Comparison of Conventional Technique versus Modified Tube First Technique of Awake Nasotracheal Fiber-optic Intubation: A Randomized Control Open-Label Trial.

BACKGROUND: Although the conventional awake fiber-optic nasal intubation is most commonly used in anticipated difficult tracheal intubation, it has several potential difficulties. AIMS: The aim of this study is to compare another technique modified tube first (MTF) technique with the conventional one in terms of time taken, ease of glottis visualization, number of attempts needed, and complications. SETTINGS AND
DESIGN: This was a prospective, randomized, open-label trial conducted on 60 patients with an anticipated difficult airway undergoing oromaxillofacial surgery at a tertiary care center.
MATERIALS AND METHODS: The patients were randomized into the MTF and conventional technique groups. Times from insertion of the fiber-optic scope into nares till vocal cord visualization (T1) and from T1 to complete intubation (T2) were measured and compared. STATISTICAL ANALYSIS USED: Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) software version 21.
RESULTS: Time taken to visualize glottis was significantly less in the MTF technique as compared to the conventional method (mean ± standard deviation = 108.6 ± 43.1 vs. 142 ± 49.2 s, respectively, P = 0.007). Similarly, the total time taken for nasotracheal intubation with modified technique is significantly less as compared to the conventional technique (P = 0.004). Furthermore, there is significantly better ease of glottis visualization (P = 0.001), higher success in minimal attempts (P = 0.02) with significantly lesser incidence of desaturation in MTF technique (P = 0.026).
CONCLUSION: The alternative technique (MTF) is a quicker, easier approach with higher success rate and lesser complications for the placement of an endotracheal tube in a difficult airway scenario. Copyright:

INTRODUCTION

In recent years, awake nasal fiber-optic intubation has emerged as the standard of care for anticipated difficult tracheal intubation.[12345] Nasal fiber-optic intubation is generally carried by the conventional technique in which a bronchoscope with a mounted endotracheal tube (ETT) is passed through the nostrils. The scope is then gradually advanced further till it enters the trachea, and the ETT is then railroaded over the bronchoscope into the trachea.[6] During this technique, there is a chance of soiling of bronchoscope camera with nasal and oropharyngeal secretions, and there is difficulty in the glottis visualization as well as in the subsequent passage of tube across the glottis.[7] Even in the experienced hands, technical difficulties, and a failure rate of 1%–10% have been reported, which provokes the need to find a different approach to secure the airway.[891011] The fiber-optic intubation can also be done by the modified tube first (MTF) technique in which an ETT is inserted first into the nasopharynx followed by the bronchoscope.[12] Although this technique has been described in the literature, it has seldomly been practiced and very few studies documenting its feasibility are available.[12]

The purpose of this study was to compare the conventional technique with MTF technique for awake nasotracheal fiber-optic intubation. We hypothesize that the MTF is a better technique than the conventional one for awake nasotracheal fiber-optic intubation in terms of shorter intubation time. Furthermore, we compared the ease of visualization of vocal cords, number of attempts, and the use of additional maneuvers for successful intubation.

MATERIALS AND METHODS

This prospective, randomized, open-label trial was conducted at a tertiary care center between July 2014 and August 2015. The study protocol was approved by the Institutional Review Board (KGMU10623/Ethics/dated 27/11/2015). The study was registered with the Clinical Trial Registry of India (CTRI/2017/10/010042). The study was done as per International Conference on Harmonization – Good Clinical Practice, Declaration of Helsinki (1964), and other regulatory guidelines.

All patients undergoing oral maxillofacial surgery with difficult intubation were screened for the eligibility criteria. Patients of either sex, between 18 and 55 years of age with American Society of Anesthesiologists (ASA) physical status classes I and II, having anticipated difficult airway (Mallampatti grade[MMG]≥3) posted for elective surgery and willing to provide written informed consent were included in the study. Patients with nasal mass, bleeding disorder, base of skull fracture, history of nasopharyngeal surgery, allergy to study medication, uncontrolled hypertension, pregnancy, ischemic heart disease, hepatic disorders, renal disorders, and who refused to give written consent were excluded from the study. Written informed consent was obtained from all the participants for the participation in the study as well as for the use of the patient data for research and educational purpose

Patients were randomly allocated into a 1:1 ratio into two groups of nasal intubation using the variable block randomization technique. Blocks sizes of 4 and 6 were selected to divide all the patients equally into modified technique first group (Group M) and conventional technique group (Group C). The randomization sequence was computer generated.

Allocation concealment was done by opaque-sealed envelopes that were opened just before shifting of the patient in the operation theater. It was not possible to blind the device operator due to obvious technical reasons, but the observer recording the data, and the participants were blinded to the group allocation. All fiber-optic intubations were done by two anesthesiologists who had an experience of performing a minimum of 50 awake fiber-optic intubations before this study and were not involved in the collection of data of the study.

