What indicates a life-threatening asthma exacerbation?

Life-Threatening Asthma Exacerbation Indicators

Peak flow <30% of predicted or personal best (option A) is the most reliable indicator of a life-threatening asthma exacerbation. 1

Indicators of Life-Threatening Asthma

According to the British Thoracic Society guidelines, the following features indicate life-threatening asthma:

• PEF <33% of predicted normal or best (most critical indicator)
• Silent chest, cyanosis, or feeble respiratory effort
• Bradycardia or hypotension
• Exhaustion, confusion, or coma 1

Analyzing the Options

1. Peak flow <30% (Option A) - This indicates severe airflow limitation and is below the 33% threshold defined as life-threatening by guidelines. This is the correct answer.

2. O2 saturation 95% in room air (Option B) - This is a normal oxygen saturation and does not indicate severe asthma. Life-threatening asthma typically presents with severe hypoxia (PaO2 <8 kPa or SpO2 significantly lower than 95%). 1

3. Respiratory rate 28/min (Option C) - While elevated, this respiratory rate falls into the criteria for severe asthma (>25 breaths/min) but does not by itself indicate life-threatening status. 1

Arterial Blood Gas Findings in Life-Threatening Asthma

Additional markers of life-threatening asthma in arterial blood gases include:

• Normal (5-6 kPa) or high arterial carbon dioxide tension (PaCO2) in a breathless asthmatic patient
• Severe hypoxia: arterial oxygen tension (PaO2) <8 kPa despite oxygen therapy
• Low pH value 1

Clinical Significance

When a patient presents with PEF <33% of predicted or personal best, immediate aggressive treatment is required:

• High-flow oxygen
• Nebulized β-agonists (salbutamol 5 mg or terbutaline 10 mg)
• Add ipratropium bromide (0.5 mg) to the nebulizer
• Systemic corticosteroids (prednisolone 30-60 mg or IV hydrocortisone 200 mg)
• Consider IV aminophylline or IV β-agonists if no response to initial treatment 1

Common Pitfalls in Assessment

1. Overreliance on oxygen saturation: Normal oxygen saturation (as in option B) can be misleading in early stages of severe asthma. 1, 2

2. Subjective assessment of airflow obstruction: Physicians' subjective assessments are often inaccurate. Objective measures like peak flow are more reliable. 2

3. Patient-reported "personal best" PEF: Inner-city ED patients often inaccurately report their personal best PEF, making percent of predicted values more reliable in acute settings. 3

4. Underestimating the severity: Asthma severity is often underestimated by patients, relatives, and doctors due to failure to make objective measurements. 1

Remember that peak flow <30% of predicted or personal best is the most reliable indicator of life-threatening asthma among the given options and requires immediate, aggressive intervention to prevent mortality.