Laryngeal mask insertion during target-controlled infusion of propofol

To compare the Laryngeal Mask Airway (LMA; The Laryngeal Mask Airway Co., Ltd., Nicosia, Cyprus) insertion conditions produced by 6 and 8 microg/mL of target plasma concentrations (Cpt) during the induction of anesthesia with target-controlled infusion (TCI) of propofol.

Randomized, prospective, single-blind, clinical study.

University hospital.

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.

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 microg/mL of Cpt, respectively. LMA was inserted when the effect-site concentration (EC) reached 2.5 microg/mL, which was displayed on the infusion pump.

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 microg/mL of EC, and immediately, 1 minute, and 3 minutes after the insertion of LMA.

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 microg/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).

Induction with 8 microg/mL of Cpt, compared with 6 microg/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.