Intravenous lidocaine alleviates the pain of propofol injection by local anesthetic and central analgesic effects

Abstract

Objective. Lidocaine alleviates propofol injection pain. However, whether lidocaine works through a local anesthetic effect at the site of intravenous injection or through a systemic effect on the central nervous system remains unknown. This study aimed to determine the pain-alleviating mechanism of lidocaine. Design. A randomized controlled study. Setting. A gastroscopy facility. Methods. The study was divided into two parts. Part 1 involved 717 patients who were randomly assigned into five groups. Groups PR, RL20, and RL40 received normal saline or saline containing 20 or 40mg of lidocaine, injected via the vein on the right hand. Groups LL20 and LL40 received 20 or 40mg of lidocaine, injected via the vein on the left hand. Part 2 involved 378 patients who were randomly assigned into five groups. Groups RL40, RL1.2, and RL1.5 received 40 mg, 1.2 mg/kg, and 1.5 mg/kg of lidocaine, injected via the vein on the right hand. Groups LL1.2 and LL1.5 received 1.2 or 1.5 mg/kg of lidocaine, injected via the vein on the left hand. All received 2 mg/kg of propofol via the vein on the right hand two minutes later. Injection pain and patient satisfaction were recorded. Results. The incidence of pain of group RL40 was lower than that of group PR. The incidence of pain of group LL1.2 was higher than that of other groups. Conclusions. A dosage of 40mg lidocaine is an appropriate dosage to alleviate propofol injection pain within the same vein. Lidocaine reduces propofol injection pain through both a local anesthetic effect and a central analgesic effect when the dosage reaches 1.5 mg/kg.