Comparison of the Ambu AuraGain and Intersurgical i-Gel Laryngeal Masks in Elective Laparoscopic Cholecystectomy

Design: Prospective, controlled, randomized study. Participants: After approval by the local Clinical Research Ethics Committee, all patients scheduled for elective laparoscopic cholecystectomy at Hospital Plató (Barcelona) will be screened for participation. Patients will be informed about the study and they must provide written consent.

The need for orotracheal intubation during surgery will be considered as a study withdrawal criterion.

The primary outcome is the oropharyngeal leak pressure (OLP).

The secondary outcomes are: insertion time, number of attempts, ventilatory airway peak pressure, time, and success rates for gastric tube insertion and side effects.

Sample size has been calculated to detect a significant difference in oropharyngeal leak pressure (OLP) between two devices. According to the results of previous studies, the investigators assume a mean OLP of 29.2 (3.3) cmH2O for the i-Gel and of 34 (5) cmH2O for the Ambu AuraGain. In order to detect a difference of 10%, assuming a standard deviation of 5 cmH2O for both devices, 44 patients are required per group with a power of 80% and an alpha error of 0.05. To cover against a dropout rate of 10%, a total of 98 patients will be recruited.

The patients included in the study will be numbered consecutively and assigned to one of the two groups, 'LMA Ambu AuraGain' or 'i-gel', using a computer-generated random number table, by the principal investigator. The individual result will be kept in opaque envelopes. After the recruitment, the day of the procedure, the enrolling investigator will open sealed, opaque envelopes that conceal the group allocation. Participants will be blinded to their group allocation.

Procedures In the operating room, intravenous access will be secured and routine monitoring using ECG, non-invasive blood pressure, heart rate, oxygen saturation, end-tidal carbon dioxide (EtCO2) and sevoflurane (EtSevo) (Datex-Ohmeda S/5 Compact Critical Care Monitor; GE Healthcare). After pre-oxygenation with 100% oxygen by facemask for 3 min, anaesthesia will be induced with intravenous Fentanyl 50 μg/ml (2μg/kg), Propofol 1% (2-3 mg/kg) and Rocuronio 1% (0,6 mg/kg). The investigators will continue ventilating with 100% oxygen using a facemask at least for 1 min until optimum conditions for laryngeal mask insertion are achieved (loss of eyelash reflex, relaxation of the jaw, immobility, and apnoea).

Anesthesia will be maintained with Sevoflurane 2% in an air-oxygen mixture using a circle system with a fresh gas flow of 2 l/min. Additional intravenous Fentanyl will be administrated as clinically needed during anesthesia by an increase of 10-20% in blood pressure or heart rate. Laryngeal masks size will be determined according to the manufacturers weight-based recommendations and the insertion technique will be according to the recommendations of the Instruction Manual. After successful insertion, the cuff will be inflated with air until 60 cmH2O intracuff pressure (ICP) measured using an Ambu® airway pressure manometer (AMBU, S.L. B- 81040149, Alcala, Madrid, Spain). The second measurement of intracuff pressure will be performed for surgeries taking over an hour to ensure that the intracuff pressure has not changed significantly (± 5 cmH2O) since the last calibrated intracuff pressure. An effective airway will be judged by a square wave capnograph trace, bilateral chest auscultation and no audible leak with peak airway pressures at 12 cmH2O or greater during gentle manual ventilation. The device will be connected to the respiratory machine (Datex-Ohmeda S/5 Compact Critical Care Monitor; GE Healthcare) and patients will be ventilated with a tidal volume of 8 ml/kg, adjusting the respiratory rate to an end-tidal CO2 of 30-35mmHg.

A gastric tube will be inserted via the drain tube. The correct placement of the gastric tube will be confirmed by free movement during insertion and by aspiration of gastric fluid or detection of injected air by epigastric auscultation. Oropharyngeal Leak Pressure (OLP) will be measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 liters/min (maximum allowed 40 cmH2O) recording the pressure at which equilibrium has been reached or audible air is leaking.

The leak pressure will be recorded before peritoneal insufflation and during pneumoperitoneum. The peritoneal insufflation pressure will be set at 12 mmHg. At the end of the surgery, the anesthesiologist will remove the laryngeal masks when the patients obey commands. The patients will be transferred to the Post-Anaesthesia Care Unit (PACU) to be monitored after the surgery.

Statistical Analysis Data will be entered into an Excel Database. All statistical analyses will be conducted using software from the Statistical Package for the Social Sciences (SPSS, Version 18.0, Chicago, IL, USA). The distribution of data will be determined using Kolmogorov- Smirnov analysis. The quantitative variables will be summarized with means and standard deviations or with medians and percentiles P25 and P75 in case of asymmetric distributions, and qualitative variables with frequencies and percentages. To study the relationships between qualitative variables, contingency tables will be made and the Chi-square or Fisher's tests will be used. The difference in oropharyngeal leak pressure (OLP) between two devices will be analyzed by a Student ́s t-test or the Mann-Whitney U test in case of non-normal distributions. To compare the incidence of side effects between the groups, the exact Fisher test or Chi-squared tests will be used. Significant differences will be quantified with 95% confidence intervals.