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Comparison of PCEA vs nurse-administered epidural infusion for postoperative analgesia
- Jeremy J Nightingale, Bernard Higgins, Reader in Biomedical Statistics (30 March 2007)
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Comparison of PCEA Vs nurse-administered epidural infusion for post operative analgesia in patients
- Robert W Chambers (15 March 2007)
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Jeremy J Nightingale, Consultant Anaesthetist Portsmouth Hospitals NHS Trust, Bernard Higgins, Reader in Biomedical Statistics
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Editor - Thank you for the opportunity to respond to Dr. Chambers' comments. As clearly indicated in the text and stated in the results section, median scores were reported and compared using a Mann Whitney U test. We feel that he may be confused by the fact that the "mean" score of repeated measurements per patient was used as one of the outcome measures and thus formed the unit of measurement, and not the summary statistic for comparison. More precise wording may have helped, stating that the median of the mean scores per patient was found to be significantly lower in the PCEA group. Dr. Chambers also feels that presenting means and standard deviations is inappropriate. We disagree on three counts. Firstly, means and standard deviations are often used to inform sample size calculations, even in situations in which non-parametric tests are thought to be necessary. We felt that publishing these figures might help others in the quest to design studies where the same measurement tool is used. Secondly, means and standard deviations are more easily combined through meta-analyses to provide evidence from several studies in systematic reviews. Finally, this study might be considered sufficiently large to justify the use of parametric tests to compare the summary outcome measures. The Visual Analog Scale was not employed in this study and therefore parametric analysis was not employed. Conflict of Interest:None declared |
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Robert W Chambers, SHO Anaesthetics Winchester, UK
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Editor-I read with interest the study comparing Patient controlled epidural infusion with nurse administered epidural infusion for patients undergoing colonic resection 1. The authors correctly identify that the four-point verbal rating scale ( VRS ) used to assess post operative pain would produce non parametric or quantative, ordinal data and used the Mann-Whitney U-test for statistical analysis. The authors also describe the mean and standard deviation for the VRS scores which are parametric statistics and not appropriate for this data. Instead the median and inter-quartile range should be used to describe the central tendency and spread of non parametric data. The conclusion that MEAN summary pain scores are significantly lower in the PCEA group is therefore inaccurate. The Visual Analogue Scale which utilises a 100mm continuous scale to assess pain could be described as Quantative, ratio data and may be more appropriate for parametric analysis. 1. Nightingale JJ, Knight MV, Higgins B, Dean T. Randomized, double- blind comparison of patient-controlled epidural infusion vs nurse- administered epidural infusion for post operative analgesia in patients undergoing colonic resection. Br J Anaesth 2007; 98: 380-384 Conflict of Interest:None declared |
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