After proper fasting (as per standard fasting guidelines), the enrolled patients received topical anesthesia for upper airway structures. The nasal mucosa of the patent nostril was prepared with a vasoconstrictor (0.1% xylometazoline nasal drops) and lignocaine jelly. In the operation theater, multiparameter physiologic monitoring was applied, and baseline hemodynamic variables (heart rate and mean arterial pressure), SpO2, and electrocardiogram were recorded. An intravenous line was established, and each patient received lactated ringer's infusion as per the institute's protocol. All patients were premedicated with ondansetron 4 mg, glycopyrrolate 0.2 mg, midazolam 0.05 mg.kg−1, and fentanyl 1 μg.kg−1; 10 min before the start of the procedure. The superior laryngeal nerve block was given using 2 mL of 2% lignocaine bilaterally. In the modified tube first technique, ETT was inserted into the patent nostril till the tube was visible in the nasopharynx [Figure 1]. The fiberoptic bronchoscope (FUJINON-FB120 S FOB) was then inserted through it; once vocal cords were visualized, the ETT was directed into the trachea, and the cuff was inflated. While advancing the tube into the trachea, 2 mL of 1% lignocaine was flushed down the suction channel of the scope to anesthetize the tracheal mucosae. In the conventional technique, ETT was first mounted over the fiber-optic bronchoscope, the scope was then inserted into the nasal cavity through the patent nostril, and advanced through it till the vocal cords were visualized, then the ETT was railroaded over the scope and advanced through the vocal cords into the trachea and cuff was inflated.

Figure 1

Demonstration of tube first technique where first endotracheal tube was inserted into the nostril followed by fiber-optic bronchoscope

The tube was fixed about 2 cm above the carina, establishing its correct placement in the trachea as confirmed by visualization of the carina. Trained and independent observer assessed the patient's reaction to placement of the fiber-optic scope and the ETT on a scale of 1–5 (1 = no reaction, 2 = slight grimacing, 3 = severe grimacing, 4 = verbal objection, and 5 = defensive movement of head, hands, or feet). Complications encountered and additional maneuvers needed for successful intubation were also recorded. In this study, SpO2 reading of <95% was considered as the criteria for desaturation. In cases of desaturation, oxygen was first instilled through a catheter connected to the working channel of the bronchoscope.[13] While in cases where SpO2 did not improve after oxygen instillation and was ≤90%, the scope was removed, the opposite nostril was occluded, and the patient was ventilated by connecting ETT through Bain's circuit till SpO2 ≥98%. Maximum three intubation attempts or 180 s were allowed. Inability to intubate in three attempts or stipulated time was considered as failed intubation, and the patient was intubated using different modality and was excluded from the study. Once inserted in the nostril, withdrawal of the fiberoptic scope was considered as one intubation attempt.

The primary outcome measures were the time taken from the start of the procedure to the visualization of vocal cords (T1) followed by the time taken from glottis visualization to insertion of a tube into the trachea (T2) as well as the total time taken for intubation. The secondary outcome measures were ease of visualization of vocal cords and placement of ETT as assessed by trained anesthesiologists (on a scale of one as easy and two as difficult), number of attempts taken to place the fiber-optic scope and the ETT and use of facilitating maneuvers for successful intubation.

Sample size calculation

The sample size was calculated based on the study done by Mohammedzadeh et al.[12] Assuming a standard deviation (SD) of 33 and 56 s for T1 and mean difference of 50 s to be clinically significant with MTF technique versus conventional and type I error of 0.025 and with 95% power, a sample size of 26 patients per group has been calculated. As it was a single-point study, 26 patients were required to be included in each group.

Statistical analysis

Numerical data were expressed as mean along with SD or median (Inter-quartile range), and categorical data were presented in percentage. The Chi-square test was used to analyze the categorical variables including patient's reaction to placement of the fiber-optic scope and the ETT, use of facilitating maneuvers for successful intubation. Mean T1, T2, and total time taken for intubation with the conventional and modified technique were compared using the Student's t-test. P < 0.05 was considered to be significant. Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) for Windows User (version 21; IBM, Armonk, NY, USA).

RESULTS

A total of 72 patients were enrolled in the study, out of which 60 patients gave consent for participation in the study. The flow of participants was given in CONSORT flow diagram [Figure 2]. There was no significant difference in the baseline characteristics of patients regarding age, sex, Mallampati grade, and ASA class between the two groups [Table 1].

