A Prospective Crossover Study Evaluating the Efficacy of King Vision Video Laryngoscope in Patients Requiring General Anesthesia with Endotracheal Intubation

Abstract

Background:

Direct laryngoscopy used for tracheal intubation requires aligning the pharyngeal, laryngeal and oral axes to achieve a line of sight. Video laryngoscopy provides a better view of the glottis without the need for aligning the three axes.

Aims:

To evaluate the effectiveness of King vision laryngoscope over Macintosh laryngoscope in visualizing the glottis and intubating the trachea, when used on a same patient as in a cross over manner.

Settings and Design:

Department of Anaesthesia, Mediciti Institute of Medical Sciences, prospective crossover study conducted over a period of six months.

Subjects and Methods:

Sixty adult patients belonging to ASA physical status class I-II, requiring tracheal intubation were randomly assigned to intubation by King vision or Macintosh laryngoscope. Improvement, if any, in the Cormack-Lehane grading using the King vision scope, following initial grading with the Macintosh blade in the same patient was analyzed.

Statistical Analysis:

Mean and Standard deviation were calculated for different parameters under the study. Where appropriate, results were analyzed using the Mc Nemar χ2 test. A ‘p’ value less than 0.05 was considered statistically significant.

Results:

In the King Vision group, Cormack and Lehane grade improved in the majority (9/12) of patients in whom the initial Cormack and Lehane grade was >1 using the Macintosh blade.

Conclusions:

The use of the King vision blade significantly improved the laryngoscopic view over the Macintosh blade but the time for intubation was prolonged.

INTRODUCTION

The King Vision video laryngoscope is a new device for indirect laryngoscopy with a high-resolution camera incorporated. The image is displayed on a small monitor attached to the blade [Figure 1].

Figure 1.

Standard King Vision laryngoscope with monitor and TrueFlex stylet

The King Vision video laryngoscope is designed to give an improved view of the glottis, due to its ability to “look round the corner.” Video-assisted techniques circumvent the need to align the optical axes in the pharynx and mouth to visualize the glottic opening.[1] Despite an improved laryngoscopic view provided by the King Vision scope, manipulating the tip of the tracheal tube into the larynx is difficult, owing to a more acute angle of negotiation required. To overcome this difficulty, we have used the TrueFlex stylet with angulation at the tip [Figure 2] to insert the tracheal tube appropriately into the larynx.

Figure 2.

King Vision video laryngoscope and endotracheal tube loaded with TrueFlex stylet

The nonchanneled blade, which we used in this study, requires a minimum of 13-mm mouth opening and thus may be potentially useful in patients with limited mouth opening.[2]

MATERIALS AND METHODS

After obtaining Institutional Ethical Committee approval and written informed consent, 60 adult American Society of Anesthesiologists physical status I–II patients of either sex and aged between 18 and 60 years, scheduled for elective surgical procedures requiring general anesthesia with endotracheal intubation during the period January 2018 to June 2018, were included in this prospective randomized study.

Patients with known airway pathology and cervical spine injury and those who required rapid sequence induction were excluded from the study.

Patient demographic data and airway-related measurements were taken preoperatively. The same anesthetist evaluated the modified Mallampati.[3] class on all patients, and the thyromental distance was measured [Table 1]. Before the induction of anesthesia, all patients were allocated by computer-generated randomization into two groups of thirty each to intubation with either the Macintosh laryngoscope or the King Vision laryngoscope.

Table 1.

Patients’ characteristics and airway data in Macintosh and King Vision groups. Data are expressed as mean (SD)

Variable	Mcintosh	King Vision
Age (yrs)	38 (8)	42 (14)
Weight (kg)	63 (12)	67 (11)
Physical Status (ASA I/II/III)	15/15/0	13/17/0
Mallampati Class (I/II/III)	15/12/3	16/11/3
Thyromental distance (cm)	10 (1)	9.52 (0.93)
Cormack and Lehane Grade (1/2/3)	19/6/5	18/8/4

