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Empirical Investigations

Comparison of Intubation Success of Video Laryngoscopy Versus Direct Laryngoscopy in the Difficult Airway Using High-Fidelity Simulation

Narang, Aneesh T. MD; Oldeg, Paula F. MD; Medzon, Ron MD; Mahmood, Ahmed R. MD; Spector, Jordan A. MD, MS; Robinett, Derek A. MD

Author Information
Simulation in Healthcare: The Journal of the Society for Simulation in Healthcare: October 2009 - Volume 4 - Issue 3 - p 160-165
doi: 10.1097/SIH.0b013e318197d2e5
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Abstract

Effective airway management in the urgent setting is a defining skill of the emergency medicine practitioner. This task can be made more challenging by trauma, secretions or blood, unusual or difficult anatomy, or poor neck mobility due to anatomic factors or cervical spine precautions. With rapid sequence intubation now the standard of care in emergency practice, one runs the risk of encountering a paralyzed patient with an inaccessible airway, such as the “cannot-intubate-cannot-ventilate” situation.

Various prediction schemes for difficult airway have been developed to avoid the above scenario; they have not proven to be very specific or sensitive. In addition, these have been developed primarily for anesthesiologists and are not always applicable or feasible in the emergency department setting.1

The unanticipated difficult airway can be risky for the patient and harrowing on the part of the practitioner. A number of video laryngoscopes have been developed to aid in visualization of the vocal cords in these instances. The GlideScope is the apparatus available in our institution. This machine is comprised of a handle and a blade, similar to a laryngoscope, with a camera embedded in the distal end of the sharply curved blade. The camera transmits the image to a video monitor, allowing visualization of the vocal cords and placement of the endotracheal tube. The blade has a 60 degree curve, which gives the practitioner a view of the anterior glottis. Introduction of the endotracheal tube through the cords using the GlideScope varies slightly from that of traditional laryngoscopy, and there is some learning curve to its use.2 Curving the endotracheal tube to match the blade is important for placement, as is manipulation of the stylet (Fig. 1).

Figure 1.
Figure 1.:
Use of the video laryngoscope to intubate a high-fidelity simulation mannequin. Note that the operator is observing the endotracheal tube approaching the cords from the right by watching the video screen, unlike direct laryngoscopy where the operator looks directly into the patient’s mouth.

Several series in the anesthesia literature have shown that the video laryngoscope used in this study improve views of the glottic opening, particularly in difficult laryngoscopy.2–9 Argo et al4 examined glottic views achieved using a Macintosh blade and the video laryngoscope in patients wearing cervical collars undergoing general anesthesia. The Cormack-Lehane (CL) grade (I–IV) improved by one level in 14 of 15 patients (93%). In another study, a series of more than 700 patients showed that CL grade I or II views were obtained in 99% of patients using video laryngoscopy. Intubation was successful in 96% of cases using video laryngoscopy. The authors also indicated that among the 35 patients with a CL grade III or IV view by direct laryngoscopy, the view improved to a grade I view in 24 and grade II view in two of these patients with the video laryngoscope.2 The efficacy of the GlideScope video laryngoscope was evaluated in 50 patients undergoing elective surgery requiring general anesthesia.3 The video laryngoscope provided a grade I view in 44 cases and grade II view in six cases. The view using the video laryngoscope was improved in almost half (23) of the cases as compared with direct laryngoscopy.

Although anesthesiologists have found that video laryngoscopy improves views of the glottic opening and can facilitate successful intubation,2,3 it can also potentially serve as an extremely important tool for the emergency physician to use in managing the difficult airway. Our hypothesis was that the video laryngoscope (GlideScope) would be of greater value in the difficult emergency airway. We set out to test these using difficult airway settings on a high-fidelity simulator. The objective of the study is to compare the view of the airway, and timing and success of video laryngoscopy to standard laryngoscopic intubation using a high-fidelity simulation mannequin in normal and difficult airway settings. It was also designed to serve as an educational tool to allow residents and faculty members practice in using this equipment in a more controlled setting.

METHODS

Study Design

This study is a prospective, nonblinded, nonrandomized convenience sample of emergency medicine attending physicians and residents. A total of 52 residents and attending physicians of a PGY 2–4 emergency medicine residency program participated over two successive academic years (2005–2007). A single, high-fidelity simulation mannequin (Laerdal SimMan 2006, Wappinger Falls, NY) was used during the in-service as well as the study. All participants received a 10-minute demonstration of the video laryngoscope (GlideScope Saturn Biomedical System 2004, Bothell, WA) and were permitted up to three trial intubations before the study. Participants were permitted to attempt direct laryngoscopy with the mannequin before the study at the participants’ discretion. All participants were experienced with direct laryngoscopy. All participants were novices to video laryngoscopy.

