance and reliever purposes. The SYGMA 1 and 2 trials, along with the Novel START trial, demonstrated that PRN budesonide-formoterol reduces exacerbations compared to SABA-only treatment. At Step 3, low-dose ICS-formoterol is taken as daily maintenance plus PRN. Step 4 escalates to medium-dose ICS-formoterol daily plus PRN. Step 5 involves referral for phenotyping, add-on LAMA, biologic therapy, and high-dose ICS-formoterol.
Track 2 (Alternative) -- ICS-Based with SABA Reliever
At Step 1, low-dose ICS is taken whenever SABA is used. Step 2 involves daily low-dose ICS plus PRN SABA. Step 3 adds a LABA to low-dose ICS with PRN SABA. Step 4 uses medium or high-dose ICS-LABA with PRN SABA. Step 5 includes add-on therapy such as LAMA, biologics, or oral corticosteroids.
The End of SABA-Only Treatment
GINA 2023 and beyond no longer recommends SABA monotherapy without ICS for any step of asthma management. The rationale is clear: SABA-only treatment does not address underlying inflammation, and overuse (three or more canisters per year) is associated with increased exacerbation risk and death. All patients should now receive ICS in some form, whether as maintenance or as concomitant therapy with SABA.
Key Medication Classes
Inhaled corticosteroids include budesonide, fluticasone propionate, beclomethasone, mometasone, and ciclesonide. Among LABAs, formoterol has rapid onset (1 to 3 minutes) making it suitable as both maintenance and reliever, while salmeterol has slow onset and is appropriate only for maintenance. Tiotropium (LAMA) is used as add-on therapy for uncontrolled asthma at Steps 4 to 5. Montelukast (LTRA) is less effective than ICS and carries an FDA boxed warning for neuropsychiatric effects. Common ICS-LABA combinations include budesonide-formoterol (Symbicort), fluticasone-salmeterol (Advair), mometasone-formoterol, and fluticasone furoate-vilanterol (Breo).
Severe Asthma and Biologic Therapies
Definition of Severe Asthma
Severe asthma is defined as asthma requiring GINA Step 4 or 5 therapy to maintain control, or that remains uncontrolled despite this level of treatment. Before assigning this label, clinicians must confirm the diagnosis, assess medication adherence and inhaler technique, and address comorbidities such as GERD, rhinosinusitis, obesity, OSA, and vocal cord dysfunction. Approximately 5 to 10 percent of asthma patients have truly severe disease.
Biologic Therapies -- Phenotype-Guided Selection
| Biologic | Target | Phenotype | Key Biomarker Requirement | Additional Benefits |
|---|---|---|---|---|
| Omalizumab | IgE | Allergic | Elevated IgE + allergen sensitization | Chronic urticaria |
| Mepolizumab | IL-5 | Eosinophilic | Blood eos ≥150 (≥300 preferred) | EGPA |
| Benralizumab | IL-5Rα | Eosinophilic | Blood eos ≥150 (≥300 preferred) | Eosinophil depletion |
| Dupilumab | IL-4Rα | Eosinophilic / high FeNO | Blood eos ≥150 or FeNO ≥25 ppb | Atopic dermatitis, nasal polyposis |
| Tezepelumab | TSLP | Broad (all phenotypes) | Effective regardless of biomarkers | Broadest eligibility |
Omalizumab (anti-IgE) targets allergic asthma with elevated IgE and allergen sensitization, administered subcutaneously every 2 to 4 weeks. Mepolizumab (anti-IL-5) and benralizumab (anti-IL-5R alpha) target eosinophilic asthma with blood eosinophils of 150 or greater. Dupilumab (anti-IL-4R alpha) is effective for eosinophilic asthma and/or elevated FeNO, with the added advantage of treating concurrent atopic dermatitis and nasal polyposis. Tezepelumab (anti-TSLP) has the broadest mechanism and is effective across both eosinophilic and non-eosinophilic severe asthma. Itepekimab (anti-IL-33) is investigational with emerging evidence.
Phenotyping Biomarkers
Key biomarkers for guiding biologic selection include blood eosinophils (150 cells per microliter or more, with some biologics requiring 300 or more), fractional exhaled nitric oxide (FeNO of 25 ppb or greater suggests type 2 inflammation), total IgE (relevant for omalizumab dosing), and skin prick testing or specific IgE to identify allergic triggers.
Acute Severe Asthma (Status Asthmaticus)
Clinical Assessment
Indicators of severe asthma include inability to speak in full sentences, accessory muscle use, respiratory rate above 30, heart rate above 120, SpO2 below 90 percent, and PEF below 25 percent predicted. Life-threatening features include a silent chest, cyanosis, bradycardia, altered consciousness, and respiratory acidosis on ABG. A normal or rising PaCO2 during an acute asthma attack is an ominous sign indicating that the patient is fatiguing and approaching respiratory failure.
Emergency Management
Treatment begins with continuous SABA nebulization (albuterol 10 to 15 mg per hour or equivalent) and adding ipratropium to the first three nebulizer treatments, which has been proven to reduce hospitalization in severe exacerbations. Systemic corticosteroids (methylprednisolone 125 mg IV or prednisone 40 to 60 mg orally) should be administered within the first hour, followed by prednisone 40 to 50 mg daily for 5 to 7 days without a taper. IV magnesium sulfate (2 g over 20 minutes) is indicated for patients not responding to initial therapy (FEV1 below 25 percent predicted) and has Cochrane evidence supporting reduced hospitalization. Oxygen should be titrated to SpO2 of 93 to 95 percent. IM epinephrine may be considered for anaphylaxis-associated bronchospasm or severe refractory cases. Heliox (helium-oxygen mixture) may buy time by reducing airway resistance in severe cases. Clinicians should avoid sedatives (respiratory depression risk), mucolytics (may worsen bronchospasm), and aggressive hydration (may worsen pulmonary edema).
