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  Table of Contents 
Year : 2019  |  Volume : 20  |  Issue : 2  |  Page : 89-94

Intubation with King Vision® video laryngoscope and Macintosh laryngoscope in cervical spine injured: A randomized controlled trial

1 Department of Anaesthesiology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
2 Indian Spinal Injuries Centre, New Delhi, India

Date of Submission24-May-2019
Date of Acceptance28-Jun-2019
Date of Web Publication28-Aug-2019

Correspondence Address:
Dr. Mohit Kumar
Flat No. 101, Maa Vaishno Residency, Aam Bagh, Rishikesh - 249 203, Uttarakhand
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/TheIAForum.TheIAForum_35_19

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Background: Intubation of trachea with conventional laryngoscopy requires alignment of the oropharyngeal–laryngeal axis in a straight line. This causes significant movement of the cervical spine, which in case of any previous injury to the spinal cord, may be further damaged due to impingement of the cord between the broken vertebrae. King Vision® video laryngoscope due to its particular J shape and a channel to carry the tube, causes less movement of the spine and hence provides better and safer intubation conditions in patients who have cervical injury.
Methods: The study was conducted in a tertiary-level orthopedic and spine center. It was a single-blind randomized control study. After obtaining permission from Hospital Ethics Committee and patient's consent, 60 patients of cervical spine injury of American Society of Anesthesiologists I-III, and normal airway anatomy, were assessed for ease and safety of intubation by – (a) King Vision® video laryngoscope and (b) Macintosh laryngoscope. The primary criteria were Intubation Difficulty Scale (IDS), while the secondary criteria were duration of intubation, heart rate, and mean arterial pressure.
Results: Results were analyzed by Chi-square, Mann–Whitney, and Student t-test using SPSS software. P value was 0.05. The mean IDS in King Vision® video laryngoscope group was significantly less than Macintosh group. However, there was no statistical difference in duration of intubation and hemodynamic parameters.
Conclusions: Intubation in cervical spine injury patients with neck immobilization is easier with King Vision® video laryngoscope, but duration of intubation, complication rate, and hemodynamic parameters remain the same as compared with Macintosh laryngoscope.

Keywords: Intubation, laryngoscope, spine

How to cite this article:
Kumar M, Gupta A, Mahajan H, Dhanerwa R, Chauhan P. Intubation with King Vision® video laryngoscope and Macintosh laryngoscope in cervical spine injured: A randomized controlled trial. Indian Anaesth Forum 2019;20:89-94

How to cite this URL:
Kumar M, Gupta A, Mahajan H, Dhanerwa R, Chauhan P. Intubation with King Vision® video laryngoscope and Macintosh laryngoscope in cervical spine injured: A randomized controlled trial. Indian Anaesth Forum [serial online] 2019 [cited 2022 Aug 13];20:89-94. Available from: http://www.theiaforum.org/text.asp?2019/20/2/89/265653

  Introduction Top

Intubation of trachea with conventional laryngoscopy requires alignment of oropharyngeal–laryngeal axis in a straight line.[1],[2] This causes significant movement of the cervical spine, which in case of any previous injury to the spinal cord, may be further damaged due to impingement of the cord between the broken vertebrae.[3] Hence, cervical spine immobilization either with a cervical collar or with manual in-line axial stabilization during intubation is advised. However, these maneuvers make the visualization of the vocal cords with conventional laryngoscopy and the process of intubation very difficult.

King Vision® video laryngoscope due to its particular “J” shape and a channel to carry the tube, requires less movement of the spine for intubation and hence is likely to provide better and safer intubation conditions in patients who have cervical injury.

Previous studies on this device have been done by Gaszynka et al. and Valencia et al.,[4] and they their studies show superior results with King Vision video laryngoscope over conventional one. However, their studies were done in mannequins.

On the other hand, our study is most likely, a one of a kind exercise comparing this laryngoscope in real cervical injury patients with neck immobilization.

We hypothesized that both King Vision video laryngoscope and Macintosh laryngoscope would be similar in terms of difficulty in intubation, time taken, complications, and change in vital parameters after intubation.

