Comparison between McGrath and Macintosh laryngoscopes as an educational tool for successful intubation by novice airway managers: A randomised cross-over manikin-based trial

Githin M Vareed; Sara Vergis Korula; Girijanandan D Menon; Manjit George; Sam Philip; Sruthy Victor

doi:10.4103/arwy.arwy_27_21

ORIGINAL ARTICLE

Year : 2021 | Volume : 4 | Issue : 3 | Page : 168-174

Comparison between McGrath and Macintosh laryngoscopes as an educational tool for successful intubation by novice airway managers: A randomised cross-over manikin-based trial

Githin M Vareed¹, Sara Vergis Korula², Girijanandan D Menon², Manjit George², Sam Philip², Sruthy Victor²
¹ Department of Anaesthesiology, Medical Trust Hospital, Kochi, Kerala, India
² Department of Anaesthesiology and Critical Care, MOSC Medical College, Kochi, Kerala, India

Date of Submission	06-May-2021
Date of Acceptance	14-Jul-2021
Date of Web Publication	03-Sep-2021

Correspondence Address:
Dr. Sara Vergis Korula
Department of Anaesthesiology and Critical Care, MOSC Medical College, Kolenchery, Kochi - 682 311, Kerala
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/arwy.arwy_27_21

Abstract

Background: The Macintosh (MAC) laryngoscope has been the gold standard for teaching intubation till date. This manikin-based study was conducted to determine whether McGrath^™ videolaryngoscope (VL) (McG) is comparable to MAC laryngoscope as an educational tool for novice airway managers. Material and Methods: A randomised cross-over manikin-based trial was conducted in a group of 44 final-year medical students. After training for intubation with both laryngoscopes, the students were randomised to Group MAC or Group McG to decide which laryngoscope would be used first. The total time for intubation, number of attempts for successful intubation, ease of visualisation and ease of intubation were assessed. Results: The median time for intubation was 40 s (interquartile range [IQR] 16.5–93.5) for the MAC group and 35 s (IQR 17.5–54.5 s) for McG group (P = 0.22). First attempt success was significantly more in the McG group. Ease of visualisation and ease of intubation were significantly better in the McG group (P ≤ 0.05). Conclusion: The McGrath™ VL appears to be superior to MAC laryngoscope as an educational tool for training novice airway managers in endotracheal intubation.

Keywords: COVID-19, endotracheal intubation, laryngoscope, Macintosh, McGrath™, novice airway managers

How to cite this article:
Vareed GM, Korula SV, Menon GD, George M, Philip S, Victor S. Comparison between McGrath and Macintosh laryngoscopes as an educational tool for successful intubation by novice airway managers: A randomised cross-over manikin-based trial. Airway 2021;4:168-74

How to cite this URL:
Vareed GM, Korula SV, Menon GD, George M, Philip S, Victor S. Comparison between McGrath and Macintosh laryngoscopes as an educational tool for successful intubation by novice airway managers: A randomised cross-over manikin-based trial. Airway [serial online] 2021 [cited 2022 Jan 22];4:168-74. Available from: https://www.arwy.org/text.asp?2021/4/3/168/325565

Introduction

Safe airway management in critical situations can be challenging due to anatomical and physiologic characteristics. The Fourth National Audit Project Report identified deficiencies that led to adverse outcomes in airway management.^[1] Failure to intubate remains a frequent cause of morbidity and mortality in the intensive care unit (ICU) and operation theatre. Teaching young doctors the art of intubation is a necessary part of their training, especially in ICUs. Research for optimising training methods for airway management will improve patient safety.

