ABSTRACT
Background:
A difficult airway is anticipated with cervical spine injuries (CSIs) as immobilization techniques such as manual in-line stabilization (MILS) are used, which distort the oro-pharyngeal-laryngeal axis. Video laryngoscopes (VLs) make difficult airway management easy, as they do not require axis alignment. The present study aimed to compare the total time taken by Macintosh laryngoscope (ML), conventional blade, and D-blade™ of C-MAC® VL in simulated CSI scenarios using MILS.
Methods:
Ninety patients were randomly allocated into three groups: Group M (ML), Group C (conventional blade of C-MAC®), and Group D (D-blade™ of C-MAC®) with MILS applied before intubation. Primary outcome was the total time taken for successful intubation, while secondary outcomes were to assess Cormack–Lehane (CL) grade, number of attempts, hemodynamic response, and associated complications.
Results:
Total time for intubation in Group C was 23.40 ± 7.06 sec compared to 35.27 ± 6.53 and 47.27 ± 2.53 sec in groups D and M, respectively (P < 0.001). CL-grade I was observed in 15/30 (50%) in Group M, 25/30 (83.3%) in Group C, and 29/30 (96.7%) in Group D. Group M reported 7/30 (23.3%) failed intubations, while none were observed in other groups. Hemodynamic parameters were significantly higher at 3 and 5 min in Group M. Postoperative sore throat was recorded in 12/30 (40%) in Group M compared to 3/30 (10%) in groups C and D each (P value 0.037).
Conclusion:
C-MAC® VL requires less time for intubation, provides better glottic view, and has higher success, with better attenuation of hemodynamic response and fewer complications compared to ML.
KEY WORDS: Airway management, cervical vertebrae, intubation, laryngoscopes
Introduction
Intubation in cervical spine injuries (CSIs) mandates immobilization of the unstable vertebral column to prevent further neurologic deficits,[1,2,3] for which various immobilization methods, such as manual in-line stabilization (MILS), cervical collars, tape and foam blocks, long backboards, and straps, can be used.[1] All the immobilization techniques affect the glottic view by distorting the oro-pharyngeal-laryngeal (OPL) axis and impairing the Cormack–Lehane (CL) grading, thus rendering intubation difficult.[2]
MILS is a frequently used maneuver, which is performed by firmly grasping the mastoid processes of the patient, thus preventing movement of the head and neck.[2]
Macintosh laryngoscope (ML) is the gold standard for endotracheal intubation with its advantages of direct glottic visualization, cost-effectiveness, equipment availability, and a steep learning curve, but it requires alignment of the OPL axis for good glottic exposure, which is difficult in patients with CSI.[1,2,3,4]
Video laryngoscopes (VLs) have gained importance in managing difficult airways by allowing better visualization of anatomic structures without requiring alignment of the OPL axis.[4,5] The C-MAC® VL has different types of blades, that is, conventional blade and D-blade™. D-blade™ is half-moon shaped with built-in angulations of 40°, increasing the potential to handle difficult airways and providing a better view of the laryngeal structures in an anteriorly placed larynx.[6]
Very few studies have been conducted with D-blade™ along with MILS. Therefore, the present study was conducted to evaluate the efficacy of intubation with ML, conventional blade and D-blade™ of C-MAC® VL with MILS application. The primary objective of the study was to compare the total time taken for successful intubation with each laryngoscope, while the secondary objectives were to compare the CL grade, number of attempts, hemodynamic response, and complications, if any.
Materials and Methods
This prospective randomized study was conducted in our institute after obtaining approval from the institutional ethics committee (ESIPGIMSR-IEC/2019004), and participants were enrolled after clinical trial registration (CTRI/2020/07/026587). The study followed the good clinical practice guidelines and the principles of the Declaration of Helsinki (2013) and adhered to consolidated standards of reporting trials guidelines.
Ninety adult patients of either sex aged between 18 and 60 years, belonging to American Society of Anesthesiologists physical status (ASA-PS) I–II, undergoing elective procedures under general anesthesia, were included after obtaining their informed consent for recruitment in the study with a special patient information sheet. Patients with anticipated difficult airway, body mass index >35 kg m-2, any pathology of the mastoid, presence of neck trauma, or neck mass were excluded from the study.
