Reducing the pain of local anesthetic infiltration: Warming and buffering have a synergistic effect1

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Study objective: To compare room-temperature unbuffered lidocaine, warm lidocaine, buffered lidocanine, and warm buffered lidocaine to determine which of the four solutions is least painful during infiltration.

Design: Randomized, controlled, double-blinded, volunteer study.

Type of participant: Thirty-two young healthy adults.

Main results: Each subject recieved four subcutaneous injections of 1 % lidocaine: room-temperature unbuffered, warm, buffered, and warm buffered. After each injection, participants recorded their perception of pain associated with infiltration of the solution on a visual analog scale. Mean pain scores for the four solutions were determined and analyzed. The mean perceived pain score for the warm buffered solution was significantly lower than for any of the other solutions (versus warm: P=.0005; versus buffered: P=.0028; versus room temperature: P=.0001). There was no statistically significant difference between either the warm solution or buffered solution and the room-temperature unbuffered lidocaine. The difference in mean pain score for the warm buffered solution, compared with those for the warm, buffered, and room-temperature solutions, suggests that warming and buffering have a synergistic effect.

Conclusion: Skin infiltration with warm buffered lidocaine is significantly less painful than infiltration with room-temperature unbuffered lidocaine, warm lidocaine, or buffered lidocaine.

Section snippets

INTRODUCTION

Local anesthetic agents, frequently used in the emergency department, can cause considerable discomfort during injection.1, 2 To decrease the discomfort of local anesthetic administration, it has been recommended that these agents be buffered before use.3, 4, 5, 6, 7 Recently, it has been suggested that warming these solutions to body temperature before use may be equally beneficial.8, 9 This study was conducted to compare the injection discomfort of room-temperature unbuffered lidocaine, warm

MATERIALS AND METHODS

The study was granted approval by the institutional review board. Volunteers were recruited from the ED staff and ancillary services. Participants were both male and female, ranging in age from 21 to 45 years. Exclusionary criteria included pregnancy, known allergy to local anesthetic agents, and poor general health. No compensation was offered.

Twelve hours before beginning our study, six sterile 30-mL multiple dose vials of 1% plain lidocaine HCl injectable were placed in our trauma room IV

RESULTS

The 32 subjects received a total of 128 injections (Figure 2). Mean pain scores are presented (Table). The first three mean pain scores are positive, indicating greater pain than the needle stick. The mean pain score for the fourth solution, however, is negative, indicating less pain.

. Visual analog pain scores for the four solutions

Table. Mean pain scores for the four preparations

SolutionMean95% Confidence Intervals
Room-temperature5.5—4.8,15.8
Warmed2.0—11.1,15.1
Buffered1.1—7.6,9.8
Warmed/buffered

DISCUSSION

Lidocaine, an amide local anesthetic frequently used in the ED, is packaged and stored at an acidic pH to enhance stability and extend shelf life.2 Skin infiltration with lidocaine HCl for dermal procedures causes significant discomfort.1 Previous studies have determined that buffering lidocaine to a more neutral pH before use reduces the discomfort of infiltration.3, 4, 5, 6, 7 More recently, warming lidocaine to body temperature has been suggested as an equally effective method to attenuate

CONCLUSION

Based on our results, we conclude that warm buffered lidocaine is superior to room-temperature unbuffered lidocaine, warm lidocaine, and buffered lidocaine for reducing the pain of infiltration. The differences in mean pain scores, in fact, are so great as to suggest a synergistic effect. In an effort to make local anesthesia less painful and more acceptable to patients, we recommend the routine use of lidocaine that is both warm and buffered.

Acknowledgements

The authors thank the members of their department and ancillary staff for their participation in this study. They also thank their colleagues for their review of the manuscript and helpful suggestions.

References (12)

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