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LETTER TO THE EDITOR

Intrathecal Midazolam: Adverse Effects and Sources of Bias

Department of Anaesthesia, Royal Brompton Hospital, London, UK, llwalker{at}ukonline.co.uk

To the Editor:

I was interested to read the paper by Tucker et al. (1), which aims to assess the efficacy of intrathecal midazolam in potentiating the effect of intrathecal fentanyl without causing adverse effects. Unfortunately, as stated in the Discussion in their article, given the sample sizes used it was not possible to make valid comments about the incidence of adverse effects. Therefore, while it is reasonable to comment on analgesic effects, it is not feasible to subsequently draw any conclusions about the relationship between adverse effects and the study drugs as mentioned in their discussion.

In addition, I feel that two other aspects of the study require further clarification, both of which might have introduced bias, and which could invalidate the findings of an enhanced analgesic effect. First, informing patients that the injection may take up to 15 minutes to work could have exerted considerable influence on the time to request for supplemental analgesia, an important potential source of bias.

Second, the authors imply that only those requesting further analgesia more than 15 minutes after intrathecal injection were considered to have "participated completely" in the study. Were those requesting analgesia before this time specifically excluded from the trial, again potentially skewing results?

1. Tucker AP, Mezzatesta J, Nadeson R, Goodchild CS. Intrathecal midazolam: II. Combination with intrathecal fentanyl for labor pain. Anesth Analg 2004;98:1521–7.[Abstract/Free Full Text]

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