Lidocaine added to propofol decreases the severity but not the frequency of pain on injection compared to injecting lidocaine before propofol in patients undergoing colonoscopy

Abstract

Background and Aims: Pain on injection is common in non-premedicated patients receiving propofol for colonoscopy. Multiple studies have examined strategies to prevent propofol injection pain in surgical patients. However, many of these studies were not blinded or randomized and many of the studied patients received premedication prior to propofol injection. This study was designed to test the hypothesis that injecting a premixed solution of propofol/lidocaine will be associated with less pain than when lidocaine is injected separately before propofol. The study’s propofol induction protocols closely mirrored those used routinely at our institution.
Methodology: This was a randomized, double-blinded, comparative study performed with IRB approval and patients’ informed consent. One 150 patients scheduled for screening colonoscopy were randomly assigned into two groups of 75 patients in each group. In Group-LB, patients received 40 mg lidocaine IV followed by propofol from a syringe containing 19 ml propofol and 1 ml saline. In Group-ML, patients received 2 ml saline IV followed by propofol from a syringe containing 19 ml propofol and 1 ml 2% (20 mg) lidocaine. Following the initial IV injection of the 2 ml clear solution the patients were asked about symptoms of systemic lidocaine (light headedness, ringing in the ears, or metallic taste in the mouth). Disregarding the minor dilution of the 19 ml propofol with the added 1 ml clear solution, propofol 0.75 mg/kg was then injected at a constant rate over 15 seconds. The patients were asked to grade any associated pain or discomfort at the injection site on a 4 point scale: (0) no pain, (1) mild pain, (2) moderate pain, (3) severe pain and/or grimacing or withdrawal of limb. Thirty second later a second dose of 0.75 mg/kg propofol was injected. The patients continued to be questioned about pain on injection until they lost consciousness. Fisher’s exact test was used to compare the proportion of patients who experienced pain and the incidence of experiencing systemic lidocaine symptoms between the 2 groups. Wilcox rank sum test was used to compare the severity of pain for patients who experienced pain in the two groups.
Results: There was no difference in pain rates between the two groups (p=1). If they did experience pain, patients in Group-ML experienced less pain compared to patients in the Group-LB (p < 0.001). The incidence of experiencing lidocaine symptoms was significantly higher in the Group-LB (p < 0.001).