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LETTER TO THE EDITOR

Intraoperative Clonidine Administration to Neurosurgical Patients

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 0–100 but in Table 3 is presented from 0–10! Have the scores been divided by 10? Nevertheless, the clonidine group’s 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.

View larger version (23K): [in this window] [in a new window]   Figure 1. Pain scores in patients receiving either clonidine 3mcg kg–1 or saline placebo. Data are mean ± sd. Pre = baseline score before surgery. Times are minutes after the end of anesthesia. Note that there are substantial differences in mean pain score between the two groups however the small sample size and large standard deviation mean that the differences do not achieve statistical significance.

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

1. Stapelfeldt C, Lobo EP, Brown R, Talke PO. Intraoperative clonidine administration to neurosurgical patients. Anesth Analg 2005;100:226–32.[Abstract/Free Full Text]

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