Study population and ethical approval
The present study’s protocol was approved by the Sacred Heart Hospital, Hallym University, Institutional Review Board (approval No. 2018–04–024-004) and was registered with the Clinical Research Information Service of the Korea National Institute of Health (CRIS,
http://cris.nih.go.kr, identification number: KCT 0004535). Written informed consent was obtained from all patients prior to any study-related procedures. The present study adhered to CONSORT guidelines.
One hundred patients scheduled for elective surgery under general anesthesia with NTI were enrolled in this prospective, randomized, controlled, study done in a tertiary hospital. All patients were between 20 and 80 years old and had an American Society of Anesthesiologists physical status of I–III. Patients were excluded if they had an anticipated difficult endotracheal intubation (Mallampati score IV and thyromental distance of ≤6.0 cm); a tendency toward bleeding; a history of nasal deformity, obstructive sleep apnea, recurrent epistaxis, nasopharyngeal abnormality or surgery; severe obesity (body mass index [BMI] ≥ 35 kg/m2); cervical spine instability; or cervical myelopathy.
Study protocol
All patients were premedicated with 0.2 mg of intramuscular glycopyrrolate 30 min before the anesthesia induction. Prior to their arrival in the operating theater, an attending anesthesiologist conducted an airway examination which included an assessment of the thyromental distance, inter-incisor distance, neck circumstance, and modified Mallampati score. Upon arrival in the operating theater, basic monitoring including electrocardiography, noninvasive blood pressure measurement, and pulse oximetry were employed in all cases. Patients were placed in the supine position with their head on an 8-cm-high pillow and asked which nostril was easier to breathe through to determine patency. If both nostrils had same patency, NTI was first attempted in the right nostril.
A pre-formed double-curved nasotracheal tube (Shilley™ Nasal RAE Tracheal Tube Cuffed; Covidien, Mansfield, MA, USA) with an internal diameter of 7.0 mm for men and 6.5 mm for women was used for endotracheal intubation. The ETT was thermosoftened for at least 30 min before intubation by placement into a bottle of sterile isotonic saline in a warming cabinet (KRS-205; Karis, Gyeonggi-do, Korea) at 45 °C [
18]. Immediately before NTI, the ETT was withdrawn from the saline bottle and lubricated with water-soluble jelly. Before NTI, a cotton swab soaked with Bosmin solution
Ⓡ (0.1% epinephrine, 50 mL/bottle, Jeil Pharmaceutical Co., Seoul, Korea) was applied to both nasal cavities to prevent nasal bleeding.
Five minutes after preoxygenation, anesthesia was induced with propofol (1.5–2.0 mg/kg) and remifentanil (0.1–0.2 μg/kg/min). After anesthetic administration, the pillow was removed and a properly sized Philadelphia neck collar (Philadelphia Cervical Collar, Philadelphia Cervical Collar Co., Thorofare, NH, USA) was placed according to each patient’s neck circumstance or height. Following assessment of the ability to ventilate, rocuronium (0.6 mg/kg) was administered intravenously to facilitate NTI, and the patients’ lungs were manually ventilated with 2–4% sevoflurane in 100% oxygen. After 3 min, NTI was performed using the assigned device by single experienced anesthesiologist, who conducted at least 100 successful intubations using the McCoy laryngoscope and 100 successful intubations using the C-MAC D-Blade videolaryngoscope.
The primary outcome variable was total intubation time defined as the time from insertion of the ETT past the selected nostril to removal of intubation devices from oral cavity. Secondary outcomes, including time required for insertion of the ETT in each of three intubation steps (from nose into oropharynx, from oropharynx into glottic inlet, and from glottic inlet to trachea), navigation grade of ETT in each intubation steps, modified nasal intubation difficulty score (NIDS), hemodynamic changes, and several complications related to NTI.
