ORIGINAL CONTRIBUTION lidocaine

Buffered Versus Plain Lidocaine as a Local A n e s t h e t i c for Simple Laceration Repair Study objective: Buffered lidocaine was compared with plain lidocaine as a local anesthetic for simple lacerations. Design: Randomized, double-blind, prospective clinical trial. Setting: Urban emergency department. Type of participants: Ninety-one adult patients with simple linear lacerations were enrolled. Patients w~th allergy to lidocaine and patients with an abnormal mental status were excluded. Interventions: Each wound edge was anesthetized with either plain or buffered lidocaine using a randomized, double-blind protocol. The pain of infiltration was measured with a previously validated visual analog pain scale. Measurements and main results: Analysis of pooled data and paired data (using patients as their own controls) revealed that infiltrating buffered lidocaine was significantly less painful than plain lidocaine (P = .03 and P = .02, respectively). There was no significant difference in the a~esthetic effectiveness of the two agents during suturing. Conclusion: Buffered lidocaine is preferable to plain lidocaine as a local anesthetic agent for the repair of simple lacerations. [Bartfield JM, Gennis P, Barbera J, Breuer B, Gallagher EJ: Buffered versus plain lidocaine as a local anesthetic for simple laceration repair. Ann Emerg Med December 1990;19:1387-1389.]

Joel M Bartfield, MD* Paul Gennis, MD*t¢ Joseph Barbera, MD*¢ Brenda Breuer, PhD$ E John Gallagher, MD*t¢ Bronx, New York

INTRODUCTION Simple lacerations are commonly encountered in emergency practice. Anesthesia is often achieved by the local administration of lidocaine, which is known to cause painJ Recent studies using subjects with uninjured skin suggest that buffering lidocaine decreases the pain of local infiltration.2, 3 The value of buffered lidocaine as a local anesthetic for repair of lacerations has not been studied previously. We performed a randomized, double-blind clinical trial comparing buffered and plain lidocaine for the repair of simple lacerations.

Address for reprints: Paul Gennis, MD, Emergency Department, Bronx Municipal Hospital Center, Jacob 1W20, Pelham Parkway South and Eastchester Road, Bronx, New York, 10461.

From the Division of Emergency Medicine, Department of Ambulatory Care, Bronx Municipal Hospital Center;* and the Departments of Medicinet and Epidemiology and Social Medicine,S Albert Einstein College of Medicine, Bronx, New York. Received for publication March 26, 1990. Revision received June 25, 1990. Accepted for publication July 9, 1990. Presented at the Society for Academic Emergency Medicine Annual Meeting in Minneapolis, May 1990.

METHODS The study was performed in the Adult Emergency Department of the Bronx Municipal Hospital from July to September 1989. All daytime patients aged 18 years or older with linear lacerations were considered for enrollment in the study. Excluded were patients with allergy to lidocaine and patients with an abnormal mental status or other condition that interfered with pain perception. Informed consent was obtained from each patient prior to enrollment. The study was approved by the Committee on Clinical Investigation of Albert Einstein College of Medicine. Study solutions containing either plain or buffered lidocaine were freshly prepared for each case by research assistants. Each study solution contained 9 mL of 1% lidocaine and 1 mL of an unknown diluent. The unknown diluents were sodium bicarbonate (44 mEq/50 mL) or normal saline. The hospital laboratory had previously determined that the buffered lidocaine had a pH range of 7.15 to 7.27. The unknown diluents were stocked in identical vials marked with randomly generated numbers to permit the assignment of study solutions in a double-blind fashion. Previously trained research assistants administered the unknown study

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Annals of Emergency Medicine

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LIDOCAINE Bartfield et al

solutions into the inner surface of each w o u n d edge u s i n g a standardized technique of slow infiltration through a 25-gauge needle. Every patient was assigned two unknown study solutions, one for each wound edge of their linear laceration. The four possible a n e s t h e t i c combinations are shown (Table). To assure uniformity of infiltration, and to parallel clinical practice as closely as possible, each patient was assigned only one research assistant. Patients ranked the pain associated w i t h each w o u n d edge i n j e c t i o n using a previously validated visual analog pain scale. 4 Pain scales were later quantified by making measurements to the nearest millimeter from the origin of the scale to the point marked by the patient. Subsequent wound care was accomplished by the e m e r g e n c y m e d i c i n e and surgical housestaff. Adequacy of anesthesia during suturing was assessed by recording the number of wound edges requiring additional anesthesia and the number of sutures that elicited pain. Plain 1% lidocaine was used to obtain adequate anesthesia when patients complained of pain during suturing. Nonparametric data were analyzed using the Wilcoxon signed-rank test, Kruskal-Wallis test, and Wilcoxon two-sample test, the last being used for pooled data. Otherwise, data were analyzed using the Student's t test, X2 test, Fisher's exact test, and analysis of variance where applicable. For all analyses, P < .05 was considered to be statistically significant.

