Intubation using video laryngeal mask airway SaCoVLM and laryngeal mask airway Ambu® Aura-i in anesthetized children with microtia: a randomized controlled study

The Ambu Aura-i laryngeal mask is considered to be a device for blind intubation as well as for fiberoptic guided intubation. The novel video laryngeal airway mask SaCoVLM is a supraglottic airway device that allows intubation under direct vision. We hypothesized that success rates for device placement and tracheal intubation with the SaCoVLM would be comparable with the Ambu Aura-i mask. A prospective, randomized clinical trial was conducted from March 2021 to December 2021. One hundred and twenty patients were enrolled and randomized in the study. Direct intubation was performed with the SaCoVLM, and fiberoptic guided intubation was performed with the Ambu Aura-i mask. The primary outcome measure was the first success rate of LMA placement. Secondary outcome measures were the time from device placement and time from endotracheal intubation (as well as the time for LMA removal after successful intubation), differences in airway leak pressure, fiberoptic grade of the laryngeal view, and incidence of blood staining. The first success rate of LMA placement was similar for the two devices. There was no difference in the time for successful endotracheal intubation between the Ambu Aura-i and SaCoVLM groups (24.1 s ± 6.3 versus 25.7 s ± 2.1; p > 0.05). The time for removal was slower in the SaCoVLM group than in the Ambu Aura-i group (20.8 s ± 0.8 versus 14.7 s ± 6.1; p < 0.01). The airway leak pressure was higher in the SaCoVLM group than in the Ambu Aura-i group (27.0 s ± 1.0 versus 22.3 s ± 3.6; p < 0.01), and the incidence of blood staining was higher in the SaCoVLM group (16.7%). The SaCoVLM has an overall comparable performance to the Ambu Aura-i mask. However, the SaCoVLM is better relative to direct intubation without the assistance of a flexible intubation scope, which reduces the device’s demand.


Introduction
Children with microtia may experience difficult laryngoscopy; additionally, compared to children with normal ears, bilateral microtia is associated with a notably higher incidence of difficult laryngoscopy [1,2]. Due to anatomical and physiological differences, the technique of endotracheal intubation is relatively more difficult in children [3]. The use of a supraglottic airway device (SAD) as a conduit for tracheal intubation is an established means of securing the airway when difficult laryngoscopy is encountered in children [4].
The Ambu® Aura-i mask was designed to allow the passage of conventional cuffed tracheal tubes and has proven effective for fiberoptic-guided tracheal intubation in previous clinical trials [5] and in children with challenging airways. Due to the lack of direct vision, the Ambu Aura-i laryngeal mask usually needs to be assisted by a flexible intubation scope (FIS) to ensure the success rate of tracheal intubation, which, to a certain extent, limits the wide application of this method. The SaCoVLM [6] (Safe Comfortable Video Laryngeal Mask, B2020082201, ZHEJIANG UE MEDICAL CORP. Add: NO.8, YouYi Road, Baita Economic Develop Zone, Xianju, Zhejiang, China) is a visual laryngeal mask, including a visual channel and ventilation channel. The camera connected in the laryngeal mask can be used to continuously observe the entire use of the laryngeal mask, including its insertion, dwelling, and withdrawal; thus, problems that occur during its use can be discovered in a timely manner. Unlike the Aura-i mask, the SaCoVLM has a functional sight for endotracheal intubation without the need for adjuvants. However, no studies are available that compare this device with other SADs, especially for intubation in children.
We hypothesized that the LMA SaCoVLM and the LMA Aura-i are comparable with respect to success rates for mask placement and tracheal intubation. Additionally, we posit that the time for endotracheal intubation through the use of the SaCoVLM would be faster than that through the use of the Ambu Aura-i mask.
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 were scheduled for elective surgery under general endotracheal anesthesia. The patients were randomized to the LMA SaCoVLM (Group SaCoVLM; n = 60) and the LMA Ambu Aura-i (Group Ambu Aura-i; n = 60) using a sealed envelope that had been prepared after a randomization procedure using a website (http:// www. rando mizat ion. com).
The primary endpoint was the overall success rate of LMA placement with either mask after a maximum of two attempts. Secondary endpoints were the time to mask placement and to endotracheal intubation, success rate of intubation, time for LMA removal after successful intubation, differences in airway leak pressure, fiberoptic grade of the laryngeal view, incidence of blood staining, and postoperative sore throat and hoarseness.
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 > 30 kg/m 2 ).
The investigators in this study were three anesthesiologists who were highly experienced in using different kinds of laryngeal mask devices.

