|Year : 2022 | Volume
| Issue : 2 | Page : 108-114
Comparison of Macintosh, McCoy, Truview EVO2, and King Vision Laryngoscopes for Intubation in Patients with Immobilized Cervical Spine: A Randomized, Controlled Trial
Smita Gulati1, Samarendra Nath Samui2, Anisha De3
1 Department of Anaesthesia, Rajiv Gandhi Super Speciality Hospital, Delhi, India
2 Department of Anaesthesia, Purulia Government Medical College & Hospital, Purulia, West Bengal, India
3 Department of Paediatric Anesthiesia, Institute of Child Health, Kolkata, West Bengal, India
|Date of Submission||26-Dec-2021|
|Date of Decision||20-Feb-2022|
|Date of Acceptance||23-Feb-2022|
|Date of Web Publication||09-May-2022|
Rajiv Gandhi Super Speciality Hospital, Tahirpur, Delhi
Source of Support: None, Conflict of Interest: None
Background: Immobilization of the neck in cervical spine injury patients can lead to misalignment of the oral, pharyngeal, and laryngeal axis, thereby making intubation more difficult. The principal aim of our study was to compare the efficacy of King Vision, Truview Evo2, and McCoy with Macintosh laryngoscope in patients getting intubated with cervical spine immobilized using manual inline stabilization. Materials and Methods: This was a randomized, controlled trial of 160 patients who were randomized to undergo surgery under general anesthesia with endotracheal intubation. We equally divided the subjects into using either Macintosh, McCoy, Truview Evo2, and King Vision laryngoscopes to facilitate intubation. We evaluated the intubation difficulty using the Intubation Difficulty Score (IDS) and Cormack–Lehane grading. Results: King Vision, Truview Evo2, and McCoy reduced the IDS as compared to Macintosh (P < 0.001). King Vision showed a first-attempt success rate of 100%. Cormack and Lehane’s glottic views were best with King Vision followed by Truview Evo2 and there was much less need for external manipulation as compared to McCoy and Macintosh. Time taken for intubation was least with McCoy blade (22.9 ± 7.2 s, P < 0.001). Conclusion: The use of both King Vision and Truview Evo2 significantly resulted in a decreased the IDS and improved Cormack–Lehane grading as compared to Macintosh and McCoy.
Keywords: Airway management, immobilization, laryngoscopes, spinal injury, tracheal intubation
|How to cite this article:|
Gulati S, Samui SN, De A. Comparison of Macintosh, McCoy, Truview EVO2, and King Vision Laryngoscopes for Intubation in Patients with Immobilized Cervical Spine: A Randomized, Controlled Trial. Bali J Anaesthesiol 2022;6:108-14
|How to cite this URL:|
Gulati S, Samui SN, De A. Comparison of Macintosh, McCoy, Truview EVO2, and King Vision Laryngoscopes for Intubation in Patients with Immobilized Cervical Spine: A Randomized, Controlled Trial. Bali J Anaesthesiol [serial online] 2022 [cited 2022 May 27];6:108-14. Available from: https://www.bjoaonline.com/text.asp?2022/6/2/108/344881
| Introduction|| |
Patients with cervical spine injury suffer from significant morbidity and mortality. Tracheal intubation is often challenging in these patients due to cervical spine immobilization. Inadequate neck immobilization while intubating in these patients, may lead to adverse neurological outcomes. But head and neck stabilization in this position leads to misalignment of the oral, pharyngeal and laryngeal axis thereby making intubation more difficult., The chances of failed intubation are considerably increased in the first 30 s, which can be crucial in an emergency scenario. All these issues have led to the development of various alternatives, the recent most being the video laryngoscopes.
Truview EVO2 (Truphatek International Ltd, Netanya, Israel) is a modification of the traditional laryngoscope that broadens the angular view of the larynx and provides 42° anterior refraction in the line of sight, making visualization easier. McCoy laryngoscope (Penlon, Oxford, UK) is a modified Macintosh blade. Its tip is hinged and is regulated by a lever on the back of the handle, which allows for the epiglottis to be lifted while decreasing the force required. The King Vision Video laryngoscope (King Systems, Noblesville, Indiana) has two detachable parts. One is a reusable monitor and the other is a disposable blade (can be channeled or nonchanneled). The disposable blade houses the LED light and CMOS camera.
