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OR IGINA L ARTICLEThe effect of buffering on pain and duration

of local anesthetic in the face:A double blind^ randomized controlled trial

Oluwa to la AfolabI BSc MAMD Amanda Murphy BScMD Bryan Chung MD PhD Do nald H Lalonde MSc MDO Afolabi, A Murphy, B Chung, D Lalonde. Theeffect of buffering on pain and duration of localanesthetic in the face: A double-blind, randomizedcontrolled trial. Can J Plast Surg 2 01 3; 21 4) :2 09 -2 1 2 .

L'effet du tamponnage sur la douleur et la dured'un anesthsique local dans le visagealatoire et contrl double insu un essaiTHERAPEUTIC

B A C K G R O U N D : The acidity of lidocaine preparations is believed tocontribute to the pain of local anesthetic injection.OBJECTIVE: To investigate the effect of buffering lidocaine on the painof injection and duration of anestbetic effect.METHODS:A double-blind, randomized trial involving 44 bealthy vol-unteers was conducted. Tbe upper lip was injected witb a solution of:lidocaine 1% (Xylocaine, AstraZeneca, Canada, Inc) with epinepbrine;and lidocaine 1% witb epinephrine and 8.4% sodium bicarbonate.Volunteers reported pain of injection and duration of anestbetic effect.RESULTS: Twenty-six participants found the unbuffered solution to bemore painful. Fifteen participants found the buffered solution to be morepainful; tbe difference was not statistically significant. Twenty-one volun-teers reported duration of anestbetic effect. Tbe buffered solution providedlonger anesthetic effect than the unbuffered solution (P=0 .004).C O N C L U SIO N : Altbougb buffering increased tbe duration of lidocaine'sanestbetic effect in this particular model, a decrease in tbe pain of theinjection was not demonstrated, likely due to limitations of the study.Key Word s : Lidocaine; Local anesthesia; Pain; Sodium bicarbonate

HISTORIQUE : On pense que l'acidit des prparations de lidocainecontribue la douleur de l'injection d'un anesthsique local.OBJECTIF : Examiner l'effet de la lidocaine tamponne sur la douleur del'injection et la dure de l'effet anestbsique.METHODOLOGIE : Les chercheurs ont men une tude alatoire double insu auprs de 44 volontaires en bonne sant. Ceux-ci se sont faitinjecter dans la lvre suprieure une solution de lidocaine % (Xylocaine,AstraZeneca Canada, Inc.) associe de l'pinpbrine, de mme qu'unesolution de lidocaine % associe de l'pinpbrine et du bicarbonate desodium 8,4 %. Les volontaires ont rendu compte de la douleur de l'injectionet de la dure de l'effet anestbsique.RESULTATS: Vingt-six participants ont trouv la solution non tamponneplus douloureuse, tandis que 15 participants ont trouv la solution tam-ponne plus douloureuse. La diffrence n'tait pas statistiquem ent signifi-cative . Vingt et un volontaires on t prcis la dure de l'effet a nestb siqu e.La solution tamponne procurait un effet anestbsique plus long que lasolution non tamponne (P=0,004).CONCLUSION : Mm e si le tamp onnag e prolongea it l'effet anesths iquede la lidocaine dans ce modle, il ne s'associait pas une diminution de ladouleur de l'injection, probablement cause des limites de l'tude.

L idocaine, the most common choice for most plastic surgeons, is aneffective anesthetic with a rapid onset and an excellent safetyrecord. Unfortunately, the administration of l idocaine can be painful.Many factors influence the pain of injection, including the intro-

ductio n of the nee dle, the rate of injectioti , the pressure from th e fluiddistention ofthe t issue (1) and th e pH ofthe l idocaine solution (2). Aweakly basic amide, lidocaine is unstable at its pH of 7.9; therefore, itis prepare d in acidic formulations to increase its stability and shelf life.Th e res ultant p H is typically 4.7 (2 ). This is well below physiologicalpH , and the acidity can cause t issue irri tation that may be perceived bypatients as a st inging or burning pain (2,3).

