Assessment of the patient with acute asthma in the emergency department. A factor analytic study

Acute asthma is a very common medical emergency. Thus, a variety of measures are currently used to assess severity; most are logical and seem reasonably effective but have never been scientifically tested in a comprehensive manner. Additionally, simple brief measures are needed for greater specificity in describing variables and in assessing different aspects of asthma. The purpose of this study was to examine the most common clinical and objective measures utilized in the assessment of acute asthma in the emergency department for determining whether these variables comprise separate or distinct dimensions. To carry out the above purpose, we used the multivariate statistical technique of factor analysis. Measures of age, duration of attack, heart rate, respiratory rate, peak expiratory flow (PEF), FVC, FEV1 percent of predicted, accessory-muscle use, dyspnea, wheezing, steroid use, and early response to treatment in 194 patients with acute asthma (mean age = 32.8 +/- 11.9 years) were factor analyzed through the method of principal components. Factors extracted with this method were then rotated orthogonally through the Varimax procedure. The first factor contained the three measures of lung function (PEF, FVC, and FEV1 percent of predicted) and early response of treatment. The second factor extracted contained respiratory rate, accessory-muscle use, and dyspnea. Factor 3 contained heart rate and wheezing, and factor 4 contained age, duration of attack, and steroid use. Exploratory analysis of subgroups (by randomization, by severity of airflow obstruction, and by use of steroids) confirmed the results of the primary analysis. The coefficients of congruence obtained were above 0.90. Early response of treatment measured by the percent variation of FEV1 at 30 min over baseline value significantly correlated with a broad variety of asthma characteristics (PEF, FVC, FEV1 percent of predicted, accessory-muscle use, and duration of attack), resulting in a rather general measure, and suggesting that its measure can be a reliable assessment of acute adult asthma. Finally, early response to treatment was the most important predictor of the patient outcome (r = 0.48, p < 0.00). In summary, the results of this study support the hypothesis that most of the subjective and objective measures utilized in the assessment of patients with acute adult asthma represent separate and nonoverlapping dimensions and provided a useful summary of acute asthma. Early response to treatment in combination with measures of the four identified factors could be included in other acute adult asthma research protocols promoting greater comparable among studies.