Our study’s principal aim was to ascertain if the struggle during intubation would be lessened by these recent and atypical laryngoscopes, as determined by the intubation difficulty scale (IDS) score in comparison to the Macintosh laryngoscope.
| Materials and Methods|| |
This randomized, controlled trial was conducted after institutional ethical clearance and written informed consent from patients (CTRI/2017/02/007839 dated July 19, 2018). One hundred and sixty patients scheduled for elective surgery under general anesthesia, aging between 18 and 50 years, and ASA grade I–II, were included in this study. Patients with greater risk of aspiration (i.e., elderly, gastroesophageal disease, hiatus hernia), morbid obesity, anticipated difficult airway (i.e., thyromental distance <6 cm, inter incisor distance <3.5 cm, Mallampati class IV, pathology of oropharynx), central nervous system disorders, reactive airway disease or coronary artery disease were precluded from the trial.
Subjects were randomly allotted to one of the four groups (each consisted of 40 patients) based on computer-generated codes which were given to operators in a closed envelope. Subjects in Group M were intubated using Macintosh laryngoscope (blade size 3 or 4), Group MC using McCoy laryngoscope (blade size 3 or 4), Group T using TruView EVO2 laryngoscope (adult size), and Group K using King Vision laryngoscope (blade size 3). The person who analyzed the data was blinded to the device used. All intubation procedures were carried out by an expert anesthesiologist who had performed at least 20 successful intubations with the devices in routine settings.
All patients were premedicated with alprazolam 0.25 mg and standard monitoring was applied in the operating room. Intravenous fentanyl 2 mcg/kg was given prior to induction. General anesthesia was induced with Propofol (2–3 mg/kg) and Vecuronium 0.12 mg/kg. Thereafter, manual inline axial stabilization (MIAS) was applied to prevent any neck movement. MIAS was applied by an assistant gripping the neck on both sides and the mastoid processes. While applying MIAS, forces were applied to counteract those generated by the anesthesiologist, to prevent or minimize head and neck movement while decreasing axial traction at the same time While applying MIAS, forces were applied to prevent or minimize any movement while decreasing axial traction at the same time.,[7-9]
Laryngoscopy was carried out with either of the four devices. When using the Truview blade, in addition to warming the blade with hot water prior to use, insufflation of oxygen from the side port at a rate of 8 L/min was also done to prevent fogging and a stylet was inserted in the endotracheal tube (ETT). While using King Vision laryngoscope, the blade was detached from the monitor and then inserted in the midline over the center of the tongue. Once the device had passed over the back of the tongue, the monitor was connected and switched on. The trachea was intubated with an appropriate-sized cuffed ETT mounted on hockey shaped stylet (7.0 in females and 8.0 in males). Anesthesia was maintained with isoflurane in a mixture of N2O and O2. Tracheal intubation time was taken as when the laryngoscope blade was picked up and until the ETT was positioned within the vocal cords, as indicated by the anesthesiologist doing the procedure.
Our primary parameter was the IDS score. The secondary endpoints were the time taken for intubation, the first attempt success rate of intubation, ease of laryngoscope blade insertion, trauma to the airway, and hemodynamic changes (change of 20% from baseline).
Two intubation attempts were allowed with the device tested. If the tracheal intubation was unsuccessful in two attempts, then failure was recorded. The period of the first tracheal intubation or the second, in case the first was unsuccessful, was recorded. Ease of laryngoscope blade insertion was recorded as “easy” as grade 0, “slight difficulty” as grade 1, and “very difficult” as grade 2.