Preoperative detailed history was taken and general physical examination was done, and patients were randomly allocated to one of the three groups: in Group M (n = 30), intubation was done with an ML; in Group C (n = 30), it was done with the conventional blade of C-MAC® VL; and in Group D (n = 30), it was done with D-blade™ of C-MAC® VL. Screening, randomization, concealment, and patient allocation were done using sequentially numbered, sealed, opaque slips by a fellow anesthesiologist unaware of the study.
In the operation theater, standard monitors, including electrocardiography, noninvasive blood pressure, and pulse oximeter, were attached. Patients of all three groups were preoxygenated with 100% oxygen, and induction was done with inj. fentanyl (1–2 μg kg-1), inj. propofol (2–2.5 mg kg-1), followed by inj. vecuronium bromide (0.1 mg kg-1) for neuromuscular blockade. Before laryngoscopy, MILS was applied in all the groups by firmly grasping the mastoid process and the sides of the neck by an anesthesiologist, standing opposite to the anesthesiologist performing intubation.
In all the groups, intubation was performed by an anesthesiologist who had more than 3 years of experience with VL intubations, and CL grading was noted. Intubation was achieved with appropriate-size polyviny chloride (PVC) Mallinckrodt™ endotracheal tube loaded with preangulated stylet and confirmed with waveform capnography. All the patients were mechanically ventilated, and anesthesia was maintained with sevoflurane 1%–2% and incremental doses of vecuronium 0.1 mg kg-1.
Intubation time was measured in seconds from insertion of the laryngoscope to confirmation of endotracheal tube placement by waveform capnography.
In patients requiring more than one attempt, total intubation time was calculated as time from insertion of the laryngoscope for the first attempt until confirmation by waveform capnograph.
Hemodynamic parameters, including heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and saturation of peripheral oxygen (SpO2), were recorded as baseline before intubation and then at 1, 3, 5, and 10 min after intubation. An intubation attempt was considered unsuccessful if the laryngoscope blade was withdrawn from the mouth without completion of intubation. In between attempts, adequate oxygenation was ensured with bag and mask ventilation maintaining SpO2 > 90%. After two attempts or more than 120 sec, it was considered failed intubation, MILS was removed, and intubation was performed with the conventional method as per the protocol. At the end of surgery, neuromuscular blockade was reversed with inj. neostigmine (0.05 mg kg-1) and inj. glycopyrrolate (0.01 mg kg-1), followed by extubation. Complications like trauma to teeth, tongue, and lips during the procedure, sore throat, and dysphagia in the postoperative period till 24 h were noted and managed accordingly. The primary outcome was to measure the total time taken for successful intubation, while secondary objectives were to compare the CL grade, number of attempts, hemodynamic response, and complications, if any.
Chugh et al.[4] observed that the success rate in the first attempt in the C-MAC® group was 96.67%. Taking this value as a reference and assuming a difference of 25% in success rate between the C-MAC® group and the groups with ML or conventional blade, the minimum required sample size with 80% power of the study and 5% level of significance was 30 patients in each group. Categorical variables were presented as number and percentage (%), and continuous variables as mean ± standard deviation and median. Quantitative variables were compared using an unpaired t-test/Mann–Whitney test. Qualitative variables were compared using Chi-square test/Fisher’s exact test. A P value of <0.05 was considered statistically significant.
Results
A total of 90 patients were randomized into three groups and received the allocated intervention [Figure 1].
Figure 1.
Consolidated standards of reporting trials (CONSORT) flowchart
The baseline demographic profile and Mallampati class were comparable in all groups [Table 1].
Table 1.
