This study was approved by the Institutional Review Board of Kyungpook National University Hospital (KNUH 2020-11-069; February 8, 2021) and was registered at cris.nih.go.kr (KCT0006673; first registration on 18/10/2021) prior to enrollment. This study was designed as a prospective, randomized, controlled trial and was conducted at Kyungpook National University Hospital in accordance with the Declaration of Helsinki. Written informed consent was obtained preoperatively from each participant. This study adheres to the Consolidated Standards of Reporting Trials guidelines.
Inclusion and exclusion criteria
The following were the inclusion criteria: patients who were undergoing laparoscopic gynecological surgery under general anesthesia, aged 18–65 years, height of 155–167 cm, nonsmokers, expected anesthesia duration of ≤ 3 h, and an American Society of Anesthesiologists physical status of class I–II. The following were the exclusion criteria: patients with severe obesity (body mass index ≥ 30 kg/m2), thyromental distance of < 6.5 cm, Mallampati class III or IV, history of recent upper respiratory infection or sore throat within 7 days preoperatively, use of steroid medications, and pregnancy. Furthermore, patients with an anesthesia duration of < 1 or > 3 h, had airway spasms or bucking episodes during surgery and extubation, had discontinuation of intravenous patient-controlled analgesia (IV-PCA), or used analgesics other than IV-PCA were excluded from the analyses.
Patients were categorized into the following two groups: Group C (control group) and Group S (slow endotracheal tube advancement). A predetermined computer-generated random number sequence was used to generate a randomization sequence for the two groups in a ratio of 1:1. Group allocation was performed on the morning of the day of surgery using sealed, number-coded envelopes.
On arrival at the operating room, electrocardiogram, sphygmomanometer, pulse oximeter, bispectral index (BIS), and temperature were monitored. All patients were preoxygenated with 100% oxygen for 3 min. General anesthesia was induced with intravenous propofol 1.5–2 mg/kg, a target-controlled intravenous infusion of remifentanil 3.5–4.5 ng/mL, and intravenous rocuronium 0.6 mg/kg. After reducing the BIS to < 50 and ablation of the train-of-four (TOF) response (TOF 0), an investigator performed fiberoptic‐guided tracheal intubation. A Shiley™ Lo-Contour flexible reinforced endotracheal tube (Covidien Ireland Limited, Tullamore, Ireland), which had an outer diameter of 7.0 mm, was used for tracheal intubation. The endotracheal tube was premounted near the proximal site of the bronchoscope (Olympus LF-GP, Olympus Optical Co., Tokyo, Japan), and the bronchoscope was inserted into the trachea through the patient’s mouth while an assistant pulled the patient’s jaw.
Once the bronchoscope was inserted into the trachea and reached the level of the carina, the endotracheal tube was advanced over the bronchoscope to a depth where the proximal end of the tube cuff was in contact with the patient’s incisors. The tube was subsequently advanced by an additional 10 cm to a depth of 17 cm from the patient’s incisors; the time required to perform this step was measured5,6 (Fig. 1). In Group C, the operator advanced the endotracheal tube at a normal speed, whereas in Group S, the tube was advanced at a much slower speed. The final depth of the endotracheal tube was adjusted by bronchoscopic examination.
Medical staff who did not participate in the study performed the maintenance of general anesthesia and emergence. Sevoflurane in O2/air, target-controlled intravenous infusion of remifentanil (2.5–3.5 ng/mL), and intravenous rocuronium were administered to all patients. The cuff pressure of the endotracheal tube was maintained between 20 and 25 cm H2O using a manual cuff pressure manometer (Cuff Manometer, Mallinckrodt Medical, Athlone, Ireland). Intravenous sugammadex was administered at the end of the surgery. All patients received IV-PCA with fentanyl 600 µg and ketorolac 240 mg diluted with 100 mL of normal saline, at a 2-mL/h basal infusion rate, 1-mL on-demand bolus, and 10-min lockout interval.
The primary outcome of the study was the difference in postoperative sore throat scores between the groups, and the secondary outcome was the difference in the severity of postoperative hoarseness and cough.
A designated investigator who was blinded to the group allocation evaluated postoperative sore throat, hoarseness, and cough at 3 and 24 h following surgery.
Sore throat was defined as continuous throat pain and estimated using a visual analog scale (VAS) on a 100-mm scale. Postoperative hoarseness and cough were assessed using a numerical rating scale. Postoperative hoarseness was measured as follows: 0 = no hoarseness, 1 = experienced only by the patient, 2 = evident to the evaluator, and 3 = difficult to vocalize7,8. Postoperative cough was measured as follows: 0 = none, 1 = mild (less than a common cold), 2 = moderate (similar to a common cold), and 3 = severe (more than a common cold)9. The total use of analgesics through IV-PCA or other approaches was also recorded.
Statistical analyses were performed using Statistical Package for the Social Sciences (version 24, IBM Corp, Armonk, NY, USA). The sample size was calculated from a pilot study, wherein the severity of sore throat 3 h postoperatively (mean ± standard deviation) was 20.5 ± 11.6 and 11.6 ± 11.0 in Groups C and S, respectively (n = 6 per group). A two-tailed α value of 0.05 and a power of 80% were assumed; the required sample size was determined to be 56 (28 per group) to assess the severity of sore throat 3 h postoperatively and demonstrate a statistically significant difference between the two groups (effect size = 0.79). Thus, assuming potential dropouts, a target sample size of 33 patients per group was planned. None of the patients in the pilot study was included in the present study.
To present demographic data and target measurements, descriptive statistics were used. To compare the demographic data, time measurement, and amount of IV-PCA used, an independent Student’s t-test was performed according to the characteristics and distribution of the data. To assess the homogeneity of variances, Levene’s test was performed. The VAS scores of postoperative sore throat were compared using the Mann–Whitney U test. A p value of < 0.05 was considered statistically significant.