Addition of optics to laryngoscope design improves success of intubation: A prospective, observational study

Vaishali Chandrashekhar Shelgaonkar; Piyush Arvind Dhawad; Medha Akhilesh Sangawar

doi:10.4103/ARWY.ARWY_20_19

ORIGINAL ARTICLE

Year : 2019 | Volume : 2 | Issue : 3 | Page : 142-147

Addition of optics to laryngoscope design improves success of intubation: A prospective, observational study

Vaishali Chandrashekhar Shelgaonkar, Piyush Arvind Dhawad, Medha Akhilesh Sangawar
Department of Anaesthesiology, Indira Gandhi Government Medical College, Nagpur, Maharashtra, India

Date of Submission	09-Jun-2019
Date of Acceptance	03-Nov-2019
Date of Web Publication	30-Jan-2020

Correspondence Address:
Dr. Vaishali Chandrashekhar Shelgaonkar
Department of Anaesthesiology, Indira Gandhi Government Medical College, Nagpur, Maharashtra
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ARWY.ARWY_20_19

Abstract

Background: Many novel intubating videoscopes such as the GlideScope, McGrath^®, Truview EVO2^® videolaryngoscope (VLS), Airtraq^® and C-MAC^® VLS have been introduced in the recent past in an attempt to reduce airway-related morbidity and mortality. In this study, we aimed to compare the ease and success of intubation using Airtraq, Truview VLS and McCoy blade laryngoscope in non-difficult airway situations. Patients and Methods: Ninety patients with clinically normal airways belonging to American Society of Anesthesiologists Physical Status I–II were randomly assigned to be intubated using Airtraq (Group AL; n = 30), Truview VLS (Group TL; n = 30) or McCoy (Group ML; n = 30). The primary outcome measures were Intubation Difficulty Scale score and time for successful intubation. Assessment of modified Cormack–Lehane (MCL) grade at laryngoscopy, Percentage of Glottic Opening (POGO) score, haemodynamic variations, any optimisation manoeuvre required during endotracheal intubation, ease of intubation score and complications were the secondary outcomes. Results: The time for successful intubation was statistically significantly less with Airtraq as compared with both ML and Truview VLS (P < 0.05). Intubation Difficulty Score improved significantly with Airtraq and Truview VLS when compared with that of McCoy blade. Airtraq and Truview significantly improved MCL grading, POGO score and ease of intubation score. These devices also required less optimisation manoeuvres (P < 0.05) and had less haemodynamic variations although not statistically significant (P > 0.05). Conclusion: We conclude that both the Airtraq and Truview VLS are devices whose optical design improves intubating conditions in patients with non-difficult airways.

Keywords: Airtraq^®, endotracheal intubation, Truview^®, videolaryngoscope

How to cite this article:
Shelgaonkar VC, Dhawad PA, Sangawar MA. Addition of optics to laryngoscope design improves success of intubation: A prospective, observational study. Airway 2019;2:142-7

How to cite this URL:
Shelgaonkar VC, Dhawad PA, Sangawar MA. Addition of optics to laryngoscope design improves success of intubation: A prospective, observational study. Airway [serial online] 2019 [cited 2023 Mar 30];2:142-7. Available from: https://www.arwy.org/text.asp?2019/2/3/142/277322

Introduction

Airway management is the primary responsibility of anaesthesiologists.^[1] Not only does it include securing and protecting the airway during induction, but it also involves its safe preservation during maintenance and recovery from anaesthesia. Failure to do so can result in adverse consequences leading to severe morbidity and even mortality in both emergency situations and operating rooms.^[1] Orotracheal intubation is the most commonly used method to secure the airway during anaesthesia. Macintosh introduced a curved blade in 1943, still considered a gold standard, that improved the view of the glottis during orotracheal intubation.^[2] Various modifications were introduced since then to facilitate orotracheal intubation in difficult airway situations. Although the failure rates decreased with such adjuncts to facilitate intubation, there was always a quest to develop more devices. As technology advanced, application of physics and optics assisted in the visualisation of the glottic opening, leading to indirect laryngoscopy.

