Evaluation of Sa O2 as a Predictor of Outcome in 280 Children Presenting With Acute Asthma

Abstract

Study objectives: To evaluate the initial measurement of arterial oxygen saturation (Sa O 2) as a predictor of outcome in acute childhood asthma compared with other factors of past and present asthma history. Design: Prospective observational double-blind study. Setting: The emergency department of an urban pediatric hospital with a 1988 annual census of 50,000 children. Type of participants: Two hundred eighty children with recurrent wheezing that was diagnosed by a physician as asthma, who presented to the ED with wheezing. Intervention: Sa O 2 was measured on arrival in the ED, and a detailed history of the present attack and past asthma was recorded. Children were treated according to then-current practice guidelines. Parents were contacted by telephone to determine the outcome of the attack; a "poor outcome" was defined as admission to hospital or representing with ongoing symptoms to receive medical care if sent home from the ED. A "worst outcome" was defined as receiving IV aminophylline and steroids after failing to respond to repeated bronchodilation and oral steroids. Measurements and main results: The proportion of children at each percent Sa O 2 who had a poor outcome increased with decreasing Sa O 2 ( r = .97). Likelihood ratios for a poor outcome were 35 (confidence interval [CI], 11 to 150) for an Sa O 2 of 91% or less compared with 96% or more and 4.2 (CI, 2.2 to 8.8) for an Sa O 2 of 92% to 95% compared with 96% or more. An Sa O 2 of 91% or less predicted with a sensitivity of 100% and a specificity of 84% those children with a worst outcome who required IV therapy. Other factors of current or past asthma history failed to predict outcome. Conclusion: We have shown that in acute childhood asthma, the initial level of Sa O 2 reflects severity as it predicts the likelihood of poor outcome. This predictive quality of Sa O 2 is independent of current or past clinical factors. [Geelhoed GC, Landau LI, Le Souëf PN: Evaluation of Sa O 2 as a predictor of outcome in 280 children presenting with acute asthma. Ann Emerg Med June 1994;23:1236-1241.]