Anesthesiology, Article

C-MAC compared with direct laryngoscopy for intubation in patients with cervical spine immobilization: A manikin trial

a b s t r a c t

Introduction: The aim of this study was to compare C-MAC videolaryngoscopy with direct laryngoscopy for intu- bation in simulated cervical spine immobilization conditions.

Methods: The study was designed as a prospective randomized crossover manikin trial. 70 paramedics with b 5 years of medical experience participated in the study. The paramedics attempted to intubate manikins in 3 airway scenarios: normal airway without Cervical immobilization (Scenario A); manual inline cervical immobi- lization (Scenario B); cervical immobilization using cervical extraction collar (Scenario C).

Results: Scenario A: Nearly all participants performed successful intubations with both MAC and C-MAC on the first attempt (95.7% MAC vs. 100% C-MAC), with similar intubation times (16.5 s MAC vs. 18 s C-MAC). Scenario B: The results with C-MAC were significantly better than those with MAC (p b 0.05) for the time of intubation (23 s MAC vs. 19 s C-MAC), success of the first intubation attempt (88.6% MAC vs. 100% C-MAC), Cormack-Lehane grade, POGO score, severity of Dental compression, device difficulty score, and preferred airway device. Scenario C: The results with C-MAC were significantly better than those with MAC (p b 0.05) for all the analysed variables: success of the first attempt (51.4% MAC vs. 100% C-MAC), overall success rate, intubation time (27 s MAC vs. 20.5 s C-MAC), Cormack-Lehane grade, POGO score, dental compression, device difficulty score and the preferred air- way device.

Conclusion: The C-MAC videolaryngoscope is an excellent alternative to the MAC laryngoscope for intubating manikins with cervical spine immobilization.

(C) 2017


advanced airway management is frequently indicated in order to maintain sufficient oxygenation and ventilation in Out-of-hospital emergency situations. Patients with obvious or even suspected injury of the cervical spinal cord require immediate cervical spine stabilization, which makes endotracheal intubation more difficult and sometimes even impossible [1,2,3]. Although controversially discussed, direct laryngoscopy is still frequently considered the first method of choice to perform endotracheal intubation, even in the difficult out-of-hospital setting in patients with cervical spine stabilization. Direct laryngoscopy

* Corresponding author at: Department of Outcomes Research, Anaesthesiology Institute, Cleveland Clinic, Cleveland, USA.

E-mail address: [email protected] (K. Ruetzler).

in these patients is associated with the potential of secondary neck or cervical spine injury, hypoxia, and other complications [4]. During direct laryngoscopy, it is also difficult to avoid movement of the airway, and pressure may be applied indirectly to the cervical spine [5].

In cervical spine injury and/or immobilization, several airway tech- niques can be used, including direct laryngoscopy, fiberoptic intubation, and videolaryngoscopes. The best device for managing the potential dif- ficult airway especially in the out-of-hospital setting with patients hav- ing cervical spine immobilization has not been determined. In the in- hospital setting, awake fiberoptic intubation is the safest method of se- curing the airway in these patients, but this technique might be espe- cially challenging in emergency situations [7].However, there are several advantages of fiberoptic intubation, but it requires personal skills and high level of experience [6].

0735-6757/(C) 2017

Endotracheal intubation with the use of a videolaryngoscope offers some advantages and is increasingly used in both, the in-hospital and out-of-hospital setting [8,9,10,11]. It has been demonstrated, that videolaryngoscopes offer much better airway and vocal cord visualiza- tion, but if better visualization leads to decreased number of overall in- tubation and especially failed intubation attempts remains currently unclear- at least if intubation is performed by skilled providers [12].

The C-MAC videolaryngoscope (Karl Storz, Tuttlingen, Germany) has been available for clinical use for several years. The C-MAC can also be used as a direct laryngoscope and is a useful device in the event of a failed direct laryngoscopy because the operator maintains the ability to switch to the video monitor without a second intubation attempt [13]. In addition, users scored the C-MAC higher than other videolaryngoscopes and Macintosh (MAC) laryngoscope [14].

The aim of this study was to investigate, if endotracheal intubation by paramedics using the C-MAC videolaryngoscope is faster, compared to direct laryngoscopy in manikins with an immobilized cervical spine.


Study population

The trial was performed in accordance with the Consolidated Stan- dards of Reporting Trials (CONSORT) statement. The study was de- signed as a prospective randomized crossover manikin trial and was approved by the Institutional Review Board of the Polish Society of Di- saster Medicine (approval No: 15.06.2016). After providing written in- formed consent, 70 paramedics with b 10 years of medical experience voluntarily participated in the study. All paramedics had limited experi- ence with direct laryngoscopy guided endotracheal intubation in the “real patient setting” (b 50 intubations) and no prior experience with any videolaryngoscope.

