High Humidity, Low Humidity, and Mist Therapy for CroupHigh Humidity, Low Humidity, and Mist Therapy for Croup

To the Editor: In their study comparing controlled delivery of high humidity, low humidity, and mist therapy for croup in emergency departments, Dr Scolnik and colleagues¹ demonstrated that mist therapy does not lead to an improvement in croup scores. Their study also suggests that a reexamination of the use of aerosolized epinephrine in mild croup is warranted.

Aerosolized epinephrine use for croup in the emergency department has generally been reserved for moderate to severe disease for 2 reasons. First, mild disease has been believed to respond to cool mist so that aerosolized epinephrine is not necessary.² Second, all patients who get aerosolized epinephrine are believed to require several hours of observation in the emergency department prior to discharge.³

Scolnik et al cast considerable doubt on the first reason. The second, however, is dubious as well. The effect of aerosolized epinephrine is temporary, and there is some possibility of the patient returning to the pretreatment status when the effect wears off in 1 to 2 hours. However, there is evidence against the concept of aerosolized epinephrine causing a rebound effect, with worsening of illness beyond the pretreatment status.^{2 - 4} The studies of aerosolized epinephrine have generally excluded patients with mild disease so that many of the included patients are ill enough that a return to their pretreatment status would make them unsuitable for discharge. This has led to the persistence of the recommendation for a 2- or 3-hour observation period.⁵

However, this logic does not extend to patients whose initial presentation is mild, for whom a return to pretreatment status would not represent an undue risk. Some of these patients have enough discomfort from a croupy cough or mild stridor with exertion that intervention is justified—the intent of giving cool mist. Because cool mist is no better than placebo and because aerosolized epinephrine is effective, it seems reasonable to administer aerosolized epinephrine and steroids and discharge these patients without the burden of a 2- to 3-hour observation period.