Baseline demographic profile and modified Mallampati grade of each group
| Parameters | Mean±SD | P | ||
|---|---|---|---|---|
|
| ||||
| Group M | Group C | Group D | ||
| Age | 36.27±8.54 | 33.8±7.72 | 33.8±8.62 | 0.417 |
| Weight (kg) | 58.93±8.87 | 58.87±9.24 | 59.33±9.51 | 0.978 |
| Height (m) | 1.65±0.08 | 1.62±0.10 | 1.64±0.10 | 0.430 |
| BMI (kg m-2) | 21.61±1.74 | 22.37±1.4 | 21.82±1.63 | 0.171 |
| MPG I, n (%) | 18 (60.0%) | 17 (56.7%) | 18 (60.0%) | 0.955 |
| MPG II, n (%) | 12 (40.0%) | 13 (43.3%) | 12 (40.0%) | |
Data are presented as mean±SD or n (%). BMI=Body mass index, MPG=Modified Mallampati grade, SD=Standard deviation
CL grade I was observed in 29/30 (96.7%) patients of group D, 25/30 (83.3%) of group C, and 15/30 (50%) of group M [Table 2].
Table 2.
Comparison of Cormack–Lehane grade
| Cormack–Lehane grade | Group M n (%) | Group C n (%) | Group D n (%) | P | Group M versus Group C | Group M versus Group D | Group C versus Group D |
|---|---|---|---|---|---|---|---|
| I | 15 (50%) | 25 (83.3%) | 29 (96.7%) | 0.023 | 0.001 | 0.009 | 0.040 |
| II (a) | 8 (26.7%) | 3 (10.0%) | 1 (3.3%) | ||||
| II (b) | 7 (23.3%) | 2 (6.7%) | 0 (0.0%) | ||||
| Total | 30 (100%) | 30 (100%) | 30 (100%) |
Data presented as mean±SD or frequency/n (%). SD=Standard deviation
Total time taken for endotracheal intubation was significantly less in group C compared to groups D and M (P < 0.001 each) [Table 3].
Table 3.
Comparison of number of attempts and total time taken (sec) for intubation
| Parameter | GroupM n (%) | Group C n (%) | Group D n (%) | P | Group M versus Group C | Group M versus Group D | Group C versus GroupD |
|---|---|---|---|---|---|---|---|
| Number of attempts | |||||||
| 1 | 8 (26.7%) | 26 (86.7%) | 23 (76.67%) | <0.001 | <0.001 | 0.001 | 0.506 |
| 2 | 15 (50.0%) | 4 (13.3%) | 7 (23.3%) | ||||
| >2 | 7 (23.3%) | 0 (0.0%) | 0 (0.0%) | ||||
| Total time Taken (sec)/mean±SD | 47.27±2.53 | 23.40±7.06 | 35.27±6.53 | <0.001 | <0.001 | <0.001 | <0.001 |
Data presented as mean±SD or n (%). Failure: inability to intubate in more than two attempts or more than 120 sec; total intubation time: time from insertion of the laryngoscope for the first attempt until confirmation by waveform capnograph. SD=Standard deviation
In groups C and D, intubation was successful in 100% of patients compared to 76.7% in group M [Table 3], with a statistically significant P-value (P <0.001) among the three groups; however, it was not significant between groups C and D (P = 0.506) [Table 3].
None of the patients had failed intubation with conventional blade and D-blade™ of C-MAC®, whereas 23.3% of patients with direct ML had failed intubation [Table 3]. All hemodynamic parameters were significantly higher at 3 and 5 min with group M compared to groups C and D [Figure 2]. Postoperative sore throat was seen in 12/30 (40%) patients of group M, which was significant compared to groups C and D, that is, 3/30 (10%) each (P value 0.037).
Figure 2.
Comparison of hemodynamic changes in Group M (Macintosh laryngoscope), Group C (conventional blade C-MAC®), and Group D (D-blade™ of C-MAC®): 1. HR: heart rate, 2. SBP: systolic blood pressure, 3. DBP: diastolic blood pressure, 4. MAP: mean arterial pressure
Discussion
In patients undergoing tracheal intubation with simulated CSI, conventional blade C-MAC® VL needs significantly less total time for intubation compared to D-blade™ and ML. C-MAC® VL requires less number of overall attempts and has better success compared to ML. In this study, we observed significantly better CL grading with VL compared to ML. This finding is supported by various studies where VL provided better CL grading.[5,6] Among both blades of C-MAC®, the laryngoscopic view appeared significantly better with D-blade™, which can be due to the high angulation of the blade (40°). However, this necessitates the use of a curved stylet.[6,7,8,9] Therefore, we used an endotracheal tube loaded with stylet in all three groups to remove the confounding factor.
