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Correspondence
Letter to the editor
To the Editor:Apfel and colleagues recently published a systematic review and
meta-analysis on acetaminophen, specifically looking at outcomes otherthanpain,andsuggestedaninherentantiemeticeffectofthisagentonthebasis of their findings [1]. When commenting on our 2011 Cochrane re-view article [11], they note, ‘‘At the time this manuscript was being writ-ten, several systematic and narrative reviews have been published, allnoting that i.v. acetaminophen does not reduce PONV. . . This includes aCochrane review that identified only 4 papers. . . It is disconcerting thatso many studies had not been identified in the Cochrane review, despitethe explicit reporting and application of fairly complex search strategies.Further research into why this happens is certainly indicated if we wantto improve the reliability of systematic reviews.’’
Although we do not believe any review to be flawless or beyondcriticism, including ours, we do believe that this statement deservescomment and correction. Rather than 4 articles, our review actuallycontained 36 studies, and we are wondering whether the authors mis-read our reference. Subject to the different inclusion criteria for each ofthese 2 reviews, we did not include some of the studies used in the re-view of Apfel et al., and vice versa. For example, we chose to only ana-lyze articles that contained pain as a primary or secondary outcome. Itmay be a strength that Apfel and colleagues decided to search for addi-tional benefits (PONV) of the drug outside of its main indication (pain)as a primary outcome, but this approach could also be questioned.
Further, the authors’ criticism of Cochrane reviews in generalmay not be warranted. It has been demonstrated in several studiesthat Cochrane reviews are consistently of greater methodologicalquality than industry-sponsored systematic reviews [3–9]. Forexample, although we do not believe that it would have a majorbearing on the findings of Apfel and colleagues’ article, their re-view does contain unit-of-analysis errors, where the placebo grouphas been counted twice for the included studies of Arici et al. [2]and Toygar et al. [10] within each analysis in both the meta-anal-yses of nausea and vomiting (Figures 2 and 3).
We conclude that Apfel and colleagues’ review has great valuefor several reasons. However, the differences in findings betweentheir article and ours are based on differences in methodologyrather than any fundamental flaw in our earlier review or anyoverall issue with Cochrane reviews. Both studies contribute validfindings to the scientific body of evidence in their respective waysthat should be critically appreciated by readers.
Conflict of interest statement
The authors report no conflict of interest.
References
[1] Apfel CC, Turan F, Souza K, Pergolizzi J, Hornuss C. Intravenous acetaminophenreduces postoperative nausea and vomiting: a systematic review and meta-analysis. PAIN� 2013;154:677–89.
[2] Arici S, Gurbet A, Turker G, Yavascaoglu B, Sahin S. Preemptive analgesiceffects of intravenous paracetamol in total abdominal hysterectomy. AgriDergisi 2009;21:54–61.
[3] Delaney A, Bagshaw SM, Ferland A, Laupland K, Manns B, Doig C. The quality ofreports of critical care meta-analyses in the Cochrane Database of SystematicReviews: an independent appraisal. Crit Care Med 2007;35:589–94.
[4] Farmer SE, Wood D, Swain ID, Pandyan AD. Assessment of risk of bias inrehabilitation reviews. Int J Rehabil Res 2012;35:317–22.
[5] Jadad AR, Cook DJ, Jones A, Klassen TP, Tugwell P, Moher M, Moher D.Methodology and reports of systematic reviews and meta-analyses: acomparison of Cochrane reviews with articles published in paper-basedjournals. JAMA 1998;280:278–80.
[6] Jørgensen KJ, Katja L, Maric KL, Tendal B, Faurschou A, Gøtzsche PC. Industry-supported meta-analyses compared with meta-analyses with non profit or nosupport: differences in methodological quality and conclusions. BMC Med ResMethodol 2008;8:60.
[7] Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG. Epidemiology andreporting characteristics of systematic reviews. PLoS Med 2007;4:e78.
[8] Moja LP, Telaro E, D’Amico R, Moschetti I, Coe L, Liberati A. Assessment ofmethodological quality of primary studies by systematic reviews: results ofthe meta quality cross sectional study. BMJ 2005;330:1053.
[9] Olsen O, Middleton P, Ezzo J, Pete C, Gøtzsche PC, Hadhazy V, Herxheimer A,Kleijnen J, McIntosh H. Quality of Cochrane reviews: assessment of samplefrom 1998. BMJ 2001;323:829–32.
[10] Toygar P, Akkaya T, Ozkan D, Ozel O, Uslu E, Gumus H. Does iv paracetamolhave preemptive analgesic effect on lumbar disc surgeries? Agri2008;20:14–9.