Standard monitoring was established and intravenous access secured. Following preoxygenation for 2 min, anesthesia was induced with 0.02 mg/kg midazolam, 1 μg/kg fentanyl, and titrated doses of propofol until loss of verbal contact. Neuromuscular blockade was achieved using vecuronium 0.1 mg/kg. The patients were placed in the sniffing position[4] with a pillow under the head, and anesthetic depth was maintained using 1% sevoflurane in oxygen. After 3 min of mask ventilation, all patients in both the groups underwent an initial direct laryngoscopy by a separate anesthetist using a Macintosh laryngoscope, and the Cormack–Lehane grade[4] was scored. Following this, ventilation was continued and then the trachea was intubated using either the Macintosh blade or the King Vision blade according to the study allocation. These intubations were performed by a different resident anesthetist, who was under training with an experience of having performed a minimum of 100 intubations with the Macintosh blade and 20 intubations using the King vision blade. This resident anesthetist was blinded to the Cormack and Lehane grading given by the first anesthetist, and during this intubation, a second Cormack and Lehane score was given. The difference in Cormack and Lehane grading between using the Macintosh laryngoscope and the King Vision laryngoscope was our primary outcome measure.

All patients in the King Vision group were given a second laryngoscopic score (Cormack–Lehane grade), and tracheal intubation was accomplished using a cuffed tracheal tube of internal diameter 7 mm for females and 8 mm for males. A preformed stylet (The TrueFlex stylet) was inserted into the tracheal tube to facilitate intubation in the King Vision group. The parameters noted in the study were as follows: an improvement, if any, in the Cormack and Lehane score in the King Vision group, the time to achieve endotracheal intubation, and the hemodynamic response to intubation using each of the devices.

Time-to-intubation (TTI) was taken as the time from the introduction of the laryngoscope (Macintosh or King Vision) blade into the mouth to the appearance of end-tidal carbon dioxide trace on the monitor after inflation of the tracheal tube cuff.

At 1 min, 3 min, and 5 min following intubation, noninvasive mean arterial pressures and heart rates were recorded [Table 2].

Table 2.

Hemodynamic variables (mean arterial pressure in mmHg, heart rate in beats/min)

Variable	Macintosh group	King Vision group	P
MAP (immediate post intubation)	92.87±20.75	101.67±14.36	0.611
MAP (3 min post intubation)	84.23±12.38	86.87±9.41	0.3563
MAP (5 min post intubation)	79.2±6.7	83.3±9.78	0.632
HR (immediate post intubation)	97.1±13.35	97±16.16	0.9792
HR (3 min post intubation)	89±11.27	86.6±10.88	0.4048
HR (5 min post intubation)	83.17±10.08	85.9±10.65	0.3121T

MAP: Mean Arterial Pressure, HR: Heart Rate

Attempts at intubation were halted and mask ventilation was commenced, if laryngoscopy exceeded 60 s or if the oxygen saturation dropped to 90%. Patients were mask ventilated for 1 min with 1% sevoflurane in oxygen between the attempts if more than one attempt at intubation was required.

After successful intubation, the tracheal tube cuff was inflated, and anesthesia was then maintained with 1%–2% sevoflurane in 50% oxygen and 50% nitrous oxide. Following 5 min of intubation and data collection, further anesthetic management was left to the discretion of the anesthetist managing the case.

For statistical analysis of the data, SPSS (IBM SPSS Version 21.0, IBM Corporation, New York, USA) was used. The demographic statistics such as average and standard deviation were computed for the variables age and weight for both the groups. Data were analyzed using the McNemar–Chi-square tests for matched pairs to examine King Vision Cormack–Lehane grades. P < 0.05 was considered statistically significant. The TTI values were expressed with 95% confidence interval (CI) for both the groups [Table 3].

Table 3.

