Rev. Bras. Anestesiol. vol.64 número5

RevBrasAnestesiol.2014;64(5):373---375

REVISTA

BRASILEIRA

DE

ANESTESIOLOGIA

LETTERS

TO

THE

EDITOR

Comparison

between

continuous

thoracic

epidural

and

paravertebral

blocks

for

postoperative

analgesia

in

patients

undergoing

thoracotomy:

meta-analysis

of

clinical

trials

Comparac

¸ão

entre

bloqueios

peridural

e

paravertebral

torácicos

contínuos

para

analgesia

pós-operatória

em

pacientes

submetidos

a

toracotomias:

meta-análise

de

ensaios

clínicos

DearEditor,

Thearticleentitled‘‘Comparisonbetweencontinuous tho-racic epidural and paravertebral blocks for postoperative analgesia in patients undergoing thoracotomy: systematic review’’,recentlypublishedintheJournalRevistaBrasileira

deAnestesiologia,bringsouttheauthors’concerntoshow

theanesthetictherapyeffectivenessfortreating postopera-tivepaininchestsurgery.1

Reading the scientific article arouses great interest in readers,however,somepointsneedconsideration:the soft-wareusedforcalculations,thesensitivityanalysismethod bysuccessivemeta-analysis,theuseofmixed-effectmodel analysis,andthesearchtoidentifystatisticalheterogeneity. The software usedfor the search was reportedin the Method and References, but the latter is incorrect, it is impossible toidentify theplace where it is available and tohaveaccesstothesoftwareforfuturesearchessimilarto this.

Successivemeta-analysiswasusedbytheauthorsatsome point of this systematic review execution to perform the sensitivityanalysis, however,the outcome ofthis analysis was not reported in the results or discussion, which did

DOIoforiginalarticle:http://dx.doi.org/10.1016/j.bjane.2013. 10.002

夽

Researchcenter:UniversidadeFederaldeAlagoas,Maceió,AL, Brazil.

notclarify its realcontribution in this systematic review. This methodallows the identification of the likelysource ofstatisticalheterogeneityandtheexclusionornotofthe includedarticle,inanattempttoconsolidatetheresults.2

Accordingtotheauthors,themodelsofrandomandfixed effectwereusedformeta-analysiscalculation;however,the randommodel was chosen tocalculate the meta-analysis wheneverI2_{wasgreaterthan30%.Intheanalysisofvariables}

‘‘assessmentofpainatrestafter24hours’’and‘‘incidence ofhypotension’’,the valueof I2 _{waslowerthanthat}

pro-posedby the authors, not matching the researchmethod description,andalsodescribingtheresultsbythemethod ofrandomeffectinsteadoffixedeffect.Thearticlereport doesnot allowidentifyingwhether thisdescription ofthe resultswasduetotheauthors’consensualdecisionoraflaw intheresearch.

Theauthorsconsideredthepresenceofheterogeneityas aresearchbiaswhentheyreported‘‘(...)theseresultsmay

havebeenbiasedbytheincluded studiesheterogeneity’’; however,thepresence ofheterogeneity does notindicate biasinasystematicreview.Testsforheterogeneityareused to determine whether differences between the included studies aregenuine (heterogeneity) or ifit occurred ran-domlyduringtheanalysis(homogeneity).3_{Ifthedifferences}

occurredrandomly,theresultsfoundinsystematicreviews have more credibility, and if heterogeneity is found, the reasonsshouldbecarefullyevaluatedbytheauthorsto con-solidatetheirresultsandnotonlybeconsideredaresearch bias.

It was noted that the statistical heterogeneity, which is present in most analyzes, was underexploited by the authors, and it is possible to disagree with part of their conclusion:‘‘From thissystematic review, it is clear that epiduralanalgesiaisassociatedwithahigherincidenceof arterialhypotensionandurinaryretentionwhen itis used forpaincontrol afterthoracotomy in adultpatients, with evidencelevel1A’’,aslevel1Arequiresminimalorabsent heterogeneityorthatheterogeneitiesareproperlyexplored whileconductingasystematicreview.

Inshort,Icongratulatetheauthorsforthearticle,which brings important results for understanding postoperative paininthoracicsurgery.Conclusionsofsystematicreviews arelessincisiveregardingtheclinical significanceoftheir resultswhenthoseoftheincludedstudiesdifferfromeach other.3

374 LETTERSTOTHEEDITOR

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

References

1.Júnior A de P, Erdmann TR, Santos TV, et al. Comparac¸ão entre bloqueios peridural eparavertebral torácicos contínuos paraanalgesiapós-operatóriaempacientessubmetidosa tora-cotomias: revisão sistemática. Rev Bras Anestesiol. 2013;63: 433---42.

2.BuenoNB.Explorandoaheterogeneidade.In:BarbosaFT,editor. Introduc¸ãoàRevisãoSistemática:a PesquisadoFuturo.2013, availableat:http://bit.ly/lrs01[accessed2.1.14].

3.HigginsJP,ThompsonSG,DeeksJJ,etal.Measuringinconsistency inmetaanalyses.BMJ.2003;327:557---60.

FabianoTimbóBarbosaa,∗,

TatianaRosaBezerraWanderleyBarbosab_,

RafaelMartinsdaCunhac

a_{UniversidadeFederaldeAlagoas,Maceió,AL,Brazil}

b_{CentroUniversitárioUnisebInterativo,Maceió,AL,Brazil}

c_{HospitalUnimed,Maceió,Maceió,AL,Brazil}

∗_{Correspondingauthor.}

E-mail:[email protected](F.T.Barbosa).

Availableonline30July2014