An improvement up to C&L ≤ IIb in the specific 36 individuals with insufficient direct laryngoscopic view (C&L ≥ III) could be achieved significantly (P < 0.01) more often with the GlideScope (94.4%) than with the DCI laryngoscope (63.8%; Table 3). The DCI laryngoscope most frequently improved glottic view by one grade (54.2%) compared with the direct laryngoscope (Table 3). Improvement of two or three grades (10%) was seen less frequently and the DCI did not alter glottic view in 34.2%. The GlideScope enabled an improvement of two or three grades (26.7%) more often than the DCI (P < 0.001; Table 3). Deteriorated glottic view compared with direct laryngoscopy occurred in two cases (1.7%), one with the DCI laryngoscope and one with the GlideScope.
The median time needed to achieve the best laryngeal view did not differ between the three laryngoscopes (Table 4). In contrast, tracheal intubation performed with the direct laryngoscope [22.5 (12–49) s] was significantly faster than that with the DCI laryngoscope [27 (17–94) s; P < 0.05] and with the GlideScope [33 (18–68) s, P < 0.001) (Table 4)]. Compared with the DCI (2.5%) and GlideScope (2.5%), the intubation failure rate was higher using the direct laryngoscope (10%) (Table 4).
Complications such as oxygen desaturation or severe cardiovascular depression did not occur in any patient.
Difficult laryngoscopy has been defined as the inability to visualize the vocal cords, thus potentially leading to difficult intubation, with an incidence rate varying from 3 to 13% [18,19]. Many variations of laryngoscope blades have been developed to improve laryngoscopy [4,5], but as a mandatory straight line of sight on the glottic opening cannot be achieved in some patients with direct laryngoscopy, intubation devices enabling indirect laryngoscopy were designed [6–8]. As special training is mandatory for the successful use of these more complex instruments, the number of regular users still remains limited . Therefore, alternative intubation devices enabling easy and efficient use are required.
The recently introduced video laryngoscopy may be a suitable alternative. With this technique, indirect laryngoscopy enables a ‘look-around-the-corner’, whereas the video technique allows a magnified display on the monitor. This study investigates the capability of two different video laryngoscopes to improve laryngoscopic view in patients with potentially difficult airways.
As unpredicted difficult intubation may entail severe danger for the patient, numerable predictors for a difficult airway have been published [18,20]. The criteria used in our study have been demonstrated to offer acceptable sensitivity in 18 500 patients . Hence, the incidence of C&L ≥ III findings using direct laryngoscopy in our study was several times higher than that for unselected groups given in literature [18,19].
Compared with the direct laryngoscope, our data clearly demonstrate superior laryngoscopic view for both video laryngoscopes, consistent with previous findings [12,14,15,21]. The best view was obtained with the GlideScope. Apparently, its angulated blade form offers a more effective ‘look-around-the corner’ than the DCI video laryngoscope.
Our investigation also quantified the individual extent of glottic view improvement: the DCI video laryngoscope most commonly improved glottic view by one grade, which is in agreement with data given by Hofstetter et al. . However, deterioration of glottic view also occurred in two patients without sufficient explanation. Fogging of the camera lens, as sometimes experienced using the DCI video laryngoscope, impedes a clear view but does not influence C&L grading.
In contrast, the GlideScope showed a pronounced ability to enhance glottic view by more than one grade, corresponding to recent findings [14,21]. Deterioration using the GlideScope also occurred in two patients with easy (C&L I) direct laryngoscopy.
Improvement of a C&L ≥ III view up to ≤IIb is likely to enhance intubation success and safety. Whereas DCI video laryngoscope improved a direct C&L ≥ III view in nearly two-thirds of the patients, the GlideScope's capability for clinical improvement was even more remarkable. Therefore, video laryngoscopes, and the GlideScope in particular, may be helpful devices when difficult intubation is caused by insufficient laryngoscopic view.