Comparison of time to intubate between Macintosh and King Vision groups. Values are expressed as mean (95% Confidence Interval)

	Macintosh (n=30)	King Vision (n=30)
TTI (sec)	29.97 (28.05-31.89)	42.77 (40.05-45.48)
TTI (sec) for C-L grade 1	30.84 (28.56-33.12)	42.11 (38.98-45.24)
TTI (sec) for C-L grade 2	31 (23.79-38.21)	45.25 (37.84-52.66)
TTI (sec) for C-L grade 3	25.4 (24.29-26.51)	40.75 (26.55-54.95)

TTI: Time To Intubate, Sec: seconds

RESULTS

A total of 60 patients were recruited in the study. The study population was divided into two groups (Macintosh and King Vision groups) comprising 30 patients in each group. Both the groups were comparable with respect to demographic variables [Table 1]. Three patients each in the Macintosh and King Vision groups had Mallampati Class 3 airway. The mean intubation time was significantly less in the Macintosh group (29.97 s) compared to the King Vision group (42.77s), with P < 0.001, and the 95% CI for the mean difference in TTI was 9.54368–16.05632. The majority of patients in the King Vision group showed improvement in the C-L grade (P < 0.01) obtained with the King Vision scope compared with the Macintosh scope [Table 4]. 18 patients were C-L grade 1 and of the remaining 12 patients with C-L grade >1, 9(75%) had an improved laryngoscopic grade with the King Vision scope.

Table 4.

Comparison of laryngoscopy grades with the King Vision scope in the King Vision group (n=30)

Macintosh C-L grade	King Vision C-L grade
	Grade 1	Grade 2	Grade 3	Total
Grade 1	18	0	0	18
Grade 2	6*	2	0	8
Grade 3	2*	1*	1	4
Total	26	3	1	30

P<0.05 (McNemar χ²-test). *Patients with improvement in C-L grade

DISCUSSION

Various studies compared intubation using the King Vision laryngoscope with other laryngoscopes. Our study was intended to see if there would be any improvement in the Cormack and Lehane[5] grade using the King Vision blade compared to the Macintosh blade in the same set of patients as in a crossover manner. This being the primary objective makes our study stand unique among many similar works done earlier.

We based our study on previous observations by several authors that videolaryngoscopy inproves the glottic view compared to conventional Macintosh laryngoscopy. Supporting our hypothesis, our study demonstrated a significantly improved glottic view on laryngoscopy using the King Vision laryngoscope compared with the standard Macintosh laryngoscope in a crossover manner. However, it took a longer time to intubate than with the conventional Macintosh blade [Table 4]. Similar to most video laryngoscopes,[4] the King Vision laryngoscope provides a better view of the glottis without having to align the oral, pharyngeal, and laryngeal axes. However, this comes with a price in terms of prolonged intubation time. This is because the line of sight view of the glottis is essentially compromised. More number of patients in the Macintosh group required the application of external laryngeal pressure to facilitate glottic visualization but were intubated in a shorter time. Proper positioning of the King Vision laryngoscope blade in the mouth required more number of attempts when compared to the Macintosh blade. Hemodynamic responses to laryngoscopy and intubation were not statistically significant between the two groups.

A study by Ali et al.[2] has shown an improvement in the Cormack–Lehane grade using the King Vision laryngoscope compared with the Macintosh laryngoscope. Our study also is in keeping with the observations made by Ali et al. in this regard. A study done by Elhadi et al. has shown that the King Vision scope improves the laryngoscopic view, thereby achieving a better glottic view. Our results also are in accordance with the authors.[6] Patrick Schoettker and Jocelyn Corniche have shown in a study comparing Airtraq and King Vision video laryngoscopes that the Cormack–Lehane view obtained during indirect laryngoscopy was better with the King Vision device compared to the Airtraq device.[7]

Ideally, the real mettle of the video laryngoscopes is to be assessed by testing its use in potentially difficult airways. However, we had to exclude the patients with difficult airway from the study, based on the issues concerning familiarity and learning curve. This, in addition to the smaller sample size, could be a limitation of this study. Moreover, better glottic visualization with the video laryngoscope need not necessarily translate into an easier and faster intubation, as we noted in our study.

Further studies with larger sample size including patients with known difficult airways will explore the full potential of video laryngoscopes. Widespread use of video laryngoscopy holds promise as a teaching aid in airway management.[8]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.