Summary of ‘Adjusting the pH of lidocaine for reducing pain on injection’

Authors


Abstract

This is a summary of Cochrane review, published in this issue of EBCH, first published as: Cepeda MS, Tzortzopoulou A, Thackrey M, Hudcova J, Arora Gandhi P, Schumann R. Adjusting the pH of lidocaine for reducing pain on injection. Cochrane Database of Systematic Reviews 2010, Issue 12. Art. No.: CD006581. DOI: 10.1002/14651858.CD006581.pub2. Copyright © 2011 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd. The Cochrane Collaboration

Objectives

  • The aim of this review was to determine if adjusting the pH of lidocaine had any effect on pain resulting from non-intravascular injections in adults and children.

Relevance

  • Lidocaine is one of the most commonly used local anaesthetics because of its rapid onset of action, safety profile, low cost and wide availability. It is frequently used in medical care to facilitate a variety of invasive procedures including anaesthetizing the skin prior to venous or arterial cannulation and providing analgesia and anaesthesia for surgical procedures.

  • When lidocaine is used for local, subcutaneous injections, patients often complain of pain, which typically presents as a burning sensation and can be quite severe. It is suggested that this pain is likely to result from the increase in hydrogen ions in the local tissue environment due to the higher acidity of lidocaine. Addition of epinephrine further lowers the pH of lidocaine.

  • Although increasing the pH of commercial lidocaine solutions may decrease pain intensity, this alkalinization could also affect the onset, duration or degree of analgesia. This outcome was not analysed in the current review.

Participants

  • Twenty-three studies were included in the review (1067 participants). Most were adult studies but one study recruited children only (seven), and two studies recruited both children and adults (138).

Comparison

  • Double-blind randomized controlled trials that compared pH-adjusted lidocaine with unadjusted lidocaine solutions for non-intravascular injection, with or without epinephrine.

Results

Nine parallel studies reported significantly less pain with buffered versus unbuffered lidocaine (MD: − 0.95; 95% CI: − 1.42, − 0.49). This finding remained significant when examining the following subgroups:

  • Lidocaine with and without epinephrine

  • Final pH of the buffered lidocaine < 7.35 versus ≥ 7.35

  • Low and high risk of bias trials

  • Low (but not high) volume injections

  • Intravenous cannulation and insertion of epidural catheter (but not small surgical procedures)

Ten crossover studies reported significantly less pain with buffered versus unbuffered lidocaine (MD: − 1.98; 95% CI: − 2.62, − 1.34). This finding remained significant for all subgroups:

  • Lidocaine with and without epinephrine

  • Final pH of the buffered lidocaine < 7.35 versus ≥ 7.35

  • Low and high volume injections

  • Intravenous cannulation, nerve block insertion of epidural catheter and small surgical procedures

In 11 trials, patients significantly preferred buffered over unbuffered lidocaine (OR: 3.01; 95% CI: 2.19, 4.15). Three trials found no difference in adverse events or toxicity between groups.

Implications

  • Increasing the pH of commercial lidocaine preparations with bicarbonate should be considered to decrease pain on injection.

How recent is the evidence

  • Databases were searched up to June 2010.

Research gaps

  • Authors could not explain the large variation in the magnitude of pain decrease with buffered lidocaine. More research is required on the conditions or circumstances in which buffered lidocaine has maximum benefits.

Statistical abbreviations

CI: confidence interval MD: mean difference OR: odds ratio

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