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LETTER TO THE EDITOR

Intrathecal Midazolam: Adverse Effects and Sources of Bias

Department of Anaesthesia, Monash Medical Centre, Monash University, Victoria, Australia, adam.tucker{at}med.monash.edu.au

In Response:

We appreciate the interest shown in our paper by Dr. Walker. The singular aim of this study—as stated in the introduction—was to investigate the efficacy of intrathecal midazolam (1). The monitoring of adverse effects was performed as a routine. Dr. Walker is quite correct in stating that this study was underpowered as an investigation of potential neurotoxicity; however, this was not the aim of the study. We direct Dr. Walker to the accompanying study, which addresses the issue of neurotoxicity; this is a cohort study assessing the safety of intrathecal midazolam in a large number of patients (2). Clearly the incidence of neurological sequelae, if it is associated with intrathecal midazolam at all, is better described by this larger study.

The effect of informing patients that the analgesia might take 15 minutes to work was a requirement of our ethics committee. It is unlikely that this introduced any bias, as this was applied equally to all groups, and as the observers and patients were unaware of the nature of the intrathecal injection, this would not have prolonged the duration of the active study groups in comparison to the placebo group. For this reason, the comparison between groups remains valid. Furthermore, we think that a request for analgesia at 30 or 90 minutes is unlikely to have been affected by an expectation of 15 minutes without analgesia. Finally, there were no patients that withdrew from the study, either before 15 minutes or later. The authors acknowledge that this should have been stated in the article and are grateful for the opportunity to clarify this point.

References

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]
2. Tucker AP, Lai C, Nadeson R, Goodchild CS. Intrathecal midazolam: I. A cohort study investigating safety. Anesth. Analg. 2004;98:1512–20.[Abstract/Free Full Text]

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