Several studies have investigated the possibil i ty of reducing pain bybuffering lidocaine to reduce its acidity. Sodium bicarbonate is awidely used and safe alkalizer that is metabolized by the kidney.Currently, both buffered l idocaine and unbuffered l idocaine are con-sidered to be standards of care for local anesthesia, with apptoxim ately5 3 % of emergency physicians routinely adding sodium bicarbonate tolidocaine (4). While studies investigating the effect of buffering invarious anatomical si tes have been performed, a review of the l i tera-ture reveals a dearth of research on buffered lidocaine for facial surgery- the most common locat ion for plastic surgery procedures.

The face is a unique area, with several anatomical subunits of highlysensitive specialized tissue, making it possibly different from otherregions of the body. It is, therefore, important that local anesthesia forthe face be specifically studied. Th e prese nt study examine d the effect ofbuffered lidocaine on p ain sensation in the upper lip. It also investigatedthe effect of buffering o n the dura tion of anesth etic effect.

METHODSAfter obtaining Research Ethics Board approval from the Saint JohnRegional Hospital (Saint John, New Brunswick), adult health careworkers were recruited as volunteers. Volunteers were excluded firomthe study if pregnant, or there was a history of surgery or t rauma to theface, renal disease, true allergy or sensitivity to local anesthesia.Informed consent was obtained.

Subjects were randomly allocated via a block-randomized sequence.The sequence was generated by a coinvestigator not involved in theinjections. The maximum block size was 12. Both the side ofthe face tobe injected first as well as the order of buffered versus unbuffered solu-tiotis to be injected first were randomized. Sequence concealment wasachieved using opaque, sealed envelopes. Both injector and subject wereblinded to the nature of the solutions; one coinvestigator drew up th esolutions and provided them to another coinvestigator to be injected.The primary outcome of the present study was pain reduction asrated by a single question, W hich injection hu rt the most? . Based onprerecruitment sample size and power calculations, 43 participantswere set as the target.

A 10:1 mixture of 1% lidocaine (Xylocaine, AstraZeneca Canada,Inc) with 1:100 000epinephrine and 8.4% sodium bicarbonate was theexperimental solution (Figure 1). This combination has been shown toraise the pH of lidocaine to physiological pH (2). Xylocaine 1% with1:100 000 epinephrine without sodium bicarbonate was used as a con-trol solution. Solutions were used within 1 h of preparation.

The injection site was in the upper lip mid-way between the lipborder and the lateral alar base (Figure 2). A 30-gauge needle on a 3 mL

Division of Plastic Surgery, Dalhousie University, Halifax, Nova ScotiaCorrespondence: D r Oluwatola Afolabi, Suite 206A 353 St Paul Avenue, Brantford, Ontario N3R 4N3.

Telephone 5l9 770 4224, fax 5l9 770A220, email tola.afolahi@gmailcom

Can J Plast Surg Vol 21 No 4 Winter 2013 2013 Canad ian Society of Plastic Surgeons. All rigbts reserved 2 0 9

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Figure 1 Drugs that were used 1 lidocaine (Xylocaine, AstaZenecaCanada, Inc) 1 with 1:100,000 epinephrine (left) and 8.4 sodiumbic rbon te (right)

Figure 2 Injection site of each solution in the upperlipisindic tedby 'x

syringe was used to inject v olunteers with 1 mL of test solution on o neside and the same volume of control solution on the other. The twoinjections were hoth performed within 5 min of one another in eachsubject. The subject was then asked to complete a short questionnairethat assessed the pain associated with the injection (Figure 3). Part I ofthe questionnaire asked volunteers which injection was most painful.Part II asked the participants to rate the pain of each injection on a10-point visual numerical pain scale (V NS ). Part IIIasked participantshow long th e anest hetic effect of each injection lasted. Part I and IIwere submitted within minutes of the injection; part III was returnedon a subsequent day.StatisticsAll data were analyzed in an intention-to-treat manner. A one-sampletest of proportions was used to comp are th e primary outcom e, which wasthe proportion of subjects who found the buffered solution to be lesspainful to those subjects who did not find the buffered solution less pain-ful (part 1). Subjects w ho found bot h solution s equally painful wereclassified as not experiencing pain reduction with buffered lidocaine.

