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Year : 2021  |  Volume : 15  |  Issue : 1  |  Page : 57-61  

A comparative study in airway novices using king vision videolaryngoscope and conventional macintosh direct laryngoscope for endotracheal intubation

1 Department of Anaesthesiology, MS Ramaiah Medical College, Ramaiah Teaching Hospital, Bengaluru, Karnataka, India
2 Department of Anaesthesiology, Aster Al Raffah Hospital, Sohar, Oman
3 Department of Anaesthesiology, SRM Medical College and Hospital, Tiruchirappalli, Tamil Nadu, India

Date of Submission27-May-2021
Date of Acceptance18-Jun-2021
Date of Web Publication30-Aug-2021

Correspondence Address:
Dr. Vinayak Seenappa Pujari
Department of Anaesthesiology, MS Ramaiah Medical College, Ramaiah Teaching Hospital, Bengaluru - 560 054, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.aer_72_21

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Background and Objectives: Tracheal intubation using laryngoscopy is a fundamental skill, for an anesthesiologist. However, teaching this skill is difficult since Macintosh direct laryngoscope (DL) allows only one individual to view the larynx during the procedure. Hence, this study aimed to determine whether King Vision® videolaryngoscope (KVL) provides any advantage over direct laryngoscopy in teaching this skill to airway novices. Materials and Methods: In this prospective randomized crossover study, Ethical Committee clearance was obtained from the institutional review board (MSRMC/EC/2017) and the study was registered with Clinical Trial Registry. After informed consent, 53 medical students were allotted to perform laryngoscopy and endotracheal intubation on a manikin by using either KVL or Macintosh DL. The participants first performed laryngoscopy with either KVL or Macintosh DL following a brief instruction and then crossed over to the second arm of the study to perform laryngoscopy using the other scope. The primary outcome measure was the time for successful endotracheal intubation. The secondary outcome measures were incidence of esophageal intubation (EI), excess application of pressure on maxillary teeth excess maxillary pressure, and success rate. Results: Mean time for endotracheal intubation was significantly faster using KVL than in DL (44.64 vs. 87.72 s; P < 0.001). No significant difference was found in the incidence of esophageal intubation 15.1% in KVL group versus 24.5% in DL group (P = 0.223). In the KVL group, 81.1% did not apply pressure on maxillary teeth versus 26.4% in the DL group (P < 0.001). The success rate of intubation was 100% in the KVL group versus 86.8% in the DL group (P = 0.006). Conclusion: The KVL is a more effective tool to teach endotracheal intubation in comparison to Macintosh laryngoscope in airway novice medical students. Clinical trial registry India registration number: CTRI/2017/11/010491.

Keywords: Direct laryngoscopy, endotracheal intubation, King Vision videolaryngoscope, Macintosh laryngoscope

How to cite this article:
Pujari VS, Thiyagarajan B, Annamalai A, Bevinaguddaiah Y, Manjunath A C, Parate LH. A comparative study in airway novices using king vision videolaryngoscope and conventional macintosh direct laryngoscope for endotracheal intubation. Anesth Essays Res 2021;15:57-61

How to cite this URL:
Pujari VS, Thiyagarajan B, Annamalai A, Bevinaguddaiah Y, Manjunath A C, Parate LH. A comparative study in airway novices using king vision videolaryngoscope and conventional macintosh direct laryngoscope for endotracheal intubation. Anesth Essays Res [serial online] 2021 [cited 2022 Aug 9];15:57-61. Available from:

   Background Top

Endotracheal intubation using direct laryngoscopy is the gold standard for establishing an airway and it is a fundamental skill for acute care practitioners. The American Society of Anesthesiologists Closed Claims analysis concluded that the main reason for anesthesia-related morbidities was due to inability to secure the airway. However, tracheal intubation using direct laryngoscope (DL) requires technical skills and is often difficult to acquire direct laryngoscopy, often requires alignment of the three axes (oral, pharyngeal, and laryngeal axis) in a straight line. This skill is difficult to master and has a long learning curve.[1],[2] In the backdrop of the ongoing global COVID pandemic that we are experiencing today, there is a need for rapidly imparting airway skills to trainees and medical professionals.

