DOI: https://doi.org/10.21203/rs.3.rs-2297706/v1
BACKGROUND: According to the 2022 American Society of Anesthesiologists (ASA) guidelines on difficult airway management, video laryngoscope, video stylet, and flexible videoscope are recommended for intubation of complex difficult airways. Here we compare the advantages of three airway devices when intubating patients with difficult airways.
METHODS: For a comparative study on transoral intubation, 170 patients were selected and randomized into the following three groups: the video laryngoscope group (Group VL, n=59), video stylet group (Group VS, n=59), and flexible videoscope group (Group FV, n=59). The success rate of the first-pass intubation, time of tracheal intubation, level of glottic exposure and occurrence of intubation-related adverse events were recorded and analyzed.
RESULTS: A total of 177 patients were enrolled, 59 of whom were randomized to each group. All patients were successfully intubated with three devices. The first-pass intubation success rate was significantly higher in Groups VS and FV than in Group VL (96.61% vs. 93.22% vs. 83.05%, P<0.01), but the difference in the first-pass intubation success rate between Groups VS and FV was not significant(P>0.05). The number of patients categorized as Wilson-Cormack-Lehane(W-C-L) class I-II was lower in Group VL than in Groups VS and FV (77.97% vs. 98.30% vs. 100%, P=0.0281). The mean time to intubation was 44.56 ± 4.42 seconds in Group VL, 26.88 ± 4.51 seconds in the Group VS and 95.20 ± 4.01 seconds in Group FV, and the time to tracheal intubation was significantly longer in Group FV than in Groups VL and VS. Obviously, the Group VS had a significant advantage in intubation time (P < 0.01). No significant differences were found among the three groups in terms of adverse intubation reactions (P > 0.05).
CONCLUSIONS: In patients with difficult airways requiring intubation, use of the video stylet has the advantage of a relatively shorter intubation time, and the flexible videoscope and video stylet yield a higher first-pass intubation success rate and clearer glottic exposure than the use of the video laryngoscope.
Trial registration: Chinese Clinical Trial Registry. No: ChiCTR2200061560. Prospective registration.
Currently, visualization techniques are becoming increasingly popular, reducing the risk of severe intubation reactions and failed intubations. Nevertheless, both anticipated and unanticipated difficult airways still result in failed intubation, which not only puts the anesthesiologist in an embarrassing dilemma, but also threatens the life and safety of the patient. Although there are dozens of devices to deal with difficult airways, in widespread use, airway devices focus primarily on one aspect of a difficult airway. Therefore, we cannot use only one device to deal with all difficult airways encountered, and it is particularly important to choose the appropriate device for each situation.
The video laryngoscope, a conventional glottic visualization device, has been considered the gold standard device for transoral tracheal intubation by anesthesiologists worldwide, and its availability has led to unprecedented improvements in the field of view during intubation, success rates of tracheal intubation, shortened intubation times, and even reduced intubation-related airway injuries compared with conventional direct laryngoscopy [1–3]. Clinical practice, however, video laryngoscopy has certain limitations and sometimes calls for the use of laryngoscopy without effective exposure of the vocal cords to obtain a clear image, particularly in patients with special circumstances. Examples include patients with spinal cord injury who cannot tilt their head back and obese patients who have difficulty exposing the vocal tract. There is a study that showed a correlation between different blade angulation and difficulty in accessing the vocal tract with a tracheal tube [4]. This has led to the development of many new intubation devices based on traditional visualization devices to assist anesthesiologists in both routine and difficult airway management. flexible videoscope and video stylet are two of these devices that have given anesthesiologists a more powerful weapon in managing difficult airways and have been defined by the 2022 ASA Difficult Airway Guidelines as an advanced airway tool for managing difficult airways [5]
To date, no study has prospectively compared intubation the differences between a video laryngoscope, video stylet and flexible videoscope in patients with difficult airways. Therefore, the main objective of this study is to focus on patients with difficult airways categorized as modified Mallampati class III-IV and compare the three devices in these patients categorized a categorized as general anesthesia for transoral tracheal intubation, providing a clinical reference for the management of this type of difficult airway.
