ED50 and ED95 of Propofol Combined with Different Doses of Intravenous Lidocaine for First-Trimester Uterine Aspiration: A Prospective Dose-Finding Study Using Up-and-Down Sequential Allocation Method

PURPOSE: This study aimed to test the effect of different doses of intravenous lidocaine on the median effective dose (ED50) and 95% effective dose (ED95) of propofol-induction dose and identify the optimal dose. PATIENTS AND METHODS: Patients undergoing first-trimester uterine aspiration were screened and randomly enrolled into the following groups: saline (L(0)), 0.5 mg/kg lidocaine (L(0.5)), 1.0 mg/kg lidocaine (L(1.0)), and 1.5 mg/kg lidocaine (L(1.5)). Anesthesia was induced with 1.0 µg/kg fentanyl. Prepared lidocaine or saline solution was injected later according to allocation, followed by propofol. The dose of propofol for each patient was determined using the up-and-down sequential study design. The primary end point was the ED50 and ED95 of the propofol-induction dose. The total propofol doses, awakening time, and adverse events were recorded. RESULTS: The ED50 (95% confidence interval) of propofol was significantly lower in groups L(1.0) and L(1.5) than group L(0) (1.6 [1.5–1.7] mg/kg and 1.8 [1.6–1.9] mg/kg, versus 2.4 [2.3–2.5] mg/kg, respectively; p<0.001). There was no significant difference in ED50 between groups L(1.0) and L(1.5) (p>0.05). However, surprisingly, the ED50 was significantly higher in group L(0.5) than L(0) (2.8 [2.6–3.0] mg/kg vs 2.4 [2.3–2.5] mg/kg; p<0.05). The total doses of propofol in groups L(1.0) and L(1.5) were lower than those in groups L(0) and L(0.5) (p<0.05). The systolic blood pressure (SBP) decline after anesthesia induction in group L(0.5) was greater than that in group L(0) (p<0.01). The incidence of respiratory depression in group L(0.5) was greater than that in groups L(0) and L(1.0) (p<0.05). CONCLUSION: In patients who underwent first-trimester uterine aspiration, intravenous lidocaine 1.0 mg/kg prior to propofol injection significantly reduced the ED50 of propofol induction dose without severe side effects, equivalent to the effect of 1.5 mg/kg dose. We recommend 1.0 mg/kg as the optimal dose.