In this study, the total time for successful intubation in Group C was significantly less compared to groups M and D. However, Group M required the maximum time for intubation in all the three groups. In accordance with our study, Kılıçaslan A et al.[5] and McElwain et al.[10] found that the time taken to intubate was shorter with C-MAC® compared to ML. Even though D-blade™ provided better glottic view, time taken for successful intubation was least with the conventional blade of C-MAC®. This can be explained by the high angulation of D-blade™, which can cause difficulty in passage of blade through the mouth or tube through the vocal cords. Similar observations were made by Kılıçaslan et al.[5] and Shravanalakshmi et al.[11] In contrast to our study, Jain et al.[7] found that the intubation time using either blade of C-MAC® was prolonged compared to ML on mannequins with simulated CSI. The reason for this could be unfamiliarity of resident doctors participating in their study to C-MAC® VL.
In the present study, it was found that 26 (86.7%) patients had successful first-attempt intubation with conventional blades of C-MAC® compared to eight (26.7%) and 23 (76.67%) patients with ML and D-blade™, respectively. In Group M, seven (23.3%) patients could not be intubated in two attempts. Therefore, as per the established methodology, MILS was removed and conventional method of intubation was used for securing the airway as per the protocol. Similar to our findings, Aziz et al.[9] concluded that with C-MAC® VL, successful first-attempt intubation was more compared to ML, when it was done by a skilled anesthesiologist (P = 0.026).
The present study showed that intubation was successful in all patients with conventional blade and D-blade™, whereas 23.3% patients had failed intubation with ML. In coherence with the study, Kılıçaslan et al.[5] found that intubation with either blade of C-MAC® was 100% successful compared to ML in cervical spine rigidity patients. In contrast to our observations, Osman et al.[12] observed that in cases of limited cervical mobility, the use of C-MAC D-blade is a better choice with a faster intubation time compared to C-MAC video-stylet.
With ML, the increase in hemodynamic parameters, including HR, SBP, DBP, and MAP, was statistically significant at 3 and 5 min postintubation compared to conventional blade and D-blade™, which could be explained by more attempts and significantly more time for intubation with direct ML. However, at 10 min, all parameters were comparable among all the groups. Buhari and Selvaraj[13] and Aggarwal et al.[14] found that C-MAC® had a greater hemodynamic response than ML in normal patients, which was not in coherence with our result as they included normal airways and took more time for intubation with C-MAC® VL.
Our study had some limitations. We did not include difficult airway patients; in addition, blinding was not possible to the device used, and all intubations were performed by experienced anesthesiologists. Hence, our results might not apply to less-experienced users.
However, the strength of our study is that most of the simulated studies have been conducted in mannequins, and limited literature exists in humans with MILS application.[3]
In conclusion, with MILS application, conventional blade of C-MAC® VL requires less total time for successful intubation compared to C-MAC D™ blade and ML. However, use of either blade of C-MAC® VL with MILS requires less time for intubation, provides better glottic view, and has higher success, with better attenuation of hemodynamic response and fewer complications compared to ML.
Key message
Immobilization of cervical spine distorts the oro-pharyngeal-laryngeal (OPL) axis and increases Cormack-Lehane (CL) grading.
Video laryngoscope (VL) has come as a rescue as it does not require alignment of the OPL axis.
With manual in-line stabilization, the total time taken for successful intubation was best with conventional blade of the C-MAC® VL. However, CL grading was best with D-blade™ VL.
