Brief Report

Tracheal intubation using Macintosh and 2 video laryngoscopes with and without chest compressions^?

Young-Min Kim MD ^a,?, Ji-Hoon Kim MD ^a, Hyung-Goo Kang MD ^b, Hyun Soo Chung MD ^c,

Hyeon-Woo Yim MD, MPH ^d,e, Seung-Hee Jeong MPH ^e

^aDepartment of Emergency Medicine, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea

^bDepartment of Emergency Medicine, College of Medicine, Hanyang University, Seoul 133-791, Korea

^cDepartment of Emergency Medicine, College of Medicine, Yonsei University, Seoul 120-752, Korea

^dDepartment of Preventive Medicine, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea

^eCMC Clinical Research Coordinating Center, The Catholic University of Korea, Seoul 137-701, Korea

Received 17 October 2009; revised 16 February 2010; accepted 17 February 2010

Abstract

Purpose: The aim of the study was to compare the time taken for intubation (TTI) using the Macintosh and 2 video laryngoscopes (VLs) (GlideScope [GVL]; Saturn Biomedical System, Burnaby, British Columbia, Canada, and airway scope [AWS]; Pentax, Tokyo, Japan) with and without chest compressions by experienced intubators in a mannequin model.

Methods: This was a randomized crossover study. Twenty-two experienced physicians who have limited experience in the VLs participated in the study. The TTI using 3 laryngoscopes with and without compressions were compared.

Results: Median TTI difference between 2 conditions was only significant in the AWS (1.64 seconds; P = .01). There were no significant differences in the TTI between the Macintosh and the GVL or the AWS during compressions.

Conclusion: In a mannequin model, the Macintosh or the GVL was not affected by chest compressions. The TTI using the AWS was delayed by compressions but not clinically significant. Considering the lack of experience, 2 VLs may be useful adjuncts for intubation by experienced intubators during chest compressions.

(C) 2011

Introduction

^? Sources of support: Two video laryngoscopes used in these studies were donated free by the local distributors of Pentax Corporation and Saturn Biomedical System during the study period. The mannequin and simulator used in the study were supported by the local distributor of Laerdal Medical. No authors obtained any financial support from these companies.

* Corresponding author. #505 Banpo-Dong, Seocho-Gu, Seoul 137-

701, Korea. Tel.: +82 2 2258 1989; fax: +82 2 536 1984.

In direct laryngoscopic intubation using a conventional laryngoscope such as the Macintosh laryngoscope , optimal head positioning is usually required to align the oral, pharyngeal, and tracheal axes. During chest compressions, direct laryngoscopic intubation could be difficult due to movement of chest wall and neck even in experienced hands. Several video laryngoscopes (VLs) including the Glide- Scope video laryngoscope (GVL; Saturn Biomedical

0735-6757/$ - see front matter (C) 2011 doi:10.1016/j.ajem.2010.02.014

System, Burnaby, British Columbia, Canada) and the Airway Scope (AWS; Pentax, Tokyo, Japan) that incorporate a small-size video camera on the modified blades are now commercially available. The GVL and the AWS are designed to assess the airway anatomical structure indirectly and provide a glottic view without requiring alignment of 3 airway axes. With the kind of merit, both VLs may be useful for advanced airway management during cardiopulmonary resuscitation (CPR).

The GVL and the AWS have been compared in mannequin models and used successfully in the patients with Difficult airways [1-6]. However, the use of the VLs during CPR has not been extensively studied. To date, there have been one case report and one fresh Cadaver study (in press) on the use of the AWS during chest compressions and a Mannequin study comparing the MAC and the AWS with and without chest compressions ongoing [7-9]. There was no study to compare the time taken for intubation (TTI) using the MAC and 2 VLs with and without chest compressions ongoing.

The purpose of this study was to compare the TTI using the MAC and 2 VLs (GVL and AWS) with and without chest compressions by experienced intubators in a manne- quin model.

Methods

After institutional review board approval, we performed a randomized crossover mannequin study. Twenty-two emer- gency physicians who had performed more than 50 direct laryngoscopic intubations participated in this study. In- formed consent was obtained from each participant before the study. They had 1-hour prior training with the GVL and the AWS. After watching the manufacturers’ demonstration videos, participants were allowed 30 to 40 minutes to practice until they could use each device correctly. The Airway Management Trainer (Laerdal Medical, Stavanger, Norway) was used in prior training session.

After the prior training session, each participant started their intubations on a Resusci Anne Simulator (Laerdal Medical, Stavanger, Norway) that was used for airway interventions during chest compressions in a previous study [10]. The mannequin was placed on an 80-cm height hospital bed with a foam-filled mattress and rigid back board. The order of intubation using 3 laryngoscopes (a size 3 MAC [Welch Allyn Inc, NY]), an adult blade GVL, and an adult blade AWS) with or without chest compressions was randomized for each participant to minimize any learning effects. Randomization schedule came from a computer program.

