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 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.
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).
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.