Severe Asthma: Oxygen, Drugs, and the Reassessment That Matters
A 19-year-old woman with a known history of asthma is brought to the emergency department. Respiratory rate 34/min, HR 132/min, SpO2 89% on room air, peak expiratory flow 160 L/min (her personal best is 520 L/min). She speaks in two- to three-word phrases, sits tripod, and uses accessory muscles; air entry is poor bilaterally with minimal wheeze. She used six puffs of her albuterol inhaler at home over the last hour with no relief. She is alert but anxious and says she is getting tired.
1. What oxygen therapy do you start, and what saturation should you target in this patient?
Read the worked answer
Start high-flow oxygen immediately and titrate to 94–98% SpO2.
Reasoning:
- She is at 89% on room air with severe distress. Unlike the chronic CO2 retainer, the acutely bronchospastic patient should be kept in the normal range; hypoxemia here worsens shunting and increases myocardial work at a heart rate already at 132/min.
- A high-flow delivery device (non-rebreather or high-flow nasal cannula) is appropriate initially because her inspiratory flow demand is very high and a low-flow cannula will be entrained with room air. Once the SpO2 is stable, reduce to the lowest flow that maintains 94–98%.
- Do not let oxygen be the only intervention - this is temporizing support while bronchodilator therapy and steroids take effect.
- Reassess after each intervention: the trend in SpO2, respiratory rate, ability to speak, and air entry tell you more than a single number.
2. Outline the medication plan, including route and why you chose it over the alternative.
Read the worked answer
1. Inhaled short-acting beta-2 agonist, by nebulizer: albuterol 2.5–5 mg intermittent or, given severity, continuous nebulization (roughly 10–15 mg/hour). A nebulizer is chosen over an MDI-with-spacer here because she is speaking in two-word phrases with poor air entry and cannot generate a reliable, coordinated, deep inspiration; the MDI route is reasonable in mild-to-moderate attacks but is a poor bet in a patient this distressed.
2. Ipratropium bromide 0.5 mg added to the nebulized albuterol (repeated for the first hour) - additive bronchodilation in severe exacerbations.
3. Systemic corticosteroid early - prednisone 40–60 mg PO or methylprednisolone 40–125 mg IV. Steroids do not relieve bronchospasm in minutes; they are given now because the benefit appears over hours and delays cost improvement.
4. Consider IV magnesium sulfate 2 g over about 20 minutes for a severe attack not responding to inhaled therapy.
Monitor for tremor, tachycardia, and hypokalemia from beta-agonist loading, and keep the oxygen running during nebulization.
3. She receives continuous albuterol/ipratropium and steroids. One hour later she is sleepier, the wheeze is nearly absent, and the respiratory rate has fallen from 34 to 22/min. How do you interpret this, and what are your next steps?
Read the worked answer
Interpret this as deterioration, not improvement.
- Quiet chest plus decreasing respiratory rate plus drowsiness is the classic pattern of fatigue and rising PaCO2 in a severe asthma attack. Wheeze is generated by airflow; when airflow falls far enough, the wheeze disappears and the chest goes silent. A falling respiratory rate in a patient who was tachypneic and working hard is a warning sign, not relief.
- A "normal" or rising PaCO2 in this setting is alarming, because the asthmatic patient should be hyperventilating. Obtain an ABG - this is one of the few situations where a blood gas changes management.
- Next steps: move to a monitored setting, prepare for assisted ventilation, and call for senior/anesthesia support. Noninvasive ventilation is generally avoided or used with great caution in severe asthma because of the risk of air trapping and gastric insufflation; the safer plan is controlled intubation with a strategy of permissive hypercapnia, low respiratory rate, low tidal volume, long expiration, and careful attention to dynamic hyperinflation (watch for rising plateau and auto-PEEP).
- Reassess continuously: mental status, air entry, SpO2, and the work of breathing are the bedside markers - not the loudness of the wheeze.