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Year : 2022  |  Volume : 11  |  Issue : 4  |  Page : 288-294

Comparison of ease of intubation using McCoy laryngoscope and CMAC videolaryngoscope in modified Mallampati grade III and IV patients

Department of Anaesthesiology and Critical Care, Sri Venkateswara Institute and Medical Sciences, SVIMS University, Tirupati, Andhra Pradesh, India

Date of Submission11-Oct-2021
Date of Decision17-Nov-2021
Date of Acceptance05-Dec-2021
Date of Web Publication17-Mar-2023

Correspondence Address:
Dr. Hemalatha Pasupuleti
Department of Anaesthesiology and Critical Care, Sri Venkateswara Institute of Medical Sciences, SVIMS University, Tirupati - 517 507, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrntruhs.jdrntruhs_138_21

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Background and Aims: Videolaryngoscopy has been introduced for the management of difficult airway; however, it remains unclear whether it is helpful in routine prediction of a difficult airway. The aim of our study was to compare the ease of intubation using a McCoy laryngoscope and CMAC® videolayngoscope using the Adnets Intubation Difficulty Scale (IDS) score in an anticipated difficult airway (modified Mallampati grade III and grade IV).
Methods: Sixty patients belonging to the American Society of Anaesthesiologists physical status I, II, or III with modified Mallampati grade III and IV undergoing elective surgeries requiring tracheal intubation were randomly allocated into the McCoy group (n = 30) and CMAC® videolaryngoscope group (n = 30). The primary outcome of the study was to compare the ease of intubation between the McCoy laryngoscope and CMAC® videolaryngoscope using Adnet's Intubation Difficulty Scale (IDS) score. Secondary outcomes included time for glottic visualization, time to intubation, total intubation time, hemodynamic and any adverse events.
Results: Comparison of both groups showed that CMAC® videolaryngoscope had a significantly (P = 0.028) lower IDS score (1.667) compared to the McCOY laryngoscope (2.467). Time to view glottis (P = 0.002), time to intubate (P = 0.009), and total intubation time (P = 0.002) were significantly prolonged with CMAC® videolaryngoscope compared to the McCoy laryngoscope. There was no difference in the hemodynamic response and adverse events between the groups.
Conclusion: Our study concludes that although the time to intubate was prolonged in CMAC® videolaryngoscopy, the ease of intubation was better with CMAC videolaryngoscope compared to the McCoy laryngoscope. Hence, we suggest CMAC® videolaryngoscope for anticipated difficult tracheal intubation.

Keywords: Airway management, endotracheal intubation, laryngoscope, videolaryngoscope

How to cite this article:
Srinivas MV, Pasupuleti H, Samantaray A, Hemanth N, Madhusudhan M. Comparison of ease of intubation using McCoy laryngoscope and CMAC videolaryngoscope in modified Mallampati grade III and IV patients. J NTR Univ Health Sci 2022;11:288-94

How to cite this URL:
Srinivas MV, Pasupuleti H, Samantaray A, Hemanth N, Madhusudhan M. Comparison of ease of intubation using McCoy laryngoscope and CMAC videolaryngoscope in modified Mallampati grade III and IV patients. J NTR Univ Health Sci [serial online] 2022 [cited 2023 Apr 1];11:288-94. Available from: https://www.jdrntruhs.org/text.asp?2022/11/4/288/371750

  Introduction Top

Endotracheal intubation is an integral part of general anesthesia. Difficulties in tracheal intubation in the operating room are rare but may be life threatening and is an important cause of morbidity and mortality during anesthesia.[1] Common reason leading to difficult intubation is poor visualization of the glottis. To overcome this over the years, existing laryngoscopes have been modified or new laryngoscopes have been introduced.

Both McCOY laryngoscope and CMAC videolaryngoscope are modifications of the MacIntosh laryngoscope. In the McCOY laryngoscope, the MacIntosh blade is modified with a hinged tip, which, when flexed, lifts the epiglottis and improves the view of the glottis,[2],[3],[4] decreasing the Cormack–Lehane grade by 1 or 2 compared to Macintosh laryngoscope converting difficult intubation to easy intubation.[5],[6] In contrast, in CMAC videolaryngoscope (CMAC®), a videoscope is attached to the MacIntosh blade, which helps in tracheal intubation under vision. It provides a better angle of view of the glottis.[7]

Because both McCOY laryngoscope[8] and CMAC videolaryngoscope[9] improve the intubating condition and have been recommended separately by authors for the management of difficult intubation, it is unclear which is advantageous over the other when used by trained anesthesiologists for a difficult airway. Hence, we decided to compare the ease of endotracheal intubation using McCOY or CMAC® laryngoscope in patients with modified Mallampati grade III and IV (predicted difficult intubation) using Adnet's IDS score.

