The GlideScope video laryngoscope (GVL; Verathon Medical, Bothell, WA, USA) is the most commonly used device for emergency intubations [1]. Some previous comparative studies showed the GVL outperformed the direct laryngoscope (DL) in terms of glottis visualization, but there was little difference in success rate between the two methods [1-6]. These studies were limited by the fact that the analyses were performed shortly after introduction of the GVL into clinical research training. Although the GVL has been used since 2001, it is still regarded as a relatively new device compared to a conventional DL.

The National Emergency Airway Registry (NEAR) group reported that GVL use has been dramatically increasing in emergency departments (EDs) [7]. Sakles et al. [8] reported that GVL performance has significantly improved over the past seven years. It is assumed that a similar phenomenon is observed in other EDs. Alteration in performance and usage frequency of GVL may be inversely related to those of DL [5]. Though previous studies showed the overall performance of GVL was not significantly superior to DL, the changes of usage frequency and performance of these two devices in recent years can alter the DL’s equivalence with GVL. The goal of this study was to assess changes of usage frequency and intubation success rates during a first attempt using GVL and DL over ten years in two academic EDs.

During the study period, we recorded 3,386 of 3,484 (97.2%) adult ETI cases for whom DL or GVL was used. Emergency physicians were the first operators in 2817 (83.2%) cases (Fig. 1). Of these, we included 1,896 intubations in season I and 921 intubations in season II in our final analysis.

Table 1 shows the difference in distribution of variables potentially associated with FPS rate between season I and season II. GVL intubations comprised 48.0% of cases in season II, which is almost twice as high as the rate of that (24.4%) in season I. DL use decreased from 91.6% to 45.0%, while GVL usage increased from 8.4% to 55.4% over the ten-year period. There was no significant difference by gender; however, the mean age of patients was 57 (standard deviation±17.1) years and 63 (standard deviation ±16.8) years in season I and season II, respectively (P<0.001). In terms of the indications for intubation, trauma was far more frequent in season I than in season II (P<0.001), and indications in season I and season II were significantly different (P<0.001). There was no significant difference in the frequency of crash airways between season I and season II (P=0.292). Expected difficult glottis exposures in season I and season II did not differ (P=0.523). However, the rate of rapid sequence intubation (RSI) was 54.3% in season II compared to 42.4% in season I (P<0.001). There was 85.3% Cormack-Lehane I/II in season I and 91.0% in season II (P<0.001). Level of the first operator differed significantly between season I and season II; PGY 1 was the most frequent in season I (P<0.001); however, the frequency of PGY 1, PGY 2, and PGY 3 and greater did not differ in season II.

Over the ten-year period, there were changes in the frequency of DL use on the first attempt and FPS rate (Fig. 2). In 2006, 91.6% of emergency physicians chose DL on the first attempt, regardless of their training level; however, DL use fell to 45% in 2015. Consistent with the decrease in the frequency of DL use, the FPS rate using DL also declined from 90.8% in 2007 to 75.5% in 2015. On the other hand, the FPS rate using GVL increased. Comparisons of GVL and DL between season I and season II revealed that the FPS rate with the GVL increased from 89.6% to 94.8% (P=0.004) as did the frequency of more favorable glottis views (Cormack-Lehane I and II) from 93.3% to 98.2% (P<0.001). In contrast, the DL FPS rate decreased from 86.1% in season I to 76.2% in season II, and the frequency of favorable glottis views did not differ significantly between season I and season II (P=0.439) (Table 2).

Table 3 provides an overview of the changes in FPS rate over time by operator level. The DL FPS rate declined by approximately 10% in season II compared to season I across all levels of emergency physician. The FPS rate with GVL, on the other hand, increased slightly among PGY 1 and PGY 2 physicians, but the difference was not significant (P=0.237 and P=0.145, respectively). However, there was a significant increase in GVL FPS rate among PGY 3 and greater physicians (P=0.043).

