Effects of Head Positions on Awake Orotracheal Intubation Via Fiberoptic-Bronchoscope: A Randomized Controlled Trial


 Background: There are many factors affect the success rate of awake orotracheal intubation via fiberoptic bronchoscope. We performed this study to investigate the effects and safety of three head positions on awake orotracheal intubation via fiberoptic bronchoscope. Methods: Seventy-five adult patients with anticipated difficult airway, received general anaesthesia and undergoing awake orotracheal intubation were included in this study. According to the head position, the patients were randomized allocated to neutral position group (NP group), sniffing position group (SP group) or extension position group (EP group). After conscious sedation the patients were intubated by an experienced anesthesiologist. The time to view the vocal cords, the time to insert the tracheal tube into the trachea, the percentage of glottic opening scores (POGO) and the visual analog scale (VAS) scores for ease experienced of passing the tracheal tube through the glottis, the hemodynamic changes during intubation and the adverse events after surgery were recorded. Results: The time to view the vocal cords was significantly shorter and the POGO scores was significantly higher in the EP group compared with the other two groups (P<0.05); the SpO2 immediate after intubation was higher in the EP group compared with SP group (P<0.05) and the SpO2 before intubation was higher in the EP group compared with NP group (P<0.05), while at other time points the SpO2 had no significant difference among groups. The time to tracheal intubation, the VAS scores for passing the tracheal tube through glottis, the coughing scores of patients when inserted fiberoptic bronchoscope into the trachea and inserted the tracheal tube into the trachea over fiberoptic bronchoscope had no significant differences among groups (P>0.05). There were also no significant differences among the groups with regard to the incidence of postoperative complications, mean arterial pressure and heart rate at each time point (P>0.05). Conclusions: Extension position had a best view of glottic opening than neutral position or sniffing position during awake orotracheal intubation via fiberoptic bronchoscope, so extension position was recommended as the starting head position for awake orotracheal intubation using fiberoptic bronchoscope.Trial registration: Clinical Trials.gov. no. NCT 02792855. Registered at https://register.clinicaltrials.gov on 23 september 2017.

ease experienced of passing the tracheal tube through the glottis, the hemodynamic changes during intubation and the adverse events after surgery were recorded.
Results: The time to view the vocal cords was signi cantly shorter and the POGO scores was signi cantly higher in the EP group compared with the other two groups (P<0.05); the SpO 2 immediate after intubation was higher in the EP group compared with SP group (P<0.05) and the SpO 2 before intubation was higher in the EP group compared with NP group (P<0.05), while at other time points the SpO 2 had no signi cant difference among groups. The time to tracheal intubation, the VAS scores for passing the tracheal tube through glottis, the coughing scores of patients when inserted beroptic bronchoscope into the trachea and inserted the tracheal tube into the trachea over beroptic bronchoscope had no signi cant differences among groups (P>0.05). There were also no signi cant differences among the groups with regard to the incidence of postoperative complications, mean arterial pressure and heart rate at each time point (P>0.05).
Conclusions: Extension position had a best view of glottic opening than neutral position or sni ng position during awake orotracheal intubation via beroptic bronchoscope, so extension position was recommended as the starting head position for awake orotracheal intubation using beroptic bronchoscope.

Background
The incidence of di cult airway is ranging from 0.3-13% [1] and nearly 30% of all anaesthesia-related deaths attribute to di cult airway [2]. Awake tracheal intubation via Fiberoptic bronchoscope (FOB) is regarded as the golden standard for the management of di cult airway [3][4][5][6]. However, in sedated state patients, the base of tongue, soft palate and epiglottis move backward and obstruct the advancement of FOB [7,8]. Recently, several studies have examined the effects of different methods such as jaw thrust, lingual traction or head tilt on FOB intubation [9][10][11][12][13][14][15]. However, there have been no studies to determine whether the neutral head position, sni ng head position or extension head position is more suitable for Awake Fibreoptic bronchoscope Orotracheal Intubation (AFOI). Thus, the objective of this study was to investigate the effects and safety issues of three head positions during AFOI.