RESULTS Ninety-three patients met entry criteria and consented to participate in the study. Two patients were excluded because in each case their wound edges were not infiltrated by the same research assistant. The rem a i n i n g 91 patients were entered into the study. There were 68 (75%) men and 23 (25%1 women. Patient ages ranged from 18 to 86 years with a mean age of 35 -+ 17 years (SD). As shown (Table), 52 patients received plain lidocaine in one wound edge and buffered lidocaine in the other. Of these, 24 received plain lidocaine in the first wound edge and buffered in the s e c o n d (group 1). Twenty-eight received buffered lidoeaine in the first w o u n d edge and plain in the second (group 2). Thirty52/1388

TABLE. Patient groups Groups

N

First Edge

Second Edge

1

24

Plain lidocaine

2

28

Buffered lidocaine

Buffered lidocaine Plain lidocaine

3 4

24 15

Buffered lidocaine Plain lidocaine

Buffered lidocaine Plain lidocaine

nine patients received either plain or buffered lidocaine in both w o u n d edges. Of these, 24 received only buffered lidocaine (group 3), and 15 received only plain lidocaine (group 4). The four groups did not differ significantly with regard to sex, age, and race.

Pain scores for buffered versus plain lidocaine infiltration were compared for the entire study population (91). Buffered lidocaine was found to be significantly less painful than plain lidocaine (P - .03). The 52 patients who received different anesthetics (groups 1 and 2) permitted analysis of the data using patients as their own controls. The difference in pain scores between plain and buffered lidocaine was determined for each patient. Analysis of the differences also revealed that infiltration of buffered lidocaine was less painful than that with plain lidocaine (P - .02). This finding was more profound in group 1 versus group 2 (P - .02), suggesting an effect of the order of administration. Analysis of the patients who received the same anesthetic in both wound edges (groups 3 and 4, 39) revealed that there was more pain associated with infiltration of the first wound edge than the second (P = .02). The effectiveness of buffered and plain lidocaine during suturing was compared by analyzing the need for additional anesthesia. Eleven percent (100) of wound edges infiltrated with buffered lidocaine required additional anesthesia compared with 15% (82) infiltrated with plain lidocaine. In addition, 3.9% of the sutures placed with buffered lidocaine elicited pain compared with 5.7% with plain lidocaine. Neither difference was statistically significant; however, the power in each case was only 0.06. Wounds requiring additional anesthesia were more likely to be in the face or scalp than in all other sites Annals of Emergency Medicine

combined (18.0% vs 6.3%, P = .02). DISCUSSION Lidocaine, an amide anesthetic, is a weak base with a pH of 7.9. 5 Lidocaine is marketed at a pH of 5.0 to 7.0 to enhance its shelf life. 6 It is believed to have an intracellular site of action in nerve cells. The uncharged form of the molecule is thought to be needed for the drug to cross cell membranes and gain access to the intracellular space.Z,S It is known that local infiltration of lidocaine causes pain. ~ Theoretically, buffering lidocaine to a higher pH could decrease the pain of infiltration by shifting the drug to its uncharged state and enhancing its bioavailability. Previous authors using volunteers with uninjured skin have shown that infiltration of buffered lidocaine,2,3 buffered mepivacaine,2 and buffered bupivicaine 9 causes less pain than unbuffered agents. Buffered lidoeaine has also been shown to be safe and more effective than plain lidocaine as a regional anesthetic.tO-t2 We have demonstrated in a clinical setting that lidocaine, buffered by the addition of 1 mL of sodium bicarbonate (44 mEq/50 roLl to 9 mL of 1% lidocaine, causes less pain during infiltration than does unbuffered lidocaine. Analysis of pooled data revealed that infiltration of w o u n d edges with buffered lidocaine elicited significantly less pain than infiltration with plain lidocaine (P = .03). Analysis of paired data using patients as their own controls also showed that infiltration of buffered lidocaine was significantly less painful than infiltration of its more acidic counterpart (P = .02). During suturing the two agents were equally effective anesthetics. It has been shown previously that the pain of infiltration of different commercially available local anes19:12 December 1990

thetics is n o t a function of acidity, la We therefore h y p o t h e s i z e d that the pain reduction observed by buffering lidocaine was n o t s i m p l y secondary to a decrease i n acidity, b u t rather was due to the rapidity w i t h which the buffered, u n c h a r g e d l i d o c a i n e molecules diffuse into nerve cells. Once anesthesia has been achieved, the advantage of buffering, w h i c h m a y be related solely to the kinetics of lidocaine diffusion across cell m e m b r a n e s , disappears and the buffered and unbuffered forms of the drug appear to be equally effective anesthetics. A n a l t e r n a t i v e explanation for this finding is Type II or [3 error, due to sample size. If this is the case, a larger series should detect a difference i n pain scores during both infiltration and suturing w h e n buffered lidocaine is compared with plain lidocaine. We also f o u n d that p a t i e n t s who received p l a i n lidocaine i n the first w o u n d edge followed by buffered lidocaine i n the second edge had a sign i f i c a n t l y greater difference in pain scores t h a n those who received the identical a n e s t h e t i c s in the reverse order (P = .02). Because the only difference b e t w e e n these two groups of patients was the order of administration of medication, we postulated the existence of a n effect related solely to the order of infiltration. This was supported by an analysis of those patients who received the same anesthetic in both w o u n d edges. In these p a t i e n t s , t h e r e was s i g n i f i c a n t l y more p a i n associated w i t h infiltration of the first w o u n d edge than the second (P = .02). We speculate that this order effect, w h i c h is i n d e p e n d e n t of the agent used, m a y reflect cross-diffusion of local a n e s t h e t i c f r o m o n e w o u n d edge to the other. Alternatively, patients m a y have become less anxious after their first i n f i l t r a t i o n and perceived less pain with an equal stim-

