a b s t r a c t

Purpose: The purpose of this study was to compare the effectiveness of a Xenon halogen with a light-emitting diode (LED) laryngoscope light handle in a difficult airway scenario, as well as in an inhalation injury airway sce- nario that combines a difficult airway and a limited view.

Methods: We recruited forty-two anesthetists into a randomized crossover trial. Each performed tracheal intuba- tion (TI) with a Xenon halogen and a LED light handle in the two manikin scenarios. The primary endpoint was the “time to intubate”. Other endpoints were the “time to vocal cords”, the “time to ventilate”, the rate of success- ful intubation, the number of intubation attempts, the Cormack-Lehane score, the number of optimization ma- neuvers, the number of audible dental click sounds indicating dental damage and subjective impressions.

Results: In the difficult airway scenario, no significant differences in the recorded intubation times were observed. In the inhalation injury airway scenario, the Intubation times were significantly shorter using the LED light han- dle. Regarding the subjective values, the LED illuminant enabled a significant better view and illumination of the oropharyngeal space and the vocal cords, in both manikin scenarios.

Conclusion: The LED laryngoscope light handle did not affect the recorded intubation times in the simulated dif- ficult airway scenario, but provided significant advantages in the inhalation injury airway scenario that combines a difficult airway with a limited view caused by a sooted pharynx. We therefore hypothesize, that the LED illumi- nant might be beneficial in the airway management of burn patients with severe inhalation injury.

(C) 2017

Introduction

Inhalation injury has become the most frequent cause of death in acute phase of burn patients [1] and it is often associated with a difficult airway caused by facial edema, acute upper airway obstruction [2] and the presence of soot in the pharynx [3]. Thus airway management in burn patients represents a clinical challenge, even in the hands of board-certified anesthesiologists [4]. Complications arising from diffi- cult or failed tracheal intubation remain a leading cause of anesthesia associated morbidity and mortality [5]. Moreover, repeated intubation attempts are associated with decreased success rates on the first rescue intubation in the emergency department [6], transportation delays, lon- ger hospital stays, worse neurologic outcomes [7] and increased mortal- ity [8]. Therefore, the equipment for tracheal intubation in burn patients with severe inhalation trauma should meet the highest requirements.

Multiple laryngoscope characteristics, including blade size, length and shape, are known to affect intubation success [9]. The laryngoscope illumination is another important variable and may be crucial to suc- cessful tracheal intubation. Multiple factors influencing the light

* Corresponding author.

E-mail address: [email protected] (A. Moritz).

intensity have already been identified. Milne and colleagues, for exam- ple, examined the effects of different laryngoscope light handles on the light intensity from disposable Laryngoscope blades [10]. However there are enormous variations in illumination provided by reusable and dis- posable laryngoscope blades [11-13]. Several articles have proposed minimum or optimum laryngoscope light intensity requirements for in- tubation with a wide range of reported values: minimum 597 lx [14], 700 lx [15], 867 lx [16], optimum 200-1938 lx [17]. The initial draft of the lighting standard from the International Organization for Standard- ization (ISO) had proposed a minimum of 700 lx [13,15,17]. However, Moore and colleagues showed, in a non-modified airway manikin study, that the intensity of laryngoscope light, over three clinically fea- sible levels of light strength, did not affect the time to successful intuba- tion [18]. Akihisa and colleagues demonstrated that the use of a light- emitting diode (LED) laryngoscope light handle provided superior conditions for intubation with a plastic single-use blade and improved intubation performance comparative to that of a metal reusable blade during simulated CPR of an infant manikin [19]. However, to our knowledge no previous study has examined the effects of different laryngoscope illuminants on intubation neither in a difficult nor in an inhalation injury airway scenario, yet. Thus, the purpose of this study was to compare the effectiveness of a Xenon halogen with a LED

http://dx.doi.org/10.1016/j.ajem.2017.05.008

0735-6757/(C) 2017

laryngoscope light handle in a simulated difficult airway scenario caused by a rigid cervical collar as well as in a simulated inhalation inju- ry airway scenario that combines a difficult airway caused by a rigid cer- vical collar and a limited view caused by a sooted pharynx.

