This single-center prospective observational study was approved by the Ethics Committee of Clinical Research of Beijing Hospital (No. 2019BJYYEC-236-02) and registered in the China Clinical Trial Registration Center (No. ChiCTR2000028802 Date2020.01.04). Between February 2020 and December 2020, 100 adult patients who received SaCoVLM™ for general anesthesia were recruited and informed consent was obtained. The sample size of 100 cases is based on a similar preliminary evaluation of a new laryngeal mask airway by Liu et al. [5]. Inclusion criteria: age ≥ 18; gender unrestricted; ASA I-II; 18 kg/m2 ≤ BMI ≤ 30 kg/m2; Normal airway. Exclusion criteria: severe respiratory diseases; lateral or prone surgical positions; mouth opening less than 2 cm; edentulous; the presence of risk factors for gastric reflux or aspiration, including fasting, morbid obesity, gestation over 14 weeks, ileus, and hiatal hernia; other laryngeal mask contraindications, included intraoral, laryngeal surgery and thoracic surgery.

All the methods in this study were performed in accordance with the relevant guidelines and regulations in the Methods section.

Preparation of SaCoVLM™

Disposable SaCoVLM™ (Fig. 1) includes a visual channel, a ventilation (intubation) channel, a gastric tube channel, a camera (electronic camera, focal length 7 mm, field angle 90° ± 13.5%, ZHEJIANG UE MEDICAL CORP.) and connecting wires. The camera is fixed on the right side of ventral cuff, connected with the screen and inserted into the visual channel. During placement, the SaCoVLM™ is adjusted according to the image displayed on the screen. The data are stored in a chip. A rechargeable battery is used to provide energy. The SaCoVLM™ was selected according to the patient’s weight. Size 3 was used for patients weighing 30–50 kg, size 4 for patients weighing 50–70 kg, and size 5 for patients weighing 70–90 kg. Before placement, the cuff was deflated and flattened. The back of the laryngeal mask was lubricated with Lidocaine Hydrochloride Gel. The camera was inserted into the visual channel and connected with the screen before later use.

Fig. 1

SaCoVLM™ disposable video laryngeal mask

Preoperative preparation

All subjects were forbidden to drink for 6 h and fasted for 8 h before operation. The general information of the patients was asked before surgery, including age, height and weight. We measured the thyromental distance, the mouth opening of the patients, Mallampati classification, upper lip occlusion test and ASA classification.

Peripheral venous access was initiated in the operating room. Electrocardiogram (ECG), heart rate (HR), blood pressure (BP), oxygen saturation (SpO2) and bispectral index (BIS) were monitored.

Anesthesia and airway management

The patient was preoxygenated with 100% oxygen (5 L/min, 5 min) before induction using a facemask and the head was placed in the neutral supine position. General anesthesia was induced with sufentanil (0.2–0.5 μg/kg), propofol (2 mg/kg) and cis-atracurium (0.2 mg/kg). The patient’s lungs were manually ventilated when the BIS was reduced to below 60. After obtaining easy mask ventilation and a relaxed airway, the SaCoVLM™ was inserted. The anesthetist held the distal end of the ventilation channel and let the laryngeal mask slide down the palatopharyngeal curve along midline in the mouth, until the front end of SaCoVLM™ was inserted into the hypopharyngeal cavity. The SaCoVLM™ was inflated to achieve a maximum cuff pressure of 60 cmH2O (1 cmH2O = 0.098 kpa) detected by a hand-held manometer (VBM, German). Artificial ventilation was performed. The glottic visualizaiton was observed and a gastric tube (12Fr) was placed through the gastroesophageal channel. After proper fixation of SaCoVLM™, positive pressure ventilation was performed. Mechanical ventilation parameters were set: tidal volume 6–8 mL/kg, inhalation/exhalation ratio 1:2, ventilation frequency 12 times/min and PETCO2 35–45 mmHg (1 mmHg = 0.133 kPa). Fibreoptic bronchoscopy was performed to grade the glottic exposure. The SaCoVLM™ insertion was considered successful when the following criteria were met: chest movement and no air leakage during normal ventilation; more than two continuous end-expiratory carbon dioxide waveforms; positive suprasternal concave gel test; the gastric tube successfully implanted and the ventilation channel connected to the anesthesia machine for mechanical ventilation. The criteria of SaCoVLM™ insertion failure: failure to place the SaCoVLM™ correctly after more than 2 times and longer than 60 s; abnormal PETCO2 waveforms; bellows collapsing. All procedures were performed by the same anesthesiologist experienced in the use of SaCoVLM™. Time of SaCoVLM™ insertion referred to the time between SaCoVLM™-incisors contact and the first ventilation showing two PETCO2 waveforms. If the air leakage was obvious, the position of SaCoVLM™ needed to be adjusted using one or more of the following methods: the up-down maneuver, raising the jaw with both hands, the Chandy maneuver, increasing and reducing the amount of air, re-insertion and changing the size. The position and function of SaCoVLM™ was reevaluated after adjustment. If the insertion failed twice, endotracheal intubation was performed.

The pressure gauge stability method was used to measure the sealing pressure inside the SaCoVLM™ [6]. The fresh gas flow rate was adjusted to 3 L/min, the pressure was adjusted to 40 cmH2O, and mechanical ventilation was switched to manual ventilation. When the sound of air leakage was heard, the pressure was gauged as the sealing pressure. For the sake of safety, the maximum oropharyngeal leak pressure was set to be 40 cmH2O.

Anesthesia was maintained with targeted-infusion of propofol (2.5–3.5 μg/ml) and remifentanil (3-4 ng/ml), punctuated with infusion of cisatracurium. BIS was controlled at 40–60. Propofol and remifentanil infusion was stopped and muscle relaxation antagonism was performed after the skin was sutured. As the patient awakened and the mouth could open as directed, the SaCoVLM™ was removed. The patient was transferred to the Post Anesthesia Care Unit (PACU).

We divided the glottic exposure into four grades under SaCoVLM™ (Fig. 2). Grade 1: visualization of the lateral part of the right aryepiglottic fold and part of the laryngeal inlet, and the ventilation was good; Grade 2: visualization of the bilateral aryepiglottic fold and part of laryngeal inlet, and the ventilation was good; Grade 3: visualization of all laryngeal inlet and partial glottis; Grade 4: visualization of the whole glottis. Fibreoptic bronchoscopy grade is as follows [7, 8]: Grade 1: visualization of no glottis; Grade 2: visualization of glottis and the lingual surface of epiglottis; Grade 3: visualization glottis and the laryngeal surface of the epiglottis. Grade 4:visualization of glottis.

Fig. 2

SaCoVLM™ Glottic exposure grades. Grade 1: visualization of the lateral part of the right aryepiglottic fold and part of the laryngeal inlet, and the ventilation was good; Grade 2: visualization of the bilateral aryepiglottic fold and part of laryngeal inlet, and the ventilation was good; Grade 3: visualization of all laryngeal inlet and posterior glottis; Grade 4: visualization of the whole glottis

Data collection

The primary variables: visualization and grades of glottic exposure under SaCoVLM™. The secondary variables: the success rate of insertion, including the first-time success rate and the total success rate, the sealing pressure, classification under fibreoptic bronchoscopy, the insertion time, adjustment times. Other variables: intraoperative findings, secretions after SaCoVLM™ removal, soft tissue injuries (blood or bleeding), complications within postoperative 24 h (sore throat, hoarseness, difficulty swallowing).

Statistical analysis

SPSS26.0 statistical software was used. We used means and standard deviation to describe continuous data and percentages for categorical data.

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