Conventional direct laryngoscopy with Macintosh (MAC) laryngoscope is the standard technique widely used for training in intubation. Aligning the oral, pharyngeal and laryngeal axes is a prerequisite to obtain direct view of glottic aperture for intubation while using the direct laryngoscope.^[2],[3] A videolaryngoscope (VL) is an important innovation in laryngoscopes. McGrath™ MAC (McG) VL is a portable device with a single-use sterile blade whose curvature is similar to the MAC blade. The image of the glottis is seen on a colour liquid crystal display screen which is attached to the handle of the device and intubation is performed while looking at this image.^[2] The McGrath laryngoscope has been shown to be useful in a wide array of difficult airway scenarios. It provides a better view of the glottis in both normal and difficult intubation.^[4] Despite this, it is not commonly used as a training tool for intubation.

Studies comparing the MAC and McGrath laryngoscopes have been conducted and some studies have shown that the time taken for intubation was lesser using the MAC laryngoscope. Familiarity with the MAC laryngoscopes and training play a role in this variation.^[5],[6] Hence, we decided to assess intubation done on manikins by final-year medical students who were novices in intubation using both the MAC and McGrath laryngoscopes.

We planned to compare MAC laryngoscope and McGrath™ VL for ease and efficacy of intubation using total time taken for intubation (TTI) as the primary outcome. Other outcomes that we assessed were number of attempts for successful intubation, ease of visualisation of glottis and ease of intubation.

Material and Methods

This was a comparative, randomised, cross-over manikin-based study. It was conducted in the Department of Anaesthesiology and Critical Care in a tertiary care centre after obtaining Institutional Ethical Committee approval.

Taking a difference of total time for intubation of more than 10 s as significant, the sample size was calculated for 80% power and alpha error of 5%. The calculated sample size was 37; accounting for 10% dropout, we included 44 participants [Figure 1].

Figure 1: Consort flow diagram (Group MAC: Macintosh laryngoscope; Group McG : McGrath videolaryngoscope)

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Forty-four medical students of similar age group were enrolled in the study and informed written consent was taken from each. Medical students who were appearing for their final examinations in a few months were chosen to avoid bias, as young doctors and interns could have had variable exposure to the procedure of endotracheal intubation. The training given for the study would be useful for the final-year students who would soon face real-life situations that would require airway management. Students who had any physical disability that would prove a disadvantage for intubation were excluded.

All students were given a brief lecture with various clinical scenarios requiring airway management, importance of mask ventilation, laryngoscopes and endotracheal intubation. This was followed by a video presentation on how to use the MAC and McGrath (McG) laryngoscopes on the manikin. They were then asked to perform intubation under the supervision of an instructor until they achieved one successful intubation on the manikin with each laryngoscope.

One week after this training session, the students were asked to do the intubation on the manikin on their own. Randomisation was done by computer-generated random numbers and allocation concealed with opaque envelopes to decide which laryngoscope would be used first. Each student attempted intubation with both laryngoscopes. Each participant was allowed to attempt intubation until they were successful with each laryngoscope. One attempt at laryngoscopy was defined as passing of the laryngoscope beyond the incisors.

The primary outcome was time taken for intubation (TTI). This was defined as time from when the laryngoscope blade crosses the incisors to successful chest rise confirmed by auscultation by the trainer. Oesophageal intubation, the need for more than three attempts or >120 s to intubate the trachea were labelled as a 'failed attempt'. Ease of visualisation of glottis and ease of intubation were graded by study participants on a grade from 1 to 4. (Grade 1: Excellent, Grade 2: Good, Grade 3: Average, Grade 4: Poor).

Intubation was done on a SimMan^® manikin (Laerdal Medical Canada) with McGrath™ (Medtronic) and MAC laryngoscopes using a # 4 blade. A 7.5 mm ID cuffed endotracheal tube with stylet was used for all intubation attempts.

Statistical methods

Wilcoxon signed-rank test was used to compare the average time to intubation and the total number of attempts between the MAC and McGrath laryngoscopes as data violated the normality assumption. The number of first-pass success and failures of intubation were compared using the McNemar test. The ease of visualisation of glottis and ease of intubation between the two methods were analysed using the Stuart Maxwell test. P < 0.05 was considered statistically significant. All statistical analysis was performed using EZR software.

