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Comparison of the McGrath videolaryngoscope and the Macintosh laryngoscope for double lumen endobronchial tube intubation in patients with manual in-line stabilization

Abstract Background: Double lumen endobronchial tube (DLT) intubation is commonly used for one-lung ventilation in thoracic surgery. However, because of its large size and shape, it is difficult to perform intubation compared with a single lumen tube. The aim of this randomized controlled trial was to determine whether the McGrath videolaryngoscope has any advantage over the direct Macintosh laryngoscope for DLT intubation in patients with a simulated difficult airway. Methods: Forty-four patients (19–60 years of age); scheduled to undergo general anesthesia with one-lung ventilation were assigned to 1 of 2 groups: DLT intubation with the McGrath videolaryngoscope (ML group [n = 22]); or conventional Macintosh laryngoscope (DL group [n = 22]). After manual in-line stabilization was applied as a way of simulating a difficult airway, the time required for intubation and the quality of glottic view were evaluated. Results: The time to successful intubation was not different between the 2 groups (ML group, 45 s [interquartile range, 38–52 s] versus DL group, 54 s [45–59 s]; P = .089). The McGrath videolaryngoscope, however, provided a significantly better glottic view. Modified Cormack and Lehane grade was better (P < .001), and the percentage of glottis opening score was higher in the ML group (P < .001). Overall intubation difficulty scale score was lower in the ML group (1 [0–2]) versus the DL group (3 [2–4]) (P < .001). Conclusion: The McGrath videolaryngoscope improved glottic view and resulted in lower overall intubation difficulty scale score in patients with in-line stabilization.


Introduction
Difficulty in airway management represents 1 of the major problems in anesthesia practice. Recently, various types of the videolaryngoscope have been reported to play an important role in patients with difficult intubation. [1][2][3] The McGrath videolaryngoscope (Aircraft Medical, Edinburgh, Scotland), a portable device, provides a better laryngeal view than that obtained by direct Macintosh laryngoscopy, and several studies have reported that it provides improved laryngeal views and intubation conditions in patients with normal or difficult airways. [4,5] Because truly difficult airways are very rare and dangerous, studies investigating intubation conditions of difficult airways are evaluated using "simulated difficult intubation" situations. [6][7][8][9][10][11][12] One of the methods that has been proposed, manual in-line stabilization, can be applied as a way of simulating a difficult airway. [12] The double lumen endobronchial tube (DLT) is commonly used for one-lung ventilation in thoracic surgery. However, because of its large size and shape, it is difficult to intubate the trachea compared with a single lumen tube. Therefore, DLT intubation can be challenging and dangerous in patients with known or suspected difficult airways. [13] Although applications of videolaryngoscopy for DLT placement have been reported, many studies have focused on the utility of videolaryngoscopy in patients with normal airway status. [13][14][15][16][17][18][19] In patients with difficult airway, there are a few case reports describing the utility of videolaryngoscopy with placement of DLT. [20,21] The aim of this randomized controlled trial was to determine whether the McGrath videolaryngoscope has any advantage over the direct Macintosh laryngoscope for DLT intubation in patients with a simulated difficult airway.