Methods
This trial was approved by the institutional review board of the rst hospital of Qinhuangdao and all patients provided written informed consent.
Seventy-ve adult patients with anticipated di cult airway, ASA class I-II, modi ed Mallampati classi cation ≥ 3, requiring general anaesthesia and undergoing awake orotracheal intubation were included in this study. Exclusion criteria were as follows: age > 70 or < 18 years, with cervical vertebra disease, incisors loose or missing, preoperative hoarseness, bronchial asthma, a history of airway hyperresponsiveness, hypertension and abnormalities of heart, brain, liver, lung, kidney and coagulation functions.
All these patients were screened by a senior anaesthesiologist preoperatively and according to the head position, the patients were randomized allocated to neutral position group (NP group, Figure  was based on computer-generated codes which were kept in sequentially numbered opaque envelopes until the end of study. All the patients without premedication and received standard monitoring systems, including electrocardiogram (ECG), heart rate (HR), invasive arterial blood pressure (NIBP) and peripheral oxygen saturation (SpO 2 ) in the operating room. The patients were intravenously injected with midazolam 0.03 mg·kg − 1 . After mild sedation, a intratracheal injection was performed at the cricothyroid membrane with a ne needle and administered with 2% lidocaine (3-4 ml), then the patients were suggested to open the mouth as wide as possible and then the oral cavity and hypopharynx mucosa were sprayed with 2% lidocaine. After intratracheal anaesthesia, dexmedetomidine was administered at a loading dose of 1µg·kg − 1 (the infusion was completed in 10 minutes) then remifentanil was given at a loading dose of 0.5µg·kg − 1 , followed by a continuous infusion at a speed of 0.1-0.15µg·kg − 1 ·min − 1 . During this process the patients received continuous oxygen by mask at a rate of 5 L/min. Before intubation, a FOB (external diameter 5.2 mm, MDHAO Medical Technology Co, Ltd, Zhuhai china) was loaded with a tracheal tube (inner diameter 6.5 mm for female and inner diameter 7.0 mm for male) and lubricated with dyclonine hydrochloride mucilage. After deep sedation (patients breathing spontaneously but cannot be awakened by call her name), the intubation was performed and the steps were as follows: First, a bite block was placed between the teeth of patients then the operator inserted the FOB into the mouth with his left thumb and fore nger, simultaneously gripped the chin upward with the rest of his ngers. At this point, the bite block as a fulcrum to lift the mandible upward to open the space of pharynx and laryngeal cavity as far as possible ( Figure A, B, C) then advanced the FOB downward along the oropharyngeal curve with his left thumb and fore nger until viewing the epiglottis and glottis.
After the anterior of FOB passing the vocal cords, the FOB was inserted into the trachea and then the tracheal tube was pushed into the trachea over the FOB. Orotracheal intubation was suspended when SpO 2 < 90% and oxygen was supplied by mask.
The primary outcome parameters of the study were the time to view the vocal cords (TVVC) and the percentage of glottic opening scores (POGO). TVVC was de ned as the time from inserting the FOB between the teeth until the operator view the the entire vocal cords; POGO was the percentage of glottic opening scores (POGO) to evaluate the operator's rst vision of glottic opening during the FOB just passed the tongue base (score range:0-100: 0 = none, 100 = full) (11,16). The time to advance the tracheal tube into trachea over FOB (TATT) de ned as the time from the operator viewing the entire vocal cords to insert the tracheal tube into trachea successfully, the coughing scores when inserted the FOB into trachea and inserted the tracheal tube into trachea via FOB (coughing score: 0 = none, 1 = slight, 2 = moderate, 3 = severe) (17), the VAS scores of the ease experienced for inserting the tracheal tube into trachea indicated by the operator immediately after the intubation (score range:0-100, 0 = very di cult, 100 = very easy), the hemodynamic alterations of patients during intubation and postoperative complications such as hoarseness and pain of throat were also recorded. TVVC and TATT were assessed by an independent observer with a stopwatch.
In our study, the sample size was determined according to a pilot study which we recorded the POGO scores and measured the time to view the vocal cords. With signi cance set at 0.05 and power set at 80%, the sample size required to detect differences was 20 patients each group. Thus, we recruited 25 patients each group to prevent unforeseen di culties.
Analyses were performed using SPSS 21.0 statistical software. Continuous variables were presented as mean ± standard deviation (SD) and the differences among the groups were compared with ANOVA (Bonferroni or Dunnett T3 test was used for multiple comparisons). The differences of proportions were analyzed using Kruskal-Wallis test. The differences of the incidence were analyzed with Fisher's exact test. P value less than 0.05 was considered as statistically signi cant.

