Comparative Evaluation of C-MAC Videolaryngoscope with Macintosh Direct Laryngoscope in Patients with Normal Airway Predictors

Abstract

Background: 

Video laryngoscopes (VL) assist in securing the airway faster and more accurately in difficult airways. However, data regarding its usefulness in patients with normal airways are sparse.

Aim: 

We designed this study to compare the ease and success of endotracheal intubation between C-MAC and Macintosh direct laryngoscope (DL) in adult patients with no anticipated airway difficulty.

Settings and Design: 

The design involves prospective randomized case − control study.

Subjects and Methods: 

One hundred and twenty adult patients with predicted normal airway were randomized into two groups and were intubated using VL (C-MAC VL) and DL (Macintosh DL), respectively. The Cormack-Lehane (CL) grade, time taken for intubation, attempts taken (number), and need for laryngeal maneuvers or stylets were recorded and analyzed for statistical significance.

Results: 

Thirty-eight patients in the DL group and 48 patients in the VL group had CL I view, 20 patients in the DL group and 16 patients in the VL group had CL II, and two patients in the DL group had CL III view. None of the patients in Group VL had CL III view. In seven out of 60 cases in the DL group, difficulty was experienced during insertion of the laryngoscope blade as compared to two cases out of 60 in the VL group. The mean time taken for intubation was lesser in Group DL (28.48 s) as compared to 39.3 s in Group VL. Nine patients in Group DL and 16 patients in Group VL required external laryngeal manipulation. Stylets were used, in seven patients in group DL and in 11 patients in group VL.

Conclusions: 

In patients with a predicted normal airway, C-MAC provides a better glottic view compared to Macintosh DL. Time taken for intubation using the C-MAC video laryngoscope was more. However, success rates on the first attempt at endotracheal intubation and the number of intubation attempts with either laryngoscope were similar.

INTRODUCTION

Most unanticipated airway complications arise in emergency settings. The incidence of airway-related complications increases with an increase in the number of attempts at laryngoscopy.[¹] Failed airway management in these cases can lead to serious complications such as hypoxemia, aspiration, neurological damage, cardiovascular complications, and even death.[²]

Standard parameters used for airway assessment are not always accurate in predicting difficulty in laryngoscopy or endotracheal intubation. Despite many tests having been developed for predicting difficult intubation (DI), it has been hypothesized that there might be anatomical factors that are difficult to comprehend, which make intubation difficult in certain patients.[³]

Although poor glottic visualization is encountered in 1%–9% of attempts, success can generally be achieved with additional force, manipulation of the larynx externally, or with the help of gum-elastic bougies and stylets.[⁴⁵] However, poor glottic exposure is more likely to require prolonged or multiple intubation attempts and, subsequently, may be associated with complications such as hypoxia and trauma to the dentition and airway. With the introduction of video laryngoscopy in 2002,[⁶] clinicians can use a video camera along the laryngoscope blade that transmits images to an external monitor, allowing the clinician to intubate while visualizing the airway anatomy in real time on the screen instead of looking directly into the mouth of a patient. The importance of video laryngoscope (VL) in unanticipated difficult airway has been reflected in the All India Difficult Airway Association 2016 (AIDAA 2016)[⁷] and Difficult Airway Society 2015 guidelines.[⁸] AIDAA 2016 guidelines for the management of the unanticipated difficult tracheal intubation in adults recommends the use of either conventional laryngoscopy or video laryngoscopy for endotracheal intubation as per the experience and comfort level of the person managing the airway. AIDAA states that video laryngoscopy offers a superior glottic view as compared to conventional direct laryngoscopy and recommends that all anesthesiologists must have training in the use of and access to VLs.[⁷] It is important to evaluate these new devices with the goal of improving airway management. Studies of different types of VLs including C-MAC have been done in patients requiring laryngoscopy and endotracheal intubation in the emergency department, intensive care unit (ICU), in failed intubation with direct laryngoscopy, in predicted difficult airway, and in lateral position by various researchers globally, but we could not find many studies in the Indian population, comparing C-MAC video laryngoscope and the conventional direct Macintosh laryngoscope for endotracheal intubation in adult patients undergoing elective surgery.

