This study protocol was approved by the Research Ethics Board of The First People’s Hospital of Hefei (No. 2019-12), and patient enrolment was conducted after being 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: age < 18 years or > 80 years; a body mass index (BMI) was over 30 kg/m2; the Cormack and Lehane (CL) grading scale of the laryngoscopic view of 3 or 4 [11]; receiving anticoagulant therapy; a history of nasal deformity (e.g., nasal trauma, surgery, obstruction, and polyps); the presence of maxillofacial cancers; difficulty anticipated in airway management; mentally ill people; and cervical instability. Standard monitoring equipment was used in the operating room, and none of the study subjects were premedicated. All patients were randomized using computer-generated random numbers, and envelopes containing randomization numbers were divided into 2 groups (n = 30 per group) according to the different equipment that would be used to guide NTI: Magill forceps group (Group M) and tube core group (Group T).
An otorhinolaryngologist of our hospital who was blinded to the group assignment used a nasal speculum to check for deformities inside the nostrils and to select the smoother nostril. If the patency of both nostrils was equal, NTI was performed in the right nostril [3]. All patients received the same general anaesthesia with 0.3 μg/kg sufentanil and 1.5-2 mg/kg propofol intravenously, followed by muscle followed by 0.15 mg/kg cisatracurium. Manual ventilation was performed with 100% oxygen through a facemask for 3 min before intubation. The selected nostril was packed with gauze containing epinephrine to prevent bleeding. The 6.5-mm and 6.0-mm wire-reinforced tracheal tubes were used in males and females, respectively (TUORen Medical Equipment Co., Henan, China. Fig. 1, B). Anaesthesia was maintained with propofol, remifentanil, sevoflurane and cisatracurium.
An aseptic suction catheter (OD - 4.0 mm, Fig. 1, C) lubricated with liquid paraffin was inserted through the tracheal tube (Fig. 1, B) with its tip protruding approximately 15 cm, 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 using 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 process of intubation is shown in Fig. 2 for Group T. The process was performed by an anaesthesiologist who had extensive experience. Then, minute adjustments to ventilation were performed to maintain end-tidal carbon dioxide partial pressure at 35 - 45 mmHg during the whole operation.
The total NTI time, which was defined as the period from when the operator picked up the device to when three successive end-tidal carbon dioxide waves were obtained following intubation [12], was recorded. An observer blinded to the group assignments assessed epistaxis bleeding using direct laryngoscopy after five minutes of completing NTI, and it 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 the two groups was also recorded.
After the end of surgery, neostigmine 1 mg and atropine 0.5 mg were used to reverse the neuromuscular blockade, and the tracheal tube was extubated when the patient was awake. A visual analogue scale (VAS) according to a 10-cm vertical score ranging from 0 = no pain to 10 = worst pain imaginable was recorded by an investigator who was blinded to the research at the following time points: 15 min, 1 h, and 24 h after extubation.
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.
Statistical analysis
Data are expressed as the mean ± standard deviation. 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.