The aim of the study was to evaluate the ease, safety, and efficacy of King Vision® video laryngoscope in intubating cervical spine-injured patients in comparison with the conventional Macintosh laryngoscope.

The primary objective was to compare the intubation difficult scores and the secondary objective was to compare the hemodynamic changes, duration of intubation, and the number of complications and injuries during intubation in two groups.

  Methods Top

The study design was a parallel randomized controlled trial with allocation ratio of 1:1. No changes were made in the study methodology after trial commencement.

Approval from the Institutional Research Review Committee and Ethics committees were taken prior to the commencement of the study wide letter no. Ref ISIC/RP/2015/037. The trial has been registered in Clinical Trials Registry India-Registration no. CTRI/2017/10/010242.

The eligibility criteria of the participants included in the study were patients of cervical spine injury within the age group from 18 years to 65 years and American Society of Anesthesiologists (ASA) grade one to three who were posted in the operation theater for cervical spine fixation, and who needed oral intubation with neck stabilization with manual in-line axial stabilization for induction of anesthesia. The procedure was performed by a trained operator who had an experience of at least 100 intubations with King Vision video laryngoscope.

The exclusion criteria were patients who had difficult airway due to reduced mouth opening <5 cm, anatomical abnormalities such as congenital anomalies, trauma to airway, broken teeth, blood in airway making direct laryngoscopy (DL) difficult, as well as the patients who required rapid sequence intubation and those who were on inotropic or vasopressor support.

The trial was conducted in the operation theater of tertiary-level spine and orthopedic institute.


Before enrolling patients into the study, preanesthetic evaluation was done, which included, general and systemic examination as well as airway assessment. Routine blood investigations were done and on the basis of information patients were considered for inclusion in the study. The patients were divided into two groups: Group 1 – Orotracheal intubation using King Vision video laryngoscope and Group 2 – Macintosh video laryngoscope.

All patients received a standardized general anesthetic and monitoring. Before intubation, Manual in-line axial stabilization was applied and laryngoscopy was performed, by an anesthesiologist adequately experienced in the use all two laryngoscopes. Once adequate glottic view was achieved, endotracheal (ETT) tube was inserted under vision and circuit was attached.

The primary objective of the study was Intubation Difficulty Scale (IDS) score. While the secondary objectives were duration of intubation, complication during intubation – tooth, lip, tongue and pharyngeal injury, and hemodynamic response due to laryngoscopy and intubation.

Intubation Difficulty Scale

The primary endpoint was the Intubation Difficulty Scale or IDS.[5] It consists of seven parameters and each parameter is given a score of either zero or one. The final value is arrived by adding these individual scores. If the final value or IDS is zero, then it is considered as easy intubation, otherwise increasing score denotes progressively difficult intubation. The details of the scale are given in [Table 1].
Table 1: Intubation Difficulty Scale

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Duration of intubation

The duration of an intubation attempt was defined as the time taken from insertion of the laryngoscope blade in the oral cavity till the placement of the ETT tube through the vocal cords was visually confirmed by the anesthesiologist performing the intubation.

In situations where visual confirmation of the tube passing through the cords was not done, the attempt was not considered complete till the tube was connected to the breathing circuit and successful placement was confirmed by capnography/end-tidal CO2(ETCO2).

Failure was defined as laryngoscopy time exceeding 120 s.

Sample size was calculated using a computer software – “Power and Sample Size Calculation.” α was taken as 0.05, power 80%, prevalence of difficult intubation with conventional Macintosh laryngoscope in cervical immobilization with manual in-line axial stabilization (MILS) as 90% and an estimated reduction in the prevalence by 50% with King Vision scope. The sample size obtained from the software was 23. Initially, 80 patients were considered for eligibility. Out of them ten were excluded. Seventy patients were randomized and the outcome was analyzed in 60 patients.

Participant flow diagram is in [Figure 1].
Figure 1: Participant flow diagram

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Randomization was achieved using a computer-generated random number table and allocation concealment was done with the help of sequentially-numbered opaque-sealed envelopes which had the intervention written in them. The envelopes were opened after the patient was inside the operation theatre.

