Airway management is a fundamental priority in the resuscitation of critically ill or injured patients1 and tracheal intubation is widely accepted as the gold standard of advanced airway management in the out-of-hospital setting.2 However, out-of-hospital patients are not fasted, may have unknown airway difficulties and their vital functions are often already compromised. Together with the limited access space around the patient, these factors mean that the incidence of difficult tracheal intubation in the out-of-hospital setting is higher than that seen in the operating room.1,3,4 The fact that out-of-hospital tracheal intubation is often performed by personnel who do not routinely perform airway management may also be a contributory factor.5,6
In contrast to tracheal intubation undertaken in the operating room, a Macintosh laryngoscope blade for direct visualisation of the glottis is often the only device available for out-of-hospital tracheal intubation. Auxiliary devices such as fibreoptic bronchoscopes are rarely available. As such, the reported success rate of out-of-hospital tracheal intubation is low and the procedure is frequently associated with life-threatening complications, including multiple attempts, oesophageal or bronchial misplacement and intubation failure.7
During tracheal intubation, the laryngoscope blade is used to compress and displace the tongue to allow a direct line of sight from the performer's eye to the patient's glottis (direct laryngoscopy). Several anatomical or pathological factors may worsen the direct visualisation of the airway, for example a large tongue or a limited mouth opening. Difficult tracheal intubation usually occurs when direct laryngoscopy produces inadequate glottic visualisation.8
The standard device for out-of-hospital tracheal intubation is a laryngoscope with a Macintosh blade for direct visualisation, even though video laryngoscopy has already been proven to facilitate tracheal intubation for in-hospital settings.9–13 The C-MAC PM video laryngoscope (Karl Storz, Tuttlingen, Germany) uses a standard blade with a Macintosh shape that allows a direct laryngoscopic view from the perfomer's eye to the patient's glottis. In addition, a micro video camera at the distal portion of the blade produces a clear picture on a tiltable 6-cm monitor fixed to the device's handle (Fig. 1). The visual angle produced by the video camera is superior to the perspective allowed by direct line of sight. This construction provides the possibility of using the C-MAC PM as a direct laryngoscope, as well as a video laryngoscope14 and offers the opportunity to compare both methods immediately in the same patients, without the need for blade removal. Alternatively, for particularly difficult anatomical situations, Storz offers the newly developed D-Blade. This has a steeply curved angle for indirect laryngoscopy only, which is not comparable with a standard Macintosh blade.
The objective of this study was to undertake an observational study to record the laryngeal view observed with the C-MAC PM video laryngoscope and to compare this with the direct laryngoscopic view, at the same time, in the same patient, in an out-of-hospital setting.
Materials and methods
Ethical approval for this study was provided by the University of Ulm Ethical Committee (reference no. 40/12, Chairperson Prof. Dr H. Fangerau) on 9 March 2012. This prospective, observational study was undertaken at the Helicopter Emergency Medical Service (HEMS) ‘Christoph 22’, Ulm, Germany, over a 20-month period (May 2011 to December 2012). The medical team of HEMS ‘Christoph 22’, Ulm consists of an experienced anaesthesiologist and a flight paramedic. All HEMS physicians are board-certified anaesthesiologists who use the C-MAC on a routine basis during their daily work in the attached military hospital, where this device is used for difficult airway situations. HEMS ‘Christoph 22’ provides out-of-hospital care to patients in the area around the city of Ulm (radius approximately 70 km), with more than 1500 rescue missions per year, and is part of the civil rescue system in Germany.
All patients in whom tracheal intubation was performed by the medical team of HEMS ‘Christoph 22’ during the study period were enrolled in the study. With approval from the Ethical Committee, patient consent was not obtained after inclusion in the study.
According to the HEMS ‘Christoph 22’ airway protocol,15 after preoxygenation with a nonrebreathing mask for at least 60 s (unless immediate airway management was required for clinical reasons), tracheal intubation was performed as part of a rapid sequence induction (RSI), with the exception of patients undergoing cardiopulmonary resuscitation (CPR) who underwent tracheal intubation without medication. The C-MAC PM was used as the standard first-line laryngoscope for all out-of-hospital tracheal intubations performed by the team during the study period. The physicians chose the blade size (Blade size 1 to 4 or D-Blade) according to their experience and based upon patient age, size and anatomy. The standard is a Macintosh shaped, size 3 blade. In accordance with the study protocol, the physician started with initial direct laryngoscopy using the C-MAC PM without the monitor in sight. Immediately after quoting the direct laryngoscopic view according to the Cormack and Lehane grading system, the flight paramedic raised the monitor into the line of sight of the physician, and tracheal intubation was performed using the video laryngoscopic view without removing the blade. Every intubation was performed routinely using a stylet. In cases of unexpected difficulty, physicians followed a difficult airway algorithm with laryngeal mask airway insertion or cricothyrotomy as alternative startegies.16 In situations in which immobilisation of the cervical spine was required, the HEMS airway protocol recommends manual in-line stabilisation (MILS) during laryngoscopy and tracheal intubation. The ultimate decision on whether MILS or an in-situ applied cervical collar was used for cervical spine stabilisation, however, was the responsibility of the HEMS physician.