  Materials and Methods Top

This prospective, randomized, single blind study was conducted after obtaining approval from Institutional Ethics Committee. A written informed consent was obtained from all study participants. The study was registered in the clinical trials registry, India.

The study population comprised 60 patients belonging to the American Society of Anesthesiologists physical status (ASA PS) I, II and III in the age group of 18 to 60 years of either sex with MMG III and IV posted for elective surgeries requiring general anesthesia with endotracheal intubation. Patients with mouth opening less than 6 cm, restricted neck movements, not willing to participate in the study, pregnant or lactating mothers, allergy to study drugs, on drugs affecting hemodynamic parameters such as antihypertensives, severe cardiac, pulmonary and renal diseases were excluded from the study.

Sixty patients were randomly allocated to one of the two groups McCoy or CMAC® by computer-generated random number and sealed opaque envelope technique. All patients were visited in the ward for a pre-anesthesia check-up. Preoperative airway assessment was done by the anesthesiologist blinded to group allocation and study protocol. Demographic data such as age, sex, weight, body mass index (BMI), and American Society of Anesthesiologists physical status were noted.

All patients were kept nil by mouth for 6 h for solids and 2 h for clear liquids. Premedication was performed with tablet alprazolam 0.25 mg and tablet ranitidine 150 mg orally on the night before surgery and on morning 2 h before scheduled time of surgery. Standard monitoring including three lead electrocardiography, non-invasive blood pressure, oxygen saturation, and end tidal CO2 were connected, and base line vital parameters were noted. Preoxygenation was done for 3 min with 100% oxygen. Anesthesia was induced with intravenous inj. fentanyl 2 μg/kg and inj. propofol 2 mg/kg. After confirmation of mask ventilation inj. rocuronium 1.2 mg/kg was administered intravenously. After 1 min of manual ventilation, the patient head was placed in the standard intubating position and an experienced anesthesiologist performed laryngoscopy twice, first using the Macintosh laryngoscope and then by McCoy or CMAC® laryngoscope as per their random group allocation. The best laryngoscopic view obtained by both the laryngoscopes was recorded and graded according to the modified Cormack–Lehane (MCL) grade. The patients were intubated during the second laryngoscopy using McCoy or CMAC® laryngoscope as per their random group allocation with number 7.0 mm endotracheal tube for females and 8.0 mm for males. Anesthesia was maintained with oxygen and air with 0.5% to 1.2% isoflurane. At the end of the surgery, residual neuromuscular blockade was reversed with intravenous neostigmine and glycopyrrolate. The patient was extubated after satisfying the extubation criteria.

The primary study objective was to compare the ease of intubation between McCoy or CMAC® laryngoscope using the Intubation Difficulty Scale (IDS) score described by Adnet et al.[10] [Table 1]. The IDS score is a quantitative scale of seven variables of intubation difficulty that can more objectively compare the complexity of tracheal intubations. An IDS score of 0 represents ideal intubating conditions and increasing scores represent progressively more difficult intubating conditions. According to the IDS score Adnet et al.[10] have classified the degree of difficulty of tracheal intubation (IDS = 0 easy, 1–5 slight difficulty, >5 moderate to major difficulty and ∞ impossible intubation).
Table 1: Intubation Difficulty Scale

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Secondary outcomes included time for glottic visualization, time to intubation, total intubation time, and hemodynamic response to intubation. Time for glottic visualization is defined as the time from handling the laryngoscope (McCoy or CMAC®) up to the best view of the glottis, time to intubation was time taken from the best view of the glottis to the detection of the first capnograph trace and total intubation time included the sum of both time for glottic visualization and time for intubation. In all study participants, endotracheal intubations were performed by the same anesthetist with an experience of more than 50 successful intubations. An intubation attempt was defined as an insertion of the laryngoscope through the mouth. A failed intubation attempt was made, during which the trachea was not intubated. Successful tracheal intubation was confirmed by continuous capnography. Failure to intubate was defined as the inability to intubate the patient's trachea with three intubation attempts.

