Timing of injection and plasma concentration of lidocaine before endotracheal intubation.

The optimal time of intravenous lidocaine for attenuation of pressor responses to laryngoscopy and endotracheal intubation was evaluated in fifty adult patients and the correlation between plasma lidocaine level and its clinical effects were also studied. The plasma lidocaine levels were highest 0.5 min after administration of lidocaine 1.5 mg.kg(-1) intravenously. However, endotracheal intubation 0.5 min after lidocaine administration caused significant increase in mean arterial pressure (MAP) and heart rate (HR). Mean arterial pressure and HR increased with endotracheal intubation following 1, 2 and 3 min after lidocaine administration, but the magnitude of increase was not statistically significant. There were no significant differences in MAP changes among these three groups. It was concluded that the plasma lidocaine levels did not correlate with its suppressive effect on circulatory responses due to laryngoscopy and endotracheal intubation. Laryngoscopy and endotracheal intubation should be carried out at least 1 min after intravenous lidocaine administration.