The aim of this study was to evaluate the effectiveness of the C-MAC PM for out-of-hospital tracheal intubation. The primary outcome of this study was to observe any differences in laryngeal view, as assesed by the Cormack and Lehane grading system, between the C-MAC video laryngoscope and direct laryngoscopy. The secondary outcomes were to observe intubation success rates and to document difficulties in airway management.
As a basis for data analysis, the nationwide, uniform out-of-hospital data reporting record was used.17 In addition to this record, immediately after mission completion, data related to the patient and subsequent airway management were recorded by the HEMS physician on a medical study form. This medical study form comprised the following information:
- patient demographics;
- indication for tracheal intubation;
- number of intubation attempts (for this study, ‘intubation attempt’ was defined as the insertion of a laryngoscope blade into the mouth regardless of whether an attempt of endotracheal tube passage was made or not);
- direct and video laryngoscopic glottis view according to the Cormack and Lehane grading system;18
- glottic status (rated as ‘very good’, ‘good’, ‘bad’ and ‘very bad’) as a surrogate marker of depth of anaesthesia;
- case circumstances, for example limited airway access due to awkward patient position;
- difficulties overall and during videolaryngoscopy (rated as ‘moderate’ or ‘servere’ according to personal estimations of the performing physician);
- technical problems with the C-MAC PM;
- categorisation of tracheal intubation using video laryngoscopy (rated as as ‘easy’, ‘moderate’, ‘difficult’ or ‘not possible’); and
- use of alternative airway techniques or need for a surgical airway.
The data were anonymised and entered into an electronic database (Microsoft Excel; Mircrosoft Coporation, Redmond, USA). Statistical analyses were undertaken with support from the Institution of Epidemiology and Medical Biometry, University of Ulm. All values in the tables and figures are expressed as median and interquartile range (IQR) or number (proportion) unless otherwise indicated. For comparisons of Cormack and Lehane grades, Wilcoxon signed-rank test and Fisher's exact test were used. A probability value (P) of less than 0.001 was considered significant.
During the 20-month study period, out-of-hospital tracheal intubation was performed in 228 patients. Patient characteristics are summarised in Table 1. The overall success rate in securing the airway was 100%; in 227 patients (99.6%), tracheal intubation was successful. Upon arrival at the emergency room, no episodes of unrecognised bronchial or oesophageal intubation were detected. In one patient who was receiving ongoing CPR in an entrapped position, after two failed tracheal intubation attempts, a laryngeal mask airway was successfully placed. This patient died at the scene due to the severity of his injuries.
Blades 1 to 4 were used according to patient age and size (Table 2). The D-Blade was used in seven patients (3.1%), of which in five cases (2.2%) it was used for the initial attempt at tracheal intubation. In four out of these five patients, this approach was successful. In one patient, the D-Blade was switched to a Macintosh-shaped blade for a successful second attempt. As an alternative techique following a failed tracheal intubation attempt with a standard Macintosh blade, a D-Blade was used successfully for the second attempt in one case and for the third attempt in another case.
The effect on visualisation of the glottis by using the C-MAC PM video laryngoscope with a Macintosh shaped blade for the first attempt (n = 223) is presented in Fig. 2. The glottic view obtained by direct laryngoscopy in 120 patients (53.8%) was Cormack and Lehane grade II to IV. When videolaryngoscopy was used, none of these patients had a worsening of the glottic view, 18 patients (15%) had an unchanged glottic view and in 102 patients (85%) the Cormack and Lehane grade improved. The improvement in Cormack and Lehane grade was significant regardless of the initial grade (II to IV) as determined by direct laryngoscopy (P < 0.001). In 57 patients (25.6%), glottic visualisation could be improved from Cormack and Lehane grade III/IV to grade I/II, which was rated as being clinically relevant (P < 0.001). In four (3%) patients out of the 103 with a direct Cormack and Lehane grade I, a worsening of the glottic visualistaion was seen with video laryngoscopy, caused by lens contamination with blood, secretions or vomit.
