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Laryngeal mask insertion during target-controlled infusion of propofol
1Department of Anesthesiology, Tong-Dae-Mun Hospital, College of Medicine, Ewha Womans University, Seoul, South Korea. baikhj@chollian.net
Study Objective:
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.
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 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.
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 microg/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 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).
Conclusions:
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.