Tracheal intubation using direct laryngoscopy is successful in the majority of patients, even when a line-of-sight view of the glottis is not possible. Although poor glottic visualization is encountered between 1% and 9% of attempts,1,2 success can generally be achieved with additional force, external laryngeal manipulation, or the use of gum elastic bougies and stylets. However, poor glottic exposure is more likely to require prolonged or multiple intubation attempts and, subsequently, may be associated with complications such as oxygen desaturation or airway and dental injuries. In recent years, videolaryngoscopy has begun to play an important role in the management of patients with an unanticipated difficult or failed laryngoscopic intubation.3 Some videolaryngoscopes (e.g., GlideScope® and McGrath®) do not provide visualization of the tip of the blade and, therefore, demand a tube stylet to guide the endotracheal tube through the glottis.
The C-MAC® videolaryngoscope (Karl Storz, Tuttlingen, Germany) is a new videolaryngoscope using a modified Macintosh blade, which may be a useful alternative both for routine and difficult airway management and for educational purposes. In this study, we describe for the first time the use of the C-MAC videolaryngoscope for tracheal intubation in 60 patients during routine induction of anesthesia.
The C-MAC videolaryngoscope (Fig. 1) is a further development of previous videolaryngoscopes by Karl Storz (MVL, V-MAC). Compared with the MVL as described by Kaplan et al.,4 it has an original Macintosh steel blade shape with a closed blade design with no edges and gaps for hygienic traps and is now available in 3 sizes (2, 3, and 4). The C-MAC blade is flattened, resulting in a very slim blade profile (maximum 14 mm), and the edges are slanted to avoid damage to the mouth and teeth. Optionally, the blade may be equipped with a holder channel for a suction catheter (14–16 Ch). In contrast to both the MVL and V-MAC, which were based on a fiberoptic technique with an external light source, the C-MAC incorporates the smallest possible (2-mm) digital camera (Complementary Metal Oxide Semiconductor [chip], 320 × 240 pixels) and a high-power light-emitting diode, located laterally in the distal third of the blade. Thus, reduced image quality due to damaged optical fibers, need for white color balance and focusing, and immobility due to external light source were eliminated. In addition, compared with both the MVL and V-MAC, the embedded optical lens has an increased aperture angle of 80° (Fig. 2). The view obtained includes the tip of the blade and, therefore, allows visual guidance of the tip of the blade into the vallecula. A color image is displayed on a lightweight, portable high-resolution liquid crystal display monitor (resolution 800 × 480; 154 × 93 mm; 7") with lithium-ion battery technology, permitting approximately 2 working hours without recharging. The image may also be recorded as a single picture or a video stream by one-touch technique either on the monitor or the laryngoscope handle and stored using the implemented secure digital card slot (Fig. 1). Similar to other videolaryngoscopes, a view of the epiglottis and glottis is available on the video screen as soon as the camera section of the C-MAC enters the pharynx.
After approval of the IRB and obtaining written informed consent, 60 patients (ASA physical status I–III) were recruited of either gender (31 men) (age: 20–86 yr; weight: 50–179 kg) undergoing elective surgery in the supine position with general anesthesia in whom tracheal intubation was indicated, including morbidly obese patients. Patients were excluded if they had any pathology of the upper respiratory or upper alimentary tract, if they were not fasted, or if there was a history of a difficult airway requiring fiberoptic intubation. Preoperatively, we scored the reclination of the head (atlantooccipital extension according to Bellhouse and Dore5), the thyromental distance described by Patil et al.,6 and the view of the oropharynx on mouth opening described by Mallampati et al.7 and modified by Samsoon and Young.8
Standard monitoring devices were attached before induction of anesthesia, including noninvasive arterial blood pressure, heart rate, and oxygen saturation (Spo2; S/5, Datex-Ohmeda, Helsinki, Finland). The patient's head was supported on a firm pillow with an appropriate height to achieve a sniffing position. After 3 min of administration of oxygen with a face mask, anesthesia was induced with remifentanil 0.3 μg · kg−1 · min−1 and propofol 1.5–2.5 mg/kg. Appropriate neuromuscular blockade was achieved with rocuronium 0.6 mg/kg and was confirmed using a peripheral nerve stimulator (train-of-four count = 0) before airway manipulation.
Next, 1 of 3 anesthesiologists with at least 8 yr of experience (after being trained on manikins) inserted the C-MAC and advanced the tip of the blade toward the vallecula, in the same way it is advanced with a Macintosh laryngoscope. The position of the device was adjusted to have the glottis in the center of the screen (Fig. 3), and tracheal intubation was performed. The attending anesthesiologist was requested to identify the Cormack-Lehane (C/L) view,9 modified by Yentis and Lee,10 with C-MAC laryngoscopy (Size 3 blade), depending on necessity with and without external manipulation (BURP maneuver11). We recorded the ease or difficulty of intubation with the C-MAC, the time to optimal laryngoscopy and intubation, and the incidence of adverse events during anesthesia such as aspiration/regurgitation, hypoxia (Spo2 <90%), damage to teeth, and bleeding from the oropharynx. Upon completion of the study protocol, the anesthesiologist provided a subjective assessment, which was rated as very good, good, and poor. Correct tube position and subsequent successful ventilation were assessed with capnography and bilateral chest auscultation. Peripheral Spo2, mean arterial blood pressure, and heart rate were recorded at baseline before laryngoscopy, after administration of oxygen, and after laryngoscopy.