A limited accessibility to the patient upon arrival at the scene (mainly caused by entrapment) was noted in 22.8% (52/228) of the patients. By extricating 39 patients from their entrapped position with analgosedation (ketamine/midazolam) before delayed sequence intubation was performed, this proportion was significantly reduced to 5.7 % (P <[REPLACEMENT CHARACTER]0.001). Of the 13 patients in whom tracheal intubation was performed in an entrapped position, 12 patients (92.3%) were intubated successfully using the C-MAC PM. An alternative airway was required only in the one patient mentioned earlier.
Difficulties during video laryngoscopy were recorded in 32 patients (Table 3). These problems consisted mainly of bright ambient light, such as low or dazzling sunlight reducing the contrast of the monitor, and lens contamination of the micro camera at the distal end of the blade by blood, secretions and vomit. However, the provider was required to switch to direct laryngscopy in only three patients in order to perform tracheal intubation; in the fourth patient, a laryngeal mask airway was used as reported above.
Focusing on the subgroup with cervical spine immobilisation in place during laryngoscopy (n = 23), the glottic view was also significantly improved by using the C-MAC. Furthermore, apart from this improvement in visualisation, the performers evaluated the video laryngoscopic intubation with a cervical collar in place as ‘easy’ in 82.6% (19/23), ‘moderate’ in 13.0% (three out of 23) and in only one case as ‘difficult’.
Tracheal intubation is the gold standard approach for out-of-hospital airway management, typically performed by direct laryngoscopy using a Macintosh blade. Requiring a direct line of sight from the performer's eye to the glottis, this procedure has systematic limitations. In hospital settings such as the operating room, ICU or emergency room, video laryngoscopes have been proved to mitigate this problem, as they are designed to provide an easier way to view the vocal cords.12,19,20 Sakles et al.20 reported a 12-fold increase in the likelihood of successful tracheal intubation using the C-MAC compared with direct laryngoscopy. However, such data can only be applied with caution to the out-of-hospital setting, because performing tracheal intubation in this environment is more challenging for several reasons as mentioned earlier.
The success rate for tracheal intubation in the current study (99.6%) is comparable to those found by other studies evaluating out-of-hospital tracheal intubation by trained physician providers (97.4 to 100%).3,4,15 It is also similar to the success rate previously described by the same study group for out-of-hospital tracheal intubation without video laryngoscopes.21 This may underline the importance of proper training and daily routine in airway management. Furthermore, the incidence of multiple tracheal intubation attempts (more than two) in the current study is lower than that found by other researchers (0.9 vs. 2.2 to 4.3%).3,4 There was only one case of failed tracheal intubation in the current study, which was managed by the successful positioning of a laryngeal mask airway. This rate is similar to, or lower than, the rate reported by other out-of-hospital studies, when emergency medicine physicians or anaesthesia-trained emergency medicine physicians managed the airway (0.4 vs. 0.8 to 2.6%).4,15 In a randomised controlled crossover study, Cavus et al.12 reported a 100% success rate for video laryngoscopic intubations with the C-MAC (55 of 55). However, this study involved only patients undergoing elective surgery and patients with suspected difficult airways were excluded; the current study observed out-of-hospital emergency patients without any exclusion criteria.
In this study, the use of the C-MAC PM was found to be associated with a significantly better laryngeal view than direct laryngoscopy, as measured by the Cormack and Lehane grade. Furthermore, with improvements in Cormack and Lehane grades III/IV to grades I/II, the use of C-MAC PM could be rated as clinically relevant in a quarter of the patients (P < 0.001), with almost a 100% successful tracheal intubation rate. This is in contrast to studies with other video laryngoscopes, in which improvement of Cormack and Lehane grade was demonstrated, but tracheal intubation remained difficult.22–26 Most of the studied video laryngoscopes used highly curved blades with very steep angles, thereby not allowing a direct view to the glottis. Following this curve with the tube probably makes intubation more challenging and performers might be more familiar with the conventional curve of the Macintosh blade on the C-MAC. Several manufacturers offer particular stylets to facilitate intubation with these highly curved blades. This is noteworthy, as several studies have observed pharyngeal injuries with steeply curved video laryngoscopes.27–29 The D-Blade, which is also steeply curved, was very rarely used with the C-MAC PM in this study. Only in 0.9% (two out of 228) of cases was it necessary to switch to the D-Blade as an alternative after failed attempts with Macintosh-shaped blades. In an Austrian out-of-hospital randomised study, the use of the steeply curved Airtraq video laryngoscope was associated with a higher incidence of failed tracheal intubation than with direct laryngoscopywith a Macintosh blade.30
The significantly improved glottic view demonstrated in this study along with the high success rate of tracheal intubation at the first attempt not only favour the out-of-hospital use of the C-MAC PM with a Macintosh-shaped blade but also suggest that its use as a first-line device for tracheal intubation is safe and effective whilst also offering the option of using the device as a direct laryngoscope in the rare cases of compromised video laryngoscopic view by lens contamination. The steeply curved D-Blade should also be provided for particularly difficult airway situations and for failed intubation attempts using the C-MAC PM with a Macintosh-shaped blade.