The present study was approved by the Ethics Committee of the Affiliated Luan Hospital, Anhui Medical University (NO.2021LL005), and written informed consent forms were signed by all the participants or their relatives before enrollment. We recruited patients from the Affiliated Luan Hospital at Anhui Medical University (Anhui Province, China) between July and September 2022. The trial was retrospectively registered at the China Clinical Trial Registration Center (www.chictr.org.cn, ChiCTR2200061560; Principal investigator: Tao Zhang; Date of registration; 9 June, 2022).
The inclusion criteria were as follows: (1) patients requiring transoral tracheal intubation for general anesthesia for elective surgery in our hospital, (2) ASA class Ⅰ and Ⅱ, (3) 18–64 years of age, and (4) modified Mallampati class Ⅲ and Ⅳ. Patients with any of the following conditions were excluded: (1) a mouth opening < 2 cm, (2) difficulty receiving mask ventilation, (3) anatomical abnormalities of the upper airway (trauma, tumor, and deformity); (4) cervical spine instability, (5) inability to properly understand and cooperate with the experiment. (6) And those who refused to participate in this study.
Anesthesia preparation: All patients fasted from food and water before surgery. Upon entering the operating room, the patient's body temperature, heart rate, pulse, oxygen saturation, blood pressure, electrocardiogram and end-tidal carbon dioxide (PETCO2) were recorded. A Narcotrend monitor was used to measure the depth of anesthesia. For females, a reinforced endotracheal tube with an inner diameter of 7.0 mm was used, while, for males, a 7.5 mm reinforced tube was needed. Intravenous access was opened and 1 mg of valacyclovir + 10 mg of dexamethasone were administered. anesthesia was administered by endotracheal general anesthesia. In all patients, dexmedetomidine 0.8 µg/kg was pushed intravenously 10 min before induction of anesthesia.
Induction and maintenance of anesthesia: Induction anesthesia: included sequential injections of 0.05 mg/kg midazolam, 0.5 µg/kg sufentanil, 0.3 mg/kg etomidate, and 0.8 mg/kg rocuronium in all three groups. Tracheal intubation was performed 90 seconds after rocuronium injection. All intubations were performed by anesthesiologists of the same seniority.
Group VL: The video laryngoscope (TDC- K3, UE Medical Equipment Co. Ltd., Zhejiang, China, Fig. 1.A) was fitted with a disposable transparent lens jacket, and the front end of the tracheal tube was shaped to approximately 60° with the same curvature as the anterior part of the visual laryngoscope by applying a metal tube core, with the patient lying in a flat position and the anesthesiologist standing at the head end of the patient. After pushing the jaw open with the right hand, the visual laryngoscope was placed in the patient's mouth with the left hand, along the tongue surface and forward. The lingual-palatal and palatopharyngeal arches are passed to reach the pharyngeal cavity, and when the vocal fissure is exposed in the observation display, the tracheal tube is gently pushed into the trachea with the right hand, and the core is plucked out at the same time.
Group VS: The video stylet (TRS- K2, UE Medical Equipment Co. Ltd., Zhejiang, China, Fig. 1.B) is inserted into the tracheal tube, and the tracheal tube is fixed at the upper end to prevent the lens from sticking out of the tracheal tube and avoid contamination of the lens with secretions. The anesthesiologist opens the patient's mouth with the left hand, lifts the lower jaw, inserts the lens handle into the mouth from the right corner of the mouth with the right hand, following the oral cavity into the lateral wall of the pharynx. After 11–12 cm (at the level of the upper larynx), the lens is aimed to the left and middle of the neck while observing the screen to locate the vocal fold structure. The tracheal tube is fed into the trachea, the core is pulled out and the video stylet is withdrawn, and the capsule is inflated.
