Comparative Study of Intubation Performance between Macintosh, the Channeled King Vision and the C-MAC D-Blade Videolaryngoscope in Controlled Hypertensive Patients

Background: The common cause of anesthesia related injury is inability to intubate the trachea. Video laryngoscopes present an enlarged video image of glottis while intubating the trachea. The aim of this study is to compare efficacy of intubation by Macintosh with C-MAC D-Blade and King Vision video laryngoscope (VL) in controlled hypertensive patients. Patients and methods: 105 ASA I&II patients (ages 35 to 60) scheduled for elective surgery under general anesthesia were divided into three groups: Macintosh (M), C-MAC D blade(C), and King Vision (K), 35 patients each. Heart rate, mean blood pressure (MBP), SpO2, EtCO2 were recorded at T1: before induction of anesthesia; T2: just before intubation; T3: 2 min after intubation; T4: 5 min after intubation. Primary outcome: time and number of attempts required to successful intubation. Secondary outcomes: ease of laryngoscope insertion, Quality of view, Assist maneuvers, Intubation difficulty, Complications. Results: Differences in heart rate and mean blood pressure between all groups were statistically significant at T3&T4. Differences in duration of successful intubation were statistically significant between group (M) and group(C), also between group (M) and group (K). Statistically significant differences were obtained between all groups regarding quality of view of glottis, ease of insertion of laryngoscope, and use of assist maneuvers for intubation. Conclusion: Video laryngoscopes provide hemodynamic stability and better view of glottis than Macintosh during intubation. King Vision VL has advantages of ease of insertion, less need of assist maneuvers for intubation, with less complication. Thus, it is beneficial to use King Vision for intubation in hypertensive patients.


Introduction
Direct laryngoscope and passage of endotracheal tube through the larynx is a noxious stimulus, which can provoke untoward response in the cardiovascular, respiratory and other physiological systems [1]. The peak elevation in blood pressure and heart rate within one to two minutes and are usually well tolerated. However, in patients with hypertension, coronary artery disease or cerebral vascular disease, the hypertension and tachycardia are hazardous as it is associated with rise in myocardial oxygen demand, decrease in oxygen supply, the possibility of cardiac arrhythmia, myocardial ischemia and cerebral vascular accident [2].
These complications are serious enough in normotensive patients, but an exaggerated response has been reported in hypertensive patients, whether treated before or not. Majority of these stimuli arise from the stimulation of the supraglottic region by tissue tension induced by laryngoscope. Placement of endotracheal tube and inflation of the cuff in the subglottic region produces a smaller response [3].
Perioperative myocardial ischemia that develops in the presence of hemodynamic disturbances is associated with tachycardia rather than hypotension or hypertension [4]. The concern for patient safety in the operating room and critical care areas has led to the development of new technologies, training in the simulation environment, evidencebased algorithms and perioperative checklists.
Over 20 years back, American Society of Anesthesiologists (ASA) closed claims analysis concluded that the main reason of anesthesia related injury was the inability to intubate the trachea and secure the airway [3]. With advanced digital technology and complementary metal oxide semiconductors (CMOS) video chip was produced by a number of manufacturers. This led to the development of the video laryngoscopes to see the glottis while intubating the trachea.
The GlideScope was one of the technologically advanced video devices, which was created in 2001 by a vascular and a general specialist, John Pacey of Canada [5]. The video laryngoscope can present an enlarged video image of airway structures. While using conventional laryngoscopy presents a limited view of the airway structures, which may be obscured during attempts to intubate the trachea so, endotracheal tube (ETT) may slip into esophagus [6].
Both direct laryngoscopes (DL) and video-laryngoscopes (VLs) compromise of a handle and a blade, yet there is a video camera is fitted at the end of the blade of video laryngoscope, facilitating visualization of the glottis indirectly on a screen. Both types of laryngoscopes have common features, so that physicians who are familiar to use DL can use VLs with minimal added training. Videolaryngoscopes provide a wide angle image and reduce need of alignment of the oral, pharyngeal, and tracheal axes [7].
The improved view due to a magnified video image, anterior curvature of the blade, or reduced need to align a direct visual alignment. While DL may be associated with intubation failure when a laryngeal view cannot be achieved, VL frequently overcomes this obstacle. Improved laryngeal view does not mean increased intubation success. Since the success rate of intubation by DL on a normal airway is high [8]. An improved laryngeal view is mandatory to successfully intubate patients at risk for poor laryngeal view with DL [9].
C-Mac video laryngoscope is a portable laryngoscope with standard Macintosh blade designs and a metal oxide semiconductor video chip at the tip of the blade that extends a 60° optical axis in the vertical plane to a video screen [10].
King Vision video laryngoscope is the most recent and portable airway device. It provides high quality image of airway structure which is displayed on a video screen to facilitate visualization [11]. It is an indirect laryngoscope that provides a view of the glottis without alignment of the oral, pharyngeal and tracheal axes [12].
King Vision video laryngoscope compromises of a 2.4-inch reusable display and a disposable rigid blade. There are two blade types: one is a channeled blade that permits tracheal tube to be passed through the glottis, and the other is a non-channeled blade which just allows visualization of the glottis, and intubation is facilitated by use of a metal stylet [13].
The aim of this study is to compare efficacy of intubation by Macintosh laryngoscope compared with C-MAC D-Blade and King Vision video laryngoscope in controlled hypertensive patients scheduled for elective general surgery procedures.