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ulus during their second infiltration. T h e p o s s i b i l i t y of a n order effect s h o u l d be c o n s i d e r e d i n f u t u r e studies comparing local anesthetics. Eleven percent of w o u n d edges receiving buffered lidocaine, and 15% receiving plain lidocaine required additional anesthesia. This unexpected finding occurred with significantly g r e a t e r f r e q u e n c y i n t h e face a n d scalp (P = .02), perhaps related to rapid w a s h o u t of anesthetic i n highly vascular areas. 7 Although the use of e p i n e p h r i n e m a y have obviated the n e e d for a d d i t i o n a l a n e s t h e s i a i n m a n y of these lacerations, the inactivation of catecholamines by the bicarbonate 14 present i n buffered lidocaine would have introduced an unc o n t r o l l e d v a r i a b l e i n t o the s t u d y design that m i g h t have c o n f o u n d e d our results. This study had several limitations. First, the relatively small sample size was vulnerable to [3 error because it lacked the statistical power to detect small differences i n anesthetic effectiveness. T h e a n e s t h e t i c superiority of buffered lidocaine over plain lidocaine d u r i n g s u t u r i n g , n o t d e m o n s t r a t e d by t h e p r e s e n t s t u d y a n d probably less marked t h a n the anesthetic advantage seen during infiltration, m i g h t become apparent with a larger sample. A second l i m i t a t i o n was that the anesthetic superiority of buffered lid o c a i n e c a n n o t be e x t r a p o l a t e d to preparations c o n t a i n i n g epinephrine. Because of the i n t e r a c t i o n b e t w e e n bicarbonate and catecholamines, the prolonged anesthetic effect typically seen w h e n lidocaine is mixed with a vasoconstrictor might be lostfl 4 Finally, the findings of this study cannot be generalized to other local anesthetics w i t h different pHs. CONCLUSION I n f i l t r a t i o n of buffered l i d o c a i n e causes less pain than does plain lido-

Annals of Emergency Medicine

caine w h e n a d m i n i s t e r e d as a local a n e s t h e t i c for simple laceration repair. The two agents are equally efficacious d u r i n g suturing. We recomm e n d the use of buffered lidocaine over plain lidocaine to m i n i m i z e patient discomfort.

REFERENCES

1. WightmanMA, VaughanRW: Comparisonof compounds used for intradermal anesthesia. Anesthesiology 1976;45:687-689. 2. Christoph RA, BuchananL, Begalla K, et al: Pain reduction in local anesthetic administration through pH buffering. Ann Emerg Med 1988;17:117-120. 3. McKayW, Morris R, Mushlin P: Sodium bicarbonate attenuates pain on infiltration with lidocaine, with or without epinephrine.Anesth Analg 1987;66:572-574. 4. Scott J, Huskisson EC: Graphic representation of pain. Pain 1976;2:175-184. 5. DeJung RH: Local Anesthetics. Springfield, Illinois, Charles C Thomas, 1977, p 42-50. 6. Moore DC: The pH of local anesthetic solw tions. Anesth Analg 1981;60:833-834. 7. Ritchie JM, Greene NM: Local anesthetics, in Goodman L8, Gilman AG (eds): Tile Pharmacologic Basis of Therapeutics, ed 7. New York, MacMillan,1985, p 302-321. 8. Ritchie JM, Ritchie B, Greengard P: The active structure of local anesthetics. J Pharmacol Exp Ther 1965;150:152-159. 9. Cheney P, MolzenG, TandbergD: The effect of pH bufferingon reducingthe pain associated with subcutaneous injection of bupivicaine(abk stract}. Ann Ernerg Med 1990;19:474. 10. DiFazioCA, Carron H, Grosslight KR, et al: Comparison of pH-adjusted lidocaine solutions for epidural anesthesia. Anesth Analg 1986;65: 760-764. 11. Galindo A: pH-adjusted local anesthetics: Clinical experience. Reg Anesth 1983;8:35-36. 12. BuckleyFP, Neto GD, Fink BR: Acid and al kaline solutions of local anesthetics: Duration of nerve block and tissue pH. Anesth Analg i985;64:477-482. 13. Morris R, McKay W, Mushlin P: Comparison of pain with intradermal and subcutaneous infiltration with various local anesthetic soluk tions. Anesth Analg 1987;66:1180-t182. 14. American Heart Association: Textbook of Advanced Cardiac Life Support, ed 2. Dallas, AHA, 1987, p 97-99.

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Buffered versus plain lidocaine as a local anesthetic for simple laceration repair.

Buffered lidocaine was compared with plain lidocaine as a local anesthetic for simple lacerations...
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