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Children's Mercy Hospital Kansas City, MO
To the Editor:
Homnick et al (October 1998)1 conclude that "...the flutter [device] appears to be safe, efficacious, and cost effective for [cystic fibrosis] inpatients capable of undertaking this type of therapy." Unfortunately, data inconsistencies, omissions, and inadequate power preclude support of these conclusions.
Fifteen subjects were admitted one time (15 hospitalizations) and 7 subjects were admitted more than one time (22 hospitalizations). This results in a total of 37 hospitalizations. Only 33 hospitalizations were included for analysis. Why were four (11%) of the hospitalizations excluded from analysis, and which groups were they excluded from?
Seven (32%) of their subjects provided 22 of the hospitalizations analyzed (59 to 67%, depending on whether the hospitalizations excluded from analysis come from the group of one-time admissions or multiple admissions). Did the subjects admitted multiple times alternate between the flutter device and manual chest physiotherapy (CPT), or did they receive the same treatment each time they were admitted? This weighting of data could have a significant impact on results.
Regardless of the power analysis used,1 ,2 it is clear that the sample size presented in this article falls far short of sufficient. Therefore, while this article is an interesting preliminary data acquisition abstract, it does not begin to support conclusions about relative efficacy, and should not be interpreted as justification to replace standard CPT with the flutter device in the hospital or at home.
Correspondence to: Martin L. Bauer, MD, FCCP, Section of Pulmonology, Children's Mercy Hospital, 2401 Gilham Rd, Kansas City, MO 64108
References
Michigan State University Kalamazoo Center for Medical Studies Kalamazoo, MI
To the Editor:
We appreciate Dr. Bauer's comments about our study comparing chest physiotherapy (CPT) and the flutter device in hospitalized patients with cystic fibrosis.1-1 We agree with Dr. Bauer's observation that our study was underpowered. We clearly stated that this was a preliminary (pilot) study and our power analysis demonstrated that much larger subject numbers would be necessary to make definitive conclusions.
We disagree with the assertion that our study had "data inconsistencies" and "omissions." Dr. Bauer misinterpreted our study design and data analysis when he stated that we excluded some hospitalizations. We had 33 hospitalizations, not 37, and none were excluded from analysis. Fifteen subjects had only one hospitalization. Seven subjects had two or more admissions, representing 18 hospitalizations, not 22.
The subgroup analysis included the 15 one-time admission subjects and the first admission of the 7 multiple-admission subjects, resulting in a total of 22 hospitalizations. Analysis of this subgroup compared to the 33-hospitalizations group demonstrated no differences.
Assignment to flutter device or CPT was alternated for each hospitalization, regardless of the previous therapy received by multiple-admission subjects. We did not analyze whether the seven subjects received the same therapy on subsequent admissions.
We observed and stated that "the flutter [device] appears to be safe, efficacious, and cost effective" in our study. We, of course, would not recommend that any airway clearance technique or device be routinely substituted for another until proven effective in clinical trials with adequate statistical power.
Correspondence to: Douglas N. Homnick, MD, FCCP, Division of Pediatric Pulmonology, MSU, Kalamazoo Center for Medical Studies, 1000 Oakland Dr, Kalamazoo, MI 49008; e-mail: homnick@kcms.msu.edu
References
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