Statistical analysis
. The sample size calculation, using the method described by Eberl et
al. [17], was based on the retrospective sedation database of our
hospital, in which the propofol requirement for gastrointestinal
endoscopy was 300 (100) mg, presented as mean (standard deviation).
Given power of 0.80 and type I error of 0.05, we will need to study 28
subjects per group to decrease propofol requirement by about 25%. And
taking into consideration a potential dropout rate of 10%, 30 patients
for each group will be required, thus a total of 90 adult patients
should be randomly assigned.
SPSS 13.0 or the software R was performed for statistical analysis. We
used the modified Dixon’s up-and-down methodology, described in 1965
[18], to determine the EC50 of TCI propofol with
different doses of dexmedetomidine. We performed a chi-squared test for
categorical variables, ANOVA test for continuous values and
Kruskal-Wallis rank sum test for discrete values as appropriate. Data
were presented as number (n), mean (standard deviation, SD), or median
[Min, Max]. A 0.05 was set as the threshold of rejecting the null
hypothesis.