We designed this study to compare the ease and success of laryngoscopy and endotracheal intubation in adult patients with no anticipated airway difficulty, undergoing elective surgery, to determine if CL grade on laryngoscopy, and success rates of the first attempt at laryngoscopy were better using C-MAC video laryngoscope compared with the Macintosh laryngoscope.

SUBJECTS AND METHODS

Ethical clearance was obtained from the institutional review board with the number IEC/VMMC/SJH/Thesis/October/2015 (approved on October 29, 2015). After obtaining the written informed consent from patients, 120 patients of American Society of Anesthesiologists (ASA) PS class I and II, planned for elective surgery, with anticipated normal airway, between the ages of 18 and 60 years were enrolled in the study. The study was conducted for 18 months from the time of ethical clearance. Patients with any one or more of: Mallampatti Grade II, thyromental distance (TMD) ≤6.5 cm, sternomental distance (SMD) ≤12.5 cm, range of head-and-neck movement ≤90°, or abnormal dentition were excluded from the study. All the procedures were done as per the guidelines laid down in the Declaration of Helsinki (2013). The sample size was calculated as 60 in each group with 80% power and 5% level of significance based on the observation that the relative success of intubation in the emergency setting using the C-MAC and the Macintosh laryngoscopes were 97.3% and 84.4%, respectively.[⁹]

Patients were randomly allocated to one of the following groups;

• Group DL: Endotracheal intubation using Macintosh direct laryngoscope (DL)
• Group VL: Endotracheal intubation with C-MAC video laryngoscope.

Randomization was based on the computer-generated random number chart maintained in opaque-sealed envelopes. A detailed history was obtained from all the study participants. Complete physical examination, airway evaluation, and routine investigations were performed for all patients. They were fasted after the administration of tablet alprazolam 0.25 mg and tablet ranitidine 150 mg at 10 pm the night before the surgery.

The following airway characteristics and distances were assessed and recorded preoperatively by the investigator to reduce interobserver variability. Patients having buck teeth, loose teeth, and those who were edentulous were not taken up for the study. Patients having macrognathia, micrognathia, retrognathia, or prognathia were not included in the study. Modified Mallampatti class of the oropharyngeal view as described by Samsoon and Young was assessed in all the patients.[¹⁰] TMD was measured as the straight distance from the thyroid notch to the inner bony mentum, with the head in full extension and the mouth closed.[¹¹] SMD was measured as the straight distance from the upper border of the manubrium sterni to the inner bony mentum, with the head in full extension and the mouth closed. Inter-incisor distance (IID) was measured as the distance between the upper and lower incisors.

The range of head-and-neck movements was assessed using Dellikan's test.[¹²] The patient was asked to look straight with the head in the neutral position. The index finger of the left hand of the researcher was placed under the tip of the jaw, whereas the index finger of the right hand was placed on the patient's occipital tuberosity. The patient was then asked to look at the ceiling without raising the eyebrows. The extension was considered normal if the left index finger was at a higher level compared to the right.

