This study was conducted in six hospitals in China (The First Medical Center of Chinese PLA General Hospital, Henan Provincial People’s Hospital, The First Affiliated Hospital of Zhengzhou University, Tianjin Medical University General Hospital, The Second Affiliated Hospital of Air Force Medical University, Daping Hospital) from October 01, 2018, to October 31, 2019. The study was registered at the Chinese Clinical Trial Registry on September 10, 2018 (ChiCTR1800018300, Weidong Mi as the principal investigator). The study adhered to the STROBE Statement and was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from each participant before enrollment.
This study was approved by the ethics committee of Chinese PLA General Hospital(S2017–034-02), Daping Hospital of Army Medical University (2018–45), the First Affiliated Hospital of Zhengzhou University (SS-2019-038), Tianjin Medical University General Hospital (record), Henan Provincial People’s Hospital (2018–46), the Second Affiliated Hospital of Air Force Medical University (201812–09).
In this study, we included adult patients who were American Society of Anesthesiology (ASA) class 1 and 2, 18 to 70 years old, and scheduled for laparoscopic surgeries with an expected duration of surgery less than 4 h and expected blood loss less than 300 ml. Exclusion criteria consisted of BMI > 30 kg/m2, patient refusal, a suspected difficult airway, increased risk of aspiration (hiatus hernia, gastroesophageal reflux disease, non-fasting status), recent upper respiratory tract infection, inability to comply with study requirements including follow-up. All the anesthetists who participated in this study were experienced in the use of LMA with more than 200 cases of LMA insertions and were trained in the use of LMA® Protector™ (the study device) and study protocol before the beginning of the study.
All patients received standard monitoring, including electrocardiogram, non-invasive blood pressure, and oxyhemoglobin saturation in the operation room. After pre-oxygenation with a facemask for 3 min, anesthesia was induced with sufentanil 0.2–0.4 μg/kg or fentanyl 1-3 μg/kg, propofol 1-2 mg/kg oretomidate 0.2–0.3 mg/kg, and rocuronium 0.6–0.9 mg/kg or cisatracurium 0.2–0.3 mg/kg. LMA® Protector™ insertion was attempted in all patients. The choice of LMA® Protector™ size was based on the following principles: weight ≤ 50 kg for size 3; weight between 51 and 70 kg for size 4; weight>70 kg for size 5. After deflation and lubrication of the cuff, the LMA® Protector™ was inserted with the distal tip kept in the midline until resistance was felt. Then the cuff was inflated to maintain the intracuff pressure at 40 to 60 cmH2O according to the Cuff Pilot™, the integrated cuff pressure indicator . The anesthesia apparatus was connected to the LMA® Protector™ for mechanical ventilation. Chest wall movement and capnography were used to confirm the successful placement of LMA. Further extension of the head and chin lift performed by the assistant was permitted during the insertion of the study device.
The insertion time was measured from the moment the anesthetist picked up the LMA® Protector™ until the appearance of the first capnography trace by an assistant. Oropharyngeal leak pressure (OLP) was measured by setting the adjustable pressure limiting valve to 40 cmH2O at a fixed gas flow of 3 L/min and noting the steady-state airway pressure on the monitor [10, 18]. The suprasternal notch test was performed as Eckardt described,  and a lubricated 14F gastric tube was then inserted through the female drainage port. Failed insertion of LMA® Protector™ was defined by any of the following criteria:  failed passage into the pharynx ; malposition (air leaks or end-tidal capnography could not be obtained); and  ineffective ventilation (maximum expired tidal volume < 8 ml/kg, end-tidal carbon dioxide > 45 mmHg, or pulse oxygen saturation < 92% if correctly positioned) . We allowed a maximum of three attempts with the allocated device. The easiness of insertion was graded as easy, mild difficulty with resistance, moderate difficulty with resistance, and severe difficulty with resistance.
Anesthesia was maintained with intravenous or intravenous-inhalation combined anesthesia to keep bispectral index (BIS) between 40 and 60. Supplemental doses of neuromuscular blockade (rocuronium 0.1–0.2 mg/kg or cisatracurium 0.02–0.04 mg/kg) was administered intermediately during the operation. The timing of muscle relaxants during the operation was guided by clinical criteria according to the pharmacokinetics of muscle relaxants, the pathophysiological characteristics of patients, and the demand for surgical relaxation. The total dosage of neuromuscular blockade used during the surgery was recorded. Volume control ventilation was set at an inspired tidal volume of 6–8 mL/kg, a respiratory rate of 12/min, and an inspiratory/expiratory ratio of 1:2 to maintain the end-tidal CO2(EtCO2) at around 35–45 mmHg and no positive-end-expiratory pressure was used. Pneumoperitoneum was established by insufflation of carbon dioxide to a pressure of 14 mmHg. During maintenance of anesthesia, airway complications (intermittent obstruction, complete obstruction, airway leak) and airway manipulations during the procedure (position corrections, additional cuff inflation or deflation, device reinsertion) were documented. If effective ventilation could not be achieved after airway manipulations, i.e., maximum expired tidal volume < 8 ml/kg, end-tidal carbon dioxide > 45 mmHg, or pulse oxygen saturation < 92%, the LMA® Protector™ would be replaced with endotracheal intubation. Effective ventilation rate was calculated as the proportion of patients who were effectively ventilated with LMA® Protector™ throughout the procedure in all participants.
On emergence from anesthesia, the LMA® Protector™ was removed when the patient was able to breathe spontaneously and follow verbal instructions. All patients were monitored for at least 30 min in the recovery room before returning to the ward. Visible bloodstains and reflux content in the drainage channel were documented after the removal of LMA® Protector™. The operator’s satisfaction score was rated on a scale of 0 (worst) to 10 (best) by the anesthetists. On the first day after surgery, participants were interviewed to ascertain if they had the following complaints: sore throat, dysphagia, and hoarseness of voice. Vigilance against aspiration was kept especially when the patient presented with symptoms such as coughing, difficulty breathing, choking, or wheezing. Further evaluation would be taken if aspiration was suspected. Adverse events should be reported if the patient was diagnosed as aspiration during hospitalization or re-administered as aspiration pneumonia in 1 month after surgery.
The sample size was calculated based on the primary outcome of effective ventilation rate. An estimated minimum sample size of 243 patients would be required to show an effective ventilation rate of 95% with a single-sided type I error of 0.05 and power of 0.8 . As the sample dropout rate was estimated to be 20%, the final determined sample size was 300.
The Kolmogorov-Smirnov test was performed to evaluate the normality of continuous data. Mean and the standard deviation was used to describe symmetrically distributed continuous data. Asymmetrically distributed continuous data were presented as median [interquartile range]. Percentages were used to describe categorical data. Continuous data were analyzed with Student’s t test or the Mann-Whitney U test. The chi-square test or Fisher’s exact test was used for categorical data, as appropriate. All the data were analyzed using SPSS (Version 20, IBM Corp., Chicago, IL, USA).