Results
All patients were completed the AFOI. There were no signi cant differences in the demographic characteristics of patients among groups (Table 1). The time to view the vocal cords was signi cantly shorter and the POGO scores was signi cantly higher in the EP group compared with the other two groups (P < 0.05); the SpO 2 immediate after intubation was higher in the EP group compared with SP group (P < 0.05) and the SpO 2 before intubation was higher in the EP group compared with NP group (P < 0.05), while at other time points the SpO 2 had no signi cant difference among groups. The time to tracheal intubation, the VAS scores for passing the tracheal tube through glottis, the incidence of postoperative complications, the coughing scores of patients when inserted FOB into the trachea and inserted the tracheal tube into the trachea over FOB had no signi cant differences among groups (P > 0.05) ( Table 2). VAS, Visual analog scale (score range, 0-100, score 0 = very di cult, 100 = very easy); Coughing score (score range, 0 = none, 1 = slight, 2 = moderate, 3 = severe) * P < 0.05 compared with SP group, # P < 0.05 compared with NP group.
There were also no signi cant differences among the groups with regard to mean arterial pressure and heart rate during intubation (P > 0.05)( Table 3).

Discussion
Inability to maintain patient's airway associate with hypoventilation, hypoxemia, hypoxic brain injury or even death [18][19][20], so the management of the di cult airway is at high-risk. Awake intubation via FOB is still the recommended method for dealing with di cult airway [3][4][5][6] and a clear airway that allows the passage of the FOB is critical to awake intubation via FOB.
In this study, we compared the effect and safety issues of three head positions (neutral position, sni ng position and extension position) during AFOI. The results showed us that the time for viewing the vocal cords was signi cantly shorter and the POGO scores were signi cantly higher in the extension position group compared with the other two groups, in addition at before intubation, the SpO 2 was higher in the EP group compared with neutral position group and at immediate after intubation the SpO 2 was also higher in the EP group compared with the sni ng position group. The results suggested that the extension position facilitated the FOB passing through the base of the tongue and easy to view the whole glottis. The results of SpO 2 also con rmed that the extension position was better than sni ng position or neutral position to keep the airway open in sedated patients.
Tracheal intubation via laryngoscope requires the operator to view the glottis directly and clearly, therefore, how to reduce the angle of airway axes (oral, pharyngeal and laryngeal) is the key to successful intubation. Magill rst reported that the sni ng position was better than the neutral position during tracheal intubation via laryngoscopy [21]. This recommendation is based on the so-called three-axes alignment theory that the sni ng position make three axes closer alignment [22,23]. Although the clinical bene t of sni ng position is controversial [24,25], sni ng position is still recommended for tracheal intubation using laryngoscopy [26,27].
It seems to be different of tracheal intubation using FOB for the anterior of FOB can move freely, so the FOB can cross the angle among the three axes, however the FOB can not provide enough support to the laryngeal tissue, resulting in the base of tongue, soft palate and epiglottis were closer to the posterior pharyngeal wall [28], lead to the operater unable to nd the glottis easily in sedated patients using FOB. Therefore, su cient space of pharyngeal cavity and laryngeal cavity is necessary for FOB to successfully pass through the base of the tongue and quickly view the glottis during AFOI. So the space of pharyngeal cavity and laryngeal cavity is the key to successful AFOI. Several studies found that the manoeuvre of jaw-thrust elevated the epiglottis and tongue base away from the wall of posterior pharyngeal, provided more space in the pharyngeal cavity and laryngeal cavity [9][10][11][12][13][14]. So the manoeuvre of jaw thrust facilitated viewing the vocal cords and increased the success rate of oral FOB intubation [29]. Durga et al demonstrated that used jaw thrust and lingual traction alone unable to clear the airway completely, whereas the combining used of jaw thrust and lingual traction cleared the airway more effectively [10]. Stacey et al found a clear airway at the level of the palate and larynx with a combined of FOB and laryngoscopy technique [11]. The problem with these methods is that one or two trained assistants are required. Therefore, in some emergency situations, such as unpredictable di cult airway the success rate of orotracheal intubation via FOB may reduce for without the aid of assistants. In addition, during awake orotracheal intubation the patients only sedated and without the use of muscle relaxants, so the manoeuvre of jaw thrust, lingual traction or assistance by laryngoscope may increase the discomfort of patients and cause the resistance of patients. In present study, all patients in the SP group with head and cervical extension by placing a 7-cm rm pillow under the shoulders of patients, so this positions tightened the muscles and tissues in the front of neck then moved the oropharyngeal structures anteriorly and emptied the oropharyngeal airspace. In addition, with head extension position, the operator made the bite block as a fulcrum and lifted the mandible upward more easily than other two positions during intubation, which may achieve similar effects as jaw thrust that lifting the base of tongue enabling the FOB easily to pass through the base of the tongue. Most important one was the whole process of intubation with no need for the assistance of others.
Successful inserting a FOB into the trachea does not guarantee a successful AFOI, because the anterior of the tracheal tube may impinge on the laryngeal structures when advance the tracheal tube into trachea over the FOB [30,31], which may lead to serious injury of laryngeal [32] or be catastrophic in some cases [14]. This di culty can be reduced by reducing the gap between the tracheal tube and FOB [33]. In this study, the outside diameter of FOB was 5.2 mm and the inner diameter of tracheal tube was 6.5 mm for female and 7.0 mm for male, so the gap between the tracheal tube and FOB was very small, furthermore we used silicone exible tracheal tube and the inside and outside of the tracheal tube was lubricated with dyclonine hydrochloride mucilage, so the advancement of a tracheal tube over the FOB very smoothly in all the patients.
In our study, we found no statistical differences in the hemodynamic changes and coughing scores among groups, the reasons may be that topical anaesthesia of the trachea and combined use of dexmedetomidine and remifentanil not only preserved the patients' spontaneous breathing but also achieve adequate sedation depth during intubation [34].
The patients were interviewed by an independent anesthesiologist one day after operation and the results showed us that all the patients were unable to recall the procedure of topical anaesthesia and intubation, the reasons may be that the application of low dose midazolam and the combined use of dexmedetomidine and remifentanil elimination of the patients' memory of these procedure. In addition, the small size of the tracheal tube was selected and the tracheal tube was adequately lubricated with dyclonine hydrochloride mucilage which may reduced the incidence of adverse complications and improved the comfort of patients.
There were also some limitations in our study. First, this method is not suitable for patients with cervical vertebra sickness; Second, this method is not suitable for patients with incisors loose or missing; Third, this method may not be applicable to the patient with oversize-chin or the operator with little experience in the management of FOB; Fourth, it was not possible to blind investigator to the technique, consequently we cannot rule out the possibility of biases by investigator in this study.

Conclusion
Extension position had a batter view of glottic opening than neutral position or sni ng position during AFOI, so extension position may be recommended as the initial head position for AFOI.

Consent for publication
Not applicable.
Availability of data and materials The datasets are available from the corresponding author on request.

Competing interests
The authors declare that they have no competing interests Funding Not applicable.
Authors' contributions ZL collected all the patient initial data and drafted the manuscript, LZ, MQL and QQJ completed the anesthesia management. XHQ, SJL helped with manuscript editing, and modifying gures and tables. XCY contributed to the writing, review and editing of the manuscript. All the authors read and approved the nal manuscript.