Methods

Study design and setting

Forty-two anesthetists with a median clinical experience of 4.3 years (inter-quartile range (IQR): 2.5-6) participated in this randomized crossover trial. Data were anonymized and information on the perfor- mance of individual participants was not made available to anybody outside the research team. We notified the study to the local ethics com- mittee (Ethics Committee of the Friedrich-Alexander University Erlang- en-Nurnberg). The ethics committee waived a formal submission for approval.

Each anesthetist performed tracheal intubation with a laryngoscope system containing a 3.5 V Xenon halogen bulb (reusable x-lite Macin- tosh laryngoscope blade size 3, Wirutec Rusch Medical Vertriebs GmbH, Sulzbach, Germany; Heine Standard F.O. XHL metallic laryngo- scope handle, Heine Optotechnik GmbH & Co. KG, Herrsching, Germa- ny) and with a laryngoscope system containing a 3.5 V LED illuminant (reusable x-lite Macintosh laryngoscope blade size 3, Wirutec Rusch Medical Vertriebs GmbH, Sulzbach, Germany; Heine Standard F.O. 4 LED NT metallic laryngoscope handle, Heine Optotechnik GmbH & Co. KG, Herrsching, Germany) in a difficult airway scenario manikin (Fig. 1) (Laerdal Medical AS, Stavanger, Norway) as well as an inhalation in- jury airway scenario manikin (Fig. 2) (Erlanger-Inhalation Injury-Man- ikin, a modified Laerdal Medical AS manikin [20]).

To simulate an inhalation injury, we used the previous published Er- langer-Inhalation Injury-Manikin [20]. The pharynx of this manikin was pigmented with activated carbon (Fig. 3). The neck of both manikins was fixed in a neutral position by a Rigid cervical collar and thus the dis- tance between the free edge of the upper and lower incisors (interden- tal distance) was limited. These conditions turned it into a difficult intubation model [21].

The order in which the manikins were tested was randomized by opening two sealed opaque envelopes containing the names of

Fig. 1. Laerdal Airway Management Trainer. The difficult airway is simulated by Cervical immobilization applying a cervical collar.

Fig. 2. Erlanger-Inhalation Injury-Manikin, a modified Laerdal Airway Management Trainer. The difficult airway is simulated by cervical immobilization applying a cervical collar. The pharynx is pigmented with activated carbon [20].

the manikins. The sequence of laryngoscope handle use was also ran- domized for each scenario by using two sealed opaque envelopes con- taining the names of the laryngoscope illuminants.

thermal injury to Supraglottic structures results in edema and can rapidly lead to upper airway obstruction [22]. Therefore all intubations were performed with a 6.0 mm cuffed endotracheal tube (ETT; Super Safetyclear endotracheal tube, I.D. 6.0 mm, Wirutec Rusch Medical Vertriebs GmbH, Sulzbach, Germany). Before each intubation attempt, a reusable endotracheal tube introducer was inserted into the ETT. The cuff was lubricated with a silicone spray and the cuff was inflated and deflated with a 10 ml syringe.

Measurements

Objective findings

The primary endpoint was the “time to intubate”. Esophageal intu- bations, attempts requiring N 120 s and N 2 attempts were recorded as failed intubation attempts. All time measurements were made by the same person by direct observation with a stopwatch to avoid interob- server error.

Fig. 3. Oropharynx of the Erlanger-Inhalation Injury-Manikin. To simulate an inhalation injury the pharynx is pigmented with activated carbon.

In order to compare the different light handles, the intubation process was divided into different time episodes:

• The time to visualization of the glottis (“time to vocal cords”) was de- fined as the time from insertion of the blade between the teeth until the glottis was visualized.

• The time to tracheal intubation (“time to intubate”) was defined as the time from insertion of the blade between the teeth until the ETT was expected to be correctly positioned.
• The duration of a successful intubation attempt was defined as the time from insertion of the blade between the teeth until the ETT was connected to a self-inflating resuscitation bag and the presence of lung inflation was confirmed (“time to ventilate”).