Methods
This study was a single center, prospective, open-label, randomized-controlled, superiority trial with 2 parallel groups. The study was approved by the Institutional Review Board of Ajou University Hospital (AJIRB-DEV-OBS-16-108) and internationally registered for clinical trials (KCT0002150). Written informed consent was obtained from each patient. Forty-four patients, 19 to 60 years of age, scheduled for thoracic surgery and requiring one-lung ventilation were included. They were randomly allocated to 1 of 2 groups using a computer-generated random number  (Fig. 1). Patients were excluded from the study if they required rapid-sequence intubation, had a history of difficult intubation, cervical spine instability or cervical myelopathy, or a tendency to bleed.
Patient characteristics, including age, sex, and American Society of Anesthesiologists physical status, were recorded. Routine airway assessment was performed including Mallampati scoring, [22] and the measurement of thyromental distance, and mouth opening (inter-incisor distance).
No premedication was administered before surgery. Electrocardiogram, pulse oximetry, noninvasive blood pressure, and end-tidal CO 2 concentration were monitored at 1 to 5 minutes intervals. The depth of anesthesia was monitored using a bispectral index monitor (BIS VISTA monitor [4-electrode sensor], Aspect Medical Systems, Norwood, MA). Baseline measurements were obtained, and 1 minute of preoxygenation was performed before the induction of general anesthesia.
Anesthesia was induced using intravenous propofol (1.5 mg/ kg) and effect-site target-controlled infusion of remifentanil (effect-site concentration 2 ng/mL). Remifentanil infusion began at the time of anesthetic induction. After patients stopped responding to verbal commands, rocuronium (0.6 mg/kg) was administered intravenously. The patient's lungs were ventilated using 100% oxygen and 2% sevoflurane. After confirming a BIS value < 60 and neuromuscular blockade, manual in-line stabilization of the cervical spine was applied by an experienced study investigator (D.H.K.) in a standardized manner by grasping the patient's mastoid process and occiput, to limit movement of the head and the cervical spine during intubation.
Intubation was performed by 1 anesthetist (S.Y.P.) with experience in DLT (Mallinckrodt, Broncho-Cath, Covidien, Tullamore, Ireland [male: 37 Fr, female: 35 Fr]) placement using both McGrath and Macintosh laryngoscopes. The DLT was lubricated well, a stylet was inserted into the DLT to facilitate tracheal intubation, and the distal tip was bent immediately proximal to the cuff in all patients. Successful ventilation was confirmed by visible chest rise and capnograph confirmation. Intubation was defined as failed if it could not be performed within 120 seconds or in 2 attempts, esophageal intubation, or if the anesthetist believed that a repeat attempt would be unsafe. The operator was not blinded to the type of laryngoscope, and was not involved in the collection of data, except for Cormack and Lehane grade, [23] and the percentage of glottis opening (POGO). [24] In the event of failed intubation, manual in-line stabilization was terminated to facilitate tracheal intubation. In both groups, a flexible fiberoptic bronchoscope (PortaView LF-DP; Olympus Optical Company, Tokyo, Japan) with a diameter of 3.1 mm was used to confirm the correct positioning of the DLT in the left main bronchus. Blood pressure and heart rate were measured before and 1 minute after induction of anesthesia, and before and 1 minute after intubation. Sevoflurane (1-2%) and remifentanil infusion was used for the maintenance of anesthesia.
The primary outcome measure of the study was intubation time with DLT, defined as the time from when the laryngoscope passed between the patient's lips to the confirmation of end-tidal carbon dioxide on the capnograph, estimated by an independent observer. If more than 1 intubation attempt was required, the duration of the subsequent attempt was added to that of the first attempt without including the time interval between attempts. In the data analyses, only intubation time for successful tracheal intubations was analyzed. The secondary outcomes were glottis view (Cormack and Lehane grade), rate of successful intubation, POGO, the use of external laryngeal manipulation, intubation difficulty scale (IDS), [25] and oral mucosal bleeding by a blinded anesthetist.
The results of a preliminary study involving 10 patients demonstrated that the mean time to intubation using the McGrath videolaryngoscope was 49.8 ± 11.5 seconds, whereas that with the Macintosh laryngoscopes was 69.5 ± 23.3 seconds. To detect differences with 80% power at a 5% significance level, 20 patients would be necessary in each group. Therefore, the plan was to recruit 22 patients for each group considering the drop out.
Statistical analysis was performed using SPSS version 13.0 (SPSS Inc., Chicago, IL), and R (version 3.0.1, Foundation for Statistical Computing, Vienna, Austria) for Windows (Microsoft Corporation, Redmond, WA). The Mann-Whitney U test was used to assess intubation time, POGO score, and IDS. The Fisher's exact test was used to assess the number of failed intubations, Cormack and Lehane classification, the use of external laryngeal manipulation, oral bleeding. Continuous and categorical data are expressed as median [interquartile range] and number of patients, respectively; P < .05 was considered to be statistically significant.

Results
A total of 44 patients were randomly assigned to 1 of the 2 groups. Patient characteristics and assessment of airway measurements are summarized in Table 1. There was no significant difference in patient age, sex, body weight, height, American Society of Anesthesiologists physical status, thyromental distance, mouth opening, and Mallampati score between the 2 groups.
Factors related to airway management in each group are summarized in Table 2 . In group ML, 1 patient failed tracheal intubation, with duration > 120 seconds. There were 5 failed patients in the DL group, with duration > 120 seconds in 4 patients and esophageal intubation in 1 patient.
There was a significantly better view of the glottis in group ML. Cormack and Lehane grade was better (P < .001) and POGO score was higher (P < .001) in group ML. External laryngeal manipulation for tracheal intubation was necessary in 13 patients (59%) in group DL and 1 patient (4.5%) in group ML (P < .001). IDS was lower in group ML (1 [IQR 0-2]) than in group DL (3 [IQR 2-4]) (P < .001). There were no differences in the incidence of oral bleeding (P = .607).
The hemodynamic variables were comparable between the 2 groups and are summarized in Table 3. There were no episodes of hypoxia (SaO 2 < 95%) during the procedure.