Preparation of the SaCoVLM and Aura-i mask
The SaCoVLM includes a visual channel, a VENTILA-TION channel, which can be used as an intubation channel, a gastric tube channel and the camera was inserted into the visual channel and connected with the screen before later use. During placement, the SaCoVLM™ is adjusted according to the image displayed on the screen. A rechargeable battery is used to provide energy. Initial size selection for the SaCoVLM was as follows: size 2.5 for patients from 20 to 30 kg and size 3 for patients from 30 to 50 kg. However, in the pre-experimental process, it was found that the size 3 laryngeal mask was too large for the 30 kg children because it was difficult to insert the device under direct vision. Therefore, in the formal experimental process, we selected a size 2.5 for patients from 20 to 35 kg and a size 3 for patients from 35 to 50 kg. The device sizes for each child were based on the guidelines (20-30 kg (size 2.5 Aura-i mask) and 30-50 kg (size 3 Aura-i mask).
The cuff of the laryngeal mask was routinely checked before anesthesia induction. Lidocaine gel was used to fully lubricate the back of the laryngeal mask, inner wall of the airway tube of the laryngeal mask and outer wall of the tracheal tube, and then the cuff was evacuated for use. The light source was checked for clarity in the flexible intubation scope (FIS) and the stem of the FIS was lubricated.

Preoperative preparation
All children in the study were forbidden to drink for 6 h and fasted for 8 h before the operation. The general information about patients was collected prior to surgery, including age, height and weight. The modified Mallampati classification (Classes I-IV), mouth opening, thyromental distance, upper lip bite test class, hemifacial microsomia, and modified Mallampati (Samsoon and Young) classification were assessed by an anesthesiologist blinded to the study while the patient was sitting with their mouth wide open and tongue protruding without phonation [7]. The mouth opening was measured in centimeters as the difference between the upper and lower incisors at the midline using a scale. The thyromental distance was measured from the thyroid cartilage to the inside of the mentum with the neck extended using tape [8]. Peripheral venous access was initiated in the operating room, and a multifunctional monitor (Datex-Ohmeda S5, General Electric, Boston, MA, USA) was used to monitor basic vital signs, such as electrocardiogram (ECG), noninvasive blood pressure (NIBP), end-tidal-carbon dioxide (EtCO 2 ) and pulse oxygen saturation.

Anesthesia and airway management
The children were preoxygenated with 100% O 2 (5 L/min, 5 min) before induction using a face mask, and the head was placed in the neutral supine position. General anesthesia was premedicated with midazolam (0.02 mg/kg) and sufentanil (0.25 µg/kg). Anesthesia was induced with propofol (2.5 mg/ 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 the midline in the mouth until the front end of the device was inserted into the hypopharyngeal cavity). When appropriate, the extracted gas was re-injected into the laryngeal mask and, connected to the anesthesia machine to manually control breathing and observe the chest rise. The laryngeal mask allowed adequate ventilation when the APL pressure valve was at 30 cmH 2 O; additionally, when the airbag was pressed by hand, a regularly undulating thorax and end-tidal carbon dioxide waveform could be seen. If the above was not observed, the laryngeal mask needed to be adjusted (up-down/Chandy's maneuver [10], reversal method, inflating or deflating, etc.) to obtain a satisfactory position. The intracuff pressure was then standardized to 60 cmH 2 O using a cuff pressure gauge (VBM, Germany). The oropharyngeal leak pressure was measured with the expiratory valve closed and a fresh gas flow of 6 L/min until equilibrium was observed on the pressure gauge [11] (not allowed to exceed 40 cmH 2 O). A maximum of three attempts were allowed, and the number of attempts was recorded. The time for insertion of the LMAs was considered from the time of taking the device in hand to the confirmation of proper placement of the device.
Next, a fiberoptic evaluation of LMA placement was performed with a fiberoptic 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: visualization of glottis and the lingual surface of epiglottis; and 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 was as follows [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 the Ambu Aura-i group, any maneuver (such as lifting the jaw) required to improve the glottis view under fiberoptic vision was performed and noted. To achieve an optimal glottis view, fiberoptic-guided tracheal intubation was performed with the preloaded tracheal tube. In the SaCoVLM group, intubation of the lubricated tracheal tube was attempted along the airway of the SaCoVLM, which was guided by its view on the screen. Maneuvers such as inflating the laryngeal mask and rotating the tip of the tube were allowed if the placement was not successful.
Proper placement of the endotracheal tube( ETT) was confirmed by the appearance of a normal square wave capnogram and bilateral equal air entry. The time taken for intubation was recorded from the time of taking the ETT in hand to the confirmation of its proper placement. During the procedure, 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 (in which a plain tracheal tube that was one size smaller was used as a removal guide). The time taken for removal of the device was recorded as the disconnection of the breathing circuit until ventilation was successfully achieved. The attempt was terminated, and was classified as a "failure" if the total time exceeded 300 s or if the SpO2 decreased to < 91%. The trachea was intubated by direct laryngoscopy if the device was unsuccessful following three attempts. Fiberoptic intubation through the device was considered unsuccessful 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 the device/ETT) and hoarseness of voice were recorded. Patient follow-up was performed according to the standard postoperative protocols of our institution.
We assumed that the SaCoVLM would have a first attempt success rate for insertion similar to that of the Ambu Aura-i mask. Sample size estimation was performed based on observations of previous studies where the first attempt success rate for insertion was 87.5% for the Ambu Aura-i mask [14]. Assuming a success rate of 90% for the 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. The sample size was calculated using www. power andsa mples ize. com.

