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Effect of bevel direction on the tracheal tube pathway during nasotracheal intubation

A randomised trial

Won, Dongwook; Kim, Hyerim; Chang, Jee-Eun; Lee, Jung-Man; Min, Seong-Won; Jung, Jiyun; Yang, Hyo Jun; Hwang, Jin-Young; Kim, Tae Kyong

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European Journal of Anaesthesiology: February 2021 - Volume 38 - Issue 2 - p 157-163
doi: 10.1097/EJA.0000000000001347
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Abstract

Introduction

Nasotracheal intubation (NTI) is an airway instrumentation procedure that is required for some oromaxillary surgeries to provide adequate intra-oral access.1 The whole process of NTI can be divided into two consecutive parts, that is the nasal part and oral part. The oral part, the latter half of the NTI, is similar to orotracheal intubation except for the requirement for Magill forceps to advance the tracheal tube from the posterior pharyngeal arch into the glottis. The nasal part, the former half of the NTI, is carried out in the vessel-rich and narrow nasal cavity.1 As the nasal cavity is narrow and divided into sections by turbinates, the cuff of the tracheal tube or even the tracheal tube itself may cause trauma to the vessel-rich nasal mucosa.1,2 Therefore, epistaxis is a common complication during NTI with incidence rates of 18 to 88%.2–4 In rare cases, severe epistaxis may jeopardise tracheal intubation,2,5 and complications, such as accidental turbinectomy, retropharyngeal wall laceration, bacteraemia and cranial bone fracture, may occur.1,6–10 Thus, reducing the risk for complications during NTI has been a challenging task for anaesthesiologists.

Two working spaces are available during NTI, that is the upper pathway between the middle turbinate and inferior turbinate and the lower pathway between the inferior turbinate and the floor of the nasal cavity (Fig. 1).11 When the tracheal tube passes through the upper pathway, excessive force may be applied to the structures of the nasal cavity, such as the middle turbinates, resulting in complications such as accidental middle turbinectomy or fracture of the bony structure of the middle turbinate.6–8,10,12,13 Unlike the inferior turbinate, which is a part of the facial bones, the middle turbinate is part of the cranial bones, and therefore, fracture of the middle turbinate may cause cranial fractures and leakage of cerebrospinal fluid.10 Therefore, the lower pathway has been considered a better route for passage of the tracheal tube during NTI.4,14 Advancing the tracheal tube through the lower pathway during NTI is also advantageous because it reduces the risk for epistaxis.3,14 Migration of tubes between pathways is usually prevented because of the proximity of the inferior turbinate and nasal septum in the majority of patients, and therefore, selecting the lower pathway during NTI has been an important issue.14

F1
Fig. 1:
Upper and lower pathways in the nasal cavity.

Several methods, such as the use of a reinforced tracheal tube, use of a nasogastric tube or fibreoptic nasendoscopy prior to NTI and nasal tip lifting, may facilitate selection of the lower pathway during NTI.3,4,14,15 However, no previous studies have utilised the mechanical characteristic of the tracheal tube, such as the bevel of the tube, to determine the pathway. The bevel of the tube may guide the pathway of the tube as it enters the side of the nasal turbinate. We designed this randomised controlled trial based on the hypothesis that directing the bevel of the tracheal tube in the cephalad direction of the patient may facilitate tracheal tube through the lower pathway during NTI.

Materials and methods

Ethics

The study protocol was approved by the Institutional Review Board of SMG-SNU Boramae Medical Center, Seoul, South Korea (approval no. 30-2018-76; on 2 August 2018 and registered at ClinicalTrials.gov (NCT03740620). Written informed consent was obtained from each participant prior to surgeries. The study protocol conformed to the ethical guidelines of the Declaration of Helsinki.

Study design and patient selection

From January 2019 to March 2020, patients aged 18 years or older undergoing general elective surgeries requiring NTI at SMG-SNU Boramae Medical Center were included in the study. Patients with known deformities of the nasal cavity, history of severe epistaxis or epistaxis within a month, current coagulation abnormality or history of fracture or operation of the cranial base were excluded. History of nasal congestion and history of recurrent epistaxis were asked of all participants. History of nasal congestion was defined as the discomfort experienced during breathing due to decreased nasal patency within a month. History of recurrent epistaxis was defined as repeated episodes of mild to moderate spontaneous nosebleed, which were not self-limited and required treatments as cauterisation or nasal packing.16

Randomisation and blinding

On the morning of surgery, patients were allocated to the intervention group or conventional group according to a random sequence produced by a web-based random sequence generator (http://randomizer.org). Group assignments were kept in an opaque envelope by a research assistant who was not involved in the study. Patients and assessors who evaluated the nasal cavity were blinded to the group allocation. However, the intubating anaesthesiologists could not be blinded to the group allocation, as it was not possible to conceal the tracheal tube during NTI.