The advancement in digital technology has led to a number of videolaryngoscopes (VLs) being developed for clinical use. The VLs have now become a widely accepted method of the airway management as it facilitates easy visualization of the glottis without the need of proper alignment of the oral, pharyngeal, and laryngeal axes.[3],[4],[5] The short learning curve of VL makes it an attractive choice in inexperienced hands.[6]

The King Vision® videolaryngoscope (KVL) (King systems, Noblesville. IN. USA) is one such newly developed videolaryngoscope that consists of a 2.4-inch reusable display and a disposable rigid blade [Figure 1]. There are two types of blades available, one is a channeled blade that directs the tracheal tube to pass through the glottis inlet and the other is a nonchanneled blade which allows visualization of the glottis and intubation is facilitated by the use of metal stylet.[7]
Figure 1: King Vision videolaryngoscope channeled

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There is a dearth of literature on the efficacy of DL and videolaryngoscope to impart laryngoscopy skills to airway novices. A beneficial characteristic of the KVL is the availability of a channel to guide the tracheal tube tip, which facilitates intubation with a little manipulation of the tracheal tube. Therefore, our hypothesis was that these characteristics will aid in easy visualization of the glottis resulting in faster, more successful, and less traumatic intubation with KVL compared with Macintosh DL. This randomized crossover study was planned to compare the Kings Vision videolaryngoscope with the traditional Macintosh DL as a teaching aid for intubation. The primary objective of this was the time taken for successful endotracheal intubation. While the secondary outcome measures were the incidence of esophageal intubation (EI), excess application of pressure on the maxillary incisor teeth excess maxillary pressure (EMP), and success rate in both groups.

   Materials and Methods Top

We conducted this randomized crossover trial on 53 medical students pursuing their internship in the department of anesthesiology over a period of April 2017 to May 2018. Ethical Committee clearance was obtained from the institutional review board (MSRMC/EC/2017 dated 30/03/2017) and the study was registered with Clinical Trial Registry-India with registration number CTRI/2017/11/010491. This study was conducted in the simulation laboratory of the advanced learning center of our medical college. The inclusion criteria were medical students posted in anesthesiology with little or no experience in airway management (airway novices) willing to participate in the trial and exclusion criteria were medical students who have performed >5 or more laryngoscopy/intubation.

Informed written consent was obtained from all participants. The study participants were briefed for 5 min each practical use of traditional Macintosh DL or KVL depending on whichever laryngoscope was first allocated to them by a computer-generated random number table and sealed envelope technique.

The participants were then oriented to the Laerdal Airway Management Mannequin so that they could visualize the correct anatomic landmarks and the ideal insertion path of the endotracheal tube (ETT). The instructions included an introduction to the equipment and demonstration of both a misplacement of the ETT in the esophagus and the correct placement in the trachea. Demonstration was done by an anesthetist having more than 5 years of experience in anesthesia practice. There were no trial runs for the participants.

After the briefing, each of the students attempted endotracheal intubation with the allotted scope. They were timed from time of hand placement on the laryngoscope to successful intubation with a 7.0 ETT, as evidenced by visible lung excursion. When participants performed an esophageal intubation, as indicated by inflation of the stomach pouch, this was counted as an esophageal intubation (EI) and students were prompted to start again. A maximum time limit of 300 s (5 min) was set for each student. The trial ended when the student either successfully passed the ETT into the trachea or 300 s time limit reached. Failure to achieve endotracheal intubation within 300 s was defined as an “unsuccessful” intubation trial.

When excessive pressure on the upper incisors was applied during laryngoscopy the mannequin gave out an audible indication signaling tooth damage and this was recorded.

The study had a research assistant to help and prepare the ETT and the stylet, inflate the ETT cuff after intubation, and begin mechanical ventilation with an Ambu bag valve mask. This was to ensure that the intubation time reflects only the participant's ability to obtain proper visualization and to pass the ETT, the two pivotal steps of the intubation procedure. The research assistant did not assist the participants with laryngoscopy. We assessed the time taken for successful endotracheal intubation. We also recorded the number of esophageal intubations, excessive pressure on the maxillary incisor teeth and overall endotracheal intubation success rate between the two devices. After completion of the first arm of the trial, the participants then crossed over to the second arm of the study where briefing and demonstration of the second scope was done. The participants repeated the laryngoscopy and intubation using the other device. The same parameters were measured.