Data collection and statistical analysis
Data were recorded intraoperatively using a standardized data collection sheet and analyzed using a Microsoft Excel spreadsheet and 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 the Mann-Whitney U test for ordinal data. 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 the mean (SD) or median (IQR).

Results
A total of 128 patients were assessed for eligibility, of which 120 patients were enrolled in the study and randomly allocated to the SaCoVLM or Ambu Aura-i groups [ Fig. 1]. There were no dropouts. There were no significant differences between groups with regard to demographic data, ASA physical status (Table 1), or clinical predictors of a challenging airway, such as Mallampati score, mouth opening, and thyromental distance ( Table 2). Comparative data regarding attempts on device placement and tracheal intubation through the devices are presented in Table 3.
The rate for first-attempt successful SaCoVLM placement was 85%, and the rate for first-attempt successful Ambu Aura-i placement was 88.3%; notably, the success rate in all patients was 100% by the third attempt. Therefore, a second attempt was required in 13.3% of the SaCoVLM group and in 10% of the Ambu Aura-i group (p>0.05). Regarding the primary endpoint of the study, there was no difference between the LMA groups regarding successful LMA placement with the first attempt. There was no significant difference regarding the time to the first successful ventilation between the groups (Fig. 2).
In the SaCoVLM group, the glottis exposure classification on its screen is shown in Table 4. All patients were observed under fiberoptic intubation to classify the glottis again. The  fiberoptic grade of the laryngeal view was not significantly different between the two groups (90% vs. 86.7%; p = 0.245) (Fig. 4). There was no difference in the time required for successful endotracheal intubation between the Ambu Aura-i and the SaCoVLM groups (24.1 ± 6.3 s versus 25.7 ± 2.1 s; p > 0.05) (Fig. 5). The device was successfully removed in all patients in both groups without inadvertent extubation. The time for removal was significantly longer in the SaCoVLM group than in the Ambu Aura-i group (20.8 s. ±0.8 versus 14.7 s. ±6.1; p < 0.01) (Fig. 6). There was one case of bronchospasm in each group after intubation, but it was relieved by deepening anesthesia. Blood staining on the airway device was reported with six patients (10%) in the Ambu Aura-i group and with ten patients (16.7%) in the SaCoVLM group; p = 0.032). The incidence of postoperative sore throat was six patients (10%) in the Ambu Aura-i group and nine patients (15%) in the SaCoVLM group; p = 0.04) without dysphagia and hoarseness (Table 5). There were no instances of laryngospasm, regurgitation, aspiration, or postextubation stridor.