Simulation scenarios

Each participant performed intubations with a MegaCode Kelly(TM) advanced life support manikin (Laerdal Medical, Stavanger, Norway), placed on a trauma stretcher. The paramedics participated in 3 airway scenarios:

      • Scenario A: normal airway (without cervical immobilization);
      • Scenario B: manual inline cervical immobilization performed by an in- dependent instructor;
      • Scenario C: cervical immobilization using a standard Patriot cervical extraction collar (Ossur Americas, Foothill Ranch, CA, USA) applied to the manikin neck by an independent instructor.

The participants performed each endotracheal intubation scenario using two different intubation techniques: direct laryngoscopy using a standard Macintosh (MAC) with blade No. 3 (Mercury Medical, Clear- water, FL, USA), and a C-MAC videolaryngoscope with D-blade No. 3 (Karl Storz, Tuttlingen, Germany; Fig. 1). All intubations were per- formed with a 7.0 standard cuffed endotracheal tube. A semi-rigid stylet was inserted in the endotracheal tube before intubation was performed with either laryngoscope type. The airway of the manikin and the tube was wetted thoroughly with a conventional lubricant.

Study protocol

Prior to the study, all participants received a 30-minute training ses- sion covering the relevant aspects of airway management including anatomy and details about the airway management techniques using direct laryngoscopy and C-MAC videolaryngoscopes. Following the lec- ture, the paramedics observed a practical demonstration, during which intubations with both devices were performed by an independent re- searcher. The participants were then given 10 min to practice intubation with direct laryngoscopy and the C-MAC laryngoscopes in a manikin with a normal airway. However, to minimalize bias and to increase dif- ficulty, no assistance was available for the activity.

After the training session, each participant started their intubations

using MAC and C-MAC laryngoscopy in the 3 airway scenarios, in a ran- domized order. The order of interventions was randomized for each participant by a computer program (Research Randomizer, www. Each participant had a maximum of 3 intubation at- tempts using each technique for each scenario. After completing the in- tubation procedure, participants had a 30-minute break before performing intubation using the alternate intubation technique (direct laryngoscopy or videolaryngoscopy).


Three time periods were measured: the time from the first contact with the device until achievement of a successful view of the glottis (T1), until successful endotracheal tube insertion (T2), until the first successful lung ventilation (T3). The time parameters were recorded with a stopwatch on a mobile phone (Sony Ericsson, Munich, Germany).

Additionally, the success of the intubation attempts was measured. If the endotracheal tube was placed incorrectly or the intubation lasted longer than 60 s, the airway management attempt was considered a failure. In many studies, intubation failure is defined by time over

Fig. 1. Laryngoscopes used for the study: (1) a standard Macintosh #3 laryngoscope (gold standard); (2) Storz C-MAC with Macintosh #3 D-blade.

120 s [15], but we chose the cut-off of 60 s as a better indicator of good patient care [16].

After each intubation attempt, the participants were asked to rate the glottic view during the attempt according to the Cormack & Lehane grade [17]. Additionally, the percentage of Glottic opening (POGO) score was measured [31]. The severity of potential dental trauma was calcu- lated based on a previously described grading scale [16]. To assess the subjective difficulty of the procedure, the participants were asked to rate difficulty on a Visual analogue scale (VAS) with a score from 1 (ex- tremely easy) to 10 (extremely difficult). In closing, the participants were asked to indicate the method they would prefer in a real-life intubation.

Statistical analysis

All study data were entered into an electronic database (Microsoft Excel 2010; Microsoft Corp., Redmond, WA, USA) and evaluated with the use of the Statistica software, version 12.5 (StatSoft Inc., Tulsa, OK, USA). The authors described variables using percentages for qualitative variables, and medians with an in- terquartile range (IQR) for quantitative variables. The occurrence of normal distribution was confirmed by the Kolmogorov-Smirnov test. If the data were not normally distributed, non-parametric tests were used. All statistical tests were two-sided. In order to com- pare the times T1, T2, and T3, the Wilcoxon test for paired observa- tions was used. The McNemar test was applied to evaluate differences in the success of intubation, and the Stuart-Maxwell test was used to compare the degree of pressure distribution, the Cormack-Lehane grade, and the VAS score. We considered p b 0.05 as significant.