Although introduction of both video laryngoscopes was often more delicate than with the conventional Macintosh laryngoscope, because of the attached cables and in case of the GlideScope because of the angulated blade form, the average laryngoscopy time did not differ between the three instruments. Obviously, these difficulties seemed to be compensated by rapid achievement of best glottic exposure.
In contrast, the intubation time using video laryngoscopy and especially the GlideScope was longer than that with direct laryngoscopy. Apparently, intubation under indirect visual control via a monitor requires a complex hand–eye coordination. As the investigators were familiar with both video laryngoscopes, there may be only minor potential for diminution of required time. When discussing these extended intubation times, an improvement in intubation success should be considered. Whereas four patients could not successfully be intubated using direct laryngoscopy, only one intubation failed in each video laryngoscope group.
On the other hand, our findings indicate that an improved glottic view does not guarantee intubation success, in particular with the GlideScope. The specific blade form of the GlideScope lifts up the larynx, thus tilting its axis, so that the tube may proceed in a steep angle through the glottic opening. If the tube and tracheal axis do not align, it may be helpful to rotate the tube and approach not in the midline, but more from the right side. In fact, one patient with failed intubation using the GlideScope showed a C&L grade IIa. We were unable to manipulate the endotracheal tube into the trachea due to a massive tongue and a narrow palatine. No subglottic disorder was responsible, as an 8.5 mm endotracheal tube could easily be introduced using the Bonfils intubation endoscope. Similar difficulties using the GlideScope have been reported by other authors, therefore suggesting use of a controllable stylet . In contrast, the only failed intubation using the DCI video laryngoscope was associated with insufficient laryngoscopic view (C&L III). Compared with the incidence of unsuccessful intubation given in other studies [1,2,20], the intubation failure rate in our study was rather high. This may be explained by the selection criteria as well as by the study protocol limiting intubation attempts to a maximum of two.
Assessment of the role of video laryngoscopy in the management of the difficult airway has not yet been finalized. However, it may be concluded that video laryngoscopy proved to be very helpful in a variety of clinical conditions of expected difficult airway; for example, limited neck mobility, reduced thyromental distance, reduced intercessor distance or retrognathia. Our data indicate that the GlideScope enhances glottic visualization in patients with difficult conventional laryngoscopy and not only in unselected collectives [14,21]. The DCI video laryngoscope also demonstrated improved laryngoscopic view in our study, which was comparable to recent findings [12,15]. Furthermore, the DCI video laryngoscope facilitates teaching of direct laryngoscopy and may thereby improve intubation skills, thus effectively helping to reduce the incidence of critical situations in airway management [13,22].
Although routine use of video laryngoscopy may remain limited by extended costs in many institutions, it will certainly become more prevalent throughout university and teaching hospitals in the near future. Video laryngoscopy can certainly not replace awake fibreoptic intubation in many cases of a predictable difficult airway. However, awake intubation of patients with a difficult airway using the GlideScope has already been reported .
Until now, use of video laryngoscopy for managing the unexpected difficult airway has been hampered by restricted mobility and extended preparation time. Recent developments resulted in a variety of small and portable video laryngoscopes, most of them equipped with small integrated digital video cameras. Prehospital use may be one specific application area for these instruments, but innovations such as wireless signal transmission, compatibility with personal computers and integration of small hand-held LCD monitors may be beneficial for the use of video laryngoscopes in clinical routine as well.
Our study design was confronted with several limitations. First, the investigation was carried out by only two anaesthetists. However, neither of them was involved in the development of the laryngoscopes investigated. Furthermore, the study could not be blinded, thus exposing it to potential observer bias. As at least video laryngoscopic views could be witnessed by the nursing staff to control observer bias, the main findings of this study have to be considered reliable. To validate our findings, further investigation (e.g. multicentre studies) is warranted to approve increased intubation success by use of video laryngoscopes.
In conclusion, both video laryngoscopes and the GlideScope in particular enable significantly better visualization of the glottic opening compared with the direct laryngoscope. They may, therefore, be a useful alternative for the management of the difficult airway.
We are grateful to Karl Storz GmbH, Tuttlingen, Germany, and Saturn Biomedical, Burnaby, Canada, for supplying the video laryngoscopes and we are much obliged to the involved nursing staff of our department for their dedicated assistance.