Each participant was instructed to pick up the laryngo- scope and start the intubation. After the intubation was done, an assistant inflated the endotracheal tube cuff and attempted to ventilate the lung of the mannequin with a self-

inflating bag. Cricoid pressure and External laryngeal manipulation were not applied by the assistant. Each attempt was consistently timed by a third party with a stopwatch. The participants used a 7.0-mm internal diameter ETT and a standard malleable stylet for the MAC and the dedicated rigid stylet for the GVL. Chest compressions were performed by a certified basic life support provider according to current CPR guidelines [11]. The Laerdal PC Skill Reporting System (Laerdal Medical, Stavanger, Norway) connected to the mannequin was used to maintain the consistency of chest compressions.

The primary outcome measure was the time taken for successful placement of the ETT in the trachea. The TTI was measured from the time when the device passed between the incisors to clearly visible chest rising of the mannequin when ventilated. The secondary outcome measure was rates of successful intubation. An intubation attempted was consid- ered unsuccessful if the esophagus was intubated with visible inflation of the stomach bag or it took more than 30 seconds to perform because the CPR guidelines regard a lack of ventilation for more than 30 seconds as unacceptable [12,13]. This was an exploratory study, and no Power calculation was made a priori. The Wilcoxon Signed Rank Test was used to examine differences between the TTI using a device with and without chest compressions because some data were not normally distributed. To examine differences in TTI between the 2 of 3 devices, we also used the Wilcoxon signed rank test and Freidman analysis of variance. The P values derived from these tests were multiplied by 3 to correct for multiple comparisons before we considered significance. The Fisher exact test was used to compare the rates of successful intubation among 3 groups. For all statistical analysis, SAS version 8.02 for Windows (SAS Institute Inc, Cary, NC) was used. A value of P b .05 was

considered statistically significant.

Results

Participants consisted of 19 men (86%) and 3 women

(14%). Average age was 31.3 +- 2.8 years. Five (23%) were attending physicians and 17 (77%) were emergency medicine residents (postgraduate year [PGY] 5, n = 6; PGY 4, n = 6; PGY 3, n = 5).

There were no significant differences in the TTI using the MAC or the GVL between with and without chest compressions. The difference between the TTI using the AWS with and without chest compressions was statistically significant, but the median time difference was 1.64 seconds (Table 1).

In comparison of the TTI among 3 laryngoscopes, there was no significant difference between the MAC and the GVL without chest compressions (P = .180). The AWS was significantly faster than the MAC or the GVL without chest compressions (P = .002 or P b .0001, respectively). The

MAC		AWS	GVL
TTI (without compressions), s	15.60 (14.06 to 19.60)	13.58 (11.54 to 15.28)	19.36 (17.04 to 23.90)
TTI (with compressions), s	17.08 (14.40 to 20.03)	14.16 (12.32 to 17.53)	20.82 (16.72 to 24.57)
Median time difference, s	0.14 (-3.60 to 4.03)	1.64 (-0.46 to 3.96)	1.13 (-1.38 to 3.35)
P	.63	.01	.33
Values are presented as median (interquartile range).

median TTI using the AWS was significantly shorter than the GVL with chest compressions (P b .0001). However, there were no significant differences between the MAC and the GVL or the AWS in TTI with chest compressions (P = .329 or P = .180, respectively) (Table 2).

Table 1 Time taken for intubation and median time differences using 3 laryngoscopes with and without chest compressions

There was one unsuccessful intubation using the MAC without chest compressions. During chest compressions, 2 intubators using the MAC and the GVL had unsuccessful intubations, respectively. There was no significant difference in rates of successful intubation among 3 groups in both conditions (without chest compressions, P = 1.00; with chest compressions, P = .54).

In retrospective power calculation, at least 17 subjects per each group would be required to achieve 82% power to detect differences among the laryngoscopes with a 0.05 significant level.

Discussion

In this study, the MAC or the GVL was not affected by chest compressions. The TTI using the AWS significantly delayed by chest compressions but the median time difference was short (1.64 seconds) and not clinically significant. These results show that chest compressions did not significantly affect the TTI using the MAC and the 2 VLs by experienced intubators in a mannequin model. Our data correspond with the results of a previous study that included the physicians who had various intubation experiences [10]. In the study, chest compressions also had a minor effect (3.3 seconds) on the TTI using the MAC on the same mannequin model [10]. These results may support the recommendations

in current CPR guidelines that any placement of an advanced airway devices should be achieved with the least possible interruption of chest compressions and intubation using a conventional laryngoscope should be performed by experi- enced intubators during CPR [13,14]. However, there is a recognized problem with mannequin study that times to perform airway interventions are generally quicker than in real patients. Therefore, more relevant clinical investigations should be required to support these findings.