We recorded the rate of successful intubation, the number of intuba- tion attempts and the Laryngeal view according to the Cormack-Lehane score. The number of optimization maneuvers (readjustment of the head position, application of external laryngeal pressure and the need for assistance by a second person) and the number of audible dental click sounds indicating dental damage were recorded as 0, 1, and >= 2 times during the tracheal intubation attempt.

Subjective findings

After completing the procedure, each anesthetist was asked to score

• the view
• the illumination of the oropharyngeal space
• the illumination of the vocal cords
• the difficulty of tracheal intubation

using a Numeric rating scale (NRS) (0 to 100 mm, from excellent/very easy to poor/very difficult). Following each scenario, the participants were asked to indicate their preferred illuminant.

Light intensity findings

Light intensity or illuminance (lx), was measured similar to Milne and colleagues [10]. Both handle/blade combinations were tested five times. The rechargeable 3.5 V battery/handle sets were placed on a recharging unit between the tests and the intubations. The battery/han- dle sets were frequently replaced to avoid the effects of battery deple- tion on light intensity [23,24].

Data analysis

Data for the success of tracheal intubation attempts were analyzed using the chi-square test. Data for the number of intubation attempts, the “time to vocal cords”, the “time to intubate”, the “time to ventilate”, the number of optimization maneuvers, the number of Dental clicks, the Cormack-Lehane score, the view, the difficulty of tracheal intubation, the illumination of the oropharyngeal space and of the vocal cords were analyzed using the Wilcoxon signed-rank test. For statistical com- parisons of the intubation times between the two airway scenarios the Mann-Whitney U test was used. All analyses were performed by Statistica 6 software (StatSoft (Europe) GmbH, Hamburg, Germany). Statistical significance was accepted at p b 0.05. Continuous data are presented as mean (standard deviation, SD), ordinal data were present- ed as medians (interquartile range, IQR), and categorical data were pre- sented as percentages (%). The sample size estimation was based on “time to intubate”-duration compiled in a pilot study. According to this data, the mean (SD) time required for the successful intubation at- tempt was 18.9 s (8.4) in the inhalation injury airway scenario. During the design of this study we expected, that a decrease of 25% in intuba- tion time would be of clinical impact. Considering an ? error of 0.05 and ? error of 0.1, sample size calculation results, that at least 36 partic- ipants would be required.

Results

Participant characteristics

Forty-two anesthetists participated in this study: 24 (57%) were male and 18 (43%) female with a mean age of 33 years. 32 (76%) senior house officers, 7 (17%) specialist registrars and 3 (7%) consultants took part in the study.

Scenario 1: difficult airway

In the difficult airway scenario, no significant differences in the num- ber of tracheal intubation attempts, the rate of successful TI and the re- corded intubation times were observed between the Xenon halogen and the LED illuminated laryngoscope handle. There were no significant differences for the severity of Dental compression, the Cormack-Lehane score and the number of optimization maneuvers. However, regarding the subjective values the LED illuminant enabled a significant better view and illumination of the oropharyngeal space and the vocal cords (p b 0.001). 43% (95% confidence interval (CI): 28.1%-58.9%) of the par- ticipants would prefer the LED light handle, 55% (95% CI: 38.8%-69.8%) of the anesthetists would use both and only 2% (95% CI: 0.1%-14.1%) would prefer the Xenon halogen light handle in the difficult airway sce- nario (Table 1).

Scenario 2: inhalation injury airway

In the inhalation injury airway scenario, the number of tracheal intu- bation attempts and the rate of successful TI were not significantly dif- ferent between the Xenon halogen and LED illuminated laryngoscope handle. We could not find significant differences for the severity of den- tal compression, the Cormack-Lehane score and the number of optimi- zation maneuvers. However, regarding the primary endpoint, the LED light handle provided a significant shorter “time to intubation“, when compared with the Xenon halogen light handle (p b 0.001). The “time to vocal cords” (p b 0.01) and the “time to ventilate” (p b 0.01) were also significantly shorter using the LED illuminant. Furthermore, the LED illuminant enabled a significant better view and illumination of the oropharyngeal space and the vocal cords (p b 0.001). The intubation with the LED light handle was judged easier (p b 0.001) and most of the anesthetists (71%) (95% CI: 55.2%-83.8%) would prefer the LED illumi- nant (Table 2).