1 Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75:1087–1110.
2 Samsoon G, Young J. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42:487–490.
3 Cheney FW, Posner KL, Caplan RA. Adverse respiratory events infrequently leading to malpractice suits. A closed claims analysis. Anesthesiology 1991; 75:932–939.
4 McCoy EP, Mirakhur RK. The levering laryngoscope. Anaesthesia 1993; 48:516–519.
5 Gerlach K, Wenzel V, von Knobelsdorff G, et al
. A new universal laryngoscope blade: a preliminary comparison with Macintosh laryngoscope
blades. Resuscitation 2003; 57:63–67.
6 Bjoraker D. The Bullard intubating laryngoscopes. Anesthesiol Rev 1990; 17:64–70.
7 Wu TL, Chou HC. A new laryngoscope: the combination intubating device. Anesthesiology 1994; 81:1085–1087.
8 Bein B, Yan M, Tonner PH, et al
. Tracheal intubation using the Bonfils intubation fibrescope after failed direct laryngoscopy
. Anaesthesia 2004; 59:1207–1209.
9 Rosenblatt WH, Wagner PJ, Ovassapian A, Kain ZN. Practice patterns in managing the difficult airway by anesthesiologists in the United States. Anesth Analg 1998; 87:153–157.
10 Henthorn R, Red J, Szafranski J. Combining the fibreoptic bronchoscope with a laryngoscope blade aids teaching direct laryngoscopy
. Anesth Analg 1995; 80:433.
11 Weiss M, Schwarz U, Dillier C, et al
. Teaching and supervising tracheal intubation in paediatric patients using videolaryngoscopy. Paediatr Anaesth 2001; 11:343–348.
12 Hofstetter C, Scheller B, Flondor M, et al
. Videolaryngoscopy versus direct laryngoscopy
for elective endotracheal intubation. Anaesthesist 2006; 55:535–540.
13 Kaplan MB, Ward D, Hagberg CA, et al
. Seeing is believing: the importance of video laryngoscopy
in teaching and in managing the difficult airway. Surg Endosc 2006; 20(Suppl 2):S479–S483.
14 Cooper RM, Pacey JA, Bishop MJ, McCluskey SA. Early clinical experience with a new videolaryngoscope (GlideScope
) in 728 patients. Can J Anaesth 2005; 52:191–198.
15 Kaplan MB, Hagberg CA, Ward DS, et al
. Comparison of direct and video-assisted views of the larynx during routine intubation. J Clin Anesth 2006; 18:357–362.
16 Cooper RM. Use of a new videolaryngoscope (GlideScope
) in the management of a difficult airway. Can J Anaesth 2003; 50:611–613.
17 Yentis S, Lee D. Evaluation of an improved scoring system for the grading of direct laryngoscopy
. Anaesthesia 1998; 53:1041–1044.
18 Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39:1105–1111.
19 Williams K, Carli F, Cormack R. Unexpected, difficult laryngoscopy
: a prospective survey in routine general surgery. Br J Anaesth 1991; 66:38–44.
20 Rose DK, Cohen MM. The airway: problems and predictions in 18 500 patients. Can J Anaesth 1994; 41(5 Pt 1):372–383.
21 Sun DA, Warriner CB, Parsons DG, et al
. The GlideScope
video laryngoscope: randomized clinical trial in 200 patients. Br J Anaesth 2005; 94:381–384.
22 Low D, Healy D, Rasburn N. The use of the BERCI DCI video laryngoscope for teaching novices direct laryngoscopy
and tracheal intubation. Anaesthesia 2008; 63:195–201.
23 Doyle DJ. Awake intubation using the GlideScope
video laryngoscope: initial experience in four cases. Can J Anaesth 2004; 51:520–521.
Keywords:© 2010 European Society of Anaesthesiology
airway management; direct-coupled interface video laryngoscope; GlideScope; laryngoscopy; Macintosh laryngoscope; Macintosh video laryngoscope