Paired t tests were used to compare both the VNS pain ratingscores between buffered and nonbuffered lidocaine as well as durationof effect of each solution. The difference between the buffered andnonbuffered lidocaine V NS scores was also calculated by subtr actingthe pain VNS of the nonbuffered lidocaine from the pain VNS of thebuffered lidocaine. A 95 CI was calculated around the mean differ-ence in VNS score to provide a measurement of precision; P

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Effect of buffering on pain and duration of local anesthetic in the face

Subjecsn)

3

25

2

5

5

59

lain

34

BufferedMost painful injection

7

No difference

Figure 5 Effect of buffering on pain sensation o f lidocaine injectionP=0.23)

Twenty-six (59 ) participants foun d the nonbuffered solution tobe more painful. Fifteen (34 ) participants found the buffered solu-tion more painful (Figure 5). Tbree (7 ) subjects found both injec-tions equally painful. Tbe difference was not statistically significant(z=-1.2;P=0.23).Th e mean pain rating for tbe buffered injectionwas4 3(range 0 to 8).The mean pain rating of tbe plain injection was 5.1 (range of 2to 9).Tbe mean difference was 0.83 and was not statistically significant(t=0.23;P=0.82). Tbe95 Cl around the m ean difference in VNS forpain of injection between tbe buffered and nonbuffered lidocaine was0.16 to 1.49.Twenty-one volunteers (48 response rate) returned tbe third partof tbe questionnaire, wbicb focused on duration of anestbetic effect.The magnitude of effect varied (Figure 6). Tbe mean duration of anes-tbetic effect for tbe buffered side was 268.9 min (range 135 min to1282 min). Tbe mean duration of tbe anestbetic effect for tbe unbuffered side was 219.7 min (range 0 min to 1282 min). Tbe mean differ-ence was 49.2 m in. Tbe buffered solution provided significantly longeranesthetic tban did tbe unbuffered solution (t=3.27; P=0.004).

DISCUSSIONTbe present study deviated ftom most publisbed reports in that it didnot demonstrate a statistically different reduction in pain witb buf-fering of local ane sthetic, although on average, pain scores were lowerfor tbe buffered lidocaine side tban tbe nonbuffered. It is possible tbattbe effect of buffering is overestimated in tbe face, a particularly sensi-tive area witb numerous nerve endings. Furtbetmore, it is possible tbatbuffering local anestbetic in th e face reduces pain by an order of mag-nitude that is too small to be detected by our cbosen sample size,despite prerecruitment power calculations. Otber possible limitationsof out study include tbe fact tb at tbe injections were performed by twoseparate injectors. We did our best to standardize tbe angle of tbeneedle penetration, tbe amount of'wobbling' of tbe needle in tbe skinbefore tbe needle site was anestbetized (syringe stabilization) and tberate of injection of the anestbetic.Several factors b ave been sbown to affect tbe p ain of administeringlocal anestbesia. Smaller needle sizes, perpendicular needle angle totbe skin, slower speed of injection and warming the solution ate allfactors tbat decrease tbe pain of injection (1,5-7).A factor th at bas been investigated by several studies is altering tbepH of lidocaine to be more compatible witb pbysiological pH. Stockpreparations of Xylocaine are typically pH 4.7. Tbis is 1000 times moreacidic tban physiological pH. The addition of sodium bicarbonate toxylocaine can increase tbe pH to 7.4, wbicb is consistent with physio-logical pH (2,3).In a double-blind, cross-over trial study for open carpal tunneldecompression, Vossinakis et al (8) reported statistically lower rate ofpain w itb buffered lidocain e in a sample size of21patients (42 bands).

Burns et al (9) reported similar findings in tbeir double-blind study.Sixty volunteers were recruited in a cross-over trial; 65 of partici-pants found tbe unbuffered solution to be mote painful. Firky et al 10)

Figure6)Duration of nesthetic effectfor bufferedlidoc ine red diamond)and nonbuffered lidoc ine black square) (P=0.004)

demonstrated a significant reduction in pain wben buffeted local anes-thetic was used compared w ith unbuffered lidocaine for m ultidigitaltrauma surgery (10). A significant difference was also reported byFitton et al 11),wbo used buffered solution for otoplasties.A recent Cocbrane review (12) examined the effect of buffetinglocal anesthetic in 23 studies involving patients (bealtby volunteerswere excluded). A significant reduction in pain was apparent wbenlidocaine was buffered.A second outcome measured in tbe present study was tbe durationof anestbetic effect. Tbe anestbetic effect on tbe side injected witbbuffered lidocaine lasted longer than on the side injected with plainlidocaine. Few studies have examined tbe effect of buffering lidocaineon tbe duration of anestbesia. Cbtistopb et al (13) concluded thatbuffering did not affect the duration of effect of lidocaine or mepiva-caine. A discussion of the pbarmacokineticsisbeyond tbe scope of thepresent article. However, it is plausible tbat tbe prolongation of anes-tbetic witb buffering effect may be related to it being a weak base.Admittedly, our study demonstrated large variation in tbe durationof effect from subject to subject, witb one obvious outlier (Figure 5).Tbese findings are not surprising given tbe subjective nature of tbequestionnaire. However, most subjects (17 of 21) repotted a longerduration of anesthetic effect witb tbe buffeted solution provided, sug-gesting tbat tbis is a consistent finding.