Patients and Methods
With institutional ethics committee's approval and informed consent, this prospective single blinded randomized study was carried out on 105 patients scheduled for elective CABG surgery to compare efficacy of intubation by Macintosh laryngoscope with C-MAC D-Blade and King Vision video laryngoscope. We included American Society of Anesthesiologists (ASA) I and II controlled hypertensive patients of 35-60 years of age undergoing elective surgical procedures of 60-90 min duration under general anesthesia. Patients with risk of gastric aspiration, anticipated difficult intubation (interincisor less than 5 cm, Mallampati classes III and IV, thyromental distance of less than 6.5 cm), history of epilepsy, or history of myocardial infarction were excluded.
Patients were randomly allocated into 3 equal groups (35 patients each), namely group M, C and K where laryngoscopy was done either with Macintosh (blade size 3 in females and size 4 in males), C-MAC D-Blade or King Vision videolaryngoscope respectively.
Randomization was done using a computergenerated schedule and opaque, sealed envelopes. Patients remained blinded about their intubation technique until post-operative assessment was completed. A nurse not included in the study made group allocation. Anesthesia team remained blinded until the patient entered the operating room and randomization envelop was opened.
Tracheal intubation was performed by one of the three anesthesiologists who performed at least 30 intubations with the new device in the clinical setting prior to the study.
All the patients received their antihypertensive medications till the morning of surgery. All the patients premedicated with diazepam (10 mg) orally at midnight and 30 min before surgery.
The Patient was placed in the sniffing position with standard monitoring (electrocardiogram, pulse oximetry, non-invasive blood pressure, and neuromuscular monitoring with train-of-four).
Anesthesia was induced with fentanyl (1-2 mg/kg), propofol (1-2 mg/kg), and rocuronium (0.6 mg/kg). Mask ventilation was initiated using 100% Oxygen and after ensuring full muscle relaxation as assessed by a nerve stimulator, orotracheal intubation was performed using the selected intubation device for each group. Anesthesia was maintained with isoflurane 1-2%. Tachycardia or hypertension after intubation was managed with a bolus dose of fentanyl 50-100 µg and by increasing the concentration of isoflurane followed by nitroglycerine infusion. No local anesthetic (lignocaine) was used either as laryngotracheal spray or by intravenous route. No other medications administered or procedures performed during the 5 min data collection period after tracheal intubation.
Primary goal was to measure the time and number of attempts required to first successful intubation. Intubation time was defined as the time taken for insertion of the blade between the teeth till TT cuff passed through the vocal cords. Failure of intubation was defined as any intubation attempt of >120 s or inability to intubate.
Secondary goals were to measure: • Ease of laryngoscope insertion by 5-point likert scale • Quality of view by Cormack and Lehane grade • Assist maneuvers.

Sample size
The sample size was calculated using Epi-Info software statistical package created by World Health organization and center for Disease Control and Prevention, Atlanta, Georgia, USA version 2002. The sample size was calculated at N=35 The criteria used for sample size calculation were as follows: • 95% confidence limit • 80% power • The ratio between experimental and control groups is 1:1

Statistical analysis
The full detailed form is: SPSS 20, IBM, Armonk, NY, United States of America.
Quantitative data were expressed as mean ± standard deviation (SD). Qualitative data were expressed as frequency and percentage.
• A one-way analysis of variance (ANOVA) when comparing between more than two means. • Chi-square (X 2 ) test of significance was used in order to compare proportions between two qualitative parameters.