It was a single-blind study. The random number table and patient assignment were done by an independent anesthesiologist who was not a part of the study. The participants were blinded to the type of intervention, but the observer could not be blinded due to obvious reasons.

Statistical analysis

IDS score between the two groups was compared with Chi-square test.

The specific parameters of IDS such as glottic exposure, laryngeal pressure required, number of intubation attempts, and complications were compared by Chi-square test and Fischer's exact test as appropriate.

Duration of intubation and hemodynamic parameters between the two groups were compared by using Student “t”-test and Mann–Whitney test.

P < 0.05 was considered as significant for all outcomes.

SPSS (Statistical Package for the social Sciences, IBM, Chicago, United State) version 20.0 was used to analyze the results.

  Results Top

Eighty patients were initially considered eligible for the study. But out of them, only 70 were included. They were randomized into groups of 35 patients each. However, the outcome was analyzed in only 60 patients. The detailed participant flow diagram is in [Figure 1].

Recruitment was started in August 2015 and trial ended in September 2016.

The demographic parameters such as gender, age, and ASA status were compared by Pearson's Chi-square test. For the number of males and females, the P value was 0.317, for proportion of patients in various age groups, the Chi-square value was 0.278 and for patients in various ASA groups from I to III it was 0.381. Hence, we concluded that the proportion of patients is independent of the groups allotted to them. Age was also analyzed by independent samples t-test. The mean age in King Vision group was 41.9 and standard deviation (SD) 13.981. While in Macintosh group was 45.70 and SD 14.965. The P value obtained was 0.322 which is more than α =0.05. Hence, two groups had statistically similar mean age. Demographic data are shown in [Table 2].
Table 2: Comparison of two groups at baseline

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Intubation difficulty score

The median value of IDS scores was 0 in King Vision video laryngoscopy, while in case with Macintosh laryngoscopy, it was two.

Furthermore, we tried to analyze the proportion of patients who received various IDS scores from 0 to 7, using Chi-square test. Since 50% of the cells had expected count <5, we analyzed the P value of the likelihood ratio which turned out to be 0.000 which is significantly below α =0.05 meaning thereby that there is statistically significant difference in IDS scores of the both the laryngoscopes.

On analyzing the various parameters of the IDS, there was significant difference between the two laryngoscopes in terms of glottic exposure, need for external laryngeal pressure, and lifting force required for intubation.

In King Vision laryngoscope, 28 patients had glottic exposure score of 0, while in Macintosh laryngoscope, the glottic exposure score 0 was seen only in four patients, and score of one was seen in 21 patients. On applying the Chi-square test, P value was 0.000 which is highly significant.

Again, for lifting force required for conducting laryngoscopy, the P value is 0.000. While it was normal in all 30 patients in King Vision group, it was normal in only 18 patients in Macintosh group.

The necessity of laryngeal pressure in King Vision group was seen in 4 patients, while in Macintosh group in 19 patients, laryngeal pressure had to be applied. Applying Chi-square test, the P value is 0.000. The data have been given in [Table 3].
Table 3: Classification of patients according to IDS scores

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Duration of intubation

The mean intubation time in King Vision laryngoscope was 34.5 s with SD 17.89, and for Macintosh laryngoscope, it was 39.17 and SD 18.51. The means were compared with independent t-test and obtained P value was 0.325 which is statistically insignificant. Therefore, duration of intubation in both cases was similar.

Hemodynamic parameters

There was a significant increase in mean arterial pressure (MAP) as well as heart rate (HR) after intubation with Macintosh laryngoscope, but in case of King Vision video laryngoscope, only rise in HR was there. The P value for rise in HR 1 min after intubation is 0.000 in both the groups. For MAP rise 1 min after intubation in Macintosh group, it is 0.03. Refer to [Figure 2] and [Figure 3] for better understanding.
Figure 2: Trend of blood pressure before and after intubation

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Figure 3: Trend of Heart Rate with Time

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Slight oropharyngeal bleed was seen in four patients in King Vision group. No case of lip or teeth injury was seen in this group. With Macintosh laryngoscope, seven patients had oropharyngeal bleed, probably due to higher lifting force required. One patient had lip injury.