CONCLUSIONThe present study provides level 1 evidence regarding tbe use ofsodium b icarbonate and its effect on tbe pain of local anestbetic injec-tion in tbe upper lip. We were not able to demonstrate a difference intbe perceived pain of injection by buffeting tbe lidocaine. Tbis mayindica te tb at buffering is less effective in the lip. This result may alsobe due to some of tbe limitations of tbe present study. We did sbowtbat buffering increases the duration of lidocaine effect in the face.

REFFRENCES1.Scatfone RJ, Jasani M, Gracely E]. Pain of local anestbetics: Rate ofadministration and buffering. Ann Emetg Med 1998;31:36-40.2.M omsen OH , Roman CM , Mobammed BA, et al. Neutralization oflidocaine-adtenaline. A simple metbod fot less painful applicationof local anestbesia. Ugeskr Laeger 2000;162:4391-4.3. Martin AJ. pH adjustment and discomfort caused by intradermalinjection of lignocaine. Anaestbesia 1990;45:975-978.4.Mader TJ, Playe SJ. Reducing tbe pain of local anestbeticinfiltration: R esults of a nation al clinical practice survey.

A mJEmerg Med 1 998;16:617.5.Strazar R, Lalonde D. Five things to know about minimizinginjection pain in local anestbesia. CMAJ 2012;184:2015-6.

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6. Hogan ME, vanderVaart S, Perampaladas K, et al. Systematicreview and meta-analysis of the effect of wanning local anestheticson injection pain. Ann Emerg Med 2011;58:86-98.7. Lalonde DH . Hole- in-one local anesthesia for wide-awake carpaltunnel .surgery. Plast Reconstr Surg2010;126:1642-4.8. Vossinakis IC , Stavroulaki P, Paleochorlidis I, et al. Reducing thepain associated with local anesthetic infiltration for open carpaltunnel decompression. J Hand Surg Br 2004:29:399-401.9. Bums CA, Ferris G, Feng C et al. Decreasing the pain of localanesthesia: A prospective, double-blind comparison of buffered,premixed 1% lidocaine with epinephrine versus 1% lidocaine freshlymixed with epinephrine. J Am Acad Dermatol 2006;54:128-31.

10. Fikry T, al Harrar R, Harfaoui A, et al. Local digital anesthesia usinglidocaine with or w ithout bicarbonate. A comparative randomizedstudy. Rev Chir O rthop Rparatrice Appar Mot 1998;84:739-42.11. Fitton AR , Ragbir, M, Ma M. Th e use of pH adjusted lignocaine incontrolling operative pain in the day surgery unit: A prospectiverandomized trial. Br Plast Surg 1996;49:404-812. Cepeda MS, Tzortzopoulou A, Thackrey, et al. Adjusting the pH oflidocaine for reducing pain on injection. Cochrane Database SystRev2010;(12):CD006581.13. Christoph RA, Bu chanan L, Begalla K, et al. Pain reduction inlocal anesthetic administration through pH buffering. Ann EmergMed 1988;17:117-20.

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C o p y r i g h t o f C a n a d i a n J o u r n a l o f P l a s t i c S u r g e r y i s t h e p r o p e r t y o f P u l s u s G r o u p I n c . a n d i t s

c o n t e n t m a y n o t b e c o p i e d o r e m a i l e d t o m u l t i p l e s i t e s o r p o s t e d t o a l i s t s e r v w i t h o u t t h e

c o p y r i g h t h o l d e r ' s e x p r e s s w r i t t e n p e r m i s s i o n . H o w e v e r , u s e r s m a y p r i n t , d o w n l o a d , o r e m a i l

a r t i c l e s f o r i n d i v i d u a l u s e .