Participant characteristics

A total of 70 paramedics (26 female, 37%) participated in the study; 51 paramedics (17 female, 33%) worked on emergency medical service teams, and 19 (7 female, 36.8%) in hospital emergency units. The mean age of the participants was 31 +- 5 years, and mean time of work experience was 6 +- 3 years.

Scenario A: normal airway scenario

In this scenario, nearly all participants performed successful intuba- tions both with direct laryngoscopy and C-MAC videolaryngoscopy on the first attempt (96% MAC vs. 100% C-MAC), with similar intubation times (16 s direct laryngoscopy vs. 18 s C-MAC; Fig. 2). The Cormack- Lehane grade, POGO score, and dental compression score were signifi- cantly higher with the C-MAC videolaryngoscope than with direct lar- yngoscopy (p b 0.05). However, most participants preferred to use direct laryngoscopy compared with the C-MAC (p = 0.009) (Table 1).

Scenario B: manual inline cervical spine immobilization

The results with the C-MAC were significantly better than those with direct laryngoscopy (p b 0.05) for time of intubation (23 s direct laryn- goscopy vs. 19 s C-MAC; Fig. 2), success of the first intubation attempt (89% direct laryngoscopy vs. 100% C-MAC), Cormack-Lehane grade, POGO score, severity of dental compression, device difficulty score, and the preferred airway device (Table 2).

Scenario C: cervical spine immobilization with an extraction collar

In addition, the results with the C-MAC were significantly better than those with direct laryngoscopy (p b 0.05) for all analysed variables: success of the first attempt (51% direct laryngoscopy vs. 100% C-MAC), overall success rate, time to intubation (27 s direct laryngoscopy vs. 20s C-MAC; Fig. 2), Cormack-Lehane grade, POGO score, severity of den- tal compression, device difficulty score and the preferred airway device (Table 3).


The study findings demonstrate that emergency care providers per- formed endotracheal intubation much better using the C-MAC videolaryngoscope compared to direct laryngoscopy in manikins with immobilized cervical spine.

Securing the patent airway in trauma patients requires rapid rescue action to avoid hypoxia and aspiration of gastric contents. Although the first method of ventilation in trauma patients is often bag-valve ventila- tion, incorrectly performed procedures can lead to air-distention of the stomach and thereby increase the risk of aspirating gastric contents into

Fig. 2. Time to intubation using distinct laryngoscopes in 3 airway scenarios.

Table 1

Normal airway scenario (scenario A) data.

Table 3

Collar cervical spine immobilization scenario (scenario C) data.


Direct laryngoscopy





Direct laryngoscopy




Overall success rate, n (%)

70 (100%)

70 (100%)


Overall success rate, n (%)

63 (90%)

70 (100%)


duration of intubation (s)

16.5 (12-21)

18 (14-23)


Duration of intubation (s)

27 (20-34)



Duration of glottic view achievement

5 (3-8)

4.5 (3-7)




Endotracheal tube insertion time (s) 11 (7-15)

12.5 (9-16)


Duration of glottic view achievement


18 (6-12)

8 (4-9)


No. of intubation attempts

1 67 (96%)

100 (100%)


Endotracheal tube insertion time (s)

No. of intubation attempts

18 (11-21)

13 (8-14.5)




3 (4%)


36 (51%)

70 (100%)



31 (44%)

Cormack-Lehane grade

1 46




Cormack-Lehane grade

3 (4%)


2 24





3 –




4 –




POGO score 82 (71-92)

Dental compression






POGO score


33 (7-52)




None 21


Dental compression


Mild 47




Severe 2 (3%)

2 (3%)




Device difficulty score 3 (2-3.5)

2.5 (2-3.5)





Preferred airway device 42/70



Device difficulty score

6 (4.5-7.5)

4 (2.5-5)


NS – not stated, POGO – the percentage of glottic opening.

Preferred airway device




POGO – the percentage of glottic opening.

the respiratory tract [18]. Endotracheal intubation is considered the most Effective airway method to prevent pulmonary aspiration of gas- tric content [32]. Moreover, it allows the safe use of positive end-expira- tory pressure and the reliable measurement of end-expiratory carbon dioxide concentration. Finally, in cardiac arrest, it allows for asynchro- nous ventilation and Continuous chest compressions without interrup- tions in chest compressions to perform rescue breaths.