  Discussion Top

The incidence of cervical spine injury is in between 2% and 5% in blunt trauma patients. Airway management is crucial in patients with cervical spine injury as airway management techniques may cause secondary neurologic injury. Anesthesiologists prefer different approaches during airway management. Each technique has advantages and disadvantages.

Cervical spine immobilization is the standard of care. Cervical collars and manual in-line stabilization (MILS) can be used for immobilization. There are different types of collars. Rigid collars are better than semi-rigid and soft ones for restricting spinal motion. While collars restrict the spinal motion, they also limit mouth opening. MILS is used during procedures like airway management where other stabilization techniques are not appropriate. The aim of MILS is to apply opposite and equal forces to laryngoscope to fix the head and neck in a neutral position. MILS decrease laryngeal visualization and hinder intubation.

There are many techniques for intubation; DL, video laryngoscopy, and fiberoptic intubation are commonly used techniques.

DL is easy to use and performed very quickly. However, it causes greatest cervical movement and when MILS is applied, glottic view is reduced. Video laryngoscopes may improve glottic view and ease intubation, but it is not certain that they decrease cervical spine motion. Also during intubation blood and secretions may cause difficulties for video laryngoscopy. In our study, we have used King Vision Video laryngoscope and Macintosh laryngoscope for intubation and compared them on IDS in cervical injured patients. However, most of the studies comparing these two laryngoscopes were either done on manikins or cadavers.

Intubation difficult score

IDS was better with King Vision laryngoscope with 25 patients showing IDS score of zero compared to two patients in Macintosh group. IDS score zero corresponds to very easy intubation. Therefore, intubation attempts with King Vision laryngoscope in most of the patients in Kings Vision group were easy, whereas in Macintosh group, only two patients had easy intubation. Ruetzler et al.[6] compared Macintosh laryngoscope with King Vision laryngoscope and other video laryngoscopes in manikins with both normal and simulated difficult intubation settings, i.e., immobilization of neck and compared time to intubation, number of intubation attempts, glottis opening, and number of operators. They found that during simulated difficulty intubation, King Vision laryngoscope was superior and convincing than Macintosh laryngoscope.

Murphy et al.[7] compared King Vision laryngoscope with Macintosh laryngoscope in normal and difficult airway manikins, and normal and difficult airway cadavers for successful intubation, time to intubation glottic opening, and Cormack–Lahane grade visualization. They found with King Vision laryngoscopy all intubation attempts were successful. Cormack–Lehane was lower and percentage of glottic opening was also higher with King Vision laryngoscope than Macintosh laryngoscope. This is in concordance with findings in our study.

Akihisa et al.[8] compared King Vision laryngoscope with Macintosh laryngoscope in manikins for difficult intubation and found IDS score in King Vision similar to that of Macintosh laryngoscope group. This difference is again due to MILS manoeuver, which was not used in either group.

Lewis et al.[9] did a meta-analysis of 64 studies on comparison of video laryngoscopy and DL in adult patients and found that in studies with anticipated difficult airway or with simulated difficult airway, video laryngoscopes had fewer failed intubations than DL. However, no difference in studies in which there were no predicted difficult airways.

Valencia et al.[4] studied and compared King Vision with DL in normal ASA I and II patients. However, the intubation was performed by 1st-year anesthesia residents who were considered as nonexperts in intubation. They reported significant better laryngoscopy (Cormack–Lehane Grade 1) in 86.4% patients in King Vision group as compared to 59.1% patients in Macintosh group.

The duration of intubation in two groups was measured by independent observer and was defined as time taken from placement of laryngoscope into the mouth to confirmation of successful intubation either by direct visualization or by ETCO2 on monitor. The mean intubation time in King vision laryngoscope and Macintosh group is 34.50 s and 39.17 s, respectively, but the difference is not statistically significant.

Akihisa et al.[8] compared King Vision laryngoscope with Macintosh laryngoscope and found no difference in intubation time between two groups. The results are in accordance with our study.