Data are expressed as median (range), mean ± sd, or absolute numbers, as required. Differences over time between groups were analyzed using 1-way analysis of variance with Bonferroni correction. Statistical significance was considered at P < 0.05.
All patients were hemodynamically stable before, during, and after laryngoscopy (Fig. 4). It was possible to insert the blade of the C-MAC, to obtain a view of the glottis (Fig. 3), and to intubate all patients. Tracheal intubation was successful in 52 patients on the first attempt, 6 on the second, and 2 on the third. The use of a gum elastic bougie to guide the endotracheal tube to the visualized glottis was necessary in 8 patients.
Airway characteristics are shown in Table 1. The median time from touching the laryngoscope to optimal laryngoscopic view was 10 s (range, 3–25 s) and to successful intubation was 16 s (range, 6–58 s). Glottic view without and with external manipulation is shown in Table 2. There was no damage to teeth, bleeding from the oropharynx, or hypoxia. The resulting picture on the video screen showed excellent optical characteristics in all patients. Subjective assessment of handling was very good in 26 patients, good in 31, and poor in 7. In the 7 patients with poor assessment, common concerns were raised over the comfort (6 of 7) and guidance (7 of 7) of the laryngoscope handle, and less frequent insertion of the blade (5 of 7) or glottic exposure (5 of 7).
It was generally easy to insert the C-MAC, to obtain a view of the glottis, and to intubate the trachea, without major complications. Because the shape of the blade is similar to the original Macintosh blade, using a tube stylet is not required: only 8 of 60 patients in this study were intubated with the help of a gum elastic bougie. This finding is even more significant because we did not exclude morbidly obese patients. This may have important ramifications, because reports of complications such as tracheal or pharyngeal perforation with the use of a previous videolaryngoscope (GlideScope) have been described12–16; in this device, a highly angulated blade caused difficulty in advancing the tracheal tube into the trachea, because the glottis was not under direct view. There was a frequent need to adjust the shape of the tracheal tube with a stylet. With the C-MAC device, the tip of the blade may always be seen on the video screen. All participating medical personnel are able to follow both visualization of the glottis and the intubation process on the monitor, which may help to optimize the glottic view by external laryngeal manipulations. Furthermore, there are no restrictions on the type of endotracheal tube that can be placed.
In contrast to many previous videolaryngoscopes, the C-MAC has the unique advantage of obtaining both a direct laryngoscopic view and a camera view that are displayed on the video screen. On one hand, this may be very helpful for educational purposes, because the instructor may follow the student's intubation attempts directly on the video screen. On the other hand, this may have important ramifications if the video view is worse than the direct view or the intubation itself is difficult because of high blade angulations.17 Moreover, the very clear camera view, most likely a result of the combination of a CMOS chip with a true optical lens, may be stored as an image or video stream on a commercially available secure digital card and subsequently used for education or documentation.
In addition, we have obtained experience from 3 patients in whom we had unexpected difficulty with direct laryngoscopy with a conventional Macintosh laryngoscope (C/L Class 3, 4, and 4, respectively) and whose airways were successfully managed using the C-MAC Size 4 blade (improvement to C/L Class 1, 2a, and 2b, respectively; Fig. 5). Overall, we have used the C-MAC with 2 blade sizes. Because of the lower angulation of the blade, we prefer the Size 3 blade for daily practice; however, as shown in 3 patients, the Size 4 blade may be advantageous if unexpected difficulty of intubation arises. According to Figure 2, the original Macintosh Size 4 blade is more curved compared with the Size 3 blade (30° vs 18°; angle b),18 resulting in a higher angulation with a wider view on the glottis (anterior view angle, a); it was helpful to load the visualized epiglottis (glottic side) on the tip of the blade as described by Miller19 (straight blade technique, Fig. 5). This manipulation caused the C/L score to improve by 2 classes in all 3 patients. Fogging was infrequent, because the built-in software initiates a prewarming of the optical system by the camera light.
Some limitations of this study should be noted. First, there is a lack of comparison with other videolaryngoscopes. However, based on this preliminary technical communication, further studies are warranted to compare the C-MAC with other videolaryngoscopes. Second, we have included 6 morbidly obese fasting patients. A criticism may be that these patients might have a higher risk of regurgitation and aspiration of gastric contents; however, we used standard institutional anesthetic management for obese patients, and all patients were successfully managed without complications. Third, our intraoperative data collection was performed by a nonblinded observer, which is a possible source of bias. Finally, all data of handling the airway devices are subjective.
In conclusion, the C-MAC videolaryngoscope may be suitable for both routine and difficult airway management, and for educational purposes, but these results should be confirmed by further comparative studies.
Karl Storz, Tuttlingen, Germany, provided the video intubation equipment used for this study, which was made available to the study centers at reduced cost after the study.
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