Predicting rapid and slow response to treatment in acute severe asthma

The clinical features of patients admitted with acute severe asthma which discriminated between groups who respond rapidly to treatment (attain their maximum PEFR within 3 days), slowly (maximum PEFR after 7 days) and at an intermediate rate (maximum PEFR 3-7 days), have been previously identified in this unit. These included age, atopy, duration of the present attack, the presence normally of day-long wheeze or at least three admissions within the last 12 months, the use of maintenance corticosteroids, the degree of pulsus paradoxus on admission, the rise in PEFR after 6 hours of treatment and the Pao2 after 48 hours. A further study was undertaken to apply these features prospectively to individual asthmatics on admission and again at 6 and 48 hours after the start of treatment to predict the rate of response and to assess the accuracy of these predictions. Fifty-four patients were studied of whom 53 were initially classified as either rapid or slow responders. Forty patients were predicted as rapid responders on admission of whom 14 were reclassified at 6 hours as slow responders. Thirteen patients were correctly classified as slow responders on admission and all had the combined features of maintenance corticosteroids and the presence of day-long wheeze. At 6 hours 51 of the 54 patients (94%) had been correctly classified as rapid or slow responders (P less than 0.0001) as judged by the eventual outcome. Only two patients were incorrectly classified both on admission and at 6 hours. We conclude that these clinical and physiological features allow accurate predictions of the response of an individual to the treatment of acute severe asthma.