Propofol concentration requirement for laryngeal mask airway insertion was highest with the ProSeal, next highest with the Fastrach, and lowest with the Classic type, with target-controlled infusion.

STUDY OBJECTIVE

To determine propofol concentration of plasma 50% (Cp50, concentration at which there is a 50% chance that patients show no movement in response) for the Classic-, Fastrach-, and ProSeal-type laryngeal mask airway (LMA) insertion using target-controlled infusion (TCI) technique.

DESIGN

Prospective, randomized, comparative study.

SETTING

University-affiliated hospital.

PATIENTS

Sixty American Society of Anesthesiologists physical status I and II women scheduled for minor gynecologic operations.

INTERVENTIONS

Propofol TCI (Diprifusor pharmacokinetic model) was started at target concentration using an anesthesia pump. After reaching target effect-site concentration of propofol, 1 of the 3 types of LMA was inserted. We recorded patient responses to LMA insertion as "movement" or "no movement." Test propofol concentrations started from a dosage of 4 microg/mL. Concentrations were then predetermined by a modified Dixon's up-and-down method with 0.4 microg/mL step size.

MEASUREMENTS

Patient response to LMA insertion was classified as either of "no movement" or "movement." The midpoint was defined as the average concentration value of crossover (movement/no movement) response. The Cp50 value was defined as the average of the crossover midpoints in each group, and it was estimated from calculating the midpoints.

MAIN RESULTS

Cp50 of the Classic, Fastrach, and ProSeal LMA insertion were 3.2+/-0.34, 4.0+/-0.22, and 4.9+/-0.20 microg/mL (mean+/-SD), respectively.

CONCLUSION

Required propofol TCI concentrations for LMA insertion were significantly highest for the ProSeal, second highest for the Fastrach, and lowest for the Classic LMA.