Diagnosis

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Bedside spirometry provides a rapid, objective assessment of patients and serves as a guide to the effectiveness of therapy. The forced expiratory volume in 1 s (FEV|) and the peak expiratory flow rate (PEFR) directly measure the degree of large airway obstruction.14 Patient cooperation is essential in order for these tests to be reliable. Sequential measurements help emergency physicians determine response to therapy. Signs on physical examination and a patient's report of symptoms of asthma do not necessarily correlate well with the severity of airflow obstruction. When possible, management decisions should be based on a patient's personal best PEFR or FEV1 or, if unknown, percent of predicted. Initial spirometry and response to initial treatment can be used to predict the need for hospitalization with 86

percent sensitivity and 96 percent specificity.15

Pulse oximetry is a useful and convenient method for accessing oxygenation and monitoring oxygen saturation during treatment but does not aid in predicting clinical outcomes.16

Determination of arterial blood gas (ABG) is not indicated in the majority of patients with mild to moderate asthma exacerbation. The main reason to determine ABG during an asthma attack is to assess for hypoventilation with carbon dioxide retention and respiratory acidosis. Such patients almost always have clinical evidence of severe attacks or spirometry demonstrating a PEFR or FEV-, of less than 25 percent predicted. With acute attacks, ventilation is stimulated, resulting in a decrease in partial pressure of carbon dioxide (Pco2). Therefore, a normal or slightly elevated Pco2 (e.g., 42 mmHg or more) indicates extreme airway obstruction and fatigue and may herald the onset of acute ventilatory failure.

A chest radiograph is indicated in patients with asthma exacerbation if there is clinical indication of a complication such as pneumothorax, pneumomediastinum, pneumonia, or other medical concern. Routine radiography is unnecessary, but up to one-third of patients requiring admission will demonstrate an abnormality on chest radiograph.

A routine complete blood cell count is rarely indicated and will likely show modest leukocytosis secondary to administration of b-agonist therapy or corticosteroid treatment. In patients taking theophylline prior to ED presentation, a serum theophylline level should be determined. Routine electrocardiogram is also unnecessary but may reveal right ventricular strain, abnormal P waves, or nonspecific ST-T-wave abnormalities, which resolve with treatment. Older patients, especially those with coexisting heart disease, should have cardiac monitoring during treatment. Asthma index scores have failed to predict outcome better than clinical judgment.

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