FV group: The flexible videoscope (TIC, UE Medical Equipment Co. Ltd., Zhejiang, China, Fig. 1. C) is inserted into the tracheal tube, the tracheal tube is fixed at the upper end of the light-guiding hose, the patient's jaw is lifted to open the mouth and put in the disposable mouth pad. The anesthesiologist holds the handle of the flexible visualization mirror in the left hand. The right hand is used to extend the light-guiding hose through the mouth pad into the patient's mouth and afterward to the pharynx. After the vocal cords are exposed, pass between the vocal cords. The anesthesiologist can adjust the direction of the front end to enter the trachea. At 3 cm from the bulge, the right hand is used to gently push the tracheal tube into the trachea, withdraw the light-guiding hose, and inflate the cuff.
After successful intubation of the tracheal tube, the patient was connected to the anesthesia machine for mechanical ventilation, the tidal volume was adjusted to 10 ml/kg, and the respiratory rate required 12 breaths/min to maintain PETCO2 at 35–45 mmHg. Anesthesia maintenance: Propofol 4–6 mg/kg/h and remifentanil 0.1–0.2 µg/kg/min were pushed in both groups and discontinued at the time of skin closure. This dosage was adjusted according to the measure of anesthetic depth using bispectral index monitoring (BIS) at a target zone of 40–60. Rocuronium and sufentanil were administered as needed during surgery. After surgery, patients were sent to the post-anesthesia care unit (PACU).
The success rate of the first intubation was recorded as the primary observation. The Wilson-C-L classification of the glottic exposure grade (W-C-L 1 = all vocal folds are visible; W-C-L 2 = half of the vocal folds are visible; W-C-L 3 = only the spongy cartilage is visible; W-C-L 4 = only the epiglottis is visible, and not the vocal folds; and W-C-L 5 = no anatomical part of the larynx is visible) and intubation time (time between the end of mask ventilation and confirmation of the waveform by end-tidal carbon dioxide monitoring) were used as secondary observations. According to the consensus of the reviewed literature, successful intubation was defined as the ability to see the true vocal cords and successfully pass the tracheal tube through the true vocal cords within 100 seconds, and intubation was attempted a maximum of three times; failure of all three intubations resulted in withdrawal from the experiment. The intubation device was withdrawn from patients who experienced a failed first intubation and patients were re-oxygenated for three minutes before a second intubation was performed; and the time of intubation was recorded again. Failed intubation was defined as an intubation time longer than 3 minutes or patient oxygen saturation reduced to less than 90%. Patients were followed up in the PACU after the procedure and asked whether they had a sore throat, hoarseness, and other discomfort, to record the occurrence of adverse effects associated with intubation.
To calculate the sample size, we performed a preliminary experiment with 20 patients in each group (60 patients in total), and the first-pass intubation success rate in each group was 75% in Group VL, 95% in Group VS, and 90% in Group FV. With α = 0.05 and test efficacy 1-β = 0.8, a minimum sample size of 155 could be calculated according to PASS15.0.5 software. A total of 189 patients were finally included after supplementing a 20% loss of follow-up rate. Prior to the start of the study, all patient names were randomly placed in opaque envelopes using computer-generated random numbers according to the equipment used for intubation, by someone other than the investigator, and the envelopes containing the random numbers were divided into 3 groups (59 per group). After completion of the procedure, case questionnaires containing only the random numbers were submitted by the researchers, but the followers who conducted the follow-up survey were not aware of the random groupings.
The data were analyzed using SPSS 26.0 statistical software. Continuous variables, such as the basic characteristics of patients, are expressed as the mean ± standard deviation. Comparisons of measurement data were performed using the F test if the conditions of normality and chi-squared were met; otherwise, the rank sum test was used. Comparisons of count data were performed using the chi-square test. All significance tests were two-sided tests with a test level of α = 0.05, and P < 0.05 indicated that the differences were statistically significant.
