This single-center study was approved by the University's Institutional Ethical Committee (Plastic Surgery Hospital Ethical Committee No.ZX2021–12,Beijing,China) and the trial was registered prior to patient enrollment at clinicaltrials.gov (ChiCTR2100044032, http://www.chictr.org.cn.Principal investigator: Juan Zhi; Date of registration: 2021/03/06.)
Our hospital is the largest ear reconstruction center in China with 1500 ear reconstruction surgeries per year .Between March 2021 and December 2021,120 children with microtia, scheduled for elective surgery under general endotracheal anesthesia, The patients were randomised to the LMA SaCoVLM (Group SaCoVLM; n = 60) and the LMA Ambu Aura-i(Group Ambu Aura-i; n = 60),respectively, using a sealed envelope which had been prepared after a randomisation procedure using the website Randomization.com(http://www.randomization.com).
Primary endpoint was the overall success rate of LMA placement with either mask after maximum of two attempts. Secondary endpoints were the time to mask placement and time to endotracheal intubation as well as the success rate of intubation, time for LMA removal after successful intubation, differences in airway leak pressure, the fiberoptic grade of laryngeal view, and the incidence of blood stain and postoperative score throat and hoarseness.
Inclusion criteria:ASA I–II, with ages between 5 and 15 years,gender unrestricted;18kg/m2≤BMI≤30kg/m2.
Exclusion criteria：ASA III–IV ,History of upper respiratory tract infection within 2 weeks;the presence of risk factors for gastric reflux or aspiration;bronchial asthma;morbid obesity(BMI＞30kg/m2).
The study investigators were three anaesthesiologists very well experienced in using different kinds of laryngeal mask devices.
Preparation of SaCoVLM and Aura-i
The SaCoVLM includes a visual channel.a intubation channel,a gastric tube channel,a camera 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 SaCoVLMTM is adjusted according to the image displayed on the screen.A recharged battery is used to provide energy. The camera was inserted into the visual channel and connected with the screen before later use.Initial size selection for the SaCoVLM was as follows: size 2.5 for patients 20-30 kg and size 3 for those 30-50 kg. However, in the pre-experimental process, it was found that size 3 laryngeal mask is too large for 30kg children because it is difficult to insert the device under direct vision. Therefore, in the formal experiment process, we selected size 2.5 for 20-35kg and size 3 for 35kg-50kg children.The device sizes for each child were based on the guidelines（20–30 kg (size 2.5 Aura-i); 30-50 kg (size 3 Aura-i).
Routinely check the cuff of the laryngeal mask before anesthesia induction. Use lidocaine gel to fully lubricate the back of the laryngeal mask, the inner wall of the airway tube of the laryngeal mask and the outer wall of the tracheal tube, and evacuate the cuff for use. Check the light source and clarity of the flexible intubation scope(FIS), and lubricate the stem of the flexible intubation scope.
All children were forbidden to drink for 6h and fasted for 8h before operation.The general information of the patients were asked before surgery,including age,height and weight.The modified Mallampati classification (Class I–IV), mouth opening, thyromental distance, Upper lip bite test class，Hemifacial Microsomia，Modified Mallampati (Samsoon and Young) classification was assessed by an anesthesiologist ignorant of the study while the patient was sitting with the mouth wide open and the tongue protruding without phonation ［7］. Mouth opening was measured as the difference between the upper and lower incisors at the midline in centimeters using a scale. Thyromental distance was measured from the thyroid cartilage to inside of the mentum with neck extended, using a tape ［8］. Peripheral venous access was initiated in the operating room, a multifunctional monitor (Datex-Ohmeda S5, General Electric, Boston, MA, USA) to monitor basic vital signs such as electrocardiogram(ECG), non-invasive blood pressure(NIBP) , end-tidal-carbon dioxide (EtCO2) and pulse oxygen saturation was set up.