Study Protocol and Measurements

The mannequin is operated remotely using a laptop loaded with the proprietary software. It is possible to simulate many different airway situations, including tongue edema, pharyngeal edema, trismus, and neck immobility. For our study, a standard setting was used to simulate routine, uncomplicated intubations. The two settings used to simulate difficult scenarios were cervical spine precautions by decreased neck mobility, and distortion of the airway by means of tongue edema. Participants intubated using a Macintosh blade and video laryngoscope in each scenario, and graded the best view achieved at time of intubation using the CL classification (grades I–IV). All participants reviewed this classification before the study. This grading system is used to assess and quantify laryngoscopic view of the vocal cords and glottis. CL grade I is defined as complete exposure of the glottis, the best view; in CL grade IV, neither the glottis nor epiglottis can be seen. The grade view with video laryngoscopy was confirmed by a coinvestigator viewing the video monitor. The coinvestigators used a stopwatch to record the time it took for the participants to view the vocal cords and to intubate. At time zero, the participant had the laryngoscope in hand and had not begun the intubation procedure. Time stopped when participants stated that the endotracheal tube had passed through the cords. Intubation was verified by a coinvestigator for the time to be recorded. After completion in each scenario, the coinvestigator confirmed successful intubation by two methods. Ventilation of the mannequin was attempted using a bag mask valve attached to the end of the endotracheal tube. The SimMan computer software program indicates that air is entering the lungs if intubation is successful. The coinvestigator used a Macintosh or video laryngoscope blade to confirm that the tube passed through the vocal cords in the mannequin. Outcome measures included time to view the vocal cords, time to intubation, grading of view at time of intubation, and intubation success or failure. The maximum time allowed per scenario was 300 seconds (5 minutes), the time for a moderately ill patient to desaturate below 90%.10 Data were collected anonymously and no names were recorded. The only identifying data used was the level of training of the resident or faculty member participating in the study. The participants informed the investigators of their training level, which was directly recorded at the time the study was performed.

Statistical Analysis

Data was recorded by the investigators, and entered into a Microsoft Excel (Microsoft Corporation, Redmond, WA) spreadsheet. Statistical analysis was performed using paired t tests to compare the mean differences in times to viewing the cords and intubating the mannequin between the video laryngoscope and standard laryngoscopy in each of the scenarios. Unsuccessful attempts to view cords or intubate within 5 minutes were assigned the maximum time of 300 seconds. The participants were allowed unlimited attempts at intubation before the 5-minute mark. The number of attempts was not recorded. Chi square analysis was used to compare success rates in the tongue edema setting.

This study was approved by Boston University Medical Center Institutional Review Board (IRB). Written informed consent was waived as a requirement by the IRB.

RESULTS

Fifty-two participants were enrolled. Thirty-six of these were emergency medicine residents (9 PGY2, 17 PGY3, and 10 PGY4), and 16 were attending physicians. There was a decrease in time to view the cords using the video laryngoscope when compared with the Macintosh blade in the normal scenario, but this did not reach statistical significance (1.8 seconds reduction, 95% CI −3.6 to 0.05, P = 0.055; Fig. 2). In contrast, it took less time to visualize the cords using the Macintosh blade when compared with video laryngoscope in the neck immobility scenario, but this again did not reach statistical significance (3.1 seconds reduction, 95% CI −1.0 to 7.3, P = 0.14; Fig. 2). The video laryngoscope used in this study, however, significantly reduced the time needed to view the cords (89 seconds reduction; 95% CI 54.4–123.7, P < 0.0001) for the tongue edema scenario (Fig. 2). One hundred percent of all participants successfully viewed the cords with normal neck mobility and neck immobility within the time constraints.

Figure 2.
Figure 2.:
Mean time to viewing cords using standard airway setting, stiff neck, and tongue edema on the simulation mannequin.

Participants successfully intubated the mannequin faster using the Macintosh blade in both the normal (9.4 seconds faster, 95% CI 3.2–15.7, P = 0.004) and neck immobility settings (16.1 seconds faster, 95% CI 3.6–28.7, P = 0.01; Fig. 3). The video laryngoscope reduced the time to intubation (131.3 seconds reduction, 95% CI 99.1–163.6, P < 0.0001) for the tongue edema setting (Fig. 3). One hundred percent of all participants successfully intubated the mannequin with normal neck mobility and neck immobility within the time constraints. There was a higher rate of successful intubations (83% video laryngoscopy vs. 23% standard laryngoscopy, P < 0.09) in the tongue edema scenario (Fig. 4).

