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Peninsula Medical School; University of Plymouth; Plymouth, UK; robert.sneyd{at}pms.ac.uk
To the Editor:
Stapelfeldt el al. (1) demonstrated that clonidine 3 µg/kg reduces shivering; however, there are several remaining concerns.
One stated goal was "to evaluate the effect of clonidine on recovery from anesthesia..."yet the Methods section offers no power calculation or primary outcome measure.
With 17 patients receiving clonidine in Study 2, this investigation was likely underpowered for "recovery from anesthesia" endpoints. Subsequent robust statements are not supported by the data.
The visual analog scale ranges from 0100 but in Table 3 is presented from 010! Have the scores been divided by 10? Nevertheless, the clonidine groups mean pain score at 30 min is 40% below placebo (Figure 1). Surely this difference is clinically significant, even if, because the study is underpowered, it is not statistically significant.
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Sedation data are misrepresented. Clonidine increased eye opening time from 5 to 9 min and delayed extubation of the trachea from 6 to 9 min. These differences are not significant because of inadequate sample size.
Survival analysis shows clonidine delaying recovery in some patients. However, the discussion states "clonidine does not have clinically significance sedative...effects" and later "clonidine...neither delayed emergence from anesthesia nor had clinically significant sedative...effects"!
Reference
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