The NTI was subdivided into three steps according to ETT passage as follows: 1) nose to oropharynx, 2) oropharynx into the glottic inlet, and 3) glottic inlet to trachea. The time taken and grade of difficulty were assessed for each of these three steps. In the first step, difficulty of ETT passage was graded as follows: grade 1) easy to advance, grade 2) slight resistance confronted, or grade 3) the ETT was unable to be advanced into the chosen nasal cavity and was inserted through contralateral nasal cavity. In the second step, difficulty was graded as follows: grade 1) smooth ETT passage from the oropharynx to the glottic inlet or grade 2) the ETT tip failed to align with the glottic inlet, and a lifting force or/and external pressure was applied to the larynx (BURP; backward, upward, and rightward pressure maneuver) to expose the vocal cords and align the ETT into glottic inlet. In the third step, ETT passage was graded as follows: grade 1) smooth passage of ETT into the trachea, grade 2) slight ETT manipulation (rotation and slight pressure) or/and Magill forceps were necessary to facilitate ETT advancement into the trachea.
To score the intubating conditions after NTI completion, a modified NIDS was used (Table
1). The total NIDS was categorized as follows: no difficulty (score = 0), mild difficulty (score between 0 and 5), moderate difficulty (score between 6 and 11), or profound difficulty (score of 12 or more) [
19].
Table 1Modified nasal intubation-difficulty scale (NIDS)
N1: Intubation attempts | Each additional intubation attempt after the first one adds 1 point |
N2: Operators to attempt intubation | Each additional operator required to attempt intubation adds 1 point |
N3: Alternative intubation techniques or change head position | Each alternative intubation technique or change head position adds 1 point |
N4: Glottic exposure | 0 = good visualization of vocal cords with little manipulation 1 = tools manipulated in all directions to identify the vocal cords 2 = tools extensively manipulated in all directions to identify the vocal cords |
N5: Lifting force required to expose the vocal cords | 0 = lifting without assistance 1 = lifting required by assistant to improve view of the vocal cords |
N6: Optimize glottis exposure with BURP (backward, upward and right ward pressure) | 0 = none 1 = BURP applied |
N7: Techniques to aid intubation | 0 = none 1 = cuff inflation or Magill forceps |
The following data were also recorded. Based on the observed laryngoscopic view, the CL classification score [
20] and percentage of glottic opening (POGO) scale [
21] were noted for each patient. The POGO represented the glottic opening along the linear span from the anterior commissure to the inter-arytenoid notch. A 100% POGO was a full view of the glottis from the anterior commissure to the inter-arytenoid notch while a POGO of 0 indicated that even the inter-arytenoid notch was unseen. Mean arterial pressure (MAP), heart rate (HR), and peripheral oxygen saturation (SpO
2) were recorded just before NTI, and at 1 and 3 min after intubation. In addition, 3 min after intubation, a separate anesthesiologist assessed for oropharyngeal bleeding by inspecting the laryngoscope blade for blood and the patient for mucosal bleeding. In the postoperative recovery room, complications related to NTI including a sore throat and hoarseness were evaluated.
Failure to intubate was defined as an inability to intubate the patient’s trachea within 120 s, or within three intubation attempts, or if the patient’s SpO2 dropped below 95% during NTI. In that case, the Philadelphia neck collar was removed and NTI was performed in the traditional position using the desired device by another skilled anesthesiologist with > 15 years of clinical experience.
Anesthesia was maintained with air and oxygen (50,50) and sevoflurane 2.0–3.5 vol%. Fentanyl (0.5 μg/kg) was administered 15 min before the end of surgery for postoperative analgesia.
Statistical analyses
All quantitative variables including age, BMI, thyromental distance, neck circumstance, inter-incisor distance and total intubation time, time taken in each three steps, visual analog scale (VAS) of facemask ventilation difficulty, POGO score, VAS of sore throat were analyzed using descriptive statistics and summarized as means ± SDs or median (interquartile range 25th–75th). All qualitative variables (e.g., gender, ASA class, grade of difficulty, etc.) were presented as frequencies and percentages. Quantitative parameter normality was tested with the Shapiro–Wilk test. These outcomes were then assessed by a Student’s t test or the Mann–Whitney U test for independent groups, as appropriate. Qualitative data were assessed via the Chi square or Fisher’s exact test. For repeated measures including MAP and HR, a repeated measured ANOVA with adjustment for multiple comparisons via the Bonferroni post-hoc correction was used. All statistical analyses were performed using SPSS software version 24.0 (SPSS Inc., Chicago, IL, USA) for Windows (Microsoft Corporation, Redmond, WA, USA). P values < 0.05 were considered statistically significant for all parameters.