Figure 3.
Figure 3.:
Mean time to intubation of simulation mannequin using standard airway setting, stiff neck, and tongue edema settings.
Figure 4.
Figure 4.:
Success rates in viewing cords and intubating a simulation mannequin using tongue edema scenario.

A direct comparison between CL grades obtained at time of intubation using video and direct laryngoscopy consistently demonstrated better views using the Glidescope (Table 1). In the tongue edema setting, video laryngoscopy provided a higher success rate of obtaining a CL grade I or II ie, viewing the cords at time of intubation (50% video laryngoscopy vs. 12% standard laryngoscopy, P < 0.0001; Fig. 4). Some participants were able to establish a grade 3 CL view just at the time limit of 300 seconds, and thus were unable to complete the intubation. Furthermore, intubation was also successful in some CL grade 3 or 4 views.

Table 1
Table 1:
Grade View of Simulation Mannequin’s Vocal Cords Using CL Classification in Angioedema Scenario

DISCUSSION

Our results show that video laryngoscopy provided an enhanced view of the cords using less time, increased intubation success, and decreased the time to intubation in the most difficult airway scenario used. The failed intubations in the most difficult airway scenario using the video laryngoscope were due to multiple reasons. Our participants reported the most common one being difficulty in maneuvering the endotracheal tube through the vocal cords. It is a technology that is quickly learned, but requires some practice. Study participants had similar success rates or superior intubation success using video laryngoscopy having had only a brief in-service and three practice attempts. This superior performance is remarkable because the operators had a single in-service on the device, and most had substantial experience with direct laryngoscopy. This lack of experience using video laryngoscopy may account for the decrease in time to intubation observed in the normal neck mobility and neck immobility scenarios using the Macintosh blade. With experience, the operators might become as proficient in all airway scenarios using video laryngoscopy, but this remains to be tested.

The literature has several examples11–12 addressing the use of simulation to teach medical students the principles of routine, uncomplicated intubation. Medical student educators have found that students can be proficient in the techniques of intubation on simple trainers within 75 to 90 minutes of training, provided that the teacher-to-student ratio is kept small, preferably at 2:1.11 Medical students in Singapore who received both lecture and simulation training in intubations performed significantly better than their peers who did not receive the training. At 3 months, the simulation group showed significantly less decay in their skill level with a success rate of 78% versus the 41% of the group who received no simulation-based training.12

Prehospital Emergency Medical Services (EMS) teach intubation to paramedics, and in the past relied heavily on their students gaining experience doing elective intubations in hospital operating rooms (ORs). A surprising result came out of a study in 2005 that directly compared one group of paramedic students trained to intubate a simulation mannequin with a second group who spent time in the OR. Once training was complete, a look at their success in the field revealed that there was no difference between either group in its ability to successfully intubate live patients, first pass success, or complication rate.13 Some EMS programs around the country now accept simulation-based intubations as equal to OR-based intubations for their students’ procedure quotas. One study group that was missing from the EMS study was a group who received both simulation training and OR training. It would have been very helpful to know if such a group would score even better having had both simulated and live patient experiences. Although there do not seem to be any large studies in the emergency medicine literature, it seems very likely that emergency medicine trainees would have similar success rates in the clinical setting using a combination of simulated experiences with intubations, as well as live patient experiences in the OR, but this remains to be tested.

The video laryngoscope used in this study design confers the potential benefits of improved laryngeal exposure, first-pass successful intubation, and video monitoring, allowing others to see the anatomy and observe the procedure. The largest practical difference between GlideScope laryngoscope and traditional laryngoscopy is negotiating the tube into the trachea. Despite an equal or improved view of the cords on the screen, an increased time to intubation in typical and neck immobility scenarios was noted in other series, as well as in our own data.5,7 One study noted that maneuvering the tube was the barrier to successful intubation, as 14 of 26 of the failures in a large series occurred with CL grade I view.2 This was also demonstrated in a study with anesthesiologists in the OR setting, which found that there was no significant difference in time to intubate patients with CL grade III airways.5 Even though there was an improved view with video laryngoscopy compared with Macintosh laryngoscopy when the CL grade was >I, it also showed increased time to intubation of 16 seconds over all cases using GlideScope. The manufacturer suggests curving the endotracheal tube over a stylet at a 60 degree angle to match that of the blade14; anecdotal experience of our own and other series suggest the distal end of the tube is often caught on the arytenoids or other anatomic structures. The manufacturer in-service advises advancing the tube to the level of the cords, withdrawing the stylet about 4 cm, and then advancing the tube through the cords under direct visualization. Other suggested methods to ease the procedure include using a more rigid stylet, using a “hockey stick” configuration with 90 degree distal curvature, or a rigid stylet with flexible tip.15–18

