Comparison of Propofol ED50and Insertion Conditions of LMA between Fentanyl and Alfentanil Adjuvant Group

The Determination of an Appropriate Time for Placement of the Classic Laryngeal Mask Airway in Patients Undergoing General Anesthesia

Background

The management of the airways is an essential component of anesthesia planning. Laryngeal mask airway (LMA) plays an important role in modern anesthesia, however, intubation by LMA has some complications. It may cause inadequate anesthesia depth, which can lead to adverse events. The aim of this study was to evaluate the optimal time for intubation by LMA under general anesthesia.

Methods

This study was conducted on 96 patients, who underwent operation and were appropriate candidates for intubation with appropriate LMA. The participants were divided to four groups, each with 24 cases, based on the time interval between anesthetic agent administration and intubation with LMA; 15 seconds for the first group, 16 to 30 seconds for the second group, 31 to 45 seconds for the third group, and 45 to 60 seconds for the fourth group. The patients involved in these groups were selected based on the following prerequisites, patients’ age, gender, easy intubation, need for additional drug administration, basic blood pressure before drug administration, within the time intervals one, three, and five minutes after placement of LMA, duration of LMA, SaO₂ before and after placement of LMA, coughing, patient’s movement, laryngospasm, gag reflex after intubation, allowing appropriate ventilation, presence of sore throat after surgery, number of attempts, extent of mouth opening and leak in peri-LMA space.

Results

Overall, 72 males and 24 females participated in this study with a mean age of 40.64. Intubation by LMA was performed easily during the first attempt in 58% of the participants, with minimal resistance in 28.6% and with some problems during the second attempt in 10.5% of the cases. Throat pain after the operation was significantly lower. Systolic and diastolic pressure and heart rate had no statistically significant difference.

Conclusions

The results showed that in the first 15 seconds after the drug (e.g. propofol) administration, there were lower complications, rapid placement, and optimized time for the placement of LMA. The rate of success and its quality were reduced during the first attempt of insertion and termination of the effect of propofol.

Estimation of effect-site concentration of propofol for laryngeal mask airway insertion using fentanyl or morphine as adjuvant

BACKGROUND AND AIMS

Insertion of laryngeal mask airway (LMA) requires adequate depth of anaesthesia, which provides jaw relaxation and suppression of upper airway reflexes. Propofol can provide these conditions especially when combined with narcotics. This study had been designed to find out the effect-site concentration (EC50) of propofol using target controlled infusion (TCI) when fentanyl or morphine is added as an adjuvant.

METHODS

Patients satisfying inclusion criteria were divided into fentanyl and morphine groups. Intravenous glycopyrrolate 0.2 mg was given 15 min before induction. Patients were given either intravenous fentanyl (1 μg/kg) or morphine (0.1 mg/kg) before propofol infusion depending on the group. Patients in either groups were induced by continuous infusion of propofol at an EC of 6 μg/mL by TCI with Schneider pharmacokinetic model. The LMA supreme of appropriate size was inserted 1 min after achieving target concentration. Patient movement at LMA insertion or within 1 min of insertion was classified as failure. For subsequent patients, the target EC was increased/decreased depending on previous patients' response. Dixons up and down method was used to determine the EC50. The EC50 is defined as the mean of crossover midpoints in each pair of failure to success.

RESULTS

The EC50 of propofol in the fentanyl group for LMA insertion was 5.95 ± 0.6 μg/ml and morphine group was 5.75 ± 0.8 μg/ml. No significant difference in insertion conditions was noticed between the two groups (P = 0.3).

CONCLUSION

We conclude that there was no significant difference in propofol EC50 for insertion of LMA and insertion conditions were similar when fentanyl or morphine was used as an adjuvant drug.