Ethics and study design
This prospective study was performed at Samsung Medical Center in Seoul, Korea, after approval from Samsung Medical Center Institutional Review Board (IRB No. 2018-10-111). This trial was registered at Clinical Trials of Korea (KCT 0003512). This study was retrospectively registered(February 15, 2019) after enrolment of the first participant(February 04,2019). Patients with an American Society of Anaesthesiologists physical status of I-III and who were scheduled for elective laparoscopic hepatectomy were enrolled between February 2019 and March 2019. Patients were excluded if they had lung disease, upper respiratory infection symptoms, esophageal varix, or previous stomach surgery. Written informed consent was obtained from all participants. This manuscript adhered to the CONSORT guidelines (Fig. 1).
Blinding And Randomisation
All patients were randomly assigned to one of two groups using a randomisation list administered by a nurse who did not participate in the study. A sealed envelope with group assignment was given to the investigator just before the operation. One experienced investigator performed the airway management, and the intraoperative data were recorded by those who did not participate in airway management.
Anaesthesia Protocol
All patients underwent midnight NPO. Standard monitoring such as electrocardiography, pulse oximetry, noninvasive blood pressure, and bispectral index monitoring were performed on arrival at the operating room. Anaesthesia was induced using 5 mg kg− 1 of thiopental sodium and 8 vol% of sevoflurane. After loss of consciousness (LOC) was confirmed, 0.8 mg/kg rocuronium was administered. Mask ventilation was performed such that the airway pressure did not exceed 20 cm H2O. Endotracheal intubation or SGA insertion was performed after confirming maximum neuromuscular blockade with twice Train-of-Four (TOF) count 0. And, the surgical procedure was performed in a deep neuromuscular block (no responses to TOF and two or fewer responses to post-tetanic count). Endotracheal tube (Shiley™, Hi-Contour Oral Tracheal Tube Cuffed, Covidien, Germany) intubation (Group ETT) or second-generation SGA (LMA® Protector™, Teleflex Medical Ltd., Athlone, Ireland) insertion (Group SGA) was performed. Mask ventilation was performed such that the airway pressure did not exceed 20 cm H2O. The SGA size was selected according to manufacturer recommendations. Air was insufflated into the SGA cuff until the pilot balloon black line was located within the green zone.[10] After successful ventilation was confirmed on capnography, mechanical ventilation was started. Cuff pressure of the SGA was adjusted using a digital cuff pressure monitor (Shiley™ Pressure Control, Covidien, Germany) to maintain less than or equal to 60 cm H2O. SGA devices were replaced by ETTs in the following situations for patient safety if a) the SGA was not inserted in more than 3 attempts, b) persistent oropharyngeal leak with inadequate ventilation (end-tidal CO2 ≥ 45 mmHg during pneumoperitoneum), and/or c) the stomach was inflated enough to cause visual disturbance under laparoscopic view. If the SGA was replaced by ETT, the patient was dropped from the study. The ETT size was selected according to sex (7.0 mm for women, 8.0 mm for men). The ETT cuff pressure was monitored using a digital cuff pressure monitor to ensure that it did not exceed 25 cm H2O.[11, 12]
Tidal volume was 8 mL kg− 1 (ideal body weight), and respiratory rate was adjusted as required to maintain end-tidal CO2 at 35 to 40 mmHg. Tidal volume was reduced if airway pressure exceeded 25 cm H2O. After ETT intubation or SGA insertion, a non-compressible 14 French gastric drainage catheter (ST probe, Lucky Medical Co., LTD, Seoul, Korea) was inserted and fixed up to 60 cm through the mouth or the SGA gastric drainage port. After anaesthesia induction, patient posture was adjusted to the lithotomy and left tilting position by surgeon request. The surgeon inserted a trocar into the peritoneal cavity, and the CO2 insufflator was maintained to 12 mmHg during pneumoperitoneum. The surgeon confirmed that the gastric drainage catheter tip was located on the stomach. After operation, the gastric drainage catheter was sufficiently suctioned and carefully removed.
Intra-gastric Pressure Monitoring And Data Acquisition
After gastric drainage catheter insertion, sufficient intragastric suction was performed. The gastric drainage catheter with a three-way stopcock was connected to the pressure monitoring device and filled with normal saline. Intra-gastric pressure was continuously measured by a pressure monitoring device (Edward Life Science, TruWave™ 3 cc / 60 in; Fig. 2.). The gastric drainage catheter with a three-way stopcock was connected to the pressure monitoring device and filled with normal saline. The pressure transducer was calibrated and placed at the intersection of the anterior axillary line and a transverse line at the level of the xyphoid.[13] In SGA, the airway sealing pressure was controlled by a pressure value that reached equilibrium at a fresh gas flow of 3 L min− 1 with the adjustable pressure limiting valve closed.[14] If the sealing pressure increased above 30 cm H2O, we stopped the measurement. Intra-gastric pressure was collected at several time points (baseline, T1-T6 during pneumoperitoneum every 30 min, and at the end of surgery) during the anaesthesia period by the monitoring computer program (Picis Care Suit Anaesthesia Manager; Picis Ltd., Wakefield, MA, USA). The pH was measured after removing the SGA by sampling secretions on the tip of the SGA using a spatula and placing the drop at the tip of a pH meter (2K712, ISFETCOM Co., Ltd., Japan). Total anaesthesia time, total operation time, and total pneumoperitoneum time were recorded. Postoperative complications such as sore throat, cough, hoarseness, and laryngospasm were assessed from the time immediately after removal of the airway device to discharge from the post anaesthesia care unit.
Statistics
In an initial pilot study, sample size calculations were performed using a non-inferiority test with Student’s t-test to identify differences between intra-gastric baseline and peak pressures in ETT and SGA. Changes of intra-gastric pressure during surgery were 14.8 mmHg in ETT and 14 mmHg in SGA (standard deviation 2.8, non-inferiority margin 3.0). The sample size was calculated with a power of 0.9 and an alpha error of 0.05. Assuming a 10% dropout rate, we planned to recruit a total of 66 patients (33 subjects for each group).
The change of difference between intra-gastric baseline and peak pressures in ETT and SGA was calculated with a 95% confidence interval (CI). If the lower limit of the 95% CI was less than 3 mmHg, non-inferiority of SGA compared with ETT was demonstrated. Continuous variables are presented as the mean ± standard deviation (SD) or median (interquartile range, IQR) as appropriate. Continuous variables were compared using Student’s t-test or Wilcoxon’s signed-rank test, and the Shapiro–Wilk test was used to explore normality. Categorical variables were analyzed using Pearson’s chi-square test or Fisher’s exact test as appropriate. The difference between baseline and each time point of intra-gastric pressure between the two groups was analyzed using generalized estimating equations (GEE). Bonferroni’s correction for post-hoc analysis was applied. Statistical analyses were performed using SPSS version 22 (SPSS Inc., Chicago, IL, USA). A p-value less than 0.05 was considered statistically significant.