Ethical approval for this study (Ethical Committee NO.4–2019) was provided by the Ethical Issues Committee, Yiji Shan Hospital of Wannan Medical College, Anhui, China (Chairperson Prof Wu P) on March 6, 2019. Written informed consent was obtained from all the patients prior to participation. This study is an interventional, randomized controlled trial and was registered in the Chinese Clinical Trial Registry (ChiCTR1900023252). Our study was adhered to the applicable Consolidated Standards of Reporting Trials (CONSORT) guidelines. The participants were randomly and equally allocated to two groups: right-sided approach group (Group R) and midline approach group (Group M). The randomized sequence was generated by computer, and all allocations were included in sealed opaque envelopes. For randomization, the envelopes will be opened only after transporting the patient to the operating room, and only one envelope can be opened per patient. Because of the nature of the study, the outcome observer could not be blinded to the patients’ group allocation. This was a single-blind clinical trial—that is, patients were blinded to interventions.
Patients older than 18 years, with American Society of Anesthesiology (ASA) physical status I-III, and scheduled to undergo elective surgical procedure under general endotracheal anaesthesia, were all included. Patients were excluded due to the following criteria: 1) patients with a predictable difficult airway: Mallampati score ≥ IV, an interincisor gap less than 3.5 cm, a thyromental distance less than 6.5 cm, a sternomental distance less than 12.5 cm; 2) patients with reduced neck extension and flexion, airway obstruction (infectious, traumatic, foreign body, anaphylaxis), recent airway surgery, or a history of a difficult airway; 3) patients with the need for a rapid sequence induction, an alternative intubation method or known or suspected oral, pharyngeal or laryngeal masses; 4) patients with poor dentition, symptomatic gastro-oesophageal reflux, cervical spine instability, unstable hypertension, coronary artery disease, cerebral disease or patients for whom the resources were not available to conduct the procedure on the scheduled date of surgery.
After transfer to the operative room, the patients were monitored for non-invasive blood pressure (BP), heart rate (HR), pulse oximetry (SpO2) and end-tidal carbon dioxide partial pressure (PETCO2). The demographic and clinical characteristics of the patients were collected. The patients then underwent a uniform induction technique with midazolam 0.05 mg/kg, propofol 2.0 to 2.5 mg/kg and then were adequately relaxed with cisatracurium 0.15 mg/kg as evident by the loss of all trains of four responses using a peripheral nerve stimulator. With the induction of anaesthesia, the patients could also be administered 0.5 μg/kg of sulfentanyl. All the tracheas were intubated by the oral route using a Glidescope video laryngoscope, size 3 blades (GlideScope® GVL, Verathon Inc., BAothell, WA, USA). For patients in group R, the blade flange was inserted from the right side of the mouth to obtain glottic opening. A midline approach was conducted in group M. In both groups, video laryngoscopy-assisted tracheal intubations were performed by an experienced anaesthesiologist. Intraoperative anaesthesia was intravenously maintained with propofol 4–8 mg/kg/h and remifentanil 0.1–0.2 μg/kg /min. The bispectrality index (BIS) was used to monitor the depth of anaesthesia and keep the BIS value between 45 and 60.
Our primary outcome was CLV and the FPS rate. The CLV was determined by the modified Cormack-Lehane view of the glottis based on the view obtained at video laryngoscopy: grade I, the glottis is completely visible; grade IIa, the glottis opening is partially visible; grade IIb, only arytenoid cartilage is visible; grade III, only the tip of the epiglottis is visible; and grade IV, no glottis structures are visible . Our secondary outcomes were the times to glottis exposure, intubation procedure time and tracheal intubation time. We defined the time to glottis exposure as the time from the insertion of the blade into the mouth until exposure of the glottis, the time to intubation procedure as the time from finishing exposure of the glottis and ending at blade removal from the mouth and the time to tracheal intubation as the time from starting at blade insertion and ending at blade removal from the mouth. Other outcomes, including hypoxemia (SpO2 < 90%), haemodynamic changes [systolic blood pressure (SBP) and heart rate were recorded before intubation, and 1 min, 2 min and 5 min post-intubation], minor injury (oropharyngeal mucosal injury), hoarseness or sore throat on the first postoperative day assessed by a blinded anaesthetist, were also recorded.
We conducted a pilot study of 60 patients for sample size assessment. In this pilot study, the number of CVL grade I-II was 30 (100%) in Group M and 28 (93.3%) in Group R. A sample size of 218 (109 in each group) allowed the detection of a 20% difference between the groups, with an α of 0.05 (two tailed), a β of 0.20, and a power of 0.8. To account for 20% attrition, a total sample size of 262 (131 in each group) was selected.
Continuous variables, such as the height, weight, body mass index (BMI) of the patients and metrics of airway assessments are presented as the mean ± SD. The categorical data are presented as percentages. Ninety-five percent confidence intervals (CIs) for all counts and proportions were also calculated. The primary efficacy variable of the laryngoscopic views, FPS rate and adverse events in different groups were analysed using chi squared test (χ2) or Fisher’s exact test. The Mann-Whitney U test or Student’s t test was used to compare both groups with respect to basic characteristics and other outcomes including the time to glottis exposure, SBP and HR. All the statistical tests were two-sided tests (test level α = 0.05). A P value< 0.05 was considered statistically significant.