Anesthesia and airway management
The children were preoxygenated with 100% O2(5L/min,5min) before induction using a facemask and the head was placed in the neutral supine position.General anesthesia was pre-medicated with midazolam (0.02mg/kg), sufentanil (0.25ug/kg), and. Anaesthesia was induced with propofol (2.5mg/kg). After adequate ventilation using mask ventilation, rocuronium (0.6 mg/kg) was administered for muscle relaxation. Adequate anesthetic depth was confirmed by the disappearance of the eyelash reflex when the jaw was completely relaxed ［9］. Both devices were placed using a standard midline insertion technique(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 device was inserted into the hypopharyngeal cavity). When appropriate, re-inject the extracted gas into the laryngeal mask, connect the anesthesia machine to manually control breathing, and observe the chest rise. When the APL pressure valve is at 30cmH2O, when the airbag is pressed by hand, the thorax can be seen regularly undulating, and the end-tidal carbon dioxide waveform can be seen, which means that the laryngeal mask is well ventilated. Otherwise, the laryngeal mask needs to be adjusted (up–down/Chandy's manoeuvre ［10］, reversal method, inflating or deflating etc.) to obtain a satisfactory position. The intra-cuff pressure was then standardized to 60 cm H2O using cuff pressure gauge(VBM,German). The oropharyngeal leak pressure was measured with the expiratory valve closed and a fresh gas flow of 6 L/min until equilibrium was seen on the pressure gauge ［11］(not allowed to exceed 40 cm H2O). A maximum of three attempts were allowed and the number of attempts was recorded. Time for insertion of LMAs was from the time of taking the device in hand to the confirmation of proper placement of the device.
Next, a fibreoptic evaluation of LMA placement was performed with a fibreoptic intubation scope,The glottis view was assessed and graded as follows［12］:Grade 4: full view of the glottis;Grade 3: partial view of the glottis;Grade 2: no visualization of the glottis directly but can be found;Grade 1: no visualization of the glottis.Additionally ,the view on the screen was recorded.The classification of the glottis seen under the display of the SaCoVLM visual laryngeal mask［13］:Grade 4: full view of the glottis;Grade 3: visualization of all laryngeal inlet and partial glottis;Grade 2: visualization of the bilateral aryepiglottic fold and part of the laryngeal inlet and the ventilation was good; Grade 1: the lateral part of the right aryepiglottic fold and part of the laryngeal inlet and the ventilation was good.
In group Ambu Aura-i, any maneuver(such as lifting the jaw ) required to improve the glottis view under fiberoptic vision was performed and noted. On achieving optimum glottis view, fiberoptic-guided tracheal intubation was done with the preloaded tracheal tube. In group SaCoVLM, intubation of the lubricated tracheal tube was attempted along the airway of the SaCoVLM guided by its view on the screen. Manoeuvres such as inflating the laryngeal mask and rotating the tip of tube were allowed if the placement was not successful.
Proper placement of the ETT was confirmed by the appearance of normal square wave capnogram and bilateral equal air entry. Time taken for intubation was recorded from the time of taking ETT in hand to the confirmation of proper placement of the ETT. During the procure, children were administered additional boluses of propofol(20–40 mg) to ensure adequate anesthetic depth.
After successful intubation, the LMA was removed using a stabilizing rod(a plain tracheal tube one size smaller was used as a removal guide). Time taken for removal of the device was recorded as the disconnection of the breathing circuit till ventilation successfully .The attempt was terminated and the attempt classified as “failure” if total time exceeded 300s or SpO2 decreased to < 91% and the trachea would be intubated by direct laryngoscopy if the device was not achieved correctly after three attempts, fiberoptic intubation through the device was not successful after two attempts, or if the tracheal tube was dislodged during device removal.
Maintenance of anesthesia was realized using anesthetics(Oxygen+sevoflurane+propofol+remifentanil).Anesthetics were stopped at the end of surgery.Complications such as desaturation (SpO2<90%), regurgitation or aspiration, laryngospasm/bronchospasm, oropharyngeal or laryngeal trauma (blood staining of device/ETT) and hoarseness of voice were recorded. Patient follow-up was according to standard postoperative protocols at our institution.
We assumed that SaCoVLM would have the first attempt success rate for insertion similar to that of Ambu Aura-i. Sample size estimation was done based on observations of previous studies where the first attempt success rate for insertion was 87.5% for Ambu Aura-i［14］. Assuming a success rate of 90% for SaCoVLM and a noninferiority margin of 10% between the groups, a minimum of 51 patients would be required to achieve a power of 90%, at the type I error level of 0.05. We included 60 patients in each group to compensate for possible dropouts. Sample size was calculated using www.powerandsamplesize.com.
Data collection and statistical analysis
Data were recorded intraoperatively using a standardized data collection sheet and analyzed using Microsoft Excel Spreadsheet and the statistical software IBM SPSS software version 22 (SPSS Inc. Chicago, IL, USA). Statistical comparisons between cohorts were performed using student’s t-tests for continuous data, chi-square tests for categorical data, and Mann–Whitney U-test for ordinal data. A Spearman’s correlation coefficient was calculated for the relationship between the fiberoptic grade of view and time to tracheal intubation. Proportions were compared with Fisher’s exact test or the Chi-square test, as appropriate. Study data are presented as mean (SD) or median (IQR).