BACKGROUND: The aim of the study was to compare the laryngeal tube (LT) insertion conditions at 3.0 and 3.5µgram/ml effect site concentrations (ECs) during anesthesia induction using the target-controlled infusion (TCI) of propofol.

METHODS: The forty patients were randomly divided into two groups. The patients received TCI of propofol with a 6.0 µgram/ml target plasma concentration (C_pt) and then an LT was inserted without the aid of a muscle relaxant when the predicted EC reached 3.0µgram/ml (group 1) or 3.5µgram/ml (group 2). The conditions of LT insertion, i.e., mouth opening, gagging, coughing, head or limb movement, laryngospasm, and overall ease, and hemodynamic responses were evaluated 3 min after midazolam injection, at loss of consciousness and eyelash reflex, and immediately before, immediately after, 1 min after, and 3 min after LT insertion. We also compared times required to insert LTs, cuff volumes, and incidences of blood staining and of postoperative sore throat.

RESULTS: The conditions of LT insertion, except laryngospasm and overall ease, were not significantly different in the two groups. The incidence of laryngospasm in group 1 (25%) was significantly higher than in group 2 (0%) and group 2 was better than group 1 in terms of overall ease of insertion (P<0.05). No significant differences were observed between the two groups in terms of hemodynamic responses. Minimum cuff volume to 60 cmH₂O was 64.0 ± 8.3 ml in Group 1 and 63.9 ± 6.5 ml in Group 2, and time required for LT insertion was 21.0 ± 11.0 sec in Group 1 and 24.7 ± 16.6 sec in Group 2. Postoperative sore throat and blood stain incidences were not significantly different in the two groups.

CONCLUSIONS: After induction with 6µgram/ml of Cpt using propofol TCI for LT insertion, LT insertion at 3.5µgram/ml of EC provided a lower incidence of laryngospasm and better overall ease than insertion at 3.0µgram/ml of EC.