Results

Forty-four final-year medical students of similar age group who were untrained in intubation were enrolled in this study. The time taken for successful intubation using the two laryngoscopes was compared by the Wilcoxon signed-rank test. The median time taken was 40 s (interquartile range [IQR] 16.5–93.5 s) with MAC laryngoscope and 35 s (IQR 17.5–54.5 s) for the McGrath laryngoscope. This difference was not statistically significant [Figure 2].

Figure 2: Box-and-whisker plot showing time taken for intubation (seconds)

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The number of attempts the participants took for successful intubation was also compared by the Wilcoxon signed-rank test, and there was no significant difference in the average number of attempts in the two groups. First pass success was more with the McGrath laryngoscope. Successful intubation at the first attempt was possible in 70% of students using McGrath, while it was only 48% with MAC. The difference compared by the McNemar test was statistically significant [Table 1]. The numbers of failed intubations were also significantly higher in the MAC group (8 vs. 3). Of the 8 failed intubations in Group MAC, 7 required more than 3 intubation attempts and one took more than 120 s.

Table 1: Attempts for successful intubation

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The ease of visualisation of the glottis and ease of intubation were reported by the participants using a numerical rating scale, grade 1 being excellent and grade 4 being poor [Table 2]. The results were assessed using the Stuart Maxwell test, and we found there was a statistically significant difference between the two groups (P = 0.001). Most of the participants found visualisation of glottic opening easier with the McGrath laryngoscope. While using the MAC laryngoscope, 34% of the participants found visualisation to be poor.

Table 2: Ease of visualisation/ease of intubation

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The participants found intubation was significantly easier with McGrath laryngoscope. Ease of intubation was excellent in 50% of the students when using McGrath laryngoscope, while 23% of the participants found intubation with MAC laryngoscope excellent. Intubation was poor with MAC laryngoscope for 32% of the participants.

Discussion

Although endotracheal intubation is regarded as the 'gold standard' in securing the airway in emergency situations, the incidence of failed intubation or misplaced tube is between 6% and 14% in retrospective studies.^[7] Hence, the importance of training junior doctors in intubation is emphasised. For many years, the MAC laryngoscope has been the laryngoscope of choice for training due to its widespread availability and familiarity.^[8] New equipment such as the VL have been used primarily for managing difficult airways. The COVID pandemic has forced us to use innovative techniques to reduce the risk due to viral aerosol during intubation. Videolaryngoscopy increases “mouth-to-mouth” distance compared with direct laryngoscopy.^[9] Videolaryngoscopy has been advised in COVID guidelines as the first choice for intubation.^[10] We therefore decided to compare, using a randomised cross-over design, the McGrath laryngoscope with the MAC laryngoscope as an educational tool for intubation by novice airway managers.

The TTI is important to assess the efficacy of intubation. In our study, the median TTI was comparable in both MAC and McG groups. This is similar to a previous study comparing the MAC, McGrath and GlideScope laryngoscopes by novices.^[11] The mean time for intubation using the McGrath laryngoscope was 30.8 ± 16.9 s in their study and 35 s (17.5–54.5 s) in ours. The time to intubation using McGrath has been found to be more than MAC when used by anaesthesiologists experienced in only MAC and also when they are experienced in both MAC and McGrath laryngoscopes.^{[5],[12],[13],[14]} Direct laryngoscopy using the MAC laryngoscope is a primary skill acquired by anaesthesiologists and maintained with constant practice. VLs are mostly used in difficult airway scenarios and are not being used very often as they are not available in all institutions. The participants in this study were novices to both laryngoscopes, and this could explain the similar timings with both laryngoscopes. There are a few clinical studies looking at the use of VLs in patients by novice doctors. Di Marco et al. compared learning and performance of intubation when novices used Airtraq VL or MAC laryngoscope.^[15] Airtraq VL was easier to use and had a shorter time to intubation than MAC. This may not be directly comparable with our study wherein we used a nonchannelled VL.