Discussion
The first-time success rate of SaCoVLM insertion was 85% in children with microtia, confirming that the success rate of SaCoVLM insertion is basically the same as that of Ambu Aura-i insertion; however, the success rate is much lower than that in adults with normal airways [13]. This may be due to the anatomical differences in children with microtia, in which a narrow laryngeal space may exist. Notably, after manual adjustment [14,15] and reinsertion, the final success rate of device insertion can reach 100%. The SaCoVLM contains a camera to capture the images of the glottis on a screen. We graded the images of 60 patients. The TotalTrack mask can visualize the glottis in 83% of patients [16], while the SaCoVLM only visualized the glottis in 39 cases (65%) after the first insertion but in 51 patients (85%) after adjustment. Although the blind placement of the laryngeal mask can obtain satisfactory ventilation, it does not mean that the laryngeal mask is in good alignment with the glottis. The visualization of the laryngeal mask can better observe the glottis position to facilitate the guidance of endotracheal intubation. Additional advantages of its use include a means for providing continuous oxygenation with a hands-free airway while potentially overcoming upper airway obstructions [17]. The partial or whole  laryngeal inlet could be observed in all of the children in the study, thereby laying a foundation for tracheal intubation. Alignment and oropharyngeal leak pressure (OLP) are often used as key factors that determine the effectiveness of a laryngeal mask airway. OLP is used as a marker for the quality of the airway seal, with > 25 cmH 2 O recommended [11,18]. We found that the SaCoVLM achieved an average OLP of 28.0 cmH 2 O, over 30 cmH 2 O in 24 (40%) patients, and these values were much higher than those achieved by the Aura-i mask, which is consistent with other studies [13,19]. In our study, the SaCoVLM demonstrated higher leak pressures than the Ambu Aura-i mask. The SaCoVLM has a larger mask size, which may occupy a greater area in the posterior pharynx and contribute to a better seal. Additionally, the real-time, vision-guided insertion of the SaCoVLM can allow immediate correction of incorrect cuff inflation, which may decrease the risk of airway and oral tissue trauma caused by hyperinflation [20,21]. Therefore, the SaCoVLM can serve as an effective supraglottic airway management tool.
The time for successful endotracheal intubation was similar in the Ambu Aura-i and SaCoVLM groups. Previous findings suggest that blind intubation through supraglottic airway devices should not be performed in children, as epiglottic downfolding may be present [19][20][21][22]. Therefore, supplementary intubation instruments, such as fibrobronchoscopy and bougie, are sometimes needed;; however, in the SaCoVLM group, video-guided intubation can better locate the glottis and provide a more unobstructed airway, which decreases equipment demand. Notably, a more complete glottis display correlates with a higher success rate of direct intubation. When the image displayed by the glottis is unsatisfactory, the exposure range of the glottis can be increased by increasing the amount of inflation and adjusting the depth of the laryngeal mask or rotating the tip of the endotracheal tube.
The time for removal was significantly higher in the SaCoVLM group than in the Ambu Aura-i group. This may be because the mask body of the SaCoVLM is too large, and the oropharyngeal cavity volume of children with microtia [1,3] may be too small. When removing the laryngeal mask,    it is difficult for the operator to put their fingers in the mouth to hold the tracheal tube, which requires relatively high requirements for the operator. However, this difference may not be clinically significant, as evidence of oxygen desaturation was not seen with either device. Another reasonable option may be to leave both the ETT and SaCoVLM in place until the conclusion of the procedure. Related complications, including sore throat and blood staining on the LMA, were higher in the SaCoVLM group, all of which were resolved 24 h after the operation; this was more common with the size 3 SaCoVLM. The above complications may be explained not only by the association between the small pharyngeal cavity volume and microtia for children but also by the structure of the SaCoVLM. Specifically, the mask body of the size 3 SaCoVLM may be too large for children, and the deformability of the front end is insufficient, making it easy to block the throat wall, which increases the difficulty of insertion and leads to injury.  Therefore, the incidence of severe complications related to the SaCoVLM was not found, suggesting that it is relatively safe to use in clinical practice. In this study, the classification of the SaCoVLM and FIS was quite different. The reason for this may be that they were observed at different sites. For FIS, the laryngeal mask vent tube was used to observe the glottis at the end of the vent tube. The SaCoVLM camera was located on the right side of the vent cuff, which was prone to the right side of the end of the vent opening. However, this difference did not affect the intubation process. Table 2 shows no difference in the intubation time between the two groups.
This study had several limitations. First, we did not study neonates or children with normal ears, and it may be recommended to collaborate with other institutions for further study. Second, complications such as the blood staining of these devices should be studied in more detail. Third, data were collected in an unblinded fashion, which may have introduced bias. This single-center study is an initial study, aiming to lay a foundation for a later large multicenter sample study.

Conclusion
In this study, the SaCoVLM has an overall comparable performance as the Ambu Aura-i mask. However, the SaCoVLM is better for direct intubation without the help of FIS/bougie, which reduces device demand. Based on the above point, the performance of the SaCoVLM is better. Therefore, we recommend the SaCoVLM as an alternative to the Ambu Aura-i mask.
Financial support and sponsorship.

Author contributions
Author's individual contribution to the manuscript: JZ: this author helped with the conception, design and drafting of the manuscript. FY: this author assisted in analysis of the data. L-XW: this author aided in acquisition of the data. DY: this author helped with interpretation of the data. XD: this author gave final approval of this version to be published.
Funding None.

Declarations
Conflict of interest There are no conflicts of interest.
Clinical trial number and registry URL This study was approved by the University's Institutional Review Board (Plastic Surgery Hospital Ethical Committee no. ZX2021-12), and written informed consent was obtained from all subjects participating in the trial. The trial was registered prior to patient enrollment at clinicaltrials.gov