Results
The sample size was chosen after reviewing many randomized control studies on the same subject. One hundred and five patients were included in the current study. The demographic data of the study group M, C and K are presented in Table 2  There was increase in heart rate with statistical significant differences between three groups 2 min and 5 min after intubation. No significant difference between group (C) and group (K) ( Table 3 and Figure 1).
There was decrease in MBP with statistical significant differences between three groups 2 min and 5 min after intubation but of no clinical importance (Table 4 and Figure 2).
No statistical significance between three groups regarding oxygen saturation and end tidal carbon dioxide as shown in Table 4.    Time taken to intubate the trachea with Macintosh laryngoscope was significantly lower than time taken during using C-MAC and King Vision videolaryngoscope (VL). The success of first trial of intubation was achieved more with King Vision VL but with no statistical significance among three groups. No failure of intubation was obtained (Table 5 and Figure 3).
As regard laryngoscopic view,Cormack-Lehane grading (C L grade) was used for visualizing the glottis (Table 6 and Figure 4). Good visualization grade (CL grade 1) was obtained when using King Vision VL for intubation with statistical significance among three groups.
Ease of insertion was noted based on five point Likert scales (Table 7 and Figure 5). Insertion of blade was more easy with Macintosh (grade 1and 2 in Likert scale). Difficult insertion of laryngoscope was observed in group C and K with statistical significance among three groups.     Degree of difficulty of intubation was evaluated by using intubation difficulty score (IDS). We found that easy intubation was obtained in more patients when using King Vision VL with no statistical significance between three groups (  Regarding use of assist maneuvers during intubation, there was statistical significance among three groups. No assist maneuvers were needed for intubation in group K. Also, increased lifting force of laryngoscopic blade was used in both group M and group C (Table 9 and Figure 6).  Table 9: Comparison of using assist maneuvers during tracheal intubation in goup M, C, and K. Less complication occurred with using C-MAC and King Vision VL for intubation compared with Macintosh laryngoscope which is clinically important but of no statistical significance as shown in Table  10. Esophageal intubation 0 (0%) 0 (0%) 0 (0%) -Desaturation 0 (0%) 0 (0%) 0 (0%) -Bronchospasm 0 (0%) 0 (0%) 0 (0%) -