Table 4 shows the results of multivariate logistic regression analysis for predicting FPS rate according to time period. During season I, the adjusted OR of GVL FPS rate was 0.799, and this result was not statistically significant (P=0.274). However, the adjusted OR of GVL FPS rate was 3.744 during season II, and it was statistically significant (P<0.001). The expected glottis exposure and glottis exposure grade had a significant independent effect on FPS during both seasons. If the first operator was a PGY 3 or greater, the OR for FPS was significant in season I (OR, 2.026; confidence interval, 1.319 to 3.112; P<0.001), but not in season II (OR, 1.373; confidence interval, 0.777 to 2.246; P=0.275).

This study was conducted using an airway registry maintained in two academic EDs. We used logistic regression analysis of the registry data by time change (season I and II) because we found that circumstances surrounding intubation differed significantly between season I and season II. Over the ten-year period documented by the registry, we observed some notable changes in airway management associated with the rate of RSI, grade of the first operator and type of device used between the two seasons. The rate of RSI increased from 42.4% to 54.3%, but after excluding cases of crash airway that did not require RSI, the rate of RSI rose from 75.5% to 93.2%. The increase in the rate of RSI in our study might be attributed to critical factors such as registry management providing feedback on RSI and continuous education including a member of Korean Emergency Airway Management Society in order to boost the implementation of RSI. With regard to the first operator’s level of experience, there was a higher percentage of first operators with little experience (PGY 1) in season I, but there was a higher rate of senior operators such as PGY 3 and greater performing the first intubation in season II. Above all, the biggest change we observed over the ten-year study period was the equipment selected for the first attempt. The two academic EDs participating in this study began using the GVL immediately after its introduction in 2006 and thus many of the physicians are skilled with this method. Over time, the preference for GVL has increased because it enables a good view of the glottis, is easy to learn, and is used more frequently than DL. One odd case of a temporary increase in DL use was observed in 2013, which was attributed to the fact that some faculty felt it would be difficult for operators to maintain appropriate DL technique due to the gradual decrease in its frequency of use and therefore they instructed emergency medicine residents, particularly PGY 1, to use DL preferentially. However, this intentional action ultimately did not change operator preference. Eventually the GVL was used more often than DL in 2015 and this trend is likely to continue in the future.

The less a medical device is used, the less experience can be gained, and the converse may be true. Previous studies have shown that the GVL provides better glottis views than DL, and it is easier for a physician even with little intubation experience to learn the GVL procedure than conventional laryngoscopy [2,4]. However, despite these advantages over DL, the overall performance of the GVL is not superior to that of DL [1,2,4,5]. The most likely reason for this result is that an experienced operator optimizes his or her ability to overcome the disadvantages of conventional intubation methods with DL [1-3,5,6,11-13]. In this study, the FPS rate with DL dropped from 86.1% to 76.2%. We assumed that it is mostly due to decreased frequency of DL usage. In the same context, it is reasonable to assume that the increased GVL’s FPS rate (89.6% to 94.8%) was due to increasing frequency of GVL usage. These phenomenon may contribute to the selection of GVL becoming the most effective factor for FPS in season II.

We found in our study that the level of the first operator rarely affected success rate, as the success rate of GVL performed by PGY 1 and PGY 2 physicians increased alongside an increase in the frequency of GVL. In contrast, the decreased number of DL attempts by PGY 3 and over decreased the DL success rate.

Other researchers have reported that use of video laryngoscopy including the GVL has been rapidly increasing [7,8,14]. In our analysis, a greater than 90% FPS rate was observed with GVL regardless of the operator’s level of training; therefore, we presume that the GVL will be a routinely recommended device, not an alternative device or first choice only for special situations. We also found that the LEMON mnemonic and good glottis exposure remain critical factors in determining FPS, irrespective of the device type. Thus, we believe that assessment using the LEMON mnemonic is needed for the GVL.

There are several limitations to this study. First, we used registry data for ETIs performed at just two academic EDs in Korea. Thus, these results may not be generalizable to all ED settings. In addition, we did not attempt to collect data on other variables (patients, operators, and environmental factors) that could potentially affect the FPS rate. Last, there could have been operator bias given that the data were self-reported.

We found over a ten-year period that the DL’s FPS rate decreased along with its frequency of use, and more and more operators used the GVL, and the success rate increased. The FPS rate of the GVL has become significantly higher than that of DL, particularly over the last two years. This seems to be associated with changing frequency of usage of the two devices.