In our view-limited inhalation injury airway scenario, the recorded intubation times were significantly increased with both the Xenon hal- ogen (p b 0.001) and the LED light handle (p b 0.05 “time to vocal cords” and “time to ventilate”; p b 0.01 “time to intubate”) when compared with the intubation times in the difficult airway scenario.

Light intensity characteristics

The mean (SD) light intensity measured from the different light han- dles in conjunction with the reusable Macintosh laryngoscope blade was 6090 (112) lx for the Heine 3.5 V Xenon halogen light handle and 14938 (390) lx for the Heine 3.5 V LED light handle.

Discussion

In this study, the LED illuminant enabled a significant better view and illumination of the oropharyngeal space and the vocal cords in the simulated difficult airway scenario as well as in the simulated inhalation injury airway scenario that combines a difficult airway and a limited view, when compared with the Xenon laryngoscope light handle. This could be due to the emitted light spectrum and the different brightness of illumination. The light intensity measured in conjunction with the re- usable Macintosh laryngoscope blade, that provides higher illuminance values than other metal and plastic disposable blades [10], was 2.5 times

Table 1

Tracheal intubation data for Xenon halogen and LED laryngoscope light handle in the difficult airway scenario. Data are presented as median (inter-quartile range, IQR) or as number, n (%) (95% confidence interval, including continuity correction). ???p b 0.001, LED handle vs. Xenon halogen handle.

	Xenon halogen	LED
overall success rate, n (%) [95% CI]	42 (100) [89.6-100]	42 (100) [89.6-100]
Number of intubation attempts, n (%) [95% CI]
1	42 (100) [89.6-100]	42 (100) [89.6-100]
2	0 (0) [0-10.4]	0 (0) [0-10.4]
3	0 (0) [0-10.4]	0 (0) [0-10.4]
Median (IQR)	1 (1-1)	1 (1-1)
Severity of dental compression, n (%) [95% CI] 0	40 (95.2) [82.6-99.2]	39 (92.9) [79.5-98.1]
1	2 (4.8) [0.8-17.4]	3 (7.1) [1.9-20.6]
>= 2	0 (0) [0-10.4]	0 (0) [0-10.4]
Median (IQR)	0 (0-0)	0 (0-0)
Number of optimization maneuvers, n (%) [95% CI] 0	42 (100) [89.6-100]	42 (100) [89.6-100]
1	0 (0) [0-10.4]	0 (0) [0-10.4]
>= 2	0 (0) [0-10.4]	0 (0) [0-10.4]
Median (IQR)	0 (0-0)	0 (0-0)
Time to vocal cords, s, median (IQR)	4 (3.3-6)	4.1 (3.1-5.3)
Time to intubate, s, median (IQR)	8.9 (7.2-10.5)	8.4 (6.7-10.6)
Time to ventilate, s, median (IQR)	17.3 (14-20.2)	16.4 (14.2-20)
View, cm, median (IQR)	1 (0.8-2.8)	0.9 (0-1.5)???
Illumination of the oropharynx, cm, median (IQR)	1.7 (0.9-2.9)	1 (0-1.4)???
Illumination of the vocal cords, cm, median (IQR)	1.5 (1-2.9)	1 (0.1-1.4)???
Difficulty of tracheal intubation, cm, median (IQR)	1 (0.3-2)	1 (0.1-1.5)
Cormack-Lehane score, median (IQR)	1 (1-1)	1 (1-1)
Preferred illuminant, n (%) [95% CI]
LED	18 (42.9) [28.1-58.9]
Xenon halogen	1 (2.4) [0.1-14.1]
No difference	23 (54.8) [38.8-69.8]