A total of 189 patients requiring general anesthesia for elective surgery were recruited for the present study. The CONSORT flow chart of the included patients is shown in Fig. 2. Two patients did not meet the inclusion criteria due to extremely limited mouth openings (< 2 cm), 6 patients refused to participate in the study, and 4 others were excluded due to surgical cancellation. A total of 177 patients were included, 59 in Group VL, 59 in Group VL, and 59 in Group VL. There were no statistically significant differences between the three groups in terms of sex, age, BMI, ASA classification, or modified Mallampati classification (all P > 0.05) (Table 1).
|
Patient Information |
VL(n = 59) |
VS(n = 59) |
FV(n = 59) |
P-value |
|---|---|---|---|---|
|
Gender (M/F, n) |
0.831 |
|||
|
Male |
41 |
39 |
42 |
|
|
Female |
18 |
20 |
17 |
|
|
Age (years) |
49.66 ± 5.37 |
50.85 ± 6.06 |
49.51 ± 5.42 |
0.369 |
|
BMI(kg/m²) |
21.04 ± 2.02 |
21.26 ± 1.99 |
20.63 ± 1.82 |
0.199 |
|
ASA Classification |
0.618 |
|||
|
I (n) |
49 |
51 |
47 |
|
|
II (n) |
10 |
8 |
12 |
|
|
Modified Mallampati classification |
0.865 |
|||
|
III (n) |
51 |
50 |
52 |
|
|
Ⅳ(n) |
8 |
9 |
7 |
Data indicate the mean ± SD or n(percent); ASA American Society of Anesthesiologists, BMI Body mass index; Statistical analysis indicated no significant differences in the parameters among groups (P > 0.05). Modified Mallampati classification: I = can see the soft palate, pharyngopalatine arch, uvula, and hard palate; II = can see the soft palate, uvula, and hard palate; III = you can see the soft palate and hard palate; Ⅳ= can only see the hard palate.
The first-pass intubation success rate was significantly better in the VS and FV groups than in the VL group (96.61% vs. 93.22% vs. 83.05%, P < 0.01), and the second intubation was successful in all three groups for patients whose first intubation was unsuccessful (Fig. 3). The level of acoustic exposure was grade I-II in all the FV groups and 58 in the VS group, both more than the 49 in the VL group (P < 0.01), and the difference between the VS and FL groups was not significantly different. The mean time to intubation was 44.56 ± 4.42 seconds in the VL group and 95.20 ± 4.01 seconds in the FV group, indicating that the VL group had a shorter intubation time than the FV group. The VS group had the shortest mean intubation time of 26.88 ± 4.51 seconds, i.e., the VS group had a significant advantage in regard to the intubation time (P < 0.01) (Table 2, Fig. 4). There was no significant difference in the occurrence of intubation-related adverse reactions between the groups (P > 0.05).
|
VL(n = 59) |
VS(n = 59) |
FV(n = 59) |
P-value |
|
|---|---|---|---|---|
|
W-C-L classification |
0.01 |
|||
|
1, 2(n) |
46 |
58 |
59 |
|
|
3, 4(n) |
13 |
1 |
0 |
|
|
First-pass intubation success rate (n, percent) |
49 (83.05%) |
57 (96.61%) |
55 (93.22%) |
0.0281 |
|
Total intubation success rate (n, percent) |
59(100%) |
59(100%) |
59(100%) |
- |
|
Time to intubation(s) |
44.56 ± 4.42 |
26.88 ± 4.51 |
95.20 ± 4.01 |
0.01 |
|
Intubation-related adverse events (n) |
11 |
6 |
4 |
0.1216 |
Data indicate the mean ± SD or n(percent). W-C-L classification: Wilson-Cormack-Lehane classification.
In this randomized parallel-group study, we showed that while all three devices were ultimately effective for intubation, higher first-pass intubation success rates were obtained with the video stylet and the flexible videoscope. Endotracheal intubation with the video stylet resulted in shorter intubation time when compared with the video laryngoscope and flexible videoscope. Although statistically significant differences in intubation-related adverse events were not observed between the three groups, anesthesiologists were objectively more likely to cause injury to patients with difficult airways when using the video laryngoscope, and the flexible videoscope was more advantageous in this regard.