Statistical methods

Sample size calculation: To calculate the required number of participants to perform the study, we considered the previous study conducted by Prescher et al.[8] who observed that time taken for intubation with DL scopy was found to be 118 ± 67 s, whereas with videolaryngoscope using C-MAC, it was found to be 81.9 ± 57.1 s. In the present study, we were expecting similar results with a power of 80% confidence level of 95% and considering 30 s difference as clinical significant between the two groups, the crossover study required a total of 53 subjects with 53 subjects in each arm of the study.

Descriptive statistics of time taken for successful endotracheal intubation was analyzed and summarized in terms of mean with standard deviation. Chi-square test and Fisher's exact test were used to know the association for categorical data. Mann–Whitney U-test was used for comparing the quantitative data. Data were entered into MS Excel and analyzed using SPSS© (Statistical Package for the Social Sciences) version 18 (IBM © Corp., Armonk, NY, USA). P < 0.05 was considered as significant.

   Results Top

Fifty-three medical students were recruited, and all participants successfully completed this study. The mean age of the participants was 23.22 ± 1.42 years. There were 29 female and 24 male participants. Twenty-four participants (45%) had never seen laryngoscopy or intubation and none of the participants of our study had performed intubation [Table 1].
Table 1: Demographic data

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Students using the KVL intubated significantly faster (44.64 ± 28.727 s) than the Macintosh DL scope who needed (87.72 ± 72.493 s). Furthermore, the number of esophageal intubations was higher in the DL scopy group 24.5% compared to 15.1% in the KVL group, but it was not statistically significant [Table 2].
Table 2: Intubation characteristics and performance of the conventional macintosh direct laryngoscope and the King Vision videolaryngoscope

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Excessive pressure on maxillary teeth during laryngoscopy was more significantly more common using Macintosh DL scope (73.6%), whereas while using KVL, it was only 18.9%. Utilizing the KVL, 100% of the students successfully completed intubation within the set time of 300 s when compared to 86.8% using the Macintosh DL scope, this was statistically significant [Table 2].

   Discussion Top

In our study, the time taken for intubation and application of pressure on maxillary teeth was significantly lower when airway novices used KVL for intubation. In addition, we also found that the success rate of intubation was high by using KVL when compared to Macintosh DL scope, but there was no statistically significant difference in the esophageal intubation between the two groups [Figure 2].
Figure 2: Comparison of esophageal intubations, maxillary pressure and successful intubations between the groups

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In our study, airway novices intubated faster using the KVL than Macintosh DL scope. Studies have found shorter mean intubation times with improved glottic view in both mannequins and human patients, when using videolaryngoscopy.[5],[6],[7],[8],[9],[10],[11],[12] In contrast to our study, Murphy et al.[10] reported in their study that time of intubation was not different using KVL and Macintosh laryngoscope in normal and difficult airways, but the intubations in their study were done by clinicians with experience in managing the airway. The mean duration for intubation was shorter using KVL in our study as it provides a good view of glottic structure, the ETT can be visualized entering the glottis inlet and also the perfect alignment of airway axis is not essential.

Esophageal intubation can cause various complications including pulmonary aspiration of gastric contents, cerebral hypoxia, and cardiac arrest. In our study, although the incidence of EI was higher using Macintosh DL scopy, it was not significantly different between the two groups. In contrast to our study, Akihisa et al.[7] found that 10% of intubation attempts were esophageal intubations with Macintosh DL scope, no esophageal intubation occurred with KVL. Other studies have observed in airway novices EI occurred less frequently during videolaryngoscopy when compared to traditional intubation.[8],[11]

In our study, airway novices using KVL did not apply significant pressure on maxillary teeth in comparison with DL scopy. Lee et al.[13],[14] similarly demonstrated that significantly lower force applied to maxillary teeth with videolaryngoscope compared with standard Macintosh DL scope blade. McElwain et al.[14] found that C MAC resulted in less dental compression than Macintosh or Glide scope but significantly greater compression than Airtraq. In contrast, the study conducted by Prescher et al.[8] found no significant difference in the application of EMP 51.8% in the VL group versus 57.8% in the DL group.

