Comparison between continuous thoracic epidural and paravertebral blocks for postoperative analgesia in patients undergoing thoracotomy: meta-analysis of clinical trials^☆

Dear Editor:

The article entitled "Comparison between continuous thoracic epidural and paravertebral blocks for postoperative analgesia in patients undergoing thoracotomy: a systematic review", recently published in the Brazilian Journal of Anesthesiology, demonstrates the authors' concern to show the therapy effectiveness for anesthetic management of postoperative pain in chest surgeries. 1

Reading the scientific article arouses great interest to readers; however, some points need to be considered, such as: the software used for calculations, the sensitivity analysis method by successive meta-analysis, the use of mixed-effect model analysis, and the search to identify statistical heterogeneity.

The software used in the search was described in the sections Method and References, but the latter is incorrect, and it is impossible to identify the place where it is available and to have access to the software for future searches similar to this.

The method of successive meta-analysis was used by the authors at some point of the systematic review execution to perform the sensitivity analysis; however, the outcome of this analysis was not reported in the results or discussion, which did not clarify its real contribution in this systematic review. This method allows the identification of a likely source of statistical heterogeneity and the exclusion or not of the article, in an attempt to consolidate the results.2

The authors reported the use of random and fixed effect model for meta-analysis calculation; however, the random model was chosen to calculate the meta-analysis whenever I ² was greater than 30%. In the analysis of variables "assessment of pain at rest after 24 h and "incidence of hypotension", the value of I ² was lower than that proposed by the authors, not matching the research method description, and the results were also described by the random instead of fixed effect method. The article does not indicate whether this description of the results was due to consensus decision of the authors or a failure to conduct the research.

The authors considered the presence of heterogeneity as a research bias when they reported "(...) these results may have been biased by the included studies heterogeneity"; however, the presence of heterogeneity does not indicate bias in a systematic review. Tests of heterogeneity are used to determine whether differences between the included studies are genuine (heterogeneity) or if it occurred randomly during the analysis (homogeneity).3 If the differences occurred randomly, the results found in systematic reviews have more credibility, and if heterogeneity is found, the reasons should be carefully evaluated by the authors to consolidate the results and not only be considered a research bias.

It is noticed that the statistical heterogeneity present in most analysis was little explored by the authors, and it is possible to disagree with part of their conclusion that says: "From this systematic review, it is clear that epidural analgesia is associated with a higher incidence of arterial hypotension and urinary retention when it is used for lateral pain control after thoracotomy in adult patients, with evidence level 1A", as level 1A requires minimal or absent heterogeneity or that it is properly explored while performing a systematic review.

In short, I congratulate the authors for the article, which brings important results for the understanding of post-operative pain in thoracic surgery. Systematic review conclusions are less incisive regarding the clinical significance of its results when those of the included studies differ from each other.3

References

• 1. Júnior AdP, Erdmann TR, Santos TV, et al. Comparac¸ão entre bloqueios peridural e paravertebral torácicos contínuos para analgesia pós-operatória em pacientes submetidos a toraco-tomias: revisão sistemática. Rev Bras Anestesiol. 2013;63: 433-42.
• 2. Bueno NB. Explorando a heterogeneidade. In: Barbosa FT, edi-tor. Introduc¸ão à revisão sistemática: a pesquisa do futuro. 2013. Available at:Available at: http://bit.ly/lrs01 [accessed 02.01.14].
  » http://bit.ly/lrs01
• 3. Higgins JP, Thompson SG, Deeks JJ, et al. Measur- metaanalyses. BMJ. 2003;327: 557-60.

• 1
  ☆Universidade Federal de Alagoas, Maceió, AL, Brazil.

Publication Dates

• Publication in this collection
  Sep-Oct 2015