The increasing number of airway management devices that are being developed and used has changed the definition of a difficult airway [6, 7]. Some studies have shown that, compared with the traditional direct laryngoscope, the video laryngoscope does not require the three lines of the mouth and throat to overlap, and the glottis can be seen by clearly displaying the pharyngeal structures on the screen through the camera at its front end, allowing the anesthesiologist to directly view the tracheal tube insertion into the glottis through an indirect field of view, completely changing the traditional direct laryngoscope field of view exposure method, easing the difficulty of glottic exposure, and improving the success rate of intubation [8, 9]. Although the use of video laryngoscopy is recommended in difficult airway management guidelines, repeated intubation attempts with the same device are no longer recommended when multiple attempts are unsuccessful, as this may cause unnecessary injury to the patient or delay resuscitation. Jaime B. Hyman's team has shown that the success rate of intubation with a conventional video laryngoscope is not ideal for patients with head and neck injuries. Most likely because the laryngeal tube is fixed to the scope, the patient's head must be tilted back and the atlantoaxial joint must be lengthened when the scope is placed in the patient's mouth, and these maneuvers may harm patients who need cervical bracing [10].
No significant differences in the clinical experience of anesthesiologists were observed between the three groups during our current study, indicating that differences in the data within the same group were not due to technical factors. We found that the first-pass success rate of intubation in 177 patients intubated with modified Mallampati class III/IV was much lower in Group VL than in Group VS and Group FV. Ten patients in Group VL failed first intubation and had the laryngeal lens withdrawn, were reoxygenated for three minutes, had their heads tilted back more, and their mouths opened by an assistant with both hands. At times, an assistant was asked to use both hands for the successfully intubation of the patient. Thus, the intubation restriction in Group VL not only included patients with poor head and neck mobility but also included patients with difficult airways such as difficult vocal openings, which increased the intubation time and undoubtedly increased the risk of injury to the patient.
The video stylet does not require a large degree of mouth opening and head tilt, and does not require the epiglottis to be lifted up, which may effectively reduce the degree and force of instrument contact with the oropharynx. Therefore, the damage to the oropharyngeal mucosa from intubation is reduced, which is an obvious advantage for intubation in patients with cervical bracing[11]. The study by B. D. Alvis et al. indicated that the use of such devices in difficult airway patients who do not require awake intubation can replace a flexible videoscope and that time to intubation would be shorter, which is consistent with what we have observed [12]. Among the 59 patients intubated with the video stylet, the total intubation success rate was 100%, but 2 patients required a second intubation because the video stylet lens, after entering the patient's mouth, was contaminated with a large amount of oropharyngeal secretions after entering the patient’s mouth, resulting in blurred visualization. Thus, the anesthesiologist did not have a clear view of the glottis, forcing him to withdraw the stylet and reintubate the patient after aspiration and reoxygenation. We aimed to overcome this limitation and found that we could obtain a very clear view by placing the lens at Murphy's orifice of the tracheal tube without moving the lens over the tip during the present study. Even if the patient had secretions in the mouth, the video stylus was operated very smoothly to find the glottis.
The flexible videoscope has the advantage of not limiting the diameter of the tracheal tube and, due to the softness of its light-guiding hose, is also better than a regular video laryngoscope in terms of reducing damage to the patient's mouth and airway during intubation. However, we found that its intubation time was shorter than that of the video laryngoscope and video stylet, probably because the flexible videoscope light-guiding hose was difficult to fix during the operation and it was more difficult to operate. Additionally, because muscarinic drugs and gravity reduce tension in the epiglottis and tongue, an assistant sometimes needed to help tilt the head back and elevate the jaw to open the epiglottis and obtain a view of the glottis. At the same time, it also shows that the use of the flexible videoscope for transoral intubation is a challenging skill for anesthesiologists to master and requires repeated practice [13]. Flexible videoscope guided tracheal intubation has been shown to produce more dramatic hemodynamic changes [14, 15]. However, most of them employ transnasal intubation, and in our study, transoral tracheal intubation was used for patients with modified Mallampati class III/IV. The light-guiding hose has the advantage of being more flexible and smaller in caliber, and it performs better in terms of glottic exposure than the video laryngoscope. All 59 patients in our study with Wilson-C-L classification were grade I-II, and in 4 patients, due to the resistance encountered when pushing the tracheal tube into the airway, the catheter hose was withdrawn after 3 attempts to avoid damage to the vocal hilum. The patient's neck was fully tilted back and the lower jaw was lifted, after which the tracheal tube was reintubated and successfully delivered into the trachea. The remaining 55 patients were successfully intubated in a single attempt, and the study by J. Adam Law et al. also showed that physicians skilled in the use of a flexible videoscope have a high intubation success rate in managing difficult airways [16]. This reflects the consensus that using a flexible videoscope is considered the gold standard for difficult airway management [5, 17].