The intubation success rate was 100% in airway novices using KVL group compared to Macintosh DL scope. In the study conducted by Prescher et al.,[8] 91.1% of students successfully completed their intubation versus 65.6% of the students in the DL group. A study conducted by Akihisa et al.[7] found that there was no significant difference in success rates between the MAC and the KVL. Murphy et al.[10] inferred 100% intubation success rate by using KVL when compared to 69.7% using Macintosh laryngoscopy. Narang et al.[15] during a high-fidelity simulation found that all participants could successfully intubate a mannequin with normal neck mobility and simulated difficult airway within the time allotted in their study comparing successful intubation using videolaryngoscopy and direct laryngoscopy. There was a higher rate of successful intubations (83% videolaryngoscopy vs. 23% standard laryngoscopy P < 0.09). Kleine-Brueggeney et al.[16] showed that the success rate of intubation was better with C MAC than KVL.

We have used traditional instructions with a demonstration of the laryngoscopy and intubation to teach the technique of airway management. Low et al. found no difference in novices intubation success rate when video-assisted instruction with laryngoscope (84%) was compared with traditional instruction with a conventional laryngoscope (87%) in standard manikins with normal airway.[17] Some studies have generated a learning curve for intubation and have noted a mean success rate of about 45% after 10 attempts.[1],[18] After only three attempts with video-assisted instruction, trainees in their study showed a 69% success rate, implying that videolaryngoscopy could potentially decrease the learning curve and shorten the time needed for teaching.[18] The participants in our study received only a brief instruction with demonstration on manikin about performing and were 100% successful in endotracheal intubation using KVL.

Owen and Plummer showed that first-time success has an important impact on learning. Using novice trainees on an airway manikin, they were able to demonstrate that a novice trainee learns as much from one successful endotracheal intubation as from 12 failed trails.[2] Low et al.,[17] in a study on novice learners, demonstrated that training with videolaryngoscope improves intubation performance and increases confidence compared to a standard Macintosh laryngoscopy in a simulated difficult airway scenario. Hence, it appears that starting an airway management training program with the introduction to VL might shorten the learning curve for mastering this fundamental skill.[15],[19],[20] Another study has concluded that for global skill improvement in an airway management course for novices, teaching only videolaryngoscopy using KVL may be sufficient and in addition, they found better skill transfer from KVL to Macintosh blade than vice versa with fewer esophageal intubations when using KVL.[21] The high success of intubation using Macintosh DL may have been due to some transference of skills across devices in our study.

An important limitation of the study relates to just how realistic is the upper airway of the manikin compared to a patient, but allowing complete airway novices without training to manage the airway would be unethical. Manikin-based airway research for assessment of the efficacy of new airway devices is now widely accepted.[22],[23],[24],[25] Future studies can be planned on transference of airway skills using KVL to DL and weather the observed results hold good while intubating patients.

   Conclusion Top

We conclude that KVL is superior to Macintosh DL as it provides better success for endotracheal intubation in terms of rapidity, low incidence of dental trauma, and high success rate compared to Macintosh DL in airway novices. KVL would be a good tool for imparting intubation skills to airway novices in the backdrop of a global pandemic.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Mulcaster JT, Mills J, Hung OR, MacQuarrie K, Law JA, Pytka S, et al. Laryngoscopic intubation: Learning and performance. Anesthesiology 2003;98:23-7.  Back to cited text no. 1
Owen H, Plummer JL. Improving learning of a clinical skill: The first year's experience of teaching endotracheal intubation in a clinical simulation facility. Med Educ 2002;36:635-42.  Back to cited text no. 2
Cooper RM, Pacey JA, Bishop MJ, McCluskey SA. Early clinical experience with a new videolaryngoscope (GlideScope) in 728 patients. Can J Anaesth 2005;52:191-8.  Back to cited text no. 3
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Maharaj CH, O'Croinin D, Curley G, Harte BH, Laffey JG. A comparison of tracheal intubation using the Airtraq or the Macintosh laryngoscope in routine airway management: A randomised, controlled clinical trial. Anaesthesia 2006;61:1093-9.  Back to cited text no. 5
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Narang AT, Oldeg PF, Medzon R, Mahmood AR, Spector JA, Robinett DA. Comparison of intubation success of video laryngoscopy versus direct laryngoscopy in the difficult airway using high-fidelity simulation. Simul Healthc 2009;4:160-5.  Back to cited text no. 15
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Maharaj CH, Higgins BD, Harte BH, Laffey JG. Evaluation of intubation using the Airtraq or Macintosh laryngoscope by anaesthetists in easy and simulated difficult laryngoscopy – A manikin study. Anaesthesia 2006;61:469-77.  Back to cited text no. 24
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