On arrival at the operation theater, routine monitoring with electrocardiography, pulse oximetry, and noninvasive blood pressure monitoring were started and baseline parameters were recorded. Intravenous (i.v.) access was established using an 18G i.v. cannula. Injection ranitidine 50 mg and injection metoclopramide 10 mg were added to an isotonic i.v. fluid, either Ringer lactate or normal saline. The patient was preoxygenated for 3 min with an appropriate-sized face mask, using Bain's circuit. Anesthesia was induced with an injection of fentanyl 2 μg.kg⁻¹ i.v. and injection propofol 2 mg.kg⁻¹, i.v., till there was the loss of verbal response or eyelash reflex. After checking the adequacy of mask ventilation, a nondepolarizing neuromuscular blocker (vecuronium bromide 0.1 mg.kg⁻¹) was administered. Hemodynamic parameters, oxygen saturation (SpO₂), and end-tidal CO₂ were monitored. The patient was ventilated with oxygen (40%), nitrous oxide (60%), and isoflurane (0.6%–0.8%) for at least 4 min before laryngoscopy and intubation, ensuring an SpO₂ of 95% throughout the procedure. The patient's head was placed in the sniffing position with the help of a small pillow placed below the occiput. The blade sizes of both the laryngoscopes (Macintosh or C-MAC) as well as the size of the endotracheal tube were chosen in accordance with the department protocol and were finally based on the clinical assessment. It was not affected by this study protocol.

Laryngoscopy was performed using either the DL with Macintosh size 3 or 4 blades or the C-MAC video laryngoscope size 3 or 4 in accordance with the group that the patient was allotted to by the computer-generated randomization number.

The laryngoscopic view was graded by Cormack − Lehane grading scale as under:

Grade 1: complete visualization of the vocal cords

Grade 2: visualization of the posterior portion of the glottis

Grade 3: visualization of only the epiglottis

Grade 4: not able to visualize any portion of the glottis or the epiglottis[¹³]

We confirmed intubation with the help of end-tidal CO₂ tracing and chest auscultation.[⁷]

After confirming tracheal intubation, the following parameters were recorded:

1. Ease of laryngoscopy as assessed by:
1. Ease of insertion of laryngoscope graded as either easy or difficult
2. CL grade.
2. Ease and success of oral endotracheal intubation were assessed by:
1. Time taken for intubation[¹⁴]
2. Attempts taken (number)
3. Need for laryngeal maneuvers or stylets.
3. Airway complications in the form of mucosal trauma, dental injury, or esophageal intubation.

If more than one intubation attempt was required, time from insertion of the laryngoscope for the first intubation attempt until confirmation of successful intubation by capnography was considered to be the total intubation time.[¹⁴] Thereafter, anesthesia management was according to the standard requirements of the case.

RESULTS

A total of 120 patients between the age group of 18 and 60 years of either sex and ASA class I and II having airway parameters that did not predict a difficult laryngoscopy or endotracheal intubation were included in the study and randomized into two groups: Group DL (endotracheal intubation using Macintosh DL) and Group VL (endotracheal intubation using C-MAC VL). The demographic profiles of the patients in both groups were comparable with respect to age, gender, and body mass index (BMI). The distribution of patients in the groups was similar according to the ASA PS classifications as well as the parameters predicting DI [Tables 1 and 2].

Table 1: Demographic parameters

Table 2: Comparison of predictors of difficult intubation

In seven out of 60 cases in the DL group, difficulty was experienced during the insertion of the laryngoscope blade as compared to two cases out of 60 in the VL group. This difference was statistically insignificant (P = 0.163). Cormack–Lehane grade in both the groups was comparable (P = 0.237). Thirty-eight patients in the DL group and 48 patients in the VL group had CL I view, 20 patients in the DL group and12 patients in the VL group had CL II, and two patients in the DL group had CL III view. None of the patients in Group VL had CL III view. Although this difference in CL grading between the two groups was statistically insignificant, clinically, the laryngoscopic view was better with the C-MAC videolaryngoscope.

The mean time taken for intubation was lesser in Group DL, i.e., 28.48 s as compared to 39.3 s in Group VL. The difference was statistically significant (P < 0.0001). Fifty-six patients in Group DL and 55 patients in Group VL were intubated in the first attempt, whereas four patients in Group DL and five patients in Group VL required two attempts for intubation. Nine patients in Group DL and 16 patients in Group VL required external laryngeal manipulation for obtaining an adequate glottic view for intubation. Although this was statistically insignificant (P = 0.116), it appeared to be clinically significant [Table 3]. Stylet was required for endotracheal intubation in seven patients in Group DL and in 11 patients in Group VL. This difference was not significant statistically (P = 0.306); however, it was significant clinically. None of the patients had untoward incidents or complications such as dental injury, mucosal injury, desaturation, or esophageal intubation.

