Requirements of Propofol With Target Controlled Infusions for Supraglottic Airway Devices

The investigators enrolled ASA physical status I-III patients who were 18-70 years old and scheduled for general anesthesia for elective non-cardiac surgery with SGA devices.Adults with a potentially difficult airway (cervical spine disease, Mallampati classification IV, or a mouth opening less than 2.5 cm.), reactive airway disease, signs of respiratory infection or a plan to remain intubated were excluded from the study. The investigators also excluded patients who had a risk of gastric aspiration or morbid obesity (body mass index > 35 kg/m2).

Patients were randomized into 4 groups (I-gel™, Supreme™, ProSeal™ and Laryngeal Tube Suction II™ SGAs) according to a computer generated randomization list and patients were allocated consecutively. The sample size of each group required 10 patients.

All patients were pre-oxygenated with 100% oxygen. After the administration of 2 µg/ml intravenous fentanyl for 5 minutes, anesthesia was induced with the Schnider pharmacokinetic TCI system. After equilibration of the plasma-site and effect-site concentrations in propofol TCI, 1 of the 4 types of SGA was randomly inserted by two anesthesiologists (resident trainee and staff doctor) who were unaware of the actual plasma concentration of propofol without the use of a muscle relaxant.

The response of each patient determined the effect-site concentration of propofol of the next patient. "No Response" was defined as Laryngeal Mask Airway Insertion Score = 0 and "Response" was defined as Laryngeal Mask Airway Insertion Score ≥ 1. If the insertion of the supraglottic airway device was successful ("No Response"), then the target effect-site concentration was decreased by a step of 0.4 µg/ml. If the insertion failed ("Response"), the target effect-site concentration was increased by the same dose. The patients' responses to LMA insertion was classified by blinded investigators.