Therefore, VL has better utilization in difficult airway due to spine immobilization.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
- 1.Heath KJ. The effect on laryngoscopy of different cervical spine immobilization techniques. Anaesthesia. 1994;49:843–5. doi: 10.1111/j.1365-2044.1994.tb04254.x. [DOI] [PubMed] [Google Scholar]
- 2.Thiboutot F, Nicole PC, Trépanier CA, Turgeon AF, Lessard MR. Effect of manual in-line stabilization of the cervical spine in adults on the rate of difficult orotracheal intubation by direct laryngoscopy: A randomized controlled trial. Can J Anaesth. 2009;56:412–8. doi: 10.1007/s12630-009-9089-7. [DOI] [PubMed] [Google Scholar]
- 3.Singleton BN, Morris FK, Yet B, Buggy DJ, Perkins ZB. Effectiveness of intubation devices in patients with cervical spine immobilisation: A systematic review and network meta-analysis. Br J Anaesth. 2021;126:1055–66. doi: 10.1016/j.bja.2020.12.041. [DOI] [PubMed] [Google Scholar]
- 4.Chugh V, Sehgal NP, Prakash A, Boro S. Comparison of the CMAC, Airtraq and McCoy laryngoscopes in patients undergoing tracheal intubation with cervical spine immobilisation-A prospective observational study. IOSR J Dent Med Sci. 2008;17:26–33. [Google Scholar]
- 5.Kılıçaslan A, Topal A, Erol A, Uzun ST. Comparison of the C-MAC D-Blade, conventional C-MAC, and Macintosh laryngoscopes in simulated easy and difficult airways. Turk J Anaesthesiol Reanim. 2014;42:182–9. doi: 10.5152/TJAR.2014.59672. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Suderman VS, Crosby ET, Lui A. Elective oral tracheal intubation in cervical spine-injured adults. Can J Anaesth. 1991;38:785–9. doi: 10.1007/BF03008461. [DOI] [PubMed] [Google Scholar]
- 7.Jain D, Dhankar M, Wig J, Jain A. Comparison of the conventional CMAC and the D-blade CMAC with the direct laryngoscopes in simulated cervical spine injury--A manikin study. Braz J Anesthesiol. 2014;64:269–74. doi: 10.1016/j.bjane.2013.06.005. [DOI] [PubMed] [Google Scholar]
- 8.Gupta N, Rath GP, Prabhakar H. Clinical evaluation of C-MAC videolaryngoscope with or without use of stylet for endotracheal intubation in patients with cervical spine immobilization. J Anesth. 2013;27:663–70. doi: 10.1007/s00540-013-1588-6. [DOI] [PubMed] [Google Scholar]
- 9.Aziz MF, Dillman D, Fu R, Brambrink AM. Comparative effectiveness of the C-MAC video laryngoscope versus direct laryngoscopy in the setting of the predicted difficult airway. Anesthesiology. 2012;116:629–36. doi: 10.1097/ALN.0b013e318246ea34. [DOI] [PubMed] [Google Scholar]
- 10.McElwain J, Malik MA, Harte BH, Flynn NM, Laffey JG. Comparison of the C-MAC videolaryngoscope with the Macintosh, Glidescope, and Airtraq laryngoscopes in easy and difficult laryngoscopy scenarios in manikins. Anaesthesia. 2010;65:483–9. doi: 10.1111/j.1365-2044.2010.06307.x. [DOI] [PubMed] [Google Scholar]
- 11.Shravanalakshmi D, Bidkar PU, Narmadalakshmi K, Lata S, Mishra SK, Adinarayanan S. Comparison of intubation success and glottic visualization using King Vision and C-MAC videolaryngoscopes in patients with cervical spine injuries with cervical immobilization: A randomized clinical trial. Surg Neurol Int. 2017;8:19. doi: 10.4103/2152-7806.199560. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Osman YM, Abd El-Raof Abd El-Aziz R. Effectiveness of C-MAC video-stylet versus C-MAC D-blade video-laryngoscope for tracheal intubation in patients with predicted difficult airway: Randomized comparative study. Egypt J Anaesth. 2023;39:233–40. [Google Scholar]
- 13.Buhari FS, Selvaraj V. Randomized controlled study comparing the hemodynamic response to laryngoscopy and endotracheal intubation with McCoy, Macintosh, and C-MAC laryngoscopes in adult patients. J Anaesthesiol Clin Pharmacol. 2016;32:505–9. doi: 10.4103/0970-9185.194766. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Aggarwal H, Kaur S, Baghla N, Kaur S. Hemodynamic response to orotracheal intubation: Comparison between Macintosh, McCoy, and C-MAC video laryngoscope. Anesth Essays Res. 2019;13:308–12. doi: 10.4103/aer.AER_7_19. [DOI] [PMC free article] [PubMed] [Google Scholar]