Ethics approval and Registration
This prospective randomized study was approved by the Ethical Committee of Zhongshan Hospital, Fudan University (Approval No: B2016-099R). The study was registered at chictr.org.cn (ChiCTR-IIC-17010875). Written informed consent was obtained from all participants.
Patient population
This study adhered to CONSORT guidelines for randomized trials. Sixty patients aged 18-65 years old who presented for elective surgery under general anesthesia were recruited at Zhongshan Hospital, Fudan University. Inclusion criteria included a body mass index (BMI) of 18.5-25 kg·m-2, American Society of Anesthesiologists (ASA) physical status I-II, and Mallampati Grade I-II. Exclusion criteria included any sign of difficult airway such as mouth and neck mass or infection, allergy to the study drugs, drug or alcohol abuse, and pregnancy.
Anesthetic technique
Using a computer-generated table and a sealed envelope with sequence of numbers, patients were randomly divided into two equal groups: an ultrasound-guided group (Group UG, n=30) and an SOS group (Group SOS, n=30).
A specified attending anesthesiologist conducted the pre-anesthetic interview to the patients. All participants were fasting according to the rules of Zhongshan Hospital without preoperative medications. After patients arrived at the operating room, an 18G peripheral venous catheter was established, and oxygen (8 L·min-1) was supplemented via face mask. Intraoperative monitoring included pulse oxygen saturation (SpO2), electrocardiogram (lead II and V5), heart rate, noninvasive blood pressure, and capnography.
After pure oxygen with a flow rate of 8 L·min-1 was inhaled for 3min via a sealed mask, plasma target-controlled infusion of propofol 4 ug·ml-1, intravenous fentanyl 2 μg·kg-1, remifentanil 0.2 μg·kg-1·min-1 and dexamethasone 5 mg were given. After loss of consciousness, rocuronium 0.6 mg·kg-1 and lidocaine 1.5 mg·kg-1 were administered. Ninety seconds later, the tracheal intubation was carried out according to the randomly allocation by a specified anesthesiologist who had performed UGTI or SOS-aided tracheal intubation for more than 50 times, respectively.
Before the manipulation of tracheal intubation in the two groups, the ready-to-use stylet was lubricated and bent to imitate the shape and structure of the airway from the central incisors to the cricoid cartilage, then an endotracheal tube (7.0 mm ID for female, 7.5mm ID for male) was mounted on it.
Group UG: A 6-13 MHz linear ultrasound probe (Sonosite EDGE ultrasound) was put transversely on the patient’s neck at the level of the cricothyroid membrane to guide intubation. The probe cloud been moved cephalad to obtain a clear image of the vocal cords that were shown as an isosceles triangle with a central tracheal shadow. The specified anesthesiologist opened patient’s mouth and maintained manual inline stabilization and jaw thrust while inserting the pre-shaped styletted tracheal tube. The tube should be kept in the midline of the mouth during the operation. Hypoechoic shadowing and widening of the vocal cords were the certification of successful placement of the tube into the trachea. When the tube was to be stuck in the midline using the ultrasound, then it was withdrawn outside form the mouth and reshaped by bending its tip downwards. Once the tracheal tube passed posterolateral of the airway to the esophagus which was a hyperechoic structure with posterior shadowing in the image of ultrasound, it should be withdrawn. Then, the tip of tube required to be bent upwards and then reinserted. 1,4
Group SOS: The specified anesthesiologist held and elevated the mandible using the left hand; the stylet was introduced from the right side of the mouth. Thereafter, a significant light spot was seen through the front of neck, the tip was inserted into the glottis under direct vision, the “tube stop” was released. The tube was uninstalled into the trachea, then the stylet was removed.
After the correct position of the tube was confirmed by the end-tidal of carbon dioxide (ETCO2) monitoring and stethoscope, the anesthesia machine was connected and parameters were set to maintain the partial pressure of ETCO2 at 30-40 mmHg. The failure of intubation attempt defined as the time >180 s or desaturation (SpO2<93%). To ensure patient safety, the intubation attempt must be stopped and ventilated with pure oxygen for 3 min to perform another attempt. Failure of intubation was considered as 2 failed attempts of insertion, then intubation was executed with a ready video laryngoscope.
The time of the intubation was from passage of the mounted tracheal tube between the teeth until the tracheal tube was confirmed in place by the capnography, and the number of tracheal intubation attempt were recorded. Complications relative to tracheal intubation including desaturation, hoarseness and sore throat were also recorded.
Data Collection
Our null hypothesis was: the success rate of UGTI at the first attempt is equal to that of SOS-aided tracheal intubation in patients with anticipated normal airway undergoing elective surgery under general anesthesia. Then, the primary outcome was to compare the success rate of intubation of the two groups on the first attempt. The secondary outcomes were to detect the overall success rate, the time of the intubation with a first-attempt success, and complications related to each method, such as desaturation and trauma.
The sample size was calculated using the PASS software version 11: Two-Sample T-Test Power Analysis. It was estimated that a sample size of 34 patients (n1=n2=17) would achieve a power of 80% (β=0.2) to detect a clinical significant difference of 5% with standard deviations of 5% between the two groups as regards the success rates at the first attempt using a T-Test with significance level at 0.05 (α=0.05).
Statistical Analysis
Data were analyzed by using IBM SPSS version 24 software. Qualitative data were described using number and were compared using the Chi-square test and the Fisher exact test, whereas normally distributed quantitative data were expressed as mean ± SD and were compared using T-Test for two independent groups, non-normally distributed quantitative data were expressed as median (Inter-Quartile Range) and were compared using Mann-Whitney U test. P<0.05 was considered statistically significant.