Intubation in Acute Asthma
Intubation is a last resort due to the high risk of dynamic hyperinflation and cardiovascular collapse. Ketamine is preferred for induction because of its bronchodilator properties. Ventilator settings should use a low respiratory rate (8 to 10), long expiratory time, and permissive hypercapnia. Auto-PEEP and pneumothorax must be monitored for closely.
Disposition
Patients should be observed in the ED for at least 1 hour after the last treatment. Discharge criteria include sustained improvement, PEF above 70 percent predicted, and SpO2 above 94 percent on room air. Discharge prescriptions should include 5 to 7 days of prednisone, ICS (or an increase in current dose), SABA, and a written asthma action plan, with follow-up within 1 to 2 weeks.
Comorbidity and Trigger Management
Allergic rhinitis should be treated with intranasal corticosteroids, which improve both upper and lower airway disease. GERD should be treated if symptomatic, but empiric PPI for asymptomatic GERD does not improve asthma (SARA trial). Weight loss of 5 to 10 percent improves asthma control in obese patients. Exercise-induced bronchoconstriction is managed with warm-up and pre-exercise SABA or ICS-formoterol PRN. NSAID/aspirin-exacerbated respiratory disease (AERD) involves the triad of nasal polyposis, asthma, and NSAID sensitivity, with potential benefit from aspirin desensitization. Occupational asthma requires identification and removal of the offending exposure, monitored by serial PEF recordings at and away from work.
<image> A GINA-based stepwise treatment algorithm for adult asthma showing Track 1 (preferred: ICS-formoterol) and Track 2 (alternative: ICS with SABA reliever) side by side across Steps 1-5. Include medication names, doses, and reliever options at each step. Highlight the key paradigm shift: no SABA-only treatment at any step. Use a green-to-red color gradient from Step 1 to Step 5 indicating increasing disease severity. </image>
<image> A phenotyping decision tree for biologic selection in severe asthma. Start with "Severe Asthma Despite Step 4-5 Therapy" and branch based on biomarkers: blood eosinophils (high vs. low), FeNO (elevated vs. normal), total IgE and allergen sensitization. Each endpoint shows the recommended biologic(s): omalizumab for allergic, mepolizumab/benralizumab for eosinophilic, dupilumab for eosinophilic/elevated FeNO, and tezepelumab for broad phenotype coverage. Include comorbidity considerations (atopic dermatitis, nasal polyposis). </image>
<image> An emergency department management flowchart for acute severe asthma. Begin with initial assessment (vital signs, PEF, SpO2, ABG if severe) and branch into mild-moderate vs. severe vs. life-threatening pathways. Show treatment escalation: nebulized SABA + ipratropium, systemic steroids, IV magnesium, and considerations for intubation. Include reassessment time points (1 hour) and disposition criteria (admit vs. discharge). Flag danger signs: silent chest, normal/rising PaCO2, altered consciousness. </image>
Clinical Pearls
SABA-only treatment for asthma is no longer recommended at any step, as all patients need ICS exposure to reduce exacerbation risk. Overuse of SABA (three or more canisters per year) is an independent risk factor for asthma death and should prompt immediate step-up in controller therapy. A "normal" PaCO2 in acute asthma is a red flag because the patient should be hyperventilating; normocapnia suggests fatigue and impending respiratory failure. Before escalating to biologics for "severe" asthma, clinicians should always re-evaluate adherence, inhaler technique, trigger avoidance, and comorbidities, since up to 50 percent of uncontrolled asthma is attributable to these factors. Montelukast carries an FDA boxed warning for neuropsychiatric effects including depression and suicidal ideation, and should be used only after discussing risks and when alternatives are insufficient. Formoterol has rapid onset (1 to 3 minutes), making budesonide-formoterol suitable as both maintenance and reliever (MART strategy), while salmeterol is not appropriate as a reliever. Blood eosinophils and FeNO should be measured before referral for severe asthma evaluation, as they guide biologic selection.
References
- Global Initiative for Asthma (GINA). 2024 Report. www.ginasthma.org.
- O'Byrne PM, et al. SYGMA 1 Trial: As-Needed Budesonide-Formoterol in Mild Asthma. NEJM. 2018.
- Bateman ED, et al. SYGMA 2 Trial: As-Needed Budesonide-Formoterol vs. Maintenance Budesonide. NEJM. 2018.
- Beasley R, et al. Novel START Trial: As-Needed Budesonide-Formoterol in Mild Asthma. NEJM. 2019.
- Menzies-Gow A, et al. Tezepelumab in Severe Uncontrolled Asthma (NAVIGATOR Trial). NEJM. 2021.
- Castro M, et al. Dupilumab in Uncontrolled Asthma (LIBERTY ASTHMA QUEST). NEJM. 2018.
- Mastronarde JG, et al. SARA Trial: Lansoprazole for Poorly Controlled Asthma. JAMA. 2009.
- Rowe BH, et al. Magnesium Sulfate for Acute Asthma. Cochrane Database Syst Rev. 2009.