Our sample size calculation was based on the IDS score. On the results of past studies conducted, we contemplated that a clinically relevant mean difference in the reduction of IDS score was assumed 2.0 between any two groups. Given an expected standard deviation of 2.5 and using alpha 0.05 and beta 0.1, for a study integrating four equivalent groups, it was predicted that 34 patients would be needed in each group. We, therefore, planned to enroll 40 patients for each group assuming an attrition rate of 10% or less. Data were analyzed using one-way analysis of variance (ANOVA), two-way repeated-measures ANOVA, or Kruskal–Wallis ANOVA on ranks as appropriate. All analyses were two-tailed and P < 0.05 was considered statistically significant. Statistical analysis was performed using SPSS software version 25 (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, version 25.0. Armonk, New York: IBM Corp.).
| Results|| |
The allocation of patients in this randomized trial is depicted in the Consort flowchart [Figure 1]. There were no significant variations between the groups in respect to the demographic data, ASA status, and the number of predictors of a difficult airway [Table 1].
Our principal target was the reduction of the IDS. The IDS was significantly higher in the Macintosh group as compared to all others (P < 0.001). The IDS was lowest in the King Vision group (0.10 ± 0.4) although the difference with Truview EVO2 (0.48 ± 0.8) was not statistically significant (P = 0.401) [Figure 2].
The first attempt success rate was highest in the King Vision group (100%), whereas it was the lowest in the Macintosh group (87.5%). However, more optimization maneuvers were required in the Macintosh and McCoy groups [Table 2]. The time for intubation was shortest with the McCoy laryngoscope followed by Truview EVO2. Cormack and Lehane’s scoring was significantly better with King Vision laryngoscope compared with all the other groups. There was mild trauma in a few patients in all the groups as evidenced by blood on the laryngoscope blade.
There was a modest increase in heart rate and blood pressure immediately after intubation in all the groups. The heart rate increase was most significant in the Macintosh group [Figure 3], whereas the mean arterial blood pressure was most significantly increased in the King Vision group. But both the parameters had returned to baseline within 5 min in all the groups.
|Figure 3: Heart rate and mean arterial pressure variation|
Graph showing the changes in heart rate (HR) and mean arterial pressure (MAP) post-intubation. The data are given as mean (SD). *Significant change in HR and MAP within each group. #Significant change in HR (P < 0.05) as compared to other groups. Two-way repeated measures ANOVA
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| Discussion|| |
For direct laryngoscopy to be successful, the line of vision should be a straight one from incisor teeth to the glottis. This can be achieved most favorably by aligning the oral, pharyngeal and laryngeal axis by flexing the cervical spine and extending the atlanto-occipital joint. In patients with unstable cervical spines, maneuvers to keep the airway patent such as chin lift and jaw protrusion cause as much movement as direct laryngoscopy.
Patients with cervical spine injuries are prescribed cervical collars to prevent any undue movement of the spine. This interferes with mouth opening as well as placement of an airway to facilitate ventilation and intubation. The MIAS method is one of the most effective ways to adequately limit the cervical spine movement of the C-spine at a minimum cost. The application of MIAS limits the cervical spine movement but it decreases mouth opening and impairs the laryngoscopic view. Fiberscope-guided nasotracheal intubation is a good choice in a non-emergency scenario. However, the procedure demands a cooperative patient and a certain skill level on behalf of the user which can make this tough to use in urgent or emergency cases.
Failure to intubate in time could lead to brain damage by hypoxia and aspiration pneumonia. These issues have prompted the search for safer alternatives to secure the airway with minimal C-spine motion and time. Visualizing the glottic opening indirectly with the help of a video laryngoscope could decrease the cervical spine movement. We aimed to assess the performance and efficacies of these recent and atypical laryngoscopes in comparison to the standard Macintosh laryngoscope in a clinical setting of a simulated difficult airway.