The sample size was estimated based on the primary outcome, the IDS score. Based on our pilot study, we considered a change in the mean IDS score of 2.0 with a standard deviation (SD) of 2.65 between the two groups as minimal clinically important change score for tracheal intubation, using α = 0.05 and β = 0.2. The estimated sample size was 28 patients per group. However, we recruited 30 patients in each group.

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) software for windows version 20. The data obtained were evaluated for normality using the Shapiro–Wilk test. Normally distributed data were presented as mean ± standard deviation (SD). Qualitative data were summarized using number and percentage, analyzed by Chi-square test or Fischer's exact test, as appropriate. Quantitative data were compared using sample Student's t-test or Mann–Whitney U test. For all statistical tests, a P < 0.05 was considered significantly different.

  Results Top

Both the groups were comparable with regard to demography and baseline characteristics. There was no difference in the Mallampati grade (MPG) between the groups with 28 and 2 patients of MP III and IV in each group, respectively. There was no statistical difference in the baseline Cormack–Lehane grade in both groups obtained after visualization with the conventional Macintosh laryngoscopy [Table 2].
Table 2: Demography, Physical Characteristics, and Airway Evaluation between the Groups

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In the CMAC group, 22 patients had as light difficult intubation (IDS 1–5) and 8 patients had an easy intubation (IDS 0). In contrast, all but one patient in the McCoy group had slight difficulty (IDS 1-5). Only one patient from the McCoy group had a moderate-to-major difficulty in intubation (IDS >5) [Table 3].
Table 3: Comparison of Intubation Difficulty Scale (IDS) Score Between Study Groups

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All patients in McCoy and CMAC groups were intubated using a size three blade. CMAC® videolaryngoscope had a lower IDS score (1.667) compared to the McCoy laryngoscope (2.467), which was significant (P = 0.028) [Table 4].
Table 4: Comparison of Device Performance between the Groups

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Time taken to view the glottis and intubate with the CMAC® videolaryngoscope was 39.33 and 80.10 s, respectively, and with McCOY laryngoscope was 15.40 and 47.50 s, respectively, with P value of 0.002 and 0.009, respectively. Total intubation time was also prolonged in the CMAC group (106.667 s) compared to the McCoy group (62.967 s), which was highly significant (0.002) [Table 4].

There was no significant difference in the intubation attempts and patients requiring optimizing maneuvers for intubation between the groups [Table 4].

The difference in hemodynamic parameters (heart rate (HR) and mean arterial pressure (MAP)) measured at baseline, 1, 3, 5, 7 and 10 minutes post intubation did not differ significantly between the groups [Figure 1] and [Figure 2].
Figure 1: Comparison of heart rate between the groups

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Figure 2: Comparison of mean arterial blood pressure between the groups

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  Discussion Top

Efforts have been made to reduce the incidence of complications of difficult intubation by developing alternative devices for tracheal intubation. Fibreoptic bronchoscope is considered as the gold standard for difficult intubation[11] but skill and knowledge are required to handle it.[12] The C-MAC videolaryngoscope is an indirect laryngoscope, recently introduced for difficult intubation.[9],[13]

Because of the high cost and logistic requirement of the new device (C-MAC videolaryngoscope), the performance of this device is better than that of other standard laryngoscopes (McCoy) used for difficult intubation. Therefore, this study was undertaken to evaluate the usefulness of the new device CMAC® with the regular McCoy laryngoscope in a randomized single blind study using Adnet's IDS score in anticipated difficult tracheal intubation (MMP grade III and grade IV), Adnet's IDS has been used as a quantitative score to gauge the degree of intubation difficulty.[10]

In our study, the performance of CMAC® videolaryngoscope was better than the McCoy laryngoscope. In the CMAC group, 26.67% experienced easy and 73.33% had slight difficulty, whereas in the McCoy group, 96.67% had slight difficulty and 3.33% moderate-to-major difficulty in endotracheal intubation [Table 3].

The current study showed significant lower IDS sore in CMAC® videolaryngoscope compared to the McCoy laryngoscope [Table 3] in accordance with previous studies by Jain et al.[14] and Seo KH et al.[15] The causes of high IDS score in the McCoy group were because of the increase in the number of attempts (N1) and decreased exposure of glottis (N4), thereby increasing the MCL grade and the necessity of application of laryngeal pressure (N6) [Table 4].

