Original Contribution

Tracheal intubation by inexperienced medical residents using the Airtraq and Macintosh laryngoscopes–a manikin study^B

Chrisen H. Maharaj MB, BSc^a,b,c, Martina Ni Chonghaile MB^a,b,c, Brendan D. Higgins PhD^b,c, Brian H. Harte MB^a,

John G. Laffey MD, MA, BSc^a,b,c,*

^aDepartment of Anaesthesia, University College Hospital Galway, Ireland

^bDepartment of Anaesthesia, Clinical Sciences Institute, National University of Ireland, Galway, Ireland

^cNational Centre for Biomedical Engineering Sciences, National University of Ireland, Galway, Ireland

Received 15 February 2006; accepted 14 March 2006

Abstract The Airtraq laryngoscope is a novel intubation device that may possess advantages over conventional direct laryngoscopes for use by personnel that are infrequently required to perform tracheal intubation. We conducted a prospective study in 20 medical residents with little prior airway management experience. After brief didactic instruction, each participant took turns performing laryngoscopy and intubation using the Macintosh (Welch Allyn, Welch Allyn, NY) and Airtraq (Prodol Ltd. Vizcaya, Spain) devices, in 3 laryngoscopy scenarios in a Laerdal Intubation Trainer (Laerdal, Stavanger, Norway) and 1 scenario in a Laerdal SimMan manikin (Laerdal, Kent, UK). They then performed tracheal intubation of the normal airway a second time to characterize the learning curve. In all scenarios tested, the Airtraq decreased the duration of intubation attempts, reduced the number of optimization maneuvers required, and reduced the potential for dental trauma. The residents found the Airtraq easier to use in all scenarios compared with the Macintosh laryngoscope. The Airtraq may constitute a superior device for use by personnel infrequently required to perform tracheal intubation. D 2006

Introduction

In the emergency setting, personnel with limited clinical experience in the skills of direct laryngoscopy may be

^B This study was funded by departmental resources.

* Corresponding author. Department of Anaesthesia, Clinical Sciences Institute, National University of Ireland, Galway, Ireland.

E-mail address: [email protected] (J.G. Laffey).

required to perform tracheal intubation. Several studies have demonstrated improved outcome in critically injured patients if the airway is secured early by endotracheal intubation [1-3]. However, difficult or failed tracheal intubation in this context constitutes an important cause of morbidity, arising from direct airway trauma and the systemic complications of hypoxia [4,5]. Novel intubation devices may reduce the potential for morbidity arising from difficulties in tracheal intubation encountered by less experienced personnel.

0735-6757/$ – see front matter D 2006 doi:10.1016/j.ajem.2006.03.014

The Airtraq is a new intubation device that has been developed for the management of the normal and the difficult airway (Fig. 1). It is designed to provide a view of the glottis without alignment of the oral, pharyngeal, and tracheal axes. The blade of the Airtraq consists of 2 side- by-side channels. One channel acts as the housing for the placement and insertion of the endotracheal tube , whereas the other channel terminates in a distal lens. A battery-operated light is present at the tip of the blade. The image is transmitted to a proximal viewfinder using a combination of lenses and prisms rather than fiber optics. The viewing lens allows visualization of the glottis and surrounding structures, and the tip of the tracheal tube. The Airtraq is anatomically shaped, and standard ETTs of all sizes can be used. The blade is inserted into the mouth in the midline, over the base of the tongue, and the tip positioned in the vallecula, using the viewfinder to optimize the view of the glottis. Once the view of the glottis has been optimized, the ETT is passed through the vocal cords, held in place, and the device removed. A clear view of the glottis and ETT is maintained throughout the intubation process and the ETT does not obstruct the view of the vocal cords.

Our group has recently demonstrated that Airtraq device performs superiorly to the conventional Macintosh laryn- goscope when used by experienced anesthesiologists in simulated difficult laryngoscopy [6]. Notably, we observed a rapid learning curve for the device. Based on these findings we proposed that the Airtraq may possess advantages over conventional laryngoscopes for use by less experienced personnel. The purpose of this study was to evaluate the usefulness of this new device for use by

Fig. 1 Photograph of the Airtraq laryngoscope with a tracheal tube in place in the side channel.

personnel with some, but limited prior experience of tracheal intubation, in anatomically correct manikins. We hypothesized that, in the hands of inexperienced laryngo- scopists, the Airtraq would be equal or superior to the Macintosh laryngoscope in the normal and simulated difficult airway.

