Asthma

Clinical Orientation

A 24-year-old with known asthma arrives in the ED unable to speak in full sentences. She is using accessory muscles, has audible expiratory wheezing, and her SpO2 is 89%. Her peak flow is 30% of her personal best. This is a severe asthma exacerbation. This chapter answers: What mechanism links asthma to bedside findings, tests, red flags, and nursing priorities?

What Goes Wrong?

Asthma = reversible airflow obstruction from three mechanisms:

1. Bronchoconstriction: Smooth muscle surrounding airways contracts in response to triggers (allergens, irritants, cold air, exercise). Mediated by mast cell degranulation → histamine, leukotrienes, prostaglandins → bronchospasm. This is the rapid component — occurs in minutes, can resolve in minutes with bronchodilators.

1. Airway inflammation: Eosinophilic (allergic) or neutrophilic (non-allergic) infiltration of the airway wall → edema, epithelial damage. This component responds to corticosteroids but takes hours to days.

1. Mucus hypersecretion: Goblet cell hyperplasia and mucus gland hypertrophy → thick, tenacious mucus plugs that obstruct airways.

The result: Air can get IN (negative inspiratory pressure opens airways somewhat) but cannot get OUT (positive expiratory pressure collapses already-narrowed airways) → air trapping → hyperinflation → increased work of breathing → respiratory muscle fatigue → hypercapnia → respiratory failure.

Severity Assessment

Critical warning: A "normal" PaCO2 (35-45) in a severe asthma exacerbation is ABNORMAL — the patient SHOULD be hyperventilating with low PaCO2. Normal PaCO2 means the patient is tiring and cannot maintain compensatory hyperventilation. A RISING PaCO2 signals impending respiratory arrest.

What the Nurse May See

• Respiratory: Tachypnea, prolonged expiration, wheezing (expiratory > inspiratory), hyperresonance to percussion, decreased breath sounds as severity worsens.
• Cardiovascular: Tachycardia, pulsus paradoxus (>10 mmHg drop in SBP during inspiration), hypertension (SNS) then hypotension (if severe).
• Neurologic: Anxiety, agitation, confusion (hypoxia/hypercapnia), somnolence (late).
• Position: Upright, tripod, unable to recline.

Nursing Priorities

1. Assess severity immediately: Speech, RR, accessory muscles, SpO2, peak flow, ability to lie down.
2. Bronchodilators: Short-acting beta-agonists (albuterol) via nebulizer or MDI with spacer — repeat every 20 minutes in severe exacerbations. Ipratropium (anticholinergic) added in severe exacerbations.
3. Systemic corticosteroids: IV methylprednisolone or oral prednisone. Reduce airway inflammation. Onset hours, not minutes — give EARLY.
4. Oxygen: Target SpO2 ≥92% (adults). Avoid over-oxygenation in COPD overlap.
5. Monitor for deterioration: Repeat peak flow, SpO2, ABG if moderate-severe. Watch for rising PaCO2 — the single most ominous sign.
6. Prepare for escalation: BiPAP may be tried before intubation. Intubation in asthma is high-risk (air trapping, auto-PEEP, barotrauma).

Red Flags

Patient Teaching

• "Asthma is airway inflammation + bronchospasm + mucus. Your rescue inhaler (albuterol) relaxes the muscles quickly. Your controller medication (inhaled corticosteroid) reduces the inflammation over time — take it every day, even when you feel well."
• Use a spacer with MDI. Know your personal best peak flow. Have an asthma action plan with green/yellow/red zones.