Prior studies have shown the superiority of the Truview EVO2 laryngoscope over both Macintosh and McCoy, in simulated difficult airway scenarios in patients. Our study confirms these findings and shows that Truview EVO2 reduced the CL grading, IDS, and optimization maneuvers in comparison to both Macintosh and McCoy. Compared to King Vision, the IDS was not significantly different, the time taken for intubation was less and it was easier to insert, although the first attempt success rate was not 100%. We did not use the camera coupling on the head of the blade to amplify the eyepiece view as it made the instrument quite difficult to use. But we did experience difficulty in advancing the tube towards the glottic opening, a problem which has been reported by others also.,
King Vision video laryngoscope is a relatively new video laryngoscope used in clinical practice. An important advantage is its single-use disposable blades. This removes the potential hazard of contamination with the use of reusable blades. Several studies indicate that it has fared well for routine intubations. Our study confirms these findings and extends them to a difficult airway scenario. There are not many studies on the use of King Vision in such scenarios. We found one study done by Dhanyasi et al. where they have explored the practicality of unchanneled blade of King Vision, C-MAC conventional, and D blades for intubation in patients with proven/suspected cervical spine injury. They have concluded that all three video laryngoscopes provide good first attempt intubation success and good grade glottic visualization although intubation time is less and ease of insertion is more with C-MAC conventional blade. In another study done by Ali et al., King Vision (channeled blade) has been compared with Macintosh and McCoy for intubation in patients with immobilized cervical spine. They concluded that with King Vision video laryngoscope intubation was easier, glottic visualization was better, and the first attempt success rate was improved as compared to Macintosh and McCoy laryngoscopes.
In our study, King vision was the only device that had a first attempt success rate of 100%, least IDS score with no requirement of external laryngeal manipulation but the duration of insertion attempt although less than that of Macintosh was significantly more than the others, which is in contrast to the finding by Ali et al. First, it could be due to the fact that the authors had some difficulty in introducing the blade in 12(30%) patients, probably because of its curvature (blade angle 90°). Second, they also experienced some difficulty in advancing the tube towards the glottic opening as an unchanneled blade had been used (Ali et al. had used a channeled blade). Third, because of the design of the instrument, it was difficult to insert it as a single piece. Dhanyasi et al. had also reported difficulty in the insertion of King Vision blade in 20% of patients but they have not included trauma due to laryngoscopy as a study parameter. Ali et al. have not included this parameter in their study although they have not reported any mucosal trauma with King Vision which could be attributed to the use of a channeled blade in their study. The use of stylet for video laryngoscopy has been related to an increased risk of soft tissue injury of the upper airway.
In their study in manikins, Van Zundert et al. reported, that the gap on the right side between the flange of the laryngoscope blade and the palatopharyngeal arch varies considerably with the type of laryngoscope used. It is widest when a Macintosh blade is used and maybe reduced substantially with video laryngoscopes. Based on their findings there would be less space available for ETT to pass through with King Vision also. Although we had both the channeled and non-channeled versions of King Vision, we chose the non-channeled one for our study as both the height and width of the blade are less than that of channel one (height; 13 mm unchanneled vs 18 mm channeled and width; 26 mm unchanneled vs. 29 mm channeled). The use of a channeled blade necessitates a larger mouth opening. On the contrary, the integration of a tube channel makes it convenient to propel the ETT in the desired direction towards the glottic opening. This might decrease the intubation time as compared to the unchanneled laryngoscope blades although a recent study has shown otherwise. There was not much difference in the hemodynamic variation caused by all the devices. At 1-min post laryngoscopy, the heart rate increase was the maximum with Macintosh which could be due to the increased laryngoscopy time and the necessity for external laryngeal pressure. Blood pressure increase was maximum at 1-min post-intubation with King Vision and Truview laryngoscopes which could be due to the use of stylet for tube guidance. Although the variables had returned to baseline within 5-min post laryngoscopy in all the groups, the use of the McCoy blade was associated with the least hemodynamic changes [Figure 3].
Some limitations arose from this study. Bias exists as the anesthetist cannot be blinded to the device used. Moreover, Cormack and Lehane’s grading is subjective and bound to be better with video laryngoscopes but even with a better CL grade, intubation may not be easier. Also, all intubations were carried out by experienced anesthesiologists. The results might not apply to less experienced users.
Further studies need to be carried out to compare all the available promising devices. In conclusion, the IDS score was the least with King Vision laryngoscope followed by Truview EVO2. King Vision had a 100% first-attempt success rate and no optimization maneuvers were required with it. It also has the advantage of having a disposable blade and an inbuilt antifogging system. Hence it appears to be more advantageous when used in patients with cervical immobilization.
| Conclusion|| |
Both King Vision and Truview Evo2 significantly decreased the IDS and improved Cormack and Lehane grading compared to Macintosh and McCoy laryngoscopes.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]