higher using the LED illuminant. Murphy and colleagues also observed that among battery-powered devices, LED light handles were vastly su- perior to incandescent laryngoscopes, with a 2.5 times greater illumi- nance [25]. Though the Xenon halogen bulb offers a color rendering index (CRI) over 80 and a higher color temperature when compared with vacuum bulbs, the LED illuminant emits a monochromatic white

light similar to daylight which may lead to a greater distinction of laryngeal and pharyngeal tissues and which would be preferable for in- tubation [17]. Crosby et al. suggested that an illuminant with higher color temperature (with less red) is probably more desirable for direct laryngoscopy as less of the light will be absorbed by the viewed tissue structures, leading to a greater appreciation of laryngeal anatomy [26].

Table 2

Tracheal intubation data for Xenon halogen and LED laryngoscope light handle in the inhalation injury airway scenario. Data are presented as median (inter-quartile range, IQR) or as num- ber, n (%). ??p b 0.01, LED handle vs. Xenon halogen handle. ???p b 0.001, LED handle vs. Xenon halogen handle.

	Xenon halogen	LED
Overall success rate, n (%) [95% CI]	42 (100) [89.6-100]	42 (100) [89.6-100]
Number of intubation attempts, n (%) [95% CI]
1	42 (100) [89.6-100]	42 (100) [89.6-100]
2	0 (0) [0-10.4]	0 (0) [0-10.4]
3	0 (0) [0-10.4]	0 (0) [0-10.4]
Median (IQR)	1 (1-1)	1 (1-1)
Severity of dental compression, n (%) [95% CI] 0	40 (95.2) [82.6-99.2]	41 (97.6) [85.9-99.9]
1	1 (2.4) [0.1-14.1]	1 (2.4) [0.1-14.1]
>= 2	1 (2.4) [0.1-14.1]	0 (0) [0-10.4]
Median (IQR)	0 (0-0)	0 (0-0)
Number of optimization maneuvers, n (%) [95% CI] 0	40 (95.2) [82.6-99.2]	42 (100) [89.6-100]
1	2 (4.8) [0.8-17.4]	0 (0) [0-10.4]
>= 2	0 (0) [0-10.4]	0 (0) [0-10.4]
Median (IQR)	0 (0-0)	0 (0-0)
Time to vocal cords, s, median (IQR)	6 (4.4-8.7)	5.1 (3.5-7)??
Time to intubate, s, median (IQR)	13.1 (9.8-17.9)	11.8 (7.7-14.4)???
Time to ventilate, s, median (IQR)	22.6 (18.6-29.1)	20 (15.3-24.9)??
View, cm, median (IQR)	3 (1.9-5)	1.7 (1-3)???
Illumination of the oropharynx, cm, median (IQR)	3.9 (2-5)	1.7 (1-2.9)???
Illumination of the vocal cords, cm, median (IQR)	3 (2-4.9)	1.9 (1-3)???
Difficulty of tracheal intubation, cm, median (IQR)	2.9 (1.1-4)	1.9 (1-3)???
Cormack-Lehane score, median (IQR)	1 (1-1)	1 (1-1)
Preferred illuminant, n (%) [95% CI]
LED	30 (71.4) [55.2-83.8]
Xenon halogen	0 (0) [0-10.4]
No difference	12 (28.6) [16.2-44.8]

The subjective ratings of the participants confirm these findings. They commented favorably on the much whiter light being emitted by the LED light handle.