The incidence of difficult airways in the general population for general anesthesia surgery is 0.5 to 10%, and the incidence of being unable to intubate and obtain effective ventilation is 0.01 to 0.07% [18]. The annual global surgical volume is more than 300 million, which means that millions of patients are at risk from having difficult airways and hundreds of thousands of patients suffer from failed intubation each year [19]. In addition to general anesthesia patients who require an artificial airway to be established via oral tracheal intubation, emergency resuscitation in and out of the operating room, such as severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19) require an artificial airway to be established via oral tracheal intubation for mechanical ventilation to assist in breathing [20]. Therefore, visual intubation equipment is essential to the clinical work of anesthesiologists.
This study has several limitations, as described below. a. The criteria for recruiting subjects may not include all patients who meet the definition of a difficult airway. For example, in recent studies, supraglottic and subglottic ultrasound measurements or upper lip biting tests have been performed to predict a difficult airway [21, 22]. In a follow-up study, we can conduct a large-scale multicenter clinical study to confirm our conclusions. b. Visual soft microscopy requires one hand to hold the mirror and one hand to operate the guiding hose, so an assistance is needed for opening the patient's mouth and placing the mouth pad, which may lead to systematic errors in the three groups. c. The anesthesiologist's proficiency with the three intubation devices did not reach the same level, although the anesthesiologist had experience in operating all three devices before the start of the experiment. Operators were experienced in their operation, the flexible videoscope and video stylet were used relatively much less frequently in the clinic than the general video laryngoscope.
When managing the airways of patients with difficult airways, all three devices can be used to achieve high intubation success rates, but the video stylet and flexible videoscope provide a better view of the vocal cords and are superior to the video laryngoscope in terms of the first-pass intubation success rate. The use of a video stylet has the advantage of relatively shorter intubation time, allowing successful intubation in a shorter period of time and reducing the patient's hypoxia time. Therefore, anesthesiologists must know all of the required intubation devices and decide which special devices are required based on the condition of the patient.
VL: Video Laryngoscope; VS: Video Stylet; FV: Flexible Videoscope; BIS: Bispectral Index Monitoring; W-C-L: Wilson-Cormack-Lehane; ASA: American Society of Anesthesiologists; PACU: Postanesthesia Care Unit; PEtCO2: End-tidal Carbon Dioxide; SARS: Severe Acute Respiratory Syndromes and COVID-19: Corona Virus Disease 2019
Ethics approval and consent to participate
The present study was approved by the Ethics Committee of the Affiliated Luan Hospital, Anhui Medical University (NO. 2021LL005), and written informed consent forms were signed by all the participants or their relatives before enrollment. As part of our study, we adhere to established international standards, including the principles outlined in the Helsinki Declaration. The trial was retrospectively registered at the China Clinical Trial Registration Center (www.chictr.org.cn, ChiCTR2200061560; Principal investigator: Tao Zhang; Date of registration; 9 June , 2022).
Competing interests
The authors declare that they have no competing interests.
Funding
This research was funded by the Anhui Province Key Research and Development Program Project (201904b11020014), and the Research Fund Project at the Hospital Level of Luan Hospital, Anhui Medical University (2021kykt05).
Authors' contributions
TZ and RHL designed the study and drafted the manuscript. HZH, XXC, and PZ completed the anesthesia management. GLZ and KYZ recruited patients. All authors read and approved the final manuscript.
Acknowledgements
Not applicable.
Availability of data and materials
The datasets used and/or analyzed during the current study were available from the corresponding author on reasonable request.