The Airtraq ^® (Prodol Meditec, Vizcaya, Spain), a channelled laryngoscope, has a preformed curvature and a channel for guiding the endotracheal tube. It is an optical intubation device that provides a view of the glottic opening without the need to align the oral, pharyngeal and laryngeal axes. Truview EVO2^® is a reusable video- and optical laryngoscope with a straight blade. It consists of a combination of an optical system with a specially profiled 12.8 mm slim steel blade and an optical apparatus which provides 42° +2° angled deflection view (around-the-corner view) through a 15 mm eyepiece.

Although these intubating gadgets are being used in difficult airway situations, they cannot be used for the first time during difficult intubation. The aim of this study was to compare the ease and success of intubation using McCoy blade, Airtraq and Truview laryngoscopes and gain experience in non-difficult airway situations.

The primary outcome measures were Intubation Difficulty Scale (IDS) score and time for successful intubation. Assessment of the modified Cormack–Lehane (MCL) grade at laryngoscopy, Percentage of Glottic Opening (POGO) score, haemodynamic variations, any optimisation manoeuvre required during endotracheal intubation, ease of intubation score and complications were the secondary outcomes.

Patients and Methods

Following approval from the Institutional Ethics Committee, this study was conducted over a period of 2 years on ninety patients from various surgical specialities posted for elective surgery under general anaesthesia. Patients with clinically normal airways belonging to American Society of Anesthesiologists Physical Status I or II of either gender aged between 18 and 60 years were included in the study.

After obtaining written informed consent, patients were randomly allocated to one of the following three groups – Airtraq laryngoscope (AL), Truview (TL) videolaryngoscope (VLS) and McCoy laryngoscope (ML). A detailed preanaesthetic evaluation was done, and airway variables such as history of snoring, presence of buck teeth, Mallampati grade, mentohyoid distance, thyromental distance, sternomental distance, neck circumference and mouth opening were noted to rule out any possible airway difficulties.

In the operating room, standard monitoring including electrocardiogram, noninvasive blood pressure, pulse oximetry and measurement of end-tidal carbon dioxide including anaesthetic gas monitoring was established. Premedication was given 10 min prior to induction with injection glycopyrrolate 4 μg/kg, injection midazolam 30 μg/kg and injection fentanyl 2 μg/kg. Preoxygenation was performed with 100% oxygen at a fresh gas flow of 6 L/min. All patients were induced with injection propofol 2 mg/kg and paralysed with injection suxamethonium 1.5 mg/kg. Endotracheal intubation was performed by a senior anaesthesiologist in all the three groups, with the patient's head placed in the sniffing position. Further management of anaesthesia was as per the need of the patient and procedure and was left to the discretion of the senior anaesthesiologist in charge of the case.

The time taken for successful intubation was noted. The duration of intubation was defined as the time from introduction of the laryngoscope blade into the mouth until the appearance of a capnographic waveform.^[3] If intubation was not successful after three attempts or the time taken for intubation was more than 120 s, it was considered as a failed intubation, and tracheal intubation was carried out using an alternate laryngoscope by the senior anaesthesiologist.

IDS is a quantitative scale of difficult intubation, with seven variables assessing the complexity of tracheal intubation. An IDS score of 0 implies best intubating condition, whereas progressively more difficult tracheal intubations result in higher scores.

MCL grade is as follows:

1: Full view of vocal cords

2a: Partial view of vocal cords

2b: Arytenoids and epiglottis visible

3a: Only epiglottis is visible and liftable

3b: Epiglottis visible but not liftable

4: Both epiglottis and glottis not visible

POGO score is graded as:

75%–100% (when the entire glottis is visible)
50%–75%
25%–50%
0%–25% (when glottis is not visible)

Ease of intubation score is graded as:

No external manipulation
External manipulation required/multiple attempts and adjuncts required
Failure to intubate

Optimisation manoeuvres used to facilitate intubation (if any) were noted. In the case of Airtraq, a twist-and-turn manoeuvre was used, whereas in the case of ML and TL, backward, upward and rightward pressure (BURP) or optimal external laryngeal manipulation (OELM) was used. In the case of the McCoy blade laryngoscope, the use of a stylet or bougie to aid intubation was also noted.