The benefits of the video laryngoscope regarding successful intubation are most distinct in the difficult airway. Studies involving patients and simulated patients intubated by practitioners of varying levels of experience showed a higher level of intubation success in difficult airways. One group of students studied had greater ease of intubation and successful intubation using the video laryngoscope in simulated CL grade III airways.7 Another study showed that anesthetists using the video laryngoscope took less time intubating, had a slightly higher success rate and found intubation easier only in the simulated difficult scenarios (grade III view) using a high-fidelity simulator, a result similar to ours.19 The video laryngoscope also improved the laryngeal view and decreased time for tracheal intubation when compared with the Macintosh laryngoscope in patients with simulated difficult airways by using in-line manual stabilization of the head and neck.20

For teachers, the use of video during laryngoscopy represents a tremendous technological advance. To be able to watch the endotracheal tube pass through the cords in real time, and to provide immediate feedback to the resident during the procedure is obviously valuable, and may translate to safer patient care. Other video systems have provided trainees with improved initial intubation success in the OR, and there is potential for more research in this area.21

One newer technology, the McGrath video laryngoscope, is a one-piece unit incorporating the blade and camera design of the GlideScope with the video screen attached to the handle, keeping the view of the cords in line with the procedure itself.22 Early reports show similar improvement in laryngeal views and successful intubation to that of the video laryngoscope used in this study.23–25

LIMITATIONS

It is unclear how closely simulated scenarios translate directly to real-life situations. The simulation mannequin did not have blood or secretions in its airway, which could limit the view of a video laryngoscope. Although this is a limitation, it should be noted that the advantage of using a simulated scenario is that each operator experiences exactly the same airway views, something impossible to accomplish in a clinical trial. Although the anesthesia literature6–7,19–20 suggests a parallel between the two, a prospective study in the emergency department comparing video laryngoscopy to direct laryngoscopy would be the next logical study to confirm our findings.

There are no standards to our knowledge that can be used to compare the outcome measures found in this study. Provided a patient is intubated while still adequately oxygenated, presumably the time to intubation is not as important, while failure in difficult airways leads to cricothyrotomy or worse complications. There was also no prestudy measurement to ensure the equivalence of video and traditional laryngoscopy skills in the participants, and this could have affected the independent variables in the study.

There are also several potential confounding factors that may account for results obtained in normal and neck immobility scenarios. First, introduction of the endotracheal tube through the cords using the video laryngoscope varies from that of traditional laryngoscopy, and there is a learning curve to its use. Given that the video laryngoscope used in this study requires a slight alteration in tube placement technique, it follows logically that the time to intubation in the normal and neck immobility scenarios was slightly increased. Although participants were allowed trial intubations with the video laryngoscope before the study, most had very little prior experience using this device.

Second, the normal and neck immobility scenarios using the SimMan proved not to be difficult for the majority of our participants using standard laryngoscopy. This may explain why the video laryngoscope did not offer any additional benefits in this setting. Some of this is likely due to the fact that learners pay less attention to a mannequin’s lips and teeth than in live patients, and the study participants were able to achieve these views at the expense of “injuring” the mannequin.

Third, the tongue edema scenario was always simulated last; participants may have felt more comfortable intubating with the video laryngoscope at this stage. As this scenario provides the most obstructive view, even if the participants do not pay close attention to the lips and teeth of the mannequin, it is extremely difficult to obtain a view of the cords. Therefore, this is less of a confounding variable, and may be why we see a difference between direct laryngoscopy and video laryngoscopy in this scenario. The Macintosh blade was used first in all participants, so some degree of comfort with the mannequin may have been established before the video laryngoscope scenarios.

There were not enough participants to perform a subgroup analysis on impact of level of training on results. There was also insufficient data to perform a statistical analysis on the grade view achieved in each scenario. These grade views were not independently verified after being reported by study participants for direct laryngoscopy.

CONCLUSIONS

Video laryngoscopy is a technology that, once perfected, will be used more frequently in emergent airway management. After only a brief in-service, using a high-fidelity simulation mannequin, our results showed that in the most difficult airway case, tongue edema, the video laryngoscope provided an enhanced view of the cords using less time, increased intubation success, and decreased the time to intubation. Our study suggests that the video laryngoscope used in this study would be an extremely valuable tool in facilitating intubation in the most challenging airways. Although standard laryngoscopic intubation was faster for normal and c-spine immobilization simulated airways, it remains to be seen whether this holds true once the operators have become more experienced and comfortable with the new technology. These questions warrant further study in clinical trials.

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Keywords:

Video laryngoscopy; GlideScope; Simulation; Difficult airway

© 2009 Lippincott Williams & Wilkins, Inc.