Aziz et al.[16] and Jungbauer, et al.[17] compared the C-MAC videolaryngoscope and Macintosh laryngoscope in suspected difficult airway (MPG III/IV, h/o difficult airway). Their observations revealed that the low IDS score in the CMAC group was due to an improved the Cormack–Lehane grade and lesser use of external manoeuvre that correlated with our findings. However, in their studies,[16],[17] the need for alternative techniques was less in the CMAC group in contrast to our study. This may be because the direct laryngoscope compared in their study was Macintosh, whereas it was McCoy.

In the present study, both McCoy laryngoscope and CMAC video laryngoscope improved the glottis vision and decreased the MCL grade (compared to the baseline MCL grade by Macintosh laryngoscope). However, the glottis visualization was much better with CMAC video laryngoscope. More number of patients in CMAC had modified Cormack–Lehane grade I (43.33%) when compared to the McCoy group (6.67%), which was statistically significant (0.004) [Table 4]. This is in accordance with the previous trials.[18],[19] In videolaryngoscopy, the digital camera and light source were mounted very close (2–3 cm) to the tip of the videolaryngoscope and close to the larynx. The laryngoscopist obtains a much wider angle of view of 80° as captured on the camera monitor, whereas in direct laryngoscopy, the distance between the vocal cords and the laryngoscopist's eye is substantial (30–40 cm), reducing the angle of view to 15°.[20]

This improved vision of glottis by CMAC® laryngoscope led to a greater number of patients having successful intubation at first attempt and required less laryngeal pressure [Table 4]. Only three (10%) patients in the CMAC group required more than one attempt compared to eight (26%) patients in the McCoy group [Table 4]. Similar results were observed in previous studies.[16],[21]

In the current study, the mean time to view glottis and time for tracheal intubation was significantly longer with the CMAC® video laryngoscope compared to the McCoy laryngoscope [Table 4]. With direct laryngoscopy (McCoy), the difficulty lies in exposing the larynx and inserting the tube into the glottic, opening without blocking the line of sight. Endotracheal tube advancement into the trachea is usually straightforward. Video laryngoscopes achieve better laryngeal exposure through indirect imaging by looking around the curve of the tongue.[22] The potential challenge is inserting and advancing the tube into the glottis because the device does not create a direct channel for tube passage; the tube must be maneuvered around the device[22] with good hand-to-eye coordination, which will be mastered by practice. Some studies[16],[19] have demonstrated a longer intubation time similar to our study, whereas others[14],[17] have shown less intubation time with videolaryngoscope when compared to direct laryngoscope. This can be attributed to the experience of the laryngoscopist with the device.

In line with earlier studies,[14],[23] we also did not observe any significant change in hemodynamics between the two different types of laryngoscopes [Figure 1] and [Figure 2].

The incidence of common complications, such as trauma, observed during laryngoscopy was more in the McCoy group (13.33%) compared to the CMAC group (3.33%) although not significant. There were no episodes of bradycardia (HR <60/beats/min) or hypoxia (SpO2 <94%) in any of the study participants. The higher number of attempts in the McCoy group[24] might have contributed to numerically more incidence of hoarseness observed in the McCoy group (73.33%) compared to the CMAC (60.00%) group; however, this did not reach statistical significance.

Our investigation had limitations such as the investigators could not be blinded to the laryngoscope used for intubation and therefore bias could not be completely ruled out. The present study was conducted anticipating difficult intubation in patients with MPG III and IV. For predicting difficult intubation, we chose the modified Mallampati test, as it has the highest sensitivity (95% confidence interval [CI]) of all bed side tests compared; however, this was the modest.[25] To increase the validity of the modified Mallampati test, the test was performed in a strict standard method as described in the literature.[26] To prevent the influence of the inter-observer variability, the grade of the Mallampati classification was confirmed by a second observer.

Our study, to the best of our knowledge, is the first investigation to compare the performance of CMAC® videolaryngoscope with McCoy laryngoscopy conducted in patients with MPGIII/IV that also included a control and comparison of modified Cormack–Lehane grade of glottis visualized with a standard Macintosh laryngoscope.

In conclusion, although the time taken to intubate was prolonged in CMAC® videolaryngoscope, it did not contribute to any morbidity. The ease of intubation was better with CMAC® videolaryngoscope with significantly better glottis visualization and higher success rate compared to the McCoy laryngoscope for difficult intubation. Hence, we suggest CMAC® videolaryngoscope as the first choice laryngoscope for anticipated difficult tracheal intubation and should be available in the difficult airway cart.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4]


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