Haemodynamic parameters noted at various time intervals were heart rate, systolic blood pressure (SBP) and diastolic blood pressure (DBP). Preintubation values were taken as the baseline values. Complications or airway morbidity in the form of dental trauma, oropharyngeal trauma, bronchospasm/laryngospasm and a drop in SpO₂ <90% were noted.

Sample size calculation was based on the IDS score. The results were presented as number, percentage, mean ± standard deviation or frequencies (%) as appropriate. Continuous data were compared using Student's t-test, whereas categorical data were compared using Fisher's exact test and Chi-square test. P < 0.05 was considered statistically significant.

Results

Patients in all the three groups were comparable with respect to age, body mass index and airway parameters [Table 1]. While a mean IDS score 0 was found in 15, 27 and 24 patients in ML, AL and TL groups respectively, an IDS score 1 was observed in 5, 3 and 6 patients respectively in these groups. An IDS score of >1 was observed in 10 patients of ML group only. The difference of IDS score was statistically significant (P < 0.001) between ML and AL groups and also between ML and TL groups [Table 2] and [Figure 1]. The median, minimum, maximum, 25^th percentile, 75^th percentile and interquartile range for intubation time (seconds) are summarised in [Table 3] and represented diagrammatically in [Figure 2]. The difference was found to be statistically significant (P < 0.001) between Airtraq and ML as also between Airtraq and TL. The difference in intubation times between Truview and MLs was not statistically significant (P > 0.05).

Table 1: Demographic data and airway parameters (n=30)

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Table 2: Parameters qualifying intubation characteristics (n=30)

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Figure 1: Intubation Difficulty Scale score distribution in the study groups (ML=McCoy blade laryngoscope; AL=Airtraq; TL=Truview videolaryngoscope)

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Table 3: Intubation time (s) with Airtraq, Truview and McCoy laryngoscopes

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Figure 2: Box-and-whisker plot showing intubation time (seconds) in Airtraq laryngoscope (AL), McCoy blade laryngoscope (ML) and Truview laryngoscope (TL)

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MCL Grade 1 was found in most of the patients as compared to other grades with the Airtraq and TL. Considering the difference in MCL Grade 1 versus further grades, the difference was statistically significant (P < 0.001) between ML and AL groups as also between ML and TL groups [Table 2].

The mean percentage of POGO score was 83.17%, 98.33% and 99% in groups ML, AL and TL respectively. The difference was statistically significant between AL and ML, as also between TL and ML groups. In addition, while comparing Score I versus scores II, III and IV, we found that the difference between ML and AL, as also TL and AL, was statistically significant (P < 0.05) [Table 2]. The BURP manoeuvre was required in eight and two patients respectively in the McCoy and Truview groups. On comparison, OELM was required in only one patient in the McCoy group. None of the patients in the Truview group required OELM. The difference in manoeuvres required to facilitate intubation was significantly high with the McCoy group as compared to the Truview group. The twist-and-turn manoeuvre (in the case of Airtraq) was required in three patients, which was statistically insignificant (P > 0.05) when compared with other optimisation manoeuvres (McCoy and Truview groups).

Ease of intubation Score I was found in all patients (30/30) with the AL, 29/30 patients in the Truview group and 21/30 patients in the McCoy group. No patient had a score of III in the three groups. Statistically significant difference (P < 0.05) was found between McCoy and Airtraq groups and McCoy and Truview groups [Table 2]. Maximum rise in heart rate, SBP and DBP was seen in the McCoy group, but the difference was statistically insignificant (P > 0.05) when compared to rise in these parameters in the Airtraq and Truview groups. The maximum rise from baseline values was seen at the time of intubation in all the groups (with the maximum being in the McCoy group).

Incidence of complications such as dental trauma was seen in one case in the McCoy group and pharyngeal trauma was seen in one case each in the Airtraq and Truview groups [Table 2].

Discussion

We compared the ease and success of endotracheal intubation using three intubating devices – AL, TL and the McCoy blade laryngoscope. The view obtained on laryngoscopy, which is a major factor in determining the ease of intubation, was obtained through MCL grading and POGO score. Significantly more number of patients intubated with Airtraq and Truview had MCL Grade I (26 and 27 respectively) and none had Grade III and Grade IV. This was due to the unique combination of an extremely curved blade and an in-built optical system in Airtraq and a 42° anterior refracted glottic view in Truview, providing a glottic view without the need to align the axes as compared to the McCoy laryngoscope.

