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Placebo-Controlled Trial of Bilevel Positive Airway Pressure

Patient characteristics in both groups were similar (Table 1). The mean FEV1 on recruitment was similar in both groups: 37.27 ± 10.7% of predicted in the BPV group and 33.8 ± 10.2% in the control group. FVC was similar as well: 48.27 ± 11.87% in the BPV group and 48.6 ± 16.05% in the control group. Placebo-Controlled Trial

Results of blood gas analysis on hospital admission were similar: there was a mild hypocarbia in both groups (mean PaC02 in the BPV group, 33.59 ± 3.48 mm Hg; control group, 34.29 ± 5.41 mm Hg). Arterial oxygen tension was slightly decreased: 82.85 ± 38.72 mm Hg in the BPV group and 85.82 ± 29.6 mm Hg in the control group. Regular use of medications was similar as well, including the regular use of inhaled corticosteroids.

Patients in both groups received a similar amount of nebulizations with salbutamol and ipratropium and similar doses of IV corticosteroids (Table 2). Table 3 demonstrates the different characteristics of the patients in both groups by the end of 3 h and 4 h of treatment. The mean rise in FEV1 in the BPV group at 3 h of treatment was 56.13 ± 16.3%, an improvement of 51.08 ± 19.3% as compared to an improvement of 24.08 ± 23.6% in the control group (p = 0.002). By the end of 4 h of treatment, mean FEV! increased to 57.4 ± 17.7% in the BPV group, an improvement of 53.53 ± 23.4% as compared to an improvement of 28.46 ± 22.6% in the control group (p = 0.006).

Figure 1 demonstrates the inspiratory and expiratory positive airway pressure during 3 h of treatment in the BPV group. It shows that most of the pressure increments occurred during the first 30 min to 1 h; thereafter, inspiratory and expiratory pressures did not change significantly. Although the study protocol allowed increments in inspiratory pressure of up to 15 cm H2O, by the time inspiratory pressure of 14 cm H2O was reached, respiratory rate has decreased in all but three patients to < 25 breaths/min. These three patients were also those patients who were hospitalized. We did attempt to increase inspiratory pressure to a maximum of 15 cm H2O in these three patients; however, they did not tolerate it and inspiratory pressures were decreased quite rapidly back to 14 cm H2O in two patients and back to 12 cm H2O in one patient. As a result, during the study none of the patients received an inspiratory pressure of > 14 cm H2O.

Figure 2 demonstrates the increase in FEV1 during 3 h of BPV application. The increase was steady and continued for another hour after termination of BPV. There was no statistically significant difference between the two groups in the decline of heart rate. Respiratory rate, however, decreased more in the BPV group, 41.3 ± 12.8%, as compared to 31 ± 11.4% in the control group (p = 0.02).

The mean stay in the emergency department (Table 4) was 5.9 ± 1.3 h in the BPV group and 5.6 ± 1.3 h in the control group (p = not significant [NS]).

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