PFTs & asthma
Diagnosis: variable airflow limitation — BD response ≥12% and 200 mL, PEF variability, methacholine drop ≥20%, or ICS response.
What you are diagnosing
Asthma is a heterogeneous condition of variable respiratory symptoms (wheeze, dyspnea, chest tightness, cough) plus variable expiratory airflow limitation (, ). Diagnostic cut-offs still differ slightly between ATS and GINA — say which one you used.
Spirometry / PEF
Bronchodilator response
↑ FEV1 or FVC ≥12% and >200 mL, or PEF ≥20% if no spirometry. Same numbers after 4 weeks of ICS, or visit-to-visit swings, or methacholine FEV1 ↓ ≥20%.
Type 2-high
Eosinophilic / allergic
↑ eos, ↑ FeNO, ↑ IgE, atopy. This is the biologic-eligible lane in severe disease.
Type 2-low
Neutrophilic
Often steroid-refractory. Do not keep escalating prednisone forever — look for ACO, smoking, obesity, vocal-cord dysfunction.
- Triggers: exercise, cold air, allergens, smoke, viruses, ASA / NSAIDs, β-blockers.
- New adult-onset: think ABPA, EGPA, systemic mastocytosis, occupational asthma (10–25%; ), AERD with nasal polyps (~7%; J Allergy Clin Immunol 2015;135:676).
Outpatient control
ICS-containing therapy is the backbone. LABA without ICS increases death (; ). GINA now prefers ICS-formoterol as both maintenance and reliever (MART) over SABA-only rescue.
See GINA 2024 page 71 for low / medium / high ICS dose tables.
| Step idea | Controller | Reliever |
|---|---|---|
| Mild / infrequent | As-needed ICS-formoterol (or low-dose ICS whenever SABA is taken) | ICS-formoterol preferred; SABA alone is outdated |
| Persistent | Daily low/medium ICS-LABA | ICS-formoterol or SABA |
| Severe | High-dose ICS-LABA ± LAMA, then biologics | Do not add LABA without ICS |
- Biologics: dupilumab (IL-4Rα), omalizumab (IgE), benralizumab / mepolizumab (IL-5 axis), tezepelumab (TSLP).
- Asthma–COPD overlap: persistent obstruction plus asthma features. ICS is essential; add LABA / LAMA; triple and biologics are on the table (; ; ).
Exacerbation
Outpatient flare: prednisone 40–50 mg for 5–7 days plus the controller/reliever; quadrupling ICS can abort a mild flare ().
Floor
- Albuterol 2.5–5 mg ± ipratropium 0.5–1.5 mg q20 min × 3. DuoNebs in the ED lower admission (Cochrane 2017).
- Prednisone 40–60 mg/day for 5–7 days (Cochrane 2016).
- Oxygen to 93–95%. >95% raises PaCO2 ().
ICU / impending failure
- Methylprednisolone 60–125 mg IV q6h, stacked DuoNebs, magnesium 2 g IV.
- NIV trial (usually BiPAP). Continuous albuterol. Rescue: ketamine, inhaled anesthetic, Heliox. ECMO last.
- Intubation: large ETT (≥8), high inspiratory flow (80–100 L/min), VT 6–8 mL/kg, RR 10–14, low PEEP, allow a long expiratory time. Permissive hypercapnia. Paralysis if stacked breaths.