Figure 2

The CONSORT flowchart of the patients enrolled in the study depicting enrolment, withdrawal, and follow-up of the participants

Table 1

Comparison of demographic data between the modified tube first and conventional nasotracheal intubation techniques

	Group M (n=30)	Group C (n=30)	df	P*
Sex, n (%)
Male	22 (73.3)	22 (73.3)	1	>0.99
Female	8 (26.7)	8 (26.7)
Age (years), mean±SD	34.8±13.6	37.7±12	58	0.326
Weight (kg), mean±SD	61.2±9.8	64.7±8.5	58	0.127
MPG grade, n (%)
III	10 (33.3)	7 (66.7)	1	0.390
IV	20 (23.3)	23 (76.6)
ASA physical status, n (%)
I	18 (60)	17 (56.7)	1	>0.99
II	12 (40)	13 (40.3)

Data expressed as mean±SD or number of cases (%). *Intergroup comparison done using the Student’s t-test for numerical data and Chi-square for categorical data. P<0.05 was taken as statistically significant. MPG: Myocardial perfusion grade, ASA: American Society of Anesthesiologists, SD: Standard deviation

The time taken for glottis visualization (T1) was significantly lesser in Group M than in Group C [108.6 ± 43.1 s vs. 142 ± 49.2; P = 0.007, difference between mean and SD was 33.40 ± 11.94; 95% confidence interval (CI) = 9.495–57.30; Table 2]. There was no significant difference in time taken for intubation till cuff inflation (T2) in modified technique as compared to conventional technique (19.53 ± 5.2 s and 22.50 ± 6.5 s, respectively, P = 0.056, 95% CI = 0.07216–6.012). Furthermore, the total time for fiber-optic intubation was significantly less with modified technique (P = 0.004). Ease of glottis visualization was significantly better in the modified technique group as compared to the conventional group (P = 0.001) [Table 2].

Table 2

Comparison of T1, T2, total time, ease of glottis visualization, ease of endotracheal insertion, facilitation maneuvers, number of intubation attempts, and complications between modified and conventional nasotracheal intubation techniques

Variable	Group M (n=30)	Group C (n=30)	df	P*
T1 (s), mean±SD	108.6±43.1	142±49.2	58	0.007
T2 (s), mean±SD	19.53±5.2	22.50±6.5	58	0.056
Total time (s), mean±SD	128.8±43.7	164.80±48	58	0.004
Ease of glottis visualization, n (%)	27 (90)	19 (63.3)	1	0.001
Difficulty in glottis visualization, n (%)	3 (10)	11 (36.7)	1	0.01
Success on second attempt, n (%)	2 (6.67)	13 (43.33)	1	0.02
Number of patients needing facilitating maneuvers, n (%)	3 (10)	6 (20)	1	0.5
Complication, n (%)
Desaturation (SpO2 <95%)	1 (3.3)	8 (26.7)	1	0.026
Traumatic bleed	2 (6.7)	1 (4.5)	1	>0.99

Data expressed as mean±SD or number of cases (%). *Intergroup comparison done using Student’s t-test for numerical data and Chi-square for categorical data. P<0.05=Statistically significant. T1: Time taken for glottis visualization, T2: Time taken for intubation till cuff inflation, SD: Standard deviation

Moreover, facilitating maneuvers such as head flexion, jaw thrust, and the anticlockwise rotation needed to ease intubation were similar with both the techniques (P = 0.5) [Table 2]. In the modified technique group, only two patients underwent second attempt, which is significantly less as compared to 13 patients in conventional group (P = 0.02). Similarly, desaturation was reported in only one patient in the modified technique group as compared to eight patients in the conventional group (P = 0.026) [Table 2]. However, there was no significant difference in the incidence of bleeding between two procedure group (P > 0.99). In both the groups, maximum patients were comfortable during awake fiber-optic intubation (Grades 1 and 2); severe grimace response (Grade 3) was shown by four patients in modified technique group and in three patients with conventional technique [Figure 3].

Figure 3

Mean difference in time taken for glottis visualization in both groups

DISCUSSION

Awake flexible fiber-optic intubation is a commonly preferred technique of choice for the management of anticipated difficult airway with restricted mouth opening in the patient undergoing an elective procedure.[141516] Most of the studies in nasal AFOI have been done by conventional technique, that is inserting the bronchoscope first and then railroading the tube over it. The literature quotes very few studies using the ETT as a conduit and then inserting fiber-optic bronchoscope through it.

The present study was undertaken to determine whether modified tube technique (MTF) is better than the conventional technique of awake nasal fiber-optic intubation. In our study, we inserted ETT blindly till the mark of 15 cm. In most of the patients, when the 15 cms mark was at the level of ala nasi, the tube has just crossed the nasopharynx, and its tip stood above the larynx acting as a conduit to guide the tip of the scope through the glottis. In contrary to the finding of Mohammedzadeh et al.,[12] the mark of 18 cms was found to be too deep for most of the Indian patients, and it does not give an appropriate space for manipulation.