Anaesthesia procedures

All patients entered the operating room without any premedication. Routine monitoring included electrocardiography, noninvasive blood pressure monitoring and pulse oximetry. After adequate pre-oxygenation, anaesthesia was induced with intravenous lidocaine (30 mg), fentanyl (1 to 2 μg kg−1), propofol (1.5 to 2 mg kg−1) and rocuronium (0.6 mg kg−1). During manual mask ventilation using sevoflurane 6 to 8% in 100% oxygen, cotton swabs soaked in topical epinephrine 0.1% were applied in both nostrils to prevent epistaxis during intubation and to assess nasal patency. A tracheal tube (Mallinckrodt Preformed Nasal RAE tube; Covidien, Mansfield, Massachusetts, USA) was put into a bottle of sterile isotonic saline at 40°C for thermosoftening 10 min before intubation (inner diameter 7.0 mm for men and 6.5 mm for women). The tracheal tube was lubricated with sterile, water-soluble jelly immediately before intubation. Unless specifically preferred by the surgeon, a suitable nostril was selected on the basis of a review of nasal radiographs and the presence of nasal congestion.

In the conventional group, the tracheal tube was inserted with the bevel of the tube facing the patient's left, that is the default direction. In the intervention group, the tracheal tube was inserted into the nostril with the bevel of the tube facing the patient's cephalad direction by rotating 90° counterclockwise from the default position, and then the tube was turned 90° clockwise back to the default position after the cuff of the tube had passed the posterior nasal aperture (Fig. 2). In both groups, the tracheal tube was directed caudally in the nasal cavity and Magill forceps was used to assist the tracheal intubation.

F2
Fig. 2:
Bevel direction of the conventional group and the intervention group.

The procedure time was recorded from insertion of the tube into the nostril to the time when capnography became evident on the monitor. Time measurements were subdivided as follows: nasal procedure time, defined as the time interval between insertion of the tube and insertion of the direct laryngoscope into the mouth; oral procedure time, defined as the time interval between insertion of the direct laryngoscope and the confirmation of the capnography. NTI was performed by two anaesthesiologists each with more than 10 years of experience. After NTI, the nasal pathway was evaluated with the fibreoptic bronchoscope (outer diameter 4.1 mm, Olympus LE-P; Olympus Optical Co., Tokyo, Japan). In addition, the severity of nasal bleeding was evaluated by direct inspection of the mouth and pharynx using the laryngoscope. Both the nasal pathway and the severity of nasal bleeding were examined by independent assessors unaware of the intervention. The severity of nasal bleeding was graded using a four-point scale: no epistaxis; mild epistaxis (blood on the tracheal tube only or tinged on the posterior pharyngeal wall); moderate epistaxis (blood pooling in the pharynx); or severe epistaxis (blood in the pharynx sufficient to impede intubation).17,18 Resistance while advancing the tube via the nasal cavity was also graded on a three-point scale: slight (when the tracheal tube passed nasal cavity smoothly); moderate (when the tube was redirected because of resistance); obstructed (when NTI failed because of resistance).4

Statistical analyses

The primary study endpoint was the success rate of tracheal tube passing through the lower pathway. Secondary endpoints included the intubation time, nasal passage time and nasal bleeding. Continuous data are expressed as the mean ± standard deviation and significance was tested with Student's t-test for data with a normal distribution determined using the Kolmogorov–Smirnov test. Nonnormal data are expressed as the median [interquartile range] and significance was tested with the Mann–Whitney U test. Categorical data are expressed as number (percentage) and were tested for significance using the χ2 test or Fisher's exact test. Ordinal data, such as severity of bleeding and resistance during insertion, were tested with the Mann–Whitney U test. In addition, we assessed the relationship between the tracheal tube nasal pathway and incidence of epistaxis using multivariate logistic regression analyses. Variables included in the univariate logistic regression were age, sex, BMI, American Society of Anesthesiologists (ASA) status classification, tube pathway, selected nostril and randomised group allocation. Only variables with P value less than 0.2 in univariate analyses were entered into multivariate logistic regression.

Calculation of the sample size was based on a study that reported the success rate of tracheal tube passing through the lower pathway as 26.7% during NTI by the conventional method.15 Taking a 40% increase in the success rate as clinically significant, each group required 29 patients to detect a difference with a type I error of 0.05 and power of 0.8. To allow for a 15% dropout rate, we included 68 patients in this study. All statistical analyses were performed using SPSS (version 19.0; IBM corp., Armonk, New York, USA). In all analyses, P value less than 0.05 was taken to indicate statistical significance.