POGO score distinguishes patients with large and small degrees of partial glottic visibility and provides a better yardstick for assessing the difference between various intubation techniques.^[4] It also has better interphysician reliability than the Cormack–Lehane grading.^[5] We found that POGO score also improved significantly with Airtraq and Truview as seen in previous studies.^[6],[7]

Optimisation manoeuvres are directly related to the glottic visualisation, which, in turn, is related to the alignment of the three axes. Although more number of patients required optimisation manoeuvres in the McCoy laryngoscope group than the TL group, the difference was statistically insignificant (P > 0.05). This could be because the McCoy blade has a flexible tip that lifts the epiglottis during difficult visualisation of the glottis, thereby requiring less optimisation manoeuvres. Similar results were also found in studies done earlier.^{[5],[8],[9],[10]}

Statistical significance (P < 0.05) was found while comparing the ease of intubation score in ML with the Airtraq. The better visualisation was probably attributable to the application of refraction and optics. An earlier study found that the McCoy blade and Truview VLS both improved the score significantly as compared to the Miller blade.^[1] Ahmed et al.^[11] and Raza et al.^[12] found no statistical significance when intergroup comparisons of videolaryngoscopes were made.

Time for successful intubation was least with Airtraq and significant also when compared with both TL and ML. The time required to intubate with the Airtraq was less, probably because the device performs laryngoscopy and intubation simultaneously. In addition, minimal hand–eye coordination (with simultaneous viewing of the glottis and passing of the preloaded tube) shortens the time to intubate. Although Truview is a VLS, it required more time as compared with McCoy (P < 0.05). The reason might be the heavy assembly, need for more hand–eye coordination and need for more technical expertise.

The exaggerated anatomical curvature of the blade of AL does not require alignment of oral, pharyngeal and laryngeal axes, thus requiring less lifting force during laryngoscopy and less haemodynamic response during intubation.^[5],[13] The McCoy blade uses a levering action and flexes the tip like a hinge to elevate the epiglottis, thus reducing the force and stress response to intubation. Our results were similar to those in a study by Moningi et al.^[14] IDS score is a blend of subjective and objective criteria that permits a qualitative and quantitative approach to the progressive nature of the difficulty of intubation. The present study found that both Airtraq (P < 0.005) and Truview (P < 0.02) improved the IDS score statistically significantly when compared to the McCoy group. The mean IDS score was 0.1 ± 0.3 and 0.21 ± 0.40 in Airtraq and Truview groups, respectively, which was highly statistically significant (P < 0.001) when compared to McCoy group (mean IDS score of 1.1 ± 1.32). Our study results were comparable to those of various other studies.^{[5],[8],[9],[10],[15]}

Limitations

The study design did not permit blinding to the device being used and hence, there was always a potential for operator bias. Subjective variations in grading of laryngoscopic views such as Cormack–Lehane grade and POGO score may have occurred as intubation was not done by the same observer in all patients. We considered Cormack–Lehane grade as one of the important parameters for comparison between the groups, but the appropriateness of this yardstick for indirect laryngoscopy is not proven. Patients with anticipated difficult intubations were not included in the study. Therefore, the applicability or advantage of these devices in difficult airway scenarios has not been assessed. As this study was not a crossover trial, improvement or otherwise of Cormack–Lehane grade with the newer optical laryngoscopes could not be evaluated. The study, however, proves that the AL and TL provide better laryngoscopic view in comparison to ML, albeit on different patients. As the intubations were done by experienced anaesthesiologists, similar results may not be reproducible in the hands of novices.

Conclusion

Videolaryngoscopes that use the principle of optics or refraction improve intubating conditions by providing better visualisation of the glottis. Haemodynamic variations are also minimised due to reduction in lifting force (due to axes alignment) when compared to conventional laryngoscopes. Airtraq proves to be beneficial being one such device with a channel for tracheal tube guidance. Experience with such devices in patients with essentially normal airways will help prepare anaesthesiologists to tackle difficult airway situations when they arise in critically ill patients both in the operation theatre and intensive care unit. Although expensive, the cost of these devices should not hamper patient safety.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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