Patient enrollment and subsequent experimental procedures were performed with approval from the Institutional Review Board on Human Subjects Research and Ethics Committee and after obtaining written informed consent from patients. We enrolled a total of 30 women judged to be at American Society of Anesthesiologists physical status 1 or 2, aged 18-65 years, and undergoing laparoscopic gynecologic operation. Patients with the following were excluded from the study: obese (body mass index more than 35 kg/m2), pregnancy, gastric reflux, and/or suspected airway difficulty (Mallampati score 3 or 4, mouth opening less than 2.5 cm). The attending anesthesiologist recorded patient demographics and measured Mallampati score preoperatively.
Enrolled patients were randomly allocated into PLMA or I-gel groups using computer-generated numbers. In the operating room before surgery, the usual monitoring occurred, which included a Bispectral Index (BIS; Aspect Medical Systems, Newton, MA, USA) sensor. The following baseline data were recorded: heart rate, noninvasive blood pressure, oxyhemoglobin saturation, and BIS.
Prior to induction, all patients assumed a neutral position, and IV access was secured. After preoxygenation of the lungs with 6 L/min, using Orchestra® Base Primea (Fresenius Kabi, Brezins, France) as the infusion equipment, total intravenous anesthesia was performed.
Once patients' full muscle relaxation was achieved using rocuronium 0.6 mg/kg intravenously, the selected airway device (PLMA or I-gel) was inserted by a single user (S.C) per the manufacturer's instructions based on patient size. Size selection of the I-gel depended on patient weight (weight < 50 kg: I-gel size 3; 50-90 kg: size 4; and > 70 kg: size 5). Size selection of the PLMA is identical to classic LMA (weight 30-50 kg: size 3; 50-70 kg: size 4; 70-100 kg: size 5). Insertion of PLMA was performed without an introducer; the index finger of operator was placed in the retaining strap.
The PLMA was pressed against the hard palate and advanced into the hypopharynx until resistance was felt. After PLMA placement, the cuff was inflated. A defined volume of air was used; the cuff pressure was set to 60 cmH2O. (Maximum cuff inflation volume; size 3: 20 ml; size 4: 30 ml; size 5: 40 ml) After insertion of the breathing apparatus and subsequent connection to the ventilation system, correct positioning of it was confirmed by visualizing verification of insertion with visualization of three expiratory carbon dioxide square waveforms and movements of chest wall during mechanical ventilation and a leak pressure greater than 20 cmH2O. During surgery rocuronium was used to achieve neuromuscular block, which was verified with a peripheral nerve stimulator. At the end of the surgery, pyridostigmine 0.2 mg/kg and glycopyrrolate 0.008 mg/kg was used to reverse the effects of rocuronium. In all experimental cases, the time required for insertion and the number of attempts was obtained. The insertion time of the device was defined as the time between grabbing the device until visualization of 3 expiratory CO2 waveforms. If the first attempt at insertion was deemed a failure according to the anesthesiologist's judgment, the next try was made via either a jaw thrust maneuver or a change in head position. When and if a third attempt was necessary, a different device size was utilized. Upon failure of third line approaches, additional devices were utilized based on the attending anesthesiologist's preference.
Oropharyngeal leak pressure was determined by closing the expiratory valve of the circle system at a fixed gas flow of 3 L/min and noting the airway pressure (maximum allowed was 40 cm H2
O) at which equilibrium was reached [10
In both groups, 10 min after insertion (T1) and 15 min after carbon dioxide pneumoperitoneum (T2), measurement of vital signs and changes to airway pressure were observed and recorded. In both groups, a carbon dioxide pneumoperitoneum was induced with a maximal intraabdominal pressure of 15 mmHg. The Ppeak, leak pressure, mean airway pressure, compliance and airway resistance were measured by spirometry via an Avance station (Datex-Ohmeda, WI, USA) during measurement time.
We labeled the gap between the inspired versus the expired tidal volume as 'leak volume' and measured it at T1 and T2. The leak fraction was calculated as the leak volume divided by inspired tidal volume at T1 and T2.
We performed a pilot study with 10 patients from the PLMA group to assess the size of our study. The mean value of leak pressure was 26.7 cmH2O, standard deviations were 4.9 cmH20. For our power calculation, we assumed equal standard deviation for both groups. To sense a difference of 5.4 cmH20 between the 2 groups with a two-tailed α = 0.05 and a power of 80%, a minimum of 13 per group were needed. A Z-test was performed to prove the lack of difference between the 2 groups. Therefore, we decided to recruit 30 patients to allow for a drop rate of 10%.
Data were expressed as the median and interquartile range or as categorical distributions. Statistical analyses were performed using the Statistical Package for Social Sciences software (SPSS 12.0 for Windows; SPSS Inc., IL, USA) and SigmaStat (SIGMASTAT 3.1; Systat Software, Inc., CA, USA). The Mann-Whitney rank sum test was used to compare and analyze the numerical data between the 2 groups. The Kruskal-Wallis one way analysis of variance was used for hemodynamic data, with a Dunn multiple comparison tests for inter-group comparison. Significance was assumed at P < 0.05.