[11] Tzortzopoulou A, McNicol ED, Cepeda MS, Francia MB, Farhat T, Schumann R.Single dose intravenous propacetamol or intravenous paracetamol forpostoperative pain. Cochrane Database Syst Rev 2011:CD007126.
Ewan McNicol⇑Department of Anesthesiology, Tufts Medical Center, 800
Washington Street, Boston, MA 02111, USADepartment of Pharmacy, Tufts Medical Center, Box 420, 800
Washington Street, Boston, MA 02111, USA⇑ Tel.: +1 617 241 0655; fax: +1 617 636 4633.
E-mail address: [email protected]
Roman SchumannDepartment of Anesthesiology, Tufts Medical Center,
800 Washington Street, Boston, MA 02111, USA
0304-3959/$36.00 � 2014 International Association for the Study of Pain. Published byElsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.pain.2013.12.026
w w w . e l s e v i e r . c o m / l o c a t e / p a i n
PAIN�
152 (2014) 1174–1180
Response to letter to the Editor
The Cochrane Collaboration has pioneered the field of ‘‘evi-dence-based medicine’’ and has established a rigorous, transpar-ent, and collaborative approach for conducting systematicreviews and meta-analyses to minimize any type of bias. Cochranereviews are known to provide health care professionals, policymakers, and patients with valuable information of consistentlyhigh methodological quality. Thus, we appreciate the Cochrane re-view on intravenous propacetamol and paracetamol [15], and thevery similar systematic review and meta-analysis published inthe British Journal of Anaesthesia [9], which clearly demonstrated
the analgesic and opioid-sparing effects of both non-opioidanalgesics.
We know that opioids are associated with a number of side ef-fects or adverse events, ranging from nausea, vomiting, and seda-tion to respiratory depression and death [11]. We also know thatthose side effects are generally dose related [12]. Not surprisingly,the perioperative use of non-steroidal anti-inflammatory drugs(NSAIDs) is associated with less pain, reduced opioid consumption,and fewer opioid-related adverse events such as postoperativenausea and vomiting (PONV) [8].
Thus, when several narrative and systematic reviews concludedthat intravenous acetaminophen reduces pain and opioid con-sumption, but not opioid-related adverse events such as PONV,we suspected this to be a power problem, leading readers to con-fuse insufficient evidence for reduced adverse events (ie, we don’tknow) with evidence for the absence of reduced adverse events (ie,apparently it does not work) [4].
The Cochrane review included a total of 36 papers that werefocused on studies for acute postoperative pain management. Ofcourse, not all reported data on PONV, but we were surprised thatthe ‘‘Cochrane review identified only 4 papers’’ in that regard.Furthermore, at the time of the last search of the Cochrane re-view, 19 studies had already been published reporting on the dif-ferences in PONV, 8 of which did report on postoperative pain butwere not included for the analysis on PONV [2,13,3,10,6,5,7,14].Of course, decisions on whether to include or exclude studiesmay not always be obvious, and we did not intend to cast anyblame in our systematic review [1] when we said that the ‘‘Coch-rane review identified only 4 papers.’’ Likewise, one could arguewhether not dividing number of patients in a control group bythe number of comparisons is double counting or whether divid-ing the control group by the number of comparison is overtlyconservative.
Instead, we were intrigued to find that ‘‘IV acetaminophen re-duced nausea when given prophylactically either before surgery,0.54 (0.40–0.74), or before arrival in the postanesthesia care unit,0.67 (0.55–0.83),’’ [1] with an effect size of 0.7 or less (ie, a riskreduction by 30% or more), which is of magnitude similar to thatof known antiemetics. Of course, if there is interest in includingour PONV data in future Cochrane reviews, we would be more thanhappy to share the data.
References
[1] Apfel CC, Turan A, Souza K, Pergolizzi J, Hornuss C. Intravenous acetaminophenreduces postoperative nausea and vomiting: a systematic review and meta-analysis. PAIN� 2013;154:677–89.
[2] Cattabriga I, Pacini D, Lamazza G, Talarico F, Di Bartolomeo R, Grillone G,Bacchi-Reggiani L. Intravenous paracetamol as adjunctive treatment forpostoperative pain after cardiac surgery: A double blind randomizedcontrolled trial. Eur J Cardiothorac Surg 2007;32:527–31.
[3] Fadly A, Ali A, Ghonem I. Intravenous paracetamol, morphine and theircombination for postoperative pain after release of post burn neckcontractures. Bas J Surg 2006;12:101.
[4] Gatchel RJ, McGeary D. Cochrane Collaboration-based reviews of health-careinterventions: are they unequivocal and valid scientifically, or simplynihilistic? Spine J 2002;2:315–9.