Table 3: Summary of results

DISCUSSION

DI cannot always be predicted even in patients with no clinical predictors of DI. The difficulty is occasionally encountered due to a combination of complex anatomical and physiological factors.[³]

Direct laryngoscopy and tracheal intubation involve three distinct challenges.[¹⁵]

1. Difficulty in visualizing the glottic opening (target)
2. Delivering the tube to the glottic opening
3. Advancing the tube into the trachea.

This study was undertaken to compare the ease and success of endotracheal intubation in patients with an anticipated normal airway planned for elective procedures. The demographic profile of study participants in both groups was comparable in terms of age, sex, height, BMI, and ASA PS Class. The commonly employed airway parameters such as modified Mallampatti grade, TMD, IID, and range of head-and-neck movements were comparable in both the groups. We did not find any statistically significant difference in the number of patients, in whom laryngoscopy was difficult in either group. The Cormack − Lehane grades between the two groups were also comparable statistically (P = 0.237), even though clinically the view was better with C-MAC. This is in agreement with other studies of similar nature.[⁹¹⁶¹⁷]

The number of intubation attempts and successful intubation at the first attempt were comparable in both the groups in our study. Other studies of a similar nature concur with our results.[⁹] However, according to studies in the ICU setting, inpatients with at least one predictor for DI, the proportion of successful intubation in the first attempt with was significantly higher when the C-MAC videolaryngoscope was used as opposed to the Macintosh blade of a DL (79% vs. 55%; P = 0.03) The Cormack − Lehane (CL) grading for glottis visualization after laryngoscopy was rated as difficult in 20% of the laryngoscopies with Macintosh DL as compared to the C-MAC VL, in which 7% of the laryngoscopies showed a CL grading of III and i.v.[¹⁸¹⁹]

In our study, the intubation time was, however, significantly longer in the VL group. Furthermore, the number of patients requiring external laryngeal manipulation was larger in the VL group. There is agreement in these respects with other authors;[¹⁶] these probably point toward the steeper learning curve associated with the use of the C-MAC.

The results of our study clearly point out that both the laryngoscopes provide more or less similar results with respect to all the parameters studied. Despite the statistical insignificance, the CL view was better with the C-MAC. However, the mean intubation time was longer with the C-MAC. This may be attributed to the relative inexperience in the use of the C-MAC laryngoscope as compared to that of the DL. We considered this as a major limitation for our study that it was a new airway device for the chief investigator and supervisor/faculty. Results may vary over time as more expertise is achieved with more frequent use. Furthermore, all patients were for elective surgeries done in an OT setup with ideal intubating conditions. The results may vary in an ICU or emergency setup. Videolaryngoscope is a valuable tool in the armamentarium of an anesthesiologist and we recommend that every anesthesiologist be familiar with its use, so that it may be readily used in situations where direct laryngoscopy may be difficult.

CONCLUSIONS

In patients with a predicted normal airway, C-MAC video laryngoscope provides a better glottic view on laryngoscopy (CL grading) as compared to Macintosh DL. The time taken for intubation using the C-MAC video laryngoscope was more. However, success rates on the first attempt at endotracheal intubation and the number of intubation attempts with either laryngoscope were similar. There may be an increased need for external laryngeal manipulations, use of intubating aids, and consequently longer intubation time while using the C-MAC video laryngoscope. The reason for this might be the need to align the endotracheal tube along the curvature of the C-MAC blade for successful intubation. Hence, efficient use of the C-MAC video laryngoscope has a learning curve.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.