Results

A total of 68 patients were enrolled in the study, and no patients met the exclusion criteria. Patient enrolment was started on 14 January 2019. The conventional group and the intervention group each consisted of 34 patients (Fig. 3). The baseline patient characteristics are summarised in Table 1. Patient demographic data, including sex, age, weight, height and ASA status classification, were comparable between the groups. Anatomical characteristics, including history of nasal congestion and epistaxis, gross appearance of the nostrils and radiologically evaluated deformities of the nasal cavities, were also similar between the groups.

F3
Fig. 3:
CONSORT Flow Diagram.
Table 1 - Patient demographics and baseline characteristics
Intervention group(n = 34) Conventional group(n = 34) P
Age (years) 46.74 ± 19.72 45.53 ± 18.38 0.795
Height (cm) 164.26 ± 12.21 165.87 ± 10.72 0.567
Weight (kg) 66.70 ± 15.97 66.05 ± 12.69 0.853
Female 14 (41.2) 10 (29.4) 0.310
ASA 1/2/3 20/13/1 22/11/1 0.898
History of recurrent epistaxis 0 (0.0) 2 (5.9) 0.493
History of nasal congestion; None/Left/Right/Both 26/1/3/4 19/6/4/5 0.175
Appearance (Wider side); Left/Right/Same 2/2/30 4/4/26 0.460
Radiologic evaluation (Wider side); Left/Right/Same 14/7/13 7/10/17 0.183
Selected nostril; Left/Right 21/13 15/19 0.145
Data are presented as the mean ± standard deviation or number (%).ASA, American Society of Anesthesiologists status classification.

There was no failed intubation at the first attempt in both groups. The success rate of tracheal tube passing through the lower pathway was significantly higher in the intervention group than the conventional group (79.4 vs. 55.9%, relative risk 1.421, 95% CI 1.007 to 2.005, P = 0.038) (Table 2). Nasal passage time and total intubation time were similar between the two groups. The resistance during nasal passage of the tracheal tube was similar in both groups.

Table 2 - Effects of tracheal tube bevel on study outcomes
Intervention group(n = 34) Conventional group(n = 34) P
Lower pathway 27 (79.4) 19 (55.9) 0.038
Resistance; Slight/Moderate/Obstructed 21/13/0 16/18/0 0.330
Epistaxis 14 (41.2) 25 (73.5) 0.007
Severity of epistaxis; None/Mild/Moderate/Severe 21/10/3/0 9/13/12/0 0.001
Intubation time (s) 47 [37 to 56] 44 [39 to 52] 0.504
Nasal passage time (s) 12 [9 to 19] 11 [9 to 18] 0.659
Data are presented as the mean ± standard deviation, number (%) or median [IQR].

The incidence of epistaxis was significantly lower in the intervention group than in the conventional group (41.2 vs. 73.5%, relative risk 0.560, 95% CI 0.357 to 0.878, P = 0.007). The severity of epistaxis was also different between the groups (P = 0.001). Moderate to severe epistaxis was less frequent in the intervention group than in the conventional group (8.8 vs. 35.3%, P = 0.008). The incidence of epistaxis was lower in the lower pathway than the upper pathway, but the difference did not reach the level of statistical significance (50.0 vs. 72.7%, P = 0.076). The effects of the tracheal tube bevel on study outcomes are summarised in Table 2. According to multivariate logistic regression analyses, ASA status classification (odds ratio 0.303, 95% CI 0.106 to 0.862, P = 0.025) and group (odds ratio 5.415, 95% CI 1.683 to 17.417, P = 0.005) were associated with epistaxis after adjusting for age, pathway, nasal passage time and resistance (Table 3).

Table 3 - Comparison of variables associated with epistaxis during nasotracheal intubation
Epistaxis No epistaxis OR 95% CI P
Pathway
 Upper pathway 16 (72.7) 6 (27.3) 1.454 0.396 to 5.344 0.573
 Lower pathway 23 (50) 23 (50)
ASA 1/2/3 29/10/0 13/14/2 0.303 0.106 to 0.862 0.025
Group
 Conventional 25 (73.5) 9 (26.5) 5.415 1.683 to 17.417 0.005
 Intervention 14 (41.2) 20 (58.8)
Data are presented as number (%).ASA, American Society of Anesthesiologists status classification; CI, confidence interval; OR, odds ratio.

Discussion

In this study, we showed that facing the bevel of the tracheal tube in the patient's cephalad direction increased the success rate of tracheal tube passing through the lower pathway during NTI and decreased the incidence of epistaxis compared with conventional NTI in patients undergoing oromaxillary surgeries.