In the simulated inhalation injury airway scenario, the recorded in- tubation times were significantly increased with both the Xenon halo- gen and the LED illuminant when compared with the intubation times in the difficult airway scenario. This data suggests, that due to the limit- ed view caused by the sooted pharynx the identification of laryngeal structures was more difficult and time-consuming than in the difficult airway scenario. Thus, the simulated inhalation injury and the described illumination characteristics of both illuminants could explain, why the LED light handle was associated with significant decreased intubation times in the simulated inhalation injury airway scenario but not in the simulated difficult airway scenario, when compared with the Xenon halogen illuminant. Scholz and colleagues showed that anesthetists can see the larynx at very low light levels but that in case of a restricted view caused by blood or soot, the likelihood of a successful intubation is higher with better illumination [17]. Without light-absorbing activated carbon, the anesthetists can identify landmarks of the anatomy and may be able to perform successful intubation with lower illumination from the laryngoscope. This correlates with the findings of Moore and col- leagues. They demonstrated in a non-modified airway manikin study, that the intensity of laryngoscope light, over three clinically feasible levels of light strength, did not affect the time to successful intubation [18]. Akihisa and colleagues showed that the use of a LED light handle provided superior conditions for intubation with a plastic single-use blade and improved intubation performance comparative to that of a metal reusable blade during chest compression and reduced glottis vi- sualization [19].

The findings of this study demonstrate an intubation benefit for the LED illuminant in the airway management of patients with severe inha- lation injury. Although the statistically significant difference in intuba- tion times between the two laryngoscope illuminants is relatively short, increased intubation times have been shown to correlate with greater morbidity and mortality, and the development of a “can’t intubate – can’t ventilate” scenario [8,27]. Furthermore, prolonged intu- bation times are considered to be a risk factor for the aspiration of gastric contents and are independently associated with Oxygen desaturation. Thus, in the emergency scenario, where all patients are strictly considered not sober and preoxygenation efforts appear to be marginally effective [28-30], the recorded difference in intubation times may be of clinical impact. Therefore, the equipment for emergen- cy tracheal intubation in patients with severe inhalation injury should meet the highest requirements.

Limitations

This study has some limitations. First, this study is a manikin and not a clinical study. However, the simulation of intubation scenarios in ana- tomically correct manikins has been described to be a reliable surrogate for the Clinical context [31]. Second, the potential for bias exists, as the study could not be blinded either to the participants or the assessors. Third, the anesthetists were aware that their actions were being timed, which could lead to an altered performance as a result of the Hawthorne effect [32]. Fourth, certain measurements used in this study, such as grading the view, have a subjective nature. Fifth, because of the potential upper airway obstruction caused by oropharyngeal edema in patients with inhalation injury, all intubations were per- formed with a 6.0 mm cuffed ETT. The results might have been different using another size or brand of ETT. Finally, we compared only one Xenon halogen and one LED illuminated laryngoscope handle. There are other types of laryngoscope illuminants available and their effects on intubation in the airway scenarios might be different and should be investigated. The maximum illumination provided by both light sources used in this study is higher than that provided by vacuum bulbs [25,33]. In addition vacuum bulbs emit a light with more red/yellow color and a

lower color temperature [17,26]. Thus using a vacuum bulb, the report- ed effect of prolonged intubation times with a Xenon halogen illumi- nant in a view-limited airway could even be higher.

Conclusions

In conclusion, the LED illuminant enabled a significant better view and illumination of the oropharyngeal space and the vocal cords in both manikin scenarios, but did not affect the recorded intubation times in the simulated difficult airway scenario. However, in the simu- lated inhalation injury airway scenario, that combines a difficult airway caused by a rigid cervical collar and a limited view caused by a sooted pharynx, the LED laryngoscope light handle provided a significant shorter “time to intubation”, “time to vocal cords” and “time to venti- late”, when compared with the Xenon halogen laryngoscope light han- dle. We therefore hypothesize, that the LED illuminant, with its monochromatic white light and higher color temperature, might be beneficial in the airway management of patients with severe inhalation injury. Further comparative studies in a clinical setting are necessary to confirm our findings.

Author’s contributions

AM conceived the study, analyzed the results and drafted the manu- script. JP and JS contributed significantly to the planning of the study and the study design. JS recruited the participants and helped to draft the manuscript.

Conflict of interest and source of funding statements

The authors declare that they have no conflict of interest and that this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgments

The authors wish to thank the entire anesthesiology staff of the Uni- versity Hospital Erlangen for the support and the participation in this manikin study.

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