Laryngeal mask insertion during target-controlled infusion of propofol

Study Objective: To compare the Laryngeal Mask Airway™ (LMA; The Laryngeal Mask Airway Co., Ltd., Nicosia, Cyprus) insertion conditions produced by 6 and 8 μg/mL of target plasma concentrations (Cpt) during the induction of anesthesia with target-controlled infusion (TCI) of propofol. Design: Randomized, prospective, single-blind, clinical study. Setting: University hospital. Patients: 44 ASA physical status I and II patients, 16 to 54 years of age, weighing between 45 and 100 kg, undergoing minor surgery in which the use of LMA was indicated. Interventions: Patients were randomly divided into two groups (1 and 2) of 22 to compare the effects of different propofol concentrations. Three minutes after intravenous (IV) injection of midazolam 0.04 mg/kg, group 1 and 2 received TCI of propofol with 6 and 8 μg/mL of Cpt, respectively. LMA was inserted when the effect-site concentration (EC) reached 2.5 μg/mL, which was displayed on the infusion pump. Measurements: The LMA insertion conditions (mouth opening, gagging, coughing, head or limb movement, laryngospasm, overall ease of insertion) were assessed, and hemodynamic responses were evaluated until 3 minutes after LMA insertion. Total dose of propofol, EC, and elapsed time since the start of TCI were recorded at five times: At the loss of consciousness and eyelash reflex, at 2.5 μg/mL of EC, and immediately, 1 minute, and 3 minutes after the insertion of LMA. Main Results: There was no significant difference between the two groups in insertion conditions, despite the significantly larger total dose and shorter elapsed time (2.6 ± 0.08 mg/kg and 109 ± 5.0 s) in Group 2 than those (2.1 ± 0.02 mg/kg and 140 ± 4.1 s) in Group 1 at 2.5 μg/mL of EC (p < 0.05). Systolic and diastolic blood pressure decreased and heart rate increased significantly throughout the study period in both groups (p < 0.05). But there was a significant decrease in arterial pressure in Group 2 compared with Group 1 1 and 3 minutes after the insertion (p < 0.05). Conclusions: Induction with 8 μg/mL of Cpt, compared with 6 μg/mL, allowed earlier LMA insertion but, could not improve the conditions for LMA insertion and required more careful attention to the decrease in blood pressure after LMA insertion.