Discussion
This study demonstrated that the McGrath videolaryngoscope improved glottic view and decreased the needs for external laryngeal manipulation for DLT tracheal intubation, resulting in an overall lower IDS score in patients with in-line stabilization compared with conventional Macintosh laryngoscope.
Although the time to successful intubation was shorter when using the McGrath videolaryngoscope, this difference was not   Yoo et al. Medicine (2018) 97:10 www.md-journal.com statistically significant. It is possible that our results underestimated the intubation time in the DL group, [12] because the intubation times for the 5 failures in group DL were excluded from data analysis. Intuitively, it is predictable that more time is required for endotracheal intubation in patients with failed or difficult intubation. In fact, in this study, the time required for intubation, including patients who failed tracheal intubation, was significantly shorter in the ML group compared with the DL group (group ML, 46 s [IQR 39-53 s] vs group DL, 57 s [IQR 47-84 s]; P = .016). Because suboptimal visualization of the glottis often leads to difficult tube placement, a complete view of the glottis is required for successful intubation. [26] In this respect, videolaryngoscopy has an advantage compared with conventional Macintosh laryngoscopy. Several studies have demonstrated the superiority of videolaryngoscopy for providing intubating conditions, [4,5] and this benefit is more pronounced in conditions of difficult airway. [27,28] However, according to some studies, a satisfactory laryngeal view does not always guarantee successful intubation. [12,[28][29][30] In studies comparing videolaryngoscopy with conventional Macintosh laryngoscopy for tracheal intubation, the videolaryngeal view quality was superior in videolaryngoscopy; however, intubation time and difficulty were controversial. Taylor et al [12] found that the McGrath laryngoscope improved laryngeal view and success rate in intubation of simulated difficult airway but delayed time to intubation (McGrath, 35.8± 20.4s vs Macintosh, 21.7± 9.4 s). The reason for this discrepancy is the geometrical mismatch between the blade and the laryngeal anatomy of the patient. [30] The McGrath videolaryngoscope incorporates a more acute angulated blade than the conventional Macintosh blade, in an attempt to optimize the view of the glottis. A common problem is that the tip of endotracheal tube can be located posterior to the glottis. [31] To overcome difficulties with tube manipulation, specific maneuvers could help: the addition of a stylet; and manipulation of the tube angle before insertion essentially compensates for the geometrical shortcoming of the blade design. [30] In our study, the tube was shaped using a malleable stylet (Mallinckrodt, Mansfield, MA) to replicate the curve of the Macintosh or McGrath laryngoscope, as appropriate. With this manipulation, advancing the DLT bronchial tip until it reaches the vocal cord was significantly easier. However, in another study, a satisfactory glottis view resulted in decreased intubation time and a high success rate. Kido et al [16] found that the intubation success rate and laryngeal view were superior; consequently, the intubation time was shorter in the McGrath group (17.1± 4.6 s) versus the Macintosh group 20.8± 5.9 s) (P = .026).
Difficulty in passing the angulated endotracheal tube through the glottis has been also reported. [1,32] In the present study, 1 patient in the ML group failed tracheal intubation at the first attempt, with duration > 120 seconds. The Cormack Lehane glottic grade was 2 and POGO score was 40 in this patient; however, we experienced difficulty in passing a DLT through the glottis because the tip of the DLT impinged on the anterior wall of the trachea because of the stylet's angle. In this case, withdrawal of the stylet, approximately 3 to 4 cm and slight rotation of the tube, facilitated the tube's passage into the trachea. [1,33] Recently, many videolaryngoscopes have been proposed as promising alternatives to the conventional laryngoscope. [34] However, difficult DLT endobronchial intubation using videolaryngoscopes was only documented in case series and a retrospective study. [17,20,21] For the present prospective randomized controlled study, we applied in-line stabilization as a simulated difficult airway. Manual in-line stabilization was used to simulate 1 type of difficult direct laryngoscope scenario, because it increases rates of failed intubation, secondary to adverse impact on the laryngeal view during direct laryngoscopy. [12,[35][36][37] To our knowledge, this was the first study to evaluate the utility of videolaryngoscopy for intubation of DLT in patients with simulated difficult airway.
This study had several limitations. First, a difficult airway situation cannot be generalized to manual in-line stabilization. This situation was used to simulate only limited head and neck movement. [12] Another maneuver creating difficult-to-intubate situations is cervical collars. [6,[9][10][11] Cervical collars restrict neck movement and also limit mouth opening, thus leading to far more difficult intubation conditions than manual in-line stabilization. [7,9] Second, the operator was not blinded to the laryngoscope device used; consequently, the potential for bias exists. Third, the DLT endobronchial intubation was only performed by 1 experienced anesthetist; this may, therefore, not be translatable to less experienced anesthesia providers.
In conclusion, compared with direct Macintosh laryngoscope, the McGrath videolaryngoscope provided a better laryngeal view and easier conditions for DLT intubation in simulated difficult intubation scenarios. These findings suggest that the McGrath videolaryngoscope may be a feasible option for DLT intubation in patients with predicted or actual difficult airway conditions.