Methods

After ethical committee approval, and written informed consent, 20 medical residents with some, but limited prior experience of performing tracheal intubation, consented to participate. All participants had received prior training with the Macintosh laryngoscope, and performed duties on the trauma and/or cardiac arrest team when on call, but had performed less than 10 tracheal intubations at the time of recruitment into the study. Each resident was given a standardized 10-minute demonstration of both the Macin- tosh and the Airtraq devices by 1 of the investigators, which included a demonstration of the intubation technique with each device and oral instructions regarding the correct use of each device. The use of optimization maneuvers, such as external laryngeal pressure, to facilitate intubation with the Macintosh was also demonstrated. Each participant was then allowed 5 practice intubations with each device, at which stage all residents could successfully perform tracheal intubation with both devices. All intubations were per- formed with a 7.5-gauge cuffed tracheal tube. The sequence in which each participant used the devices was randomized, and each participant used the devices in the same sequence throughout the protocol.

The design of the study was a randomized crossover trial. Each resident first performed tracheal intubation with each device in a Laerdal Airway Management Trainer (Laerdal, Stavanger, Norway) in the following laryngoscopy scenar- ios: (1) normal airway in the supine position; (2) normal airway in the left lateral position; and (3) Cervical immobilization. The participants then performed tracheal intubation in a SimMan manikin (Laerdal, Kent, UK) in the

(4) pharyngeal obstruction difficult laryngoscopy scenario. At the end of this protocol, each subject performed tracheal intubation of the normal airway a second time in the Laerdal Airway Management Trainer with each device to charac- terize the learning curve.

The primary end point was the duration of tracheal intubation attempts. The duration of each tracheal intubation attempt was defined as the time taken from insertion of the blade between the teeth until the ETT was deemed to be correctly positioned by each participant. Where the partic- ipant was unsure as to the position of the ETT, the time taken to connect the ETT to an Ambu bag (GaleMed, I-Lan, Taiwan) and inflate the lungs was also included in the duration of the attempt. In any case, after each intubation attempt, an investigator verified the position of the ETT tip. A failed intubation attempt was defined as an attempt in

which the trachea was not intubated or where intubation of the trachea required greater than 120 seconds to perform.

Additional end points included the rate of successful placement of the ETT in the trachea, the number of intubation attempts, the number of optimization maneuvers required (readjustment of head position, second assistant) to aid tracheal intubation, and the severity of dental trauma. The severity of dental trauma was calculated based on the number of audible teeth clicks (0, 1, or N1) with the Laerdal airway trainer and based on a grading of pressure on the teeth (none = 0, mild = 1, moderate/severe =2) in the SimMan manikin. At the end of each scenario, each participant scored the ease of use of each device on a visual analog scale (from 0 = extremely easy to 10 = extremely difficult).

Data for duration of the first and the successful intubation attempt and the instrument difficulty score were analyzed using the t test. Data for the success of tracheal intubation attempts were analyzed using v² test or Fisher exact test as appropriate. The number of intubation attempts, number of optimization maneuvers, and severity of dental trauma were analyzed using the Mann-Whitney rank sum test. Contin- uous data are presented as means F SD, and ordinal and categorical data are presented as number and as frequencies. The a level for all analyses was set as P b .05.

Results

Twenty residents consented to participate in the study. All residents were in their second to fifth year of training, and no participant had previously performed more than 10 tracheal intubations.

Fig. 2 Graph representing the duration required to success- fully intubate the trachea with each device in each scenario tested. The data are given as mean F SD. Normal Airway-start indi- cates intubation of the normal airway at the start of the protocol; left lateral, intubation of the normal airway in the left lateral position; cervical immobilization, SimMan cervical spine rigidity scenario; pharyngeal obstruction, SimMan pharyngeal obstruction scenario; normal airway-end, intubation of the normal airway at the end of the protocol. *Significantly different compared with the Macintosh laryngoscope.

