Sun28November0440PM 40

An 18-year-old female presents to the Emergency department with a two day history of increasing shortness of breath and wheeze. She has been asthmatic for five years.

On examination she has a respiratory rate of 28 breaths per minute, heart rate of 115 beats per minute, and a temperature of 37.6°C.

Which of the following are true?

True / False

Oxygen saturations of 91% on air would be an indication for performing arterial blood gases Correct

An electrocardiogram (ECG) is not indicated Correct

A chest X ray should be routine Correct

A peak expiratory flow rate (PEFR) of 45% best or predictedsuggests moderate asthma exacerbation Incorrect answer selected

A peak expiratory flow rate (PEFR) is necessary in order to assess the severity of the asthma Correct

Explanation

In a patient presenting with acute asthma any one of the following suggests acute severe asthma:

PEFR 33-50% best/predicted

Respiratory rate =25/min

Heart rate =110/min or

Inability to complete a sentence in one breath.

Saturations of less than 92% in this context suggest life threatening asthma. Patients with oxygen saturations of less that 92% on or off oxygen warrant arterial blood gas analysis looking for normo- or hypercarbia.

Chest x rays are not routinely indicated as they rarely provide additional useful information.

A chest x ray should be performed in the following circumstances:

Presence of subcutaneous emphysema

Persisting unilateral signs suggesting pneumothorax

Sins of lobar collapse or consolidation

Life-threatening asthma not responding to treatment

If the patient requires mechanical ventilation

While PEF is one of the indicators for differentiating moderate, acute, severe and life threatening asthma, other clinical parameters can also be used to make the diagnosis as described above.

One criterion to suggest life threatening asthma is arrhythmia. Together with the tachycardia an ECG would be indicated. Although one of the defining criteria for moderate asthma is PEFR 50-75% best/predicted this patient already has features suggestive of acute severe asthma with tachycardia and tachypnoea.

Reference:

British Thoracic Society. Asthma Guideline.

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