Pain of Local Anesthetics: Rate of Administration and Buffering☆,☆☆,★
Introduction
In the ED, it is frequently necessary to infiltrate intact skin with a local anesthetic before a field or digital block or before procedures such as a lumbar puncture, insertion of an arterial line, or an arthrocentesis are undertaken. However, the infiltration of the anesthetic itself is quite painful and causes patients, especially children, to become anxious and uncooperative with the ensuing procedure. There are many variables that influence the degree of pain experienced with local anesthetic infiltration. Previous studies have assessed specific agents,1, 2, 3 buffering,4, 5, 6, 7, 8 temperature,5, 9, 10, 11, 12, 13 depth of injection,10 area of the body anesthetized, needle size, and volume.
To date, there have been no studies adequately assessing the effect of administration rate on the degree of pain experienced or how the rate compares with buffering in its effect on pain. Therefore this study was conducted to compare the pain of infiltration associated with four different methods of lidocaine administration: slow and buffered (SB), slow and unbuffered (SU), rapid and buffered (RB), and rapid and unbuffered (RU). The study hypothesis was that slow administration and buffering would each result in less pain during infiltration.
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Materials and Methods
Forty-two adult volunteers gave informed consent before participation, and the study was approved by the institutional review board of St Christopher's Hospital for Children. Excluded were those subjects known to be pregnant or to have an allergy to local anesthetic agents. To minimize subject bias and ensure blinding, each participant was told that he or she would receive four different types of anesthetic solutions, rather than two different solutions at two different rates.
Study drugs were
Results
Forty-four adult volunteers were initially enrolled, 26 women and 18 men. Subsequently, one man was excluded because the needle and syringe disconnected during an infiltration, and one woman was excluded because a syringe was mislabeled. Therefore 42 subjects were evaluated. Significance testing showed that the sequence in which the four conditions were administered to each subject was in a random pattern (Table 1). Similarly, the sequence in which forearm sites were used was random with the
Discussion
This is the first study to adequately assess the effect of administration rate on the degree of pain experienced with local lidocaine and how that rate compares with buffering in its effect on the pain of administration. We found that rate of infiltration was strongly predictive and that buffering was modestly predictive of perceived pain for subcutaneous injections of lidocaine through intact skin. Each slow condition yielded lower pain ratings than either rapid condition. Also, unbuffered
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From the Department of Pediatrics, Temple University School of Medicine*; Section of Pediatric Emergency Medicine, St Christopher's Hospital for Children‡; and Department of Community and Preventive Medicine, Allegheny University of the Health Sciences, MCP Hahnemann School of Medicine,§ Philadelphia, PA.
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Reprint no. 47/1/87279
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Address for reprints: Richard J Scarfone, MD, Pediatric Emergency Medicine, St Christopher's Hospital for Children, Erie Avenue at Front Street, Philadelphia, PA 19134, 215-427-5366, Fax 215-427-4668, E-mail [email protected]