The MAP in Macintosh group increased significantly immediately after intubation. However, MAP subsequently returned to the preintubation level 3 min after minutes of laryngoscopy and intubation. Similarly, mean HR in Macintosh group before intubation was increased significantly with intubation to 123/min at 2-min postintubation. The HR decreased subsequently and reached to preintubation level at 5 min.

Therefore, in Macintosh group, presser response with laryngoscopy and intubation was high and can be dangerous in hypertensive and cardiac patients.

On the other hand, the MAP in King Vision video laryngoscope did not increase significantly immediately after intubation. At 4 and 5 min, MAP was, in fact, less than preintubation level which was also statistically significant.

The mean HRs in King Vision group before intubation was 81.07/min. Laryngoscopy and intubation were associated with significant increase in mean HR at first 3 min. The HR subsequently settled with mean HR around preintubation level and 5-min postintubation.

Although HR increased with laryngoscopy and intubation, MAP did not show any significant rise, in fact, MAP at 4 and 5 min was less than preintubation level. Therefore, this presser response with video laryngoscopy is highly favorable, especially in cardiac and hypertensive patients.

None of the studies have specifically compared Macintosh and King Vision video laryngoscope for hemodynamic responses. However, Xue et al.[10] compared Macintosh laryngoscope with Glide Scope video laryngoscope and found hemodynamic responses to orotracheal intubation was similar in both groups.

  Conclusions Top

The present study shows that King Vision laryngoscope reduces difficulty in intubation in cervical injury patients with neck immobilization by manual axial in-line stabilization by improving glottis exposure. The time of intubation and the incidence of complications like injuries were similar to DL.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Majernick TG, Bieniek R, Houston JB, Hughes HG. Cervical spine movement during orotracheal intubation. Ann Emerg Med 1986;15:417-20.  Back to cited text no. 1
Sawin PD, Todd MM, Traynelis VC, Farrell SB, Nader A, Sato Y, et al. Cervical spine motion with direct laryngoscopy and orotracheal intubation. Anin vivo cinefluoroscopic study of subjects without cervical abnormality. Anesthesiology 1996;85:26-36.  Back to cited text no. 2
Penning L. Normal movements of the cervical spine. AJR Am J Roentgenol 1978;130:317-26.  Back to cited text no. 3
Valencia JA, Pimienta K, Cohen D, Benitez D, Romero D, Amaya O, et al. Acomparison of King Vision video laryngoscopy and direct laryngoscopy as performed by residents: A randomized controlled trial. J Clin Anesth 2016;35:571-5.  Back to cited text no. 4
Adnet F, Borron SW, Racine SX, Clemessy JL, Fournier JL, Plaisance P, et al. The intubation difficulty scale (IDS): Proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997;87:1290-7.  Back to cited text no. 5
Ruetzler K, Imach S, Weiss M, Haas T, Schmidt AR. Comparison of five video laryngoscopes and conventional direct laryngoscopy: Investigations on simple and simulated difficult airways on the intubation trainer. Anaesthesist 2015;64:513-9.  Back to cited text no. 6
Murphy LD, Kovacs GJ, Reardon PM, Law JA. Comparison of the King Vision video laryngoscope with the Macintosh laryngoscope. J Emerg Med 2014;47:239-46.  Back to cited text no. 7
Akihisa Y, Maruyama K, Koyama Y, Yamada R, Ogura A, Andoh T. Comparison of intubation performance between the king vision and Macintosh laryngoscopes in novice personnel: A randomized, crossover manikin study. J Anesth 2014;28:51-7.  Back to cited text no. 8
Lewis SR, Butler AR, Parker J, Cook TM, Smith AF. Videolaryngoscopy versus direct laryngoscopy for adult patients requiring tracheal intubation. Cochrane Database Syst Rev 2016;11:CD011136.  Back to cited text no. 9
Xue FS, Zhang GH, Li XY, Sun HT, Li P, Li CW, et al. Comparison of hemodynamic responses to orotracheal intubation with the Glidescope videolaryngoscope and the Macintosh direct laryngoscope. J Clin Anesth 2007;19:245-50.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]

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