Scenario 1–normal airway at start of protocol

The duration of both the first and the successful tracheal intubation attempts were significantly shorter with the Airtraq compared with the Macintosh Laryngoscope (Table 1 and Fig. 2). All residents successfully intubated the trachea with the Airtraq, compared with 19 (95%) with the Macintosh laryngoscope (Table 1). All residents intu- bated the trachea on the first attempt with the Airtraq laryngoscope, whereas 4 required more than 1 attempt with the Macintosh laryngoscope. The severity of dental trauma was significantly lower with the Airtraq (Table 1). The

Fig. 3 Graph representing the user-rated degree of difficulty of use of each instrument in each scenario tested. The data are given as mean F SD. *Significantly different compared with the Macintosh laryngoscope.

Table 1 Data from easy laryngoscopy scenario at the start of

the protocol in the Laerdal Airway Trainer

Parameter assessed

overall success rate (%) Duration (first attempt)

No. of intubation attempts (%) 1

2

3

Macintosh

19 (95)

36.0 F 32.7

Airtraq

20 (100)

18.1 F 6.7*

16 (80)

3 (15)

1 (5)

20 (100)

0

0

No. of optimization maneuvers (%)

0 16 (80) 20 (100)

1 3 (15) 0

N1 1 (5) 0

Dental trauma (teeth clicks) (%)

0 6 (30) 18 (90)**

1 9 (45) 2 (10)

N1 5 (25) 0

Data are reported as mean F SD or as number (percentage).

* P b .05, significantly different compared with the Macintosh laryngoscope.

** P b .01, significantly different compared with the Macintosh laryngoscope.

0	7 (35)	18 (90)**	0	14 (70)	20 (100)
1	5 (25)	2 (10)	1	3 (15)	0
N1	8 (40)	0	N1	3 (15)	0

participants found the Airtraq significantly easier to use in this scenario (Fig. 3).

Table 2 Data from laryngoscopy in left lateral position

scenario in the Laerdal Airway Trainer

Parameter assessed Macintosh Airtraq Overall success rate (%) 10 (50) 16 (80)

Duration (first attempt) 89.0 F 44.0 44.3 F 40.2** No. of intubation attempts (%)

1 7 (35)

2 3 (15)

3 10 (50)

15 (75)*

1 (5)

4 (20)

No. of optimization maneuvers (%)

Dental trauma (Teeth Clicks) (%)

0 3 (15)

1 4 (20)

N1 13 (65)

15 (75)**

5 (25)

0

Data are reported as mean F SD or as number (percentage).

* P b .05, significantly different compared with the Macintosh laryngoscope.

** P b .01, significantly different compared with the Macintosh laryngoscope.

Table 4 Data from pharyngeal obstruction scenario in the

SimMan manikin

Parameter assessed Macintosh Airtraq Overall success rate (%) 18 (90) 20 (100)

Duration (first attempt) 35.0 F 32.9 12.4 F 5.5** No. of intubation attempts (%)

1 16 (80) 20 (100)

2 1 (5) 0

3 3 (15) 0

No. of optimization maneuvers (%)

Dental compression (severity) (%)

0 0

Mild (+) 7 (35)

Severe (++) 13 (65)

10 (50)**

9 (45)

1 (5)

Data are reported as mean F SD or as number (percentage).

** P b .01, significantly different compared with the Macintosh laryngoscope.

Scenario 2–normal airway with head in left lateral position

The Airtraq significantly reduced the duration (Fig. 2) and number of intubation attempts, the number of optimization maneuvers, and the severity of dental trauma (Table 2). The

participants found the Airtraq significantly easier to use in this scenario (Fig. 3).

Scenario 3–difficult airway with cervical spine rigidity

The Airtraq significantly reduced the duration (Fig. 2) and number of intubation attempts, the number of optimi- zation maneuvers, and the severity of dental trauma (Table 3). The participants found the Airtraq significantly easier to use in this scenario (Fig. 3).

