RevBrasAnestesiol.2015;65(4):310---311
REVISTA
BRASILEIRA
DE
ANESTESIOLOGIA
OfficialPublicationoftheBrazilianSocietyofAnesthesiologywww.sba.com.br
LETTERS
TO
THE
EDITOR
Effect
of
head
rotation
on
intraocular
pressure
in
prone
position:
randomized
study
夽Efeito
da
rotac
¸ão
da
cabec
¸a
na
pressão
intraocular
em
decúbito
ventral:
estudo
randomizado
DearEditor,
Thearticle entitled ‘‘Effectof headrotationon
intraocu-larpressureinproneposition:randomizedstudy’’recently
publishedintheBrazilianJournalofAnesthesiologycallsthe
reader’sattentiontotheimportanceofthe goodpractice
of anesthesiain order toprevent serious complication to
patientsundergoingsurgeryinproneposition,whichisthe
lossofvision.1
The important items that demonstrate quality in
randomized clinical trials are randomization, blindness,
losses, and exclusions.2 These items and the statistical
analysis performed in the article deserve some
com-ments.
Randomization allows the equal distribution of both
knownandunknowncharacteristicsbetweenstudygroups.2
The randomization method was not mentioned by the
authors who cited only the creation of a list, so that
patient assignment to groups may have been a
selec-tion bias. Inadequate reporting hinders the validity of
results.
Blindnessisatechniqueusedtopreventtheinterference
of the investigators’ subjectivities during the research.2
The blind nature of the study was not mentioned by the
authors.Itwasjustreportedthattheophthalmologistwho
DOIoforiginalarticle:
http://dx.doi.org/10.1016/j.bjane.2012.03.008
夽
StudyperformedatUniversidade FederaldeAlagoas,Maceió, AL,Brazil.
verifiedthedatainthepreoperative periodwasthesame
for all patients. The primary end-point for the analysis
was the postoperative period, as the main cause of loss
ofvisionisintraoperativenerveischemia.3The knowledge
of patient assignment groups by the person responsible
for postoperativedatacollectionmayhave influencedthe
results.
Losses and exclusions were not commented by the
authors, but it may be assumed that theydid not occur.
Thestudyseemstohavehadnofollow-uptime,andsome
patientsmayhavepresentedsymptomsofresearchinterest
andhavenotbeenproperlyanalyzed.
The description of sample size calculation was not
made in detail and does not allow to be reproduced
to access the statistical accuracy of the data analysis.
The frequency of vision loss reported by the authors
is 0.05% and it seems to have been used for the
cal-culation. The increased intraocular pressure magnitude,
which is reported in the objective section, should be
usedtoestimatethesamplesize.Theinadequate
descrip-tion of sample size calculation makes it possible to
have a probability of a type-I error occurrence in this
study.
Statistical tests were not described in detail, so that
severaltestshaveindicationforpairedsamplesandthe
sit-uationpresentedbytheauthors.Theresultsmaybemore
reliablewhenthetestsusedareappropriate.
Theauthorsemphasizedthepossiblebeneficialeffectsof
theirfindingsforpatientswithglaucoma,butthisinference
couldnothavebeenmade,asthisgroupofpatientswaspart
oftheexclusioncriteriaofthisstudy.
Thestudyhighlightstheneedforgreatercareinthe
exe-cution of anesthesiain patients who remainin the prone
position, regarding intraocular pressure and alsoof other
studieswheresamplesreceivebetterrandomizationmethod
descriptionandadequatestatisticalpower.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
LETTERSTOTHEEDITOR 311
References
1.Nuri Deniz M,Erakgün A, SertözN, etal. Theeffectof head rotationonintraocularpressureinproneposition:arandomized trial.RevBrasAnestesiol.2013;63:209---12.
2.JadadAR, MooreRA,Carroll D,et al.Assessingthequalityof reportsofrandomizedclinicaltrials:isblindingnecessary? Con-trolClinTrials.1996;17:1---12.
3.WalickKS,KraghJEJr,Ward JA,etal.Changesinintraocular pressure duetosurgicalpositioningstudyingpotentialriskfor postoperativevisionloss.Spine.2007;32:2591---5.
FabianoTimbóBarbosaa,∗,
TatianaRosaBezerraWanderleyBarbosaa,
RafaelMartinsdaCunhab
aCentroUniversitárioUnisebInterativo,Maceió,AL,Brazil
bHospitalUnimed,Maceió,Maceió,AL,Brazil
∗Correspondingauthor.
E-mail:fabianotimbo@yahoo.com.br(F.T.Barbosa).
Availableonline29April2015
http://dx.doi.org/10.1016/j.bjane.2014.02.019
A
question
about
ropivacaine
for
unilateral
spinal
anesthesia:
hypobaric
solution
Uma
questão
sobre
ropivacaína
para
raquianestesia
unilateral:
soluc
¸ão
hipobárica
DearEditor,
Iamadoctorfromdepartmentofanesthesiology,Shanghai
Sixth People’s hospital, Shanghai Jiao Tong University,
Shanghai, China.I have many interests in ropivacainefor
unilateral spinal anesthesia: hypobaricsolution. SoIhave
readyourliteraturetitled‘‘Ropivacaineforunilateralspinal
anesthesia; hyperbaric or hypobaric?’’1 In this article, it
wasmentionedthat‘‘groupHypo(n=30)received11.25mg
ofropivacaine(7.5mgmL−1)+2mLofdistilledwater
(den-sityatroomtemperaturewas0.997)’’.Becauseropivacaine
(7.5mgmL−1) is isobaric solution and density of distilled
water is 1, whythe density of mixed solutionwas 0.997?
Imadethesemixedsolutiontosurveythedensity,andthe
densitywas1.006.Pleasetellme theanswer, andtellme
yourwaytomakethemixedsolutionandsurveythedensity.
Thankyouverymuch.
Conflicts
of
interest
Theauthordeclaresnoconflictsofinterest.
Reference
1.CantürkM, KılcıO, OrnekD,et al.Ropivacainefor unilateral spinalanesthesia;hyperbaricorhypobaric?RevBrasAnestesiol. 2012;62:298---311.
Da-QiangZhao
DepartmentofAnesthesiology,ShanghaiJiaotong UniversityAffiliatedSixthPeople’sHospital,Shanghai, China
E-mail:hellinspy@sohu.com(D.Zhao).
Availableonline11October2014