In comparison of the TTI among 3 laryngoscopes, there were no significant differences in TTI and success rates between the MAC and the GVL or the AWS during chest compressions in our study. Our result comparing the MAC and the AWS was different to the results of a recent mannequin study of less experienced physicians [9]. In the study, intubation time was significantly faster with the AWS than the MAC during chest compressions in a mannequin model under conditions of both normal and difficult airways [9]. Although the AWS was significantly faster than the MAC without chest compressions, there was no significant difference between 2 laryngoscopes during chest compres- sions in our study.

Considering the lack of experience, 2 VLs may be potentially useful adjuncts for tracheal intubation by experienced intubators during CPR. However, some partici- pants also showed a problem associated with insertion of ETT despite good glottic visualization when they used the GVL as the previous report [2]. We also observed that tracheal intubation using the AWS on hospital bed was disturbed by chest compressions because ETT placed in the side channel was often contacted on the chest wall or hands of the compressor. Although the median TTI using the AWS was significantly shorter than the GVL during chest compres-

Table 2 Comparison of the TTIs between the laryngoscopes with and without chest compressions
Intervention	Device comparison	Median time difference, sec	P ?
Without compressions	MAC vs AWS	2.23 (0.25 to 5.38)	.002
With compressions	MAC vs GVL AWS vs GVL MAC vs AWS	-2.88 (-6.66 to 2.51) -5.80 (-9.62 to -4.37) 2.47 (-0.59 to 4.53)	.180 b.0001 .180
	MAC vs GVL AWS vs GVL	-4.43 (-8.34 to 2.06) -4.19 (-8.75 to -2.00)	.329 b.0001
Values are presented as median (interquartile range). * Bonferroni-adjusted values.

sions, the clinical significance of this 4-second difference is also questionable. This difference could be due to difference in the techniques for tube placement. The AWS has a channel to guide the ETT and target mark on the monitor; if the tip of blade is placed posterior to the epiglottis and glottis is located at the center of mark, the ETT is self-guided toward the glottis. The Airtraq laryngoscope (Prodol Meditec, Vizcaya, Spain) that has similar guiding channel such as the AWS showed shorter TTI and learning curve than the MAC or GVL in previous mannequin studies [15,16]. The GVL uses a different technique for placing the ETT; once an adequate glottic view is obtained, the intubator must steer the ETT with the right hand. Training is often required to acquire for this steering technique. Therefore, it is likely that the skills to insert the ETT with the GVL are more complex and require more time to be performed than with the AWS.

Furthermore, whether such time differences among 3 laryngoscopes exists in clinical practice and is of any clinical relevance is currently unknown. In our recent fresh cadaver study (in press), the novice intubators felt that the AWS was more difficult to handle than the MAC during chest compressions [8]. Although not in only cardiac arrest, the AWS has not also demonstrated quicker intubation times compared to direct laryngoscopy in recent randomized studies of patients with difficult airway and the GVL required significantly more time to intubate than direct laryngoscopy in a recent observational study [4,17,18]. Although a case report and mannequin study showed that the AWS was successfully used in intubation during chest compressions, further validation of the 2 VLs in the clinical setting is needed [7,9]. Furthermore, it is also necessary to evaluate the cost-effectiveness and durability of 2 VLs in emergency situations.

There are several limitations in our study. Chest compressions on a mannequin model do not perfectly represent clinical CPR. Although we used the best available mannequin that was already evaluated and also used in previous study, the difference with chest compressions in real patients may exist. As with all other mannequin studies, it is also difficult to predict how our results would translate into clinical practice. The TTI using each laryngoscope were obtained by only a single intubation attempt per each condition. The possibility that there are different results by multiple intubation attempts cannot be excluded. Successful placement of the ETT in the trachea was only verified by chest rising of the mannequin. It would be better to use more objective methods for verification. We made no optimization of intubation procedures and were unable to assess the complications associated with intubation using each laryngoscope. The stylet use was clearly different with 3 laryngoscopes. The variations may have skewed intubation times. In addition, no power calculation was made a priori. However, based on the results of retrospective power calculation, our sample size has 82% power to detect differences among the laryngoscopes with a 0.05 significant level.

Conclusion

In a mannequin model, the TTI using the MAC or the GVL was not affected by chest compressions. The TTI using the AWS significantly delayed by chest compressions but not clinically significant. Considering the lack of experience,

2 VLs may be potentially useful adjuncts for tracheal intubation by experienced intubators during chest compres- sions. Further studies are required to validate whether these findings are clinically relevant.

Acknowledgment

The authors thank Hyun-Jeung Kim, EMT-B, for data collection and management. We also appreciate James J. Menegazzi, PhD, in the Department of Emergency Medicine, University of Pittsburgh, Pittsburgh, Pa, who kindly provided the critical review of the article.

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