Study objectives: The aim of this study was to develop an acute asthma index for utilization in the early differentiation between patients with poor and good therapeutic response in the emergency department (ED) setting.
Setting: The ED of a large tertiary-care hospital in Montevideo, Uruguay.
Patients and design: The study included 145 consecutive adult patients (mean age [+/- SEM], 33.4+/-0.97) who presented to an ED (analysis sample). The inclusion criteria were: (1) age between 18 and 50 years; (2) a peak expiratory flow rate (PEFR) or FEV1 below 35% of predicted; and (3) no history of chronic cough or cardiac, hepatic, renal, or other medical disease.
Interventions: All patients were treated with salbutamol delivered by metered-dose inhaler into a spacer device in four puffs actuated at 10-min intervals. The protocol involved 3 h of this treatment. After that time, patients with poor response received hydrocortisone, 500 mg IV. The outcome was defined as the FEV1 after 3 h of treatment in a dichotomized form: < or =45% of predicted = poor response, and >45% of predicted = good response.
Results: Biserial correlations between different variables and the outcome showed that PEFR as percent of predicted and PEFR variation over baseline, both measured at 30 min, were the most important predictors of a good or poor response after 3 h of treatment. Next, we developed an acute asthma index using these predictive measures. A comparison of index sensitivity, specificity, predictive values, and the area under the receiver operating characteristic (ROC) curve across different cutoff scores indicates that a score of 4 results in the least error of classification (sensitivity = 0.79; specificity = 0.96; area under the ROC curve = 0.87; positive predictive value = 0.94; and negative predictive value = 0.86). To validate the developed index, we prospectively studied a second sample of 77 consecutive patients (mean age 32.6+/-1.22 years) who presented for treatment of acute asthma (validation sample). The area under the ROC for the analysis sample was not greater than the validation sample area (p = 0.24). Thus, the validation sample showed similar levels of sensitivity and specificity, positive and negative predictive values, and area under the ROC curve (0.80, 0.88, 0.85, 0.84, and 0.89, respectively), indicating the stability of the model.
Conclusions: The study suggested the predictive accuracy of a two-item bedside index. This acute asthma index provides a tool for assessing acute asthma severity using objective criteria easily accessible to the ED physician.