Acute Asthma Exacerbation Monitoring
A 27-year-old woman with asthma presents with 6 hours of progressive wheeze and breathlessness after a viral illness. She speaks in short phrases, respiratory rate is 28 breaths/min, and oxygen saturation is 93% on room air, with diffuse expiratory wheeze. She receives nebulised salbutamol and ipratropium plus oral prednisolone. Which of the following is the most appropriate tool to monitor her response and judge the outcome of this attack?
- A.Repeat portable chest radiography
- B.Continuous pulse oximetry
- C.Serial arterial blood gas sampling
- D.Serial peak expiratory flow measurementCorrect
Explanation
Serial peak expiratory flow (PEF), expressed as a percentage of the patient's personal best or of predicted value, is the standard objective measure for grading severity and tracking recovery in an acute asthma attack. Airflow obstruction in asthma is caused by bronchial smooth muscle contraction, mucosal oedema and mucus plugging, and PEF falls in direct proportion to that obstruction, so a rising PEF after bronchodilator therapy is the earliest reliable evidence of reversal. A PEF above 70% of best after initial treatment supports discharge, whereas persistent values below 40% identify a severe attack needing continued intensive therapy or admission. Pulse oximetry is essential for detecting hypoxaemia but saturation is often preserved until obstruction is far advanced, so it is insensitive to early deterioration or improvement. Arterial blood gas sampling is reserved for patients with saturation persistently below 92% or exhaustion, where a normal or rising arterial carbon dioxide level signals impending respiratory failure; it is painful, invasive and unsuitable for repeated monitoring. Chest radiography is indicated only when pneumothorax, consolidation or another complication is suspected, since it does not quantify airflow limitation. Documenting PEF before and after treatment also allows objective comparison at follow-up and improves discharge planning. Failure of PEF to improve despite optimal therapy is a recognised indication for escalation to intensive care.
Why each option
- A.
- Chest radiography is used to exclude complications such as pneumothorax or consolidation and provides no measure of airflow obstruction.
- B.
- Oximetry detects hypoxaemia but remains near normal in many patients with severe airflow limitation, so it does not track the degree of obstruction.
- C.
- Blood gases are reserved for severe or deteriorating cases; the invasive nature makes them unsuitable for serial monitoring of a treatment response.
- D.
- Correct. Serial PEF quantifies airflow obstruction and its reversal, and the post-treatment percentage of personal best drives disposition decisions.
Reference: Global Initiative for Asthma (GINA) Global Strategy for Asthma Management and Prevention, 2024
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