VLs have been shown to improve first-pass success in emergency intubations in trauma patients.^[16] First-pass success for direct laryngoscopy and VL were 63.2% and 79.2%, respectively. During the COVID pandemic, there is an additional risk of aerosol exposure which worsens with each intubation attempt. A teaching tool which improves first attempt success should be the goal to reduce this risk. Although the total number of attempts for successful intubation did not differ between the two laryngoscopes, the first attempt success was significantly higher with the McGrath laryngoscope (MAC 48% vs. McG 70%; P < 0.05). A previous study comparing MAC and McGrath laryngoscopes found higher first intubation success using (MAC 100% vs. McG 73.3%; P < 0.05). The participants in this particular study were anaesthesiologists. Although the participants had experience with McGrath laryngoscope, they were trained with the MAC laryngoscope and had more experience with the latter. This could be the reason for the greater success of using the MAC laryngoscope.^[6] Baek et al. in a recent study showed a higher first-attempt intubation success with VL when intubating patients in the general ward. In multivariate logistic regression analyses, VL, preintubation heart rate, preintubation SpO₂ >80%, an airway not predicted to be difficult, experienced operator and Cormack-Lehane grade were associated with first-attempt intubation success in the general ward.^[17] The higher first-pass success is very important in critically ill patients requiring intubation. Serious complications such as hypoxaemia and cardiac arrest are associated during intubation in 14%–16% of cases.^[18] These complications occur more frequently when more than one attempt was required for successful intubation.^[19],[20] The ease of visualisation as graded by the participants was significantly better when using McGrath laryngoscope. This is quite significant during training for intubation. Unlike in direct laryngoscopy with MAC laryngoscope, the McGrath VL can bring the glottic view onto the screen without the need to align the oral, pharyngeal and laryngeal axes.^[21] The easy visualisation can make identification of vocal cords and glottic opening possible without looking into the mouth of the patient. This has the added benefit of reducing aerosol exposure to the healthcare worker. While teaching intubation, the trainer can see real time what the student is seeing and guide the student through the process of intubation. This is not possible with the MAC laryngoscope.

The final-year medical students who participated in the study graded McGrath as a better device for intubation. Using MAC for intubation was found to be very difficult by 32% of the participants. This is similar to the findings of a previous study in novice users. McGrath laryngoscope was chosen as the best tool in difficult intubation scenarios in their study also.^[22]

There are a number of limitations in our study. In a manikin-based study, a standardised environment is provided for tracheal intubation. Effect of clinical situations such as fogging of the camera, restless patients in ICU and oral bleeding cannot be assessed. Although the findings cannot be fully extrapolated to real-life situations, manikins have been validated as a surrogate for evaluating intubation skills in several previous studies.^[23] There were additional ethical concerns in allowing medical students who were novice airway managers to perform intubation on patients. Training and device evaluation in a single manikin must be approached and interpreted with caution.^[24] We have assessed only a normal airway scenario. The findings in a difficult airway scenario could very well have been different. The incidence of complications during and following intubation cannot be predicted with this study. Studies which address these issues can be done on the basis of these results with a larger sample size to detect the differences between the two laryngoscopes.

Conclusion

When compared to the MAC laryngoscope, the McGrath™ MAC VL seems to improve success rate of intubation in a manikin with a normal airway by novice airway managers. The total time to intubation is comparable to MAC laryngoscope and it has a higher first-pass success. The McGrath VL gives a better view of the glottis and improves the ease of intubation as graded by novice airway managers. We should therefore consider early training with the McGrath MAC VL along with MAC direct laryngoscope to teach endotracheal intubation.

Acknowledgement

We sincerely thank the administration of MOSC Medical College, especially Dr Shaloo Ipe, Head of the Department, Anaesthesiology and Critical Care, for providing permission, infrastructure and support to conduct this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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