[5] Hong JY, Kim WO, Koo BN, Cho JS, Suk EH, Kil HK. Fentanyl-sparing effect ofacetaminophen as a mixture of fentanyl in intravenous parent-/nurse-controlled analgesia after pediatric ureteroneocystostomy. Anesthesiology2010;113:672–7.
[6] Jokela R, Ahonen J, Seitsonen E, Marjakangas P, Korttila K. The influence ofondansetron on the analgesic effect of acetaminophen after laparoscopichysterectomy. Clin Pharmacol Ther 2010;87:672–8.
[7] Kilicaslan A, Tuncer S, Yuceaktas A, Uyar M, Reisli R. The effects of intravenousparacetamol on postoperative analgesia and tramadol consumption incesarean operations. Agri 2010;22:7–12.
[8] Marret E, Kurdi O, Zufferey P, Bonnet F. Effects of nonsteroidalantiinflammatory drugs on patient-controlled analgesia morphine side
effects: meta-analysis of randomized controlled trials. Anesthesiology2005;102:1249–60.
[9] McNicol ED, Tzortzopoulou A, Cepeda MS, Francia MB, Farhat T, Schumann R.Single-dose intravenous paracetamol or propacetamol for prevention ortreatment of postoperative pain: a systematic review and meta-analysis. Br JAnaesth 2011;106:764–75.
[10] Memis D, Inal MT, Kavalci G, Sezer A, Sut N. Intravenous paracetamol reducedthe use of opioids, extubation time, and opioid-related adverse effects aftermajor surgery in intensive care unit. J Crit Care 2010;25:458–62.
[11] Okie S. A flood of opioids, a rising tide of deaths. N Engl J Med2010;363:1981–5.
[12] Roberts GW, Bekker TB, Carlsen HH, Moffatt CH, Slattery PJ, McClure AF.Postoperative nausea and vomiting are strongly influenced by postoperativeopioid use in a dose-related manner. Anesth Analg 2005;101:1343–8.
[13] Salihoglu Z, Yildirim M, Demiroluk S, Kaya G, Karatas A, Ertem M, Aytac E.Evaluation of intravenous paracetamol administration on postoperative painand recovery characteristics in patients undergoing laparoscopiccholecystectomy. Surg Laparosc Endosc Percutan Tech 2009;19:321–3.
[14] Toygar P, Akkaya T, Ozkan D, Ozel O, Uslu E, Gumus H. Does iv paracetamolhave preemptive analgesic effect on lumber disc surgeries? Agri2008;20:14–9.
[15] Tzortzopoulou A, McNicol ED, Cepeda MS, Francia MB, Farhat T,Schumann R. Single dose intravenous propacetamol or intravenousparacetamol for postoperative pain. Cochrane Database Syst Rev2011;CD007126.
Christian C. ApfelUniversity of California–San Francisco, Anesthesia, Perioperative Care,
Epidemiology and Biostatistics, San Francisco, CA, USATel.: +1 415 680 8266.
E-mail address: [email protected]
DOI of original article: http://dx.doi.org/10.1016/j.pain.2013.12.026http://dx.doi.org/10.1016/j.pain.2014.01.0280304-3959/� 2014 Published by Elsevier B.V. on behalf of International Association forthe Study of Pain.
Letter to the Editor
To the Editor:We read with interest the article by Kim et al. [4] involving
pain and hyperalgesia in patients undergoing staged bilateral to-tal knee arthroplasty (TKA). It is well established that injury,including surgery, induces central sensitization which manifestsin both primary and secondary hyperalgesia [13]. Also relevantis evidence of hyperalgesia induced by repeat injury of the samebody part at two points in time [2]. Clinical evidence of tertiaryor remote hyperalgesia, in which injury at one body site pro-duces pain at another, distant site has also been established[13]. Less common, but no less important, is remote hyperalge-sia induced by injuries at different points in time [9,10]. In a cle-ver test of this latter phenomenon, Kim et al. evaluated 30patients undergoing staged bilateral TKA in which the left orright knee was selected at random for the first TKA (TKA1)and was followed by identical surgery of the other knee(TKA2) one week later. The results showed that rest pain, move-ment-evoked pain, and analgesic consumption were significantlygreater in the second knee 24 and 48 hours after TKA2 than inthe first knee 24 and 48 hours after TKA1. The authors concludethat the enhanced pain sensitivity in the second knee was evi-dence of ‘‘tertiary’’ hyperalgesia (ie, remote hyperalgesia) duein part to central sensitization of subcortical and other brain re-gions induced by the noxious inputs arising from TKA1. A re-lated finding has been reported in a rodent model involvingneonatal paw incision. Rats that had been exposed to a pawincision at 3 days of age, displayed greater hyperalgesia in re-
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