In the subgroup of patients with cervical spine immobilisation in place, the use of the C-MAC PM was associated with better laryngoscopic views according to the Cormack and Lehane grading system. This reflects the problem caused by cervical spine immobilisation, which reduces the ability of a direct laryngoscope to create a direct line of sight to the vocal cords, a finding already indicated by other authors.31,32 This suggests that the use of the C-MAC PM may be useful in trauma patients who have undergone immobilisation of the cervical spine. Within this context, the D-Blade might be superior to Macintosh-shaped blades.
This study revealed several limitations of video laryngoscopy, namely bright ambient light reducing contrast on the monitor, and lens contamination of the micro camera by blood, secretions and vomit. In 86% of cases, the C-MAC PM presented a flawless video picture, whilst in 5.7% of cases the physicians complained about moderate problems caused by fogging. In only 0.9% of cases were there complaints about severe problems caused by either fogging or lens contamination with blood or vomit. Sakles et al.20 reported a 12.2 and 13.2% incidence of moderate and severe problems, respectively, caused by lens contamination using the C-MAC in the emergency department; In the present study, these figures were 4.0 and 7.5%, respectively. The video view was limited by bright and dazzling ambient light in 5.3 % of cases, which is a problem typically encountered in the out-of-hospital setting. In a previous publication on the factors influencing emergency intubation in the out-of-hospital setting by HEMS, this problem was reported more often (9.15%) when conventional direct laryngoscopes were used.15
By using a standard Macintosh blade, the C-MAC PM provides the ability to perform as both a video and direct laryngoscope. This is advantageous, because performers can easily switch from video to direct laryngoscopy when necessary (without removing the blade), for example in cases of lens fogging or contamination. Sakles et al.20 have also reported this benefit.
This study has several limitations. First, this is a single-centre study and all physicians involved were not only board-certified anaesthesiologists but also were experienced in the use of the C-MAC video laryngoscope. Thus, the results may not be generalisable to other out-of-hospital settings, where operators have different levels of experience with either direct or video laryngoscopy. Second, this was an observational study, allowing a comparison between direct and video larnygoscopic views by two techniques. The fact that the same physician performed both laryngoscopic techniques may have introduced bias, because video laryngoscopy was always the second method used to view the vocal cords. Third, because data related to laryngoscopy and tracheal intubation were recorded by the HEMS physician immediately after mission completion, it may be subject to self-reporting bias. Fourth, the Cormack and Lehane grading system is a subjective evaluation of the glottic view.33 Thus, the comparison between direct and video laryngoscopy in the same patient is reliable, but the interobserver reliability is limited.
To our knowledge, this is the first study evaluating the C-MAC PM in an out-of-hospital setting and comparing direct and video laryngoscopic view immediately in the same patients. In this observational study, the use of C-MAC PM video laryngoscope was associated with an improved visualisation of the glottis according to the Cormack and Lehane grading system and with an excellent first attempt success rate for out-of-hospital tracheal intubation. Similar data were published for the use of the C-MAC as the initial device for emergency tracheal intubation in the operating room and ICU.34,35 Taking into account that multiple laryngoscopic attempts for emergency airway management are associated with desaturation21 and increased morbidity and mortality,7 the results of this study suggest that the use of C-MAC PM by out-of-hospital emergency medical services as a first-line device for laryngoscopy is safe and effective and offers the option to change to direct laryngoscopy when necessary.
Acknowledgements relating to this article
Assistance with the study: the authors acknowledge Benjamin Mayer from the Institution of Epidemiology and Medical Biometry, University of Ulm, for his assistance in statistical analyses.
Financial support and sponsorship: none.
Conflicts of interest: BH has received travel funding from Karl Storz GmbH & Co. KG, Tuttlingen, Germany. VD has acted as a consultant for Karl Storz GmbH & Co. KG, Tuttlingen, Germany, has received payments and travel funding for overseas lectures from Karl Storz GmbH & Co. KG, Tuttlingen, Germany, and has received technical material, such as video laryngoscopes and emergency respirators to perform clinical studies, from Karl Storz GmbH & Co. KG, Tuttlingen Germany – Verathon, (GlideScope) Rennerod, Germany – Kingvision, ambu, Nauheim, Germany – Dräger Medical AG, Luebeck, Germany – Weinmann GmbH & Co. KG, Hamburg, Germany.
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