In addition, the duration of actual drug delivery is longer with HHN technique than the MDI-spacer (10 to 15 minutes for HHN compared with two 15-s MDI-spacer inhalations 5 minutes apart). Progressive bron-chodilation during the course of a HHN treatment may result in deeper penetration of the aerosol.
There is controversy over the equivalent dosage for the two delivery systems. Based on data from Shim and Williams in stable outpatients, metaproterenol doses of 1.95 mg via MDI without a spacer were considered equivalent to 15 mg via nebulizer. These data may not be applicable to patients with acute bronchospasm who are using a MDI-spacer combination. Two studies have compared the administration of metaproterenol delivered by HHN and MDI-spacer in patients with acute bronchospasm. A placebo-controlled parallel study by Turner et al concluded that three inhalations of metaproterenol delivered by MDI with a spacer (InspirEase) produced equivalent bronchodilation and improvement in dyspnea in patients with acute exacerbations of asthma and COPD as did metaproterenol delivered by HHN. Not only was the dose of MDI metaproterenol greater than in the present study, but both the HHN and MDI-spacer (InspirEase) treatments were administered more frequently at 30-minute intervals.