This study protocol was approved by the Institutional Research Ethics Committee of The First People’s Hospital of Hefei (No. 2019-12) and was registered in the Chinese Clinical Trial Registry (www.Chictr.org.cn, ChiCTR1900027387). Written informed consent was obtained from all patients, and the study was conducted in accordance with the Declaration of Helsinki.
We excluded patients from our study if they fell into any of the following categories: (1) age younger than 18 years or older than 80 years; (2) a body mass index (BMI) ≥ 30 kg/m2; (3) the Cormack and Lehane (CL) grading scale of the laryngoscopic view of 3 or 4[11]; (4) a history of nasal abnormality (e.g., nasal trauma, surgery, obstruction, and polyps); (5) current anticoagulation therapy; (6) the presence of an oral malignant tumour or difficulty anticipated in airway management; (7) a mental disorder diagnosis; and (8) cervical vertebra instability, trauma or rheumatoid arthritis. None of the patients were premedicated, and standard monitoring equipment, such as electrocardiograms, noninvasive arterial blood pressure measurement devices and continuous pulse oximeters, was used in the operating room. All study subjects were randomised, using computer-generated random numbers, and envelopes containing randomisation numbers were used to allocate the patients to the following two groups (n = 30 per group) according to the airway device that would be used to guide NTI: Magill forceps group (Group M) and tube core group (Group T).
An otorhinolaryngologist who was blinded to the group assignment used a nasal speculum to check for abnormalities inside the nostrils and to select the more patent nostril. If the patency of both nostrils was equal, NTI was performed in the right nostril[3]. General anaesthesia was induced with 1.5-2 mg/kg intravenous propofol and 0.3 µg/kg sufentanil, and muscle relaxation was achieved by intravenous administration of 0.15 mg/kg cisatracurium. Before intubation, manual ventilation was performed with 100% oxygen through a facemask for 3 min. The selected nostril was packed with gauze containing epinephrine to prevent bleeding. Males and females were intubated with 6.5-mm and 6.0-mm wire-reinforced tracheal tubes, respectively (TUORen Medical Equipment Co., Henan, China. Figure 1, B) with high-volume, low-pressure cuffs. Anaesthesia was maintained with propofol, remifentanil and sevoflurane.
An aseptic suction catheter (OD − 4.0 mm, Fig. 1, C) lubricated with aseptic paraffin was inserted through the tracheal tube with its tip protruding approximately 15 cm (Fig. 1, B), and the tube was then advanced through the nasopharynx. The Macintosh laryngoscope was then placed into the patient’s mouth. Then, in Group M, the tracheal tube was inserted into the trachea in a conventional technique. However, in Group T, a tube core bent to the physiological curve of the nasal cavity lubricated with aseptic liquid paraffin was inserted into the tracheal tube, and the tube core was then withdrawn after the tracheal tube was advanced through the glottis under direct vision. NTI of all patients was performed, if required, using Magill forceps. The entire intubation process is shown in Fig. 2 for Group T. All intubations were performed by an anaesthesiologist who was familiar with both techniques and had extensive experience. Minute adjustments to ventilation were performed to maintain end-tidal CO2 pressures at 35–45 mmHg after intubation.
The NTI time, which was defined as the period from when the anaesthesiologist picked up the device to when three successive end-tidal CO2 waves were obtained following intubation[12], was recorded. Epistaxis was assessed by an observer blinded to the group assignments using direct laryngoscopy at five minutes after completing NTI and was scored as one of four grades according to the following modified criteria: no epistaxis (no blood observed on either the surface of the tube or the posterior pharyngeal wall); mild epistaxis (blood apparent on the surface of the tube or posterior pharyngeal wall); moderate epistaxis (pooling of blood on the posterior pharyngeal wall); and severe epistaxis (a large amount of blood in the pharynx that impeded NTI and necessitated urgent orotracheal intubation)[13]. The frequency of using Magill forceps in two groups was also recorded.
Neuromuscular blockade was reversed using neostigmine 1 mg and atropine 0.5 mg, and the trachea was extubated when the patient was awake. An investigator who was blinded to the study assessed the nasal pain at 15 min, 1 h, and 24 h after extubation on a visual analogue scale (VAS) according to a 10-cm vertical score ranging from 0 = no pain to 10 = worst pain imaginable.
To calculate the sample size, we undertook a pilot study with 10 patients in each group (total 20 patients). The NTI time was significantly longer in the Magill forceps group than in the tube core group (Group M, 59.8 (5.1) sec vs Group T vs 53.1 (3.0) sec). For this study, the total sample size to achieve 0.95 power and an α-error of 0.05 was 12 patients per group according to G*Power 3.1.9.4 software. Sixty adult patients who were rated as American Society of Anaesthesiologists (ASA) Ι or Π and whose condition required NTI under general anaesthesia were selected.
Data are expressed as the mean (SD). Parametric data were compared between the groups by analysis of variance and post hoc testing. Categorical data were analysed using Fisher’s exact test. Statistical significance was considered at P values < 0.05. All statistical analyses were performed with Statistical Package for Social Sciences (SPSS) software 20.0.