Time taken for glottis visualization as well as the total time taken for fiber-optic intubation (primary outcomes) was significantly lesser in Group M as compared to Group G. The result was similar to the study done by Mohammedzadeh et al.[12] With the ETT in situ (as used in MTF), there is minimal soiling of scope due to blood or secretions present in the oropharynx.[1517] Moreover, insertion of the ETT first provides proper alignment to guide the scope through the nasal cavity to face the vocal cords. This may explain shorter TI as well as total time taken for intubation.

There was no statistically significant difference between the groups from glottis visualization till the ETT insertion. Advancement of the tube after glottis visualization may be difficult with the conventional technique. The primary reason for the difficulty in advancing the tube over the fiberscope is considered to be the deviation of course of the tube from that of the fiberscope (because of the gap between the two) toward the surrounding anatomical structures such as epiglottis, arytenoid cartilage, pyriform fossae, or esophagus.[1819] Katsnelson et al.[20] proposed epiglottis as the frequent site of obstruction during nasotracheal intubation.

Furthermore, this modified technique reduced the twisting of bronchoscope which may have accounted for better ease of glottis visualization in Group M as compared to Group C (P = 0.03).

Fiber-optic intubation was successful in 93% of cases in the first attempt and the second intubation attempt was needed in only 7% of cases in the modified technique, while in the conventional method, 43.36% needed a second attempt (P = 0.02).

Upper airway collapse or obstruction can be associated with AFOI. It could be attributed to the local anesthesia provided for airway preparation as well as to the sedation used to achieve appropriate patient cooperation. According to the study conducted by Law et al., either partial or complete airway obstruction accounted for 5% of complications related to AFOI.[8] In our study, the modified tube group had only 3.3% desaturation, while this incidence reached up to 26.7% in the conventional group which is statistically significant (P = 0.02). In cases of desaturation, oxygen was first instilled through a catheter connected to the working channel of the bronchoscope and if required, the scope was removed and the patient was ventilated by connecting ETT through the Bain's circuit. However, it was observed that in modified group, ventilation was easier, and saturation came to normal levels in minimal time after ventilation. The improvement in saturation was because ETT was partially inserted in the posterior nasopharynx, which acted as a nasopharyngeal airway and it stood just above the larynx, making the ventilation easier and effective. The scope had to be removed in only one patient in the modified tube group and six patients in the conventional technique to oxygenate the patients, as patient's SpO2 dropped to 88%, which again highlights the safety of this modified tube technique.

There is a lot of controversy on the adequate length of airway adjunct to be inserted in the nasal cavity. Watanabe et al.[21] in their study revealed that the appropriate nasopharyngeal airway length to release airway obstruction was 12.73 ± 0.85 cm and 11.70 ± 0.75 cm in the male and female groups, respectively, and to get the most effective ventilation was 14.55 ± 0.96 cm and 13.93 ± 1.12 cm in male and female groups, respectively. Stackhouse and Infosino[22] stated that the adequate length of nasal airway is mandatory to relieve airway obstruction and emphasized that the nasopharyngeal adjunct must be long enough to pass through the nasopharynx, but short enough to still remain above the glottis. Mohamed El-Tawansy et al.[23] found that even after using nasopharyngeal airway as a guide for fiber-optic scope, there is a possible chance of airway obstruction as in his study 7 cases out of 34 needed jaw thrust. He suggested the need of nasolaryngeal and not nasopharyngeal airway as fiber-optic nasal intubation aid. Nasolaryngeal airway can achieve the target of airway patency as well as transporting the scope tip immediately in front of the laryngeal inlet facilitating the process of laryngeal visualization and intubation even in challenging situations.

Preinsertion of ETT till 15 cms as in our study acted as a readily available laryngotracheal aid enabling not only adequate nasal patency but also gave enough space to manipulate the fiber-optic scope tip for early as well as safe intubation.

Strength and limitations

There were a few limitations to our study. First, due to the obvious differences in two techniques, the operator could not be blinded to the technique used but the patients and the observer assessing the outcomes of the trial were fully blinded. Second, our study included difficult airway patients being posted for oromaxillofacial surgeries only. Difficult airway cases posted for other surgeries were excluded from the study. Third, AFOI in our study was done by two experienced anesthetists, so our results may not apply to the untrained personnel.

The main strength of our study was that it was designed as a randomized control trial with blinded outcome assessment.

CONCLUSION

Our study results provided evidence that MTF is better than the conventional technique for awake nasotracheal fiber-optic intubation. We found that MTF is associated with better clinical outcomes requiring lesser time and attempts while maintaining airway patency. However, we need to conduct large RCTs to establish this technique as a standard practice for fiber-optic intubation. Furthermore, there is a need to explore this technique in other difficult airway cases including craniomaxillofacial anomalies and pediatric cases.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.