Department of Anesthesiology

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Neuromuscular dose-response studies: determining sample size.

TitleNeuromuscular dose-response studies: determining sample size.
Publication TypeJournal Article
Year of Publication2011
AuthorsKopman AF, Lien CA, Naguib M
JournalBr J Anaesth
Volume106
Issue2
Pagination194-8
Date Published2011 Feb
ISSN1471-6771
KeywordsAdult, Dose-Response Relationship, Drug, Humans, Neuromuscular Blockade, Neuromuscular Blocking Agents, Neuromuscular Junction, Research Design, Retrospective Studies, Sample Size
Abstract

BACKGROUND: Investigators planning dose-response studies of neuromuscular blockers have rarely used a priori power analysis to determine the minimal sample size their protocols require. Institutional Review Boards and peer-reviewed journals now generally ask for this information. This study outlines a proposed method for meeting these requirements.

METHODS: The slopes of the dose-response relationships of eight neuromuscular blocking agents were determined using regression analysis. These values were substituted for γ in the Hill equation. When this is done, the coefficient of variation (COV) around the mean value of the ED₅₀ for each drug is easily calculated. Using these values, we performed an a priori one-sample two-tailed t-test of the means to determine the required sample size when the allowable error in the ED₅₀ was varied from ±10-20%.

RESULTS: The COV averaged 22% (range 15-27%). We used a COV value of 25% in determining the sample size. If the allowable error in finding the mean ED₅₀ is ±15%, a sample size of 24 is needed to achieve a power of 80%. Increasing 'accuracy' beyond this point requires increasing greater sample sizes (e.g. an 'n' of 37 for a ±12% error).

CONCLUSIONS: On the basis of the results of this retrospective analysis, a total sample size of not less than 24 subjects should be adequate for determining a neuromuscular blocking drug's clinical potency with a reasonable degree of assurance.

DOI10.1093/bja/aeq310
Alternate JournalBr J Anaesth
PubMed ID21068050