Discussion
Laryngoscopy and tracheal intubation are accompanied with hemodynamic changes preoperatively; this is secondary to stimulation of the sympathetic nervous system [15]. Hypertensive patients have an exaggerated hemodynamic stress response compared with normotensive patients [16]. Video laryngoscope allow visualization of enlarged video image of airway structures and make alignment of the oral, pharyngeal, and tracheal axes unnecessary.
The current study was conducted to compare efficacy of intubation by Macintosh laryngoscope with C-MAC D-Blade and King Vision VL in controlled hypertensive patients admitted for general surgery (elective procedures).
Our results in the presented study showed that hemodynamic changes occurred at 2 min and 5 min after intubation. There were statistical significant differences between Macintosh and both types of VL (C-MAC D blade and King Vision) indicating that VLs maintained hemodynamic stability during intubation than Macintosh. This is in agreement with, Sherif M Elhadi, et al. [12] their study demonstrated that the KVL maintains hemodynamic stability during endotracheal intubation.
Different results obtained by Muralidhar Kanchi, et al. [17] in their study hemodynamic changes were not different between the groups. They concluded that video laryngoscopy did not provide any benefit in hemodynamic response to laryngoscopy and intubation.
Regarding number of attempts to achieve first successful intubation fewer attempts achieved by King Vision VL with no statistical significance between three groups. While, lower time needed for intubation with Macintosh laryngoscope with statistical significance between group M and each of group C and group K. Differences in time may be due to unfamiliarity to handle the laryngoscope while looking at the screen instead of looking directly at the larynx. Similar results obtained by DA Sun,et al. [8] as demonstrated that the average time of intubation was longer with glidescope compared with direct laryngoscopy for elective surgery because of the technique required to manipulate the stylet and endotracheal tube through the vocal cords.
This is in contrast with J Marrel, et al. [18] who documented that shorter duration of intubation with improved glottis view when using Video laryngoscopy compared to direct laryngoscope. Also, Donald EG Griesdale, et al. [19] found regarding successful first-attempt intubation or time to intubation was not different when they compared Glidescop video-laryngoscopy with direct laryngoscopy for endotracheal intubation.
Against our results, M. Kleine-Brueggeney et al. [20] they showed that First-attempt success rate of intubation were better with C-MAC than King Vision laryngoscope. Differnet results demonstrated by Laurel D Murphy, et al. [21] who reported in their study that time of intubation was not different when compared King Vision to Macintosh laryngoscope in normal and difficult airways.
In the present study, statistical significance was obtained in quality of glottic visualization between three groups. KVL provided better glottic view (Cormack-Lehane grade I) than with using Macintosh and C-MAC laryngoscope. Similar results obtained by Jose A, et al. [22] in a comparison of King Vision VL and direct laryngoscopy they found significant improvement of glottic view in patients without predictors of difficult airway.
Cooper RM, et al. [5] in their study to evaluate glidescope video laryngoscope documented a significantly failed intubations occurred despite good or excellent glottic visualization. So, an improved laryngeal view does not always mean an easy and successful intubation.
In our study, lower grades of difficulty for insertion of laryngoscope, based on five point Likert scale, were observed when using Macintosh compared with C-MAC and King Vision VL. Statistical significant difference between three groups with difficult insertion of C-MAC blade more than King Vision VL. This is due to differences in the curvatures of laryngoscopic blades of Macintosh, C-MAC D balde, and King Vision. In agreement with our results, Shravanalakshmi D, et al. [23] when compared C-MAC with King Vision laryngoscope they observed higher grades of difficulty for insertion of laryngoscope with use of C-MAC D blade as compared to conventional C-MAC and King Vision laryngoscope. The angulation of the blades of KVL and D blade CMAC is higher as compared to conventional blade. The KVL blade was easier to insert as compared to D blade CMAC video laryngoscope.
While, Cooper RM, et al. [5] during their study found that some operators repeatedly found intubation challenging while others experienced no such difficulty. It is possible that this results from the unfamiliar technique of manipulating the ETT while viewing the events on the monitor. In the present study, easy intubation (based on intubation difficult score) was observed with King Vision than with D blade of CMAC and Macintosh laryngoscope with no statistical significant difference between three devices.
In agreement with our results, Shravanalakshmi D, et al. [23] observed slight difficulty for intubation with D blade of CMAC video laryngoscope. Similar results obtained by LH Andersen, et al. [24] found IDS scores to be lower when using the glidescope than with direct laryngoscopy. The reductions in IDS scores were largely attributable to improved glottic views and less frequent need of applying substantial lifting force on the laryngoscope.
In the present study, no optimizing maneuvers were used to aid intubation with King Vision laryngoscope with statistical significant difference between three devices. Also, increased lifting force on the laryngoscope was needed less frequently with video laryngoscope. Similar results obtained by Michael F Aziz, et al. [10] in their study ,The use of a gum-elastic bougie or external laryngeal manipulation (or both) was required less with C-MAC compared with direct laryngoscope .
In agreement with our results, Elhadi SM, et al. [12] in their study to compare King Vision with Macintosh laryngoscope, reported that The KVL needed less optimization maneuvers, showing that it offered easier intubating conditions. Also LH Andersen. et al. [24] found less frequent need of applying substantial lifting force on the laryngoscope. In contrast to our study, Sarkılar G, et al. [25] conducted their study on video and direct laryngoscopy; they found the glottic view was better with use of video laryngoscope, whereas the use of a stylet, external pressure, and the number of trials of intubation were similar in both groups.
In our study there were more complications with use of Macintosh laryngoscope. While, less complications occurred with King Vision than C-MAC VL which is of clinical importance but with no statistical significance. In agreement with our results QE Ali, et al. [26] observed less airway trauma when using KVL which may relate to the absence of laryngoscopy like maneuver and has softer blade material. Disagreeing with our results, N Jagannathan, et al. [27] reported that Complications were not different between devices when compared King Vision VL with the Miller laryngoscope. Moreover, Soliman R, et al. [2] noted that incidence of oral trauma and bleeding related to intubation was higher with glidescope than with Macintosh laryngoscope.

Conclusion
Use of video laryngoscopes has better intubation conditions as compared to Macintosh laryngoscope as they provide good quality of visualization of the glottis, less number of attempts to achieve successful intubation with less complications and better hemodynamic response to intubation. Also, the design of both King Vision VL and Macintosh laryngoscope shares many features enabling physicians skilled with the latter to use King Vision VL with minimal added training but, still the coast is a considerable factor. Thus it is beneficial to use it for intubation of hypertensive patients.

Limitations
There are few limitations to this study. First, the study was single blinded but, data were recorded by a blind anesthesiologist. Second, it was difficult to standardize some patient's factors while conducting the study on hypertensive patients such as drug therapy which may affect hemodynamics. Third, small sample size so, further studies need to be conducting on large scale of population.