Table 5 Data from easy laryngoscopy scenario at the end of

the protocol in the Laerdal Airway Trainer

Parameter assessed

Overall success rate (%) Duration (first attempt)

No. of intubation attempts (%) 1

2

3

Macintosh

19 (95)

23.2 F 24.6

Airtraq

20 (100)

10.0 F 4.6*

18 (90)

1 (5)

1 (5)

20 (100)

0

0

No. of optimization maneuvers (%)

0 16 (80) 20 (100)

1 4 (20) 0

N1 0 0

Dental trauma (teeth clicks) (%)

0 11 (55) 20 (100)*

Data are reported as mean F SD or as number (percentage).

* P b .05, significantly different compared with the Macintosh laryngoscope.

Table 3 Data from cervical spine immobilization scenario in

the Laerdal Airway Trainer

Parameter Assessed

Overall Success Rate (%) Duration (first attempt)

No. of intubation attempts (%) 1

2

3

Macintosh

15 (75)

65.9 F 50.8

Airtraq

19 (95)

30.8 F 31.7*

11 (55)

1 (5)

8 (40)

18 (90)*

1 (5)

1 (5)

No. of optimization maneuvers (%)

0 11 (55) 20 (100)**

1 3 (15) 0

N1 6 (30) 0

Dental trauma (teeth clicks) (%)

0 4 (20)

1 4 (20)

N1 12 (60)

18 (90)**

2 (10)

0

Data are reported as mean F SD or as number (percentage).

* P b .05, significantly different compared with the Macintosh laryngoscope.

** P b .01, significantly different compared with the Macintosh laryngoscope.

1	8 (40)	0
N1	1 (5)	0

Scenario 4–difficult airway with pharyngeal obstruction

The Airtraq significantly reduced the duration of intubation attempts (Fig. 2) and the severity of dental trauma (Table 4). There was no difference in the number of intubation attempts or the number of optimization maneuvers required with each device (Table 4). The participants found the Airtraq significantly easier to use in this scenario (Fig. 3).

Scenario 5–normal airway at end of protocol

The duration of intubation attempts with the Airtraq was significantly shorter than that required at the start of the protocol, illustrating rapid Skill acquisition for this device (Fig. 2). In contrast, there was no difference in the duration of intubation attempts with the Macintosh laryngoscope compared with that required at the start of the protocol. The Airtraq significantly reduced the severity of dental trauma (Table 5) and was easier to use in this scenario (Fig. 3).

Discussion

Several studies have demonstrated improved outcome in severely ill and injured patients if the airway is secured early by tracheal intubation [1-3]. Medical personnel that are relatively inexperienced in the skills of direct laryngoscopy may therefore be required to perform tracheal intubation as a lifesaving maneuver in the ED or in the prehospital arena. However, tracheal intubation in these emergent situations poses particular difficulties. In the prehospital setting, tracheal intubation is more difficult to perform, with a lower success rate, particularly in inexperienced hands [7]. The occurrence of difficulties and/or failure to successfully intubate the trachea constitutes an important cause of morbidity [4,5,8]. The need for repeated attempts to secure the airway emergently increases airway-related complica- tions such as hypoxia, pulmonary aspiration, and adverse hemodynamic events [5]. Of particular concern, accidental Esophageal intubation in emergency situations outside the operating room results in high incidences of severe hypoxemia, regurgitation and pulmonary aspiration of gastric contents, cardiac dysrhythmias, and cardiac arrest [4]. Difficulties in tracheal intubation may also result in severe local complications such as perforation of laryngeal or pharyngeal structures [9].

These difficulties have led several commentators to question the practice of Prehospital tracheal intubation by personnel not fluent in the technique [10-12]. A slow learning curve for intubation with the Macintosh blade has been well documented among paramedical personnel [13,14] due to the lack of regular exposure to the technique. These difficulties have led to the increasing use of supra- glottic devices (such as Combitube, laryngeal tube, and

Laryngeal Mask Airway) for airway management in these contexts [15-17] because of the rapid learning curves associated with these devices [18,19]. However, trauma to the airway and aspiration injury remain a significant risk with these devices in these patients.