Direct laryngoscopy is the most frequently used method for intuba- tion in out-of-hospital emergencies in Poland. This is due to the avail- ability of Miller and Macintosh laryngoscopes to the Polish Emergency Medical Service teams. Although direct laryngoscopy is considered the gold standard for endotracheal intubation, unexpected difficult intuba- tions are still encountered and failure to secure the airway can dramat- ically increase morbidity and mortality [19]. Thus, direct laryngoscopy

Table 2

Manual inline cervical spine immobilization scenario (scenario B) data.


Direct laryngoscopy




Overall success rate, n (%)

70 (100%)

70 (100%)


Duration of intubation (s)

23 (18-28)

19 (14-25)


Duration of glottic view achievement

7.5 (3-9)

6 (3-8)



Endotracheal tube insertion time (s) No. of intubation attempts

12 (8-17)

9.5 (6-11)

NS 0.017


62 (89%)

70 (100%)


8 (11%)


Cormack-Lehane grade 0.007

1 7 40

2 55 29

3 8 1

4 – –

POGO score 57 (44-81) 83 b0.001


Dental compression 0.011


8 (11%)

21 (30%)


30 (43%)

38 (54%)

Severe 32 (46%) 11 (16%)

Device difficulty score 5 (4-7) 3.5 0.015


Preferred airway device 7/70 63/70 b0.001 NS – not stated, POGO – the percentage of glottic opening.

and endotracheal intubation of a patient with potential cervical Spinal injury is a high-risk procedure [10,20,21,22].

In normal airways, without cervical spine immobilization, the effec- tiveness of the first intubation attempt using direct laryngoscopy or C- MAC laryngoscopy was similar and amounted to 96% and 100%, respec- tively. The overall effectiveness of both types of laryngoscopes was 100%. In a study by Lee et al., the effectiveness of the first intubation at- tempt by anaesthesiologists using the C-MAC laryngoscope equalled 91%, while the average intubation time was 25 s [23]. Kaplan et al. inves- tigated 30 emergency medicine residents who attempted to intubate a manikin; the study showed that the C-MAC enabled better visualization of the glottic opening when compared with direct laryngoscopy. In that study, the trachea was successfully intubated with direct laryngoscopy by all participants (100%), as compared with 29 (97%) with the C- MAC. The authors observed a slightly shorter intubation time with di- rect laryngoscopy usage than with the C-MAC [24]. Similar results were observed in our study and also confirms prior findings by other au- thors [14,25,26].

Difficult airway caused by cervical spine immobilization leads to

lower effectiveness of intubation performed with direct laryngosco- py. In this study, the overall effectiveness of intubation using direct laryngoscopy was 100% in the case of manual inline cervical immo- bilization, and 90% when a cervical collar to stabilize the neck was used. When C-MAC was employed, the effectiveness of the first in- tubation attempt was 100% in both scenarios. It is possible that in- ability to use the “sniffing position” and limited opening of the mouth led to lower effectiveness of direct laryngoscopy in cervical spine immobilization scenarios. These elements affect the visualiza- tion of the larynx based on the Cormack-Lehane scale or POGO score, which was reflected in our study results. In a study by Akbar and Ooi, the C-MAC videolaryngoscope was superior to direct laryn- goscopy in patients requiring intubation with manual inline cervical stabilization [27]. In McElwain and Laffey’s research, C-MAC laryn- goscopy was the best method in surgical patients and led to lower intubation difficulty Scale scores, improved the Cormack and Lehane glottic view, and reduced need for optimization manoeuvers compared with direct laryngoscopy [28]. Bruck et al. also found that the use of the C-MAC provided an excellent glottic view in patients with cervical spine immobilization [29]. Similar results were also obtained by Byhahn et al. [30].

This study has several potential limitations. Firstly, as the partici- pants were emergency care providers, the findings may not apply to in- tubation attempts by highly experienced providers like anaesthesiologists. However, the study group was chosen deliberately because emergency care providers are the professional group who most often face the problem of difficult airway in spine trauma patients. Another limitation is that the study was performed on manikins and the results were not tested on patients in emergency medicine conditions. Although trials on manikins do not fully reflect endotracheal intubation in patients, they offer some advantages. In a manikin trial, researchers can standardize airway conditions for endotracheal intubation without exposing patients to potential risk and they may conduct a crossover randomized trial which would not be feasible in a clinical setting.

One of the strengths of this study is the design of a randomized crossover study. This allowed for a smaller, more efficient sample size to compare direct laryngoscopy and C-MAC laryngoscopy in three man- ikin scenarios.


In conclusion, this randomized crossover manikin trial showed the C-MAC videolaryngoscope is an excellent alternative to direct laryngos- copy for intubating manikins with cervical spine immobilization. Fur- ther clinical trials are necessary, however, to confirm the results.


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