There are several obstacles to selection of the lower pathway during NTI. First, nasal passage of the tracheal tube is usually performed blindly. We cannot select the lower pathway exclusively, as there are no clear haptic indicators by which we can differentiate between the upper and lower pathways blindly.14 Second, the axis of the nasal vestibule does not agree with that of the lower pathway, and therefore, the tracheal tube can be directed cephalad while advancing the tube. To cope with the disagreement of axes of the vestibule and lower pathway, insertion of the tracheal tube in the caudal direction as much as possible is recommended to accommodate the two axes.3,14 Aiming in the caudal direction with gentle traction of the shaft of the tracheal tube towards the cephalad direction flattens the curve by lifting the nostrils, but the diameter of the tube can interfere with this effort as the rim of the nostril has limited elasticity. However, as shown in this study, facing the bevel of the tracheal tube towards the cephalad direction during insertion may increase the success rate of tracheal tube passing through the lower pathway without increasing other complications. When the bevel of the tracheal tube encounters the turbinates, it may act as a wedge to guide the tracheal tube to the lower pathway. NTI with the tracheal tube bevel facing in the cephalad direction has an additional advantage with regard to the trajectory of the tracheal tube. When the tracheal tube meets the posterior pharyngeal wall, the bevel facing the cephalad direction of the patient would facilitate smooth transition of the tracheal tube to the larynx.1

Epistaxis, the most frequent complication of NTI, also occurred less frequently and its severity was reduced in the intervention group compared with the conventional group. Epistaxis can be reduced by decreasing mechanical injury of the vessels and mucosa induced by the tracheal tube. Epistaxis during NTI can be prevented by selecting the lower pathway, blunting the tip of the tracheal tube, thermosoftening or lubricating the tracheal tube, or contracting the capillary mucous membranes with topical vasoconstrictors.2,3,17–21 As no single manoeuvre provides complete protection against epistaxis, they are usually done simultaneously.2,3,17,19–22 In this study, changing the direction of bevel reduced the incidence of epistaxis, consistent with a previous study that used Parker Flex-Tip, which has a posterior-facing bevel and soft tip.23,24

Interestingly, the intervention had a greater effect on epistaxis in the left nostril (38.1% in intervention group vs. 80.0% in conventional group, P = 0.013) than the right nostril (46.2% in intervention group vs. 68.4% in conventional group, P = 0.208). Some previous case reports recommended that the bevel should be faced toward the turbinates.22,25 That is, the leading edge of the bevel should be advanced along the septal side. When the leading edge of the tracheal tube is forced against soft tissue, it may act as a blade and avulse the turbinates. In the left nasal cavity, the leading edge of the tube could be separated from the turbinates, but it would push against Little's area, which is the most vascularised region in the nasal cavity, in the conventional group.26 By rotating the tracheal tube 90° counterclockwise, the leading edge of the tracheal tube could be separated from both Little's area and the turbinates. By contrast, in the right nostril, the bevel faced the septum, advancing its leading edge against the turbinates. Although contact with Little's area was avoided, the turbinates are also hypervascular tissue, which can be damaged by the leading edge of the tracheal tube.27 In the right nostril, the incidence of epistaxis was also higher in the conventional group then the intervention group, although the difference was not statistically significant. The results should be interpreted with caution, however, as the statistical power may have been inadequate for this secondary outcome and there may have been bias. The selected nostril was not an independent factor in logistic regression analyses.

This study has some limitations. First, blinding the intubating anesthesiologists to group allocation was not possible due to the nature of the intervention. However, assessors who examined the severity of nasal bleeding and the nasal pathway were blinded to the group allocation. Second, nasal intubation was conducted by skilled investigators at NTI. Therefore, the results cannot be directly extrapolated to less skilled operators. Third, the results of this study in an Asian population may not be extrapolated to other ethnicities. There may be differences in anatomy of the nasal cavity among races, as racial differences in the cross-sectional area at the end of the inferior turbinate have been reported.28 Lastly, this study utilised fibreoptic bronchoscope only for evaluating the nasal cavity. Nowadays, fibreoptic NTI is frequently performed, especially for difficult intubation.1,29 A recent study has shown that fibreoptic selection and guidance during NTI reduce the incidence and severity of epistaxis in elective patients.4 However, fibreoptic NTI requires both experience and skill to perform properly, and the device is not always available for every NTI.1,30 Therefore, we believe that the technique to select the lower pathway during NTI without fibreoptic bronchoscope has a significant clinical value.

Conclusion

Orientating the tracheal tube such that the bevel faces the patient's cephalad direction may facilitate selection of the lower pathway and reduce the incidence of epistaxis during NTI in patients undergoing oromaxillary surgery.

Acknowledgements relating to this article

Assistance with the study: none.

Financial support and sponsorship: none.

Conflicts of interest: none.

Presentation: none.

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