Similar to lipid emulsion propofol, microemulsion propofol also causes a high incidence of pain during intravenous injection. Various methods have been used to minimize the incidence and severity of pain on injection of lipid emulsion propofol. In this study, we investigated the effect of a lidocaine mixture on pain induced by microemulsion propofol injection, and sought to determine the optimal dose of lidocaine that could reduce pain on injecting a propofol-lidocaine mixture.

One hundred sixty (n = 160) patients of American Society of Anesthesiologists physical status class I or II were randomly allocated to four groups: Group A, control; Group B, 20 mg lidocaine; Group C, 30 mg lidocaine; Group D, 40 mg lidocaine. In each patient, pain on microemulsion propofol solution injection was graded as none, mild, moderate, or severe.

The incidence of pain in groups A, B, C, and D was 97.5%, 80%, 65%, and 50%, respectively. Increasing the lidocaine dose significantly reduced pain (P < 0.05). One patient in Group D (2.5%) had moderate to severe pain, which was significantly lower than groups B (42.5%) and C (32.5%) (P < 0.05).

The lidocaine and propofol mixture is effective in alleviating pain associated with microemulsion propofol injection. Within this dose range and in this patients population, increasing lidocaine dosage significantly reduced pain during injection of microemulsion propofol.