Subjects
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 (ChiCTR2200061481, http://www.chictr.org.cn.Principal investigator: Juan Zhi; Date of registration: 26/06/2022. )and we confirmed that all experiments were performed in accordance with relevant guidelines and regulations (such as the Declaration of Helsinki).
Our hospital is the largest ear reconstruction center in China with 2000 ear reconstruction surgeries per year .Between June 2022 and nov 2022,children with microtia, scheduled for elective surgery under general endotracheal anesthesia.
Inclusion criteria: we obtained written informed consent from patients’ guardians ,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
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 SaCoVLM 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.
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.
Preoperative preparation
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 [7] 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. Mouth opening was measured as the difference between the upper and lower incisors at the midline in centimeters using a scale. Thyromental distance༻8༽ was measured from the thyroid cartilage to inside of the mentum with neck extended, using a tape. 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 ༻10–11༽, reversal method, inflating or deflating etc.) to obtain a satisfactory position. 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(Fig. 2) was assessed and graded as follows [12] :
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.
Data collection and statistical analysis
The primary variables first-pass success rate of guided tracheal tube placement.
The secondary variables: glottic visualization grades, the first-attempt success rate of LMA placement, the time for LMA placement and time to endotracheal intubation as well as the time for LMA removal after successful intubation, the fiberoptic grade of laryngeal view, and the incidence 24h complications after operation. Hemodynamic parameters [e.g., HR, mean arterial pressure (MAP)], were recorded at the following time points:before LMA insertion; after LMA insertion ;before intubation; after intubation;after LMA withdrawl;In addition, the baseline and postinduction hemodynamic parameters were also recorded.
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). Study data are presented as means and standard deviation (SD) to describe continusous data and percentages for categorical data.