Because each patient was compared with himself, it was hoped that factors such as concurrent bronchodilator therapy and individual differences in bronchodilator responsiveness would not obscure differential responses to the type of bronchodilator administration. It is unlikely that over the six-hour period theophylline levels, etc, would vary enough to substantially effect the results. Indeed, the analysis revealed no effect of order on the improvements in FEVj, FVC, and the Borg scores. website
Considerable intrasubject variability in bronchodilator responsiveness was noted in this study (Fig 2). Some subjects with relatively large improvements in the FEVi after one mode of therapy had little or no response to the alternate method of bronchodilator administration. Previous studies have shown considerable variability in the response to bronchodilator therapy in patients with stable COPD. Therefore, perhaps it is not surprising to find such variability in our very ill patients; however, the relatively large variances and poor correlations in bronchodilator responses reduced the power of our repeated-meas-ures design to detect a difference between MDI-spacer and nebulizer treatments. To have a power of 0.80 of detecting a 50-ml difference in the change in FEV, or 5 percent difference in the percent change in FEVi, we calculated that one would need to study 91 and 166 patients, respectively (using the variances in bronchodilator response found in our study). The corresponding numbers of patients for the change in FVC or percent change in the FVC were 87 and 160. Therefore, the possibility of beta error, that is, finding no difference between the methods of administration when one actually exists, must be recognized; however, one could argue that even if a small statistical advantage for the nebulizer treatment did exist, it would not be clinically significant and could probably be overcome by simply increasing the dose administered by the MDI-spacer system (six puffs, etc).
In summary, we found that improvements in the FEV1, FVC, and Borg scores were comparable after drug administration via an MDI-spacer system and a nebulizer system in a group of patients admitted for an acute exacerbation of COPD; however, our data cannot be used to prove that the addition of the spacer device substantially affected our results. In addition, there are patients for whom the nebulizer may offer an advantage. Severely fatigued or obstructed patients who lack the ability to master the MDI-spacer system should be treated by the nebulizer system. On the other hand, the majority of patients can be treated quite adequately with an MDI-spacer system, and the savings in costs for drugs and personnel could be substantial.