Many of the complications of tracheal intubation result from attempts, often multiple, to view glottic structures using rigid blades. Conventional direct laryngoscopic laryngoscopes, such as the Macintosh laryngoscope, require the alignment of oral and tracheal axes to view the Glottic opening. This is a difficult skill to successfully acquire [12,13,20], and to maintain [14], particularly if the opportunities to practice this skill are limited, such as in the case of nonanesthesiologists required to perform tracheal intubation in emergency situations. This difficulty is further compounded by the fact that emergent tracheal intubation, for example, in the prehospital setting, is more difficult to perform, with a lower success rate, particularly if performed by inexperienced personnel [7].

The Airtraq device has the potential to reduce the morbidity arising from difficulties in tracheal intubation encountered by personnel infrequently required to perform tracheal intubation. It has an exaggerated curvature with enhanced optics that gives an excellent view of the glottis with minimal airway manipulation. The curved laryngo- scope blade described by Macintosh in 1943 [21] remains the most popular device used to facilitate orotracheal intubation; notwithstanding recent developments in airway device technologies, it constitutes the gold standard. We therefore decided to compare the utility of the Airtraq to the Macintosh laryngoscope for use by medical residents with limited airway management experience in 2 different anatomically correct manikins, in 4 scenarios simulating easy and difficult laryngoscopy.

Our study demonstrates that, in comparison to the Macinotsh laryngoscope, the Airtraq provides superior intubating conditions in the normal airway. All residents successfully intubated the normal airway with both devices in the final scenario. At the end of the protocol, the duration required for the intubation attempt was reduced significantly for the Airtraq, but not the Macinotsh laryngoscope, illustrating the rapid learning curve with the Airtraq. The Airtraq device significantly reduced the duration of intubation, the requirement for maneuvers to optimize the laryngoscopic view obtained, and reduced the potential for dental trauma at both the start and at the end of the protocol.

The Airtraq also provided superior intubating conditions in the simulated difficult airway, a scenario not uncommon outside the operating room where intubating conditions and assistance may be suboptimal. In the simulated difficult airway scenarios, the Airtraq resulted in a higher percentage of successful intubations, reduced the time required to perform tracheal intubation, required fewer airway optimi- zation maneuvers, and caused less dental trauma than the Macintosh Laryngoscope. Of particular interest, the duration

of intubation attempts with the Airtraq compared well with that recorded by experienced anesthesiologists in our recent study [6]. This finding highlights the ease of use and the rapid learning curve associated with this device, for both experienced and inexperienced laryngoscopists. The medi- cal residents also found the Airtraq easier to use than the Macintosh laryngoscope, as reflected in their lower Instru- ment Difficulty Score for the Airtraq device.

The Airtraq provides a high-quality view of the glottis without a need to align the oral, pharyngeal, and tracheal axes, and therefore requires less force to be applied during laryngoscopy. Our present study attests to this, by the fact that, the dental trauma scores were lower with the Airtraq laryngoscope, particularly in the difficult airway scenarios. This may translate into a requirement for less operator skill to use this device compared with the Macintosh laryngo- scope, leading to more rapidly acquired proficiency in personnel who are infrequently required to perform tracheal intubation, such as ED staff. That the device exhibits a rapid learning curve, despite a deliberately brief instruction period supports this contention.

The Airtraq, as a single-use device, removes the potential for transmission of prions, which are thought to be responsible for causing variant Creutzfeldt-Jakob disease [22,23]. This complies with the guidelines of the Associa- tion of Anaesthetists of Great Britain and Ireland, which state that bsingle-use intubation aidsQ should be used where possible [24] because of difficulties in ensuring that all proteinaceous material has been removed during cleaning and sterilization [22,25].

In conclusion, the Airtraq laryngoscope appears to possess advantages over the conventional Macintosh laryn- goscope when used by inexperienced laryngoscopists. In this manikin study, the Airtraq laryngoscope performed superiorly in both the normal and the difficult airway scenarios. Further clinical studies are necessary to confirm these initial positive findings.

Acknowledgment

We would like to thank Prodol Ltd for the provision of the Airtraq device.

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