a b s t r a c t

Introduction: Pre-hospital airway management is complex and complications occur frequently. Guidelines advice using waveform capnography to confirm correct tube position, but in the emergency setting this is not universally available. Continuous visualization of the airway with a video tube (VivaSight SL(TM)) could serve as an alternative confirmation method, provided that airway structures are properly recognized. With this study we wanted to investigate whether airway management practitioners were able to recognize anatomical structures both in a circulated and in a non-circulated airway.

Methods: Ten staff anesthetists, ten trainee anesthetists and ten paramedics were asked to examine four pictures of a circulated airway, obtained in a healthy patient and four pictures of a non-circulated airway, obtained in a human cadaver. Correct recognition of the tube position in the airway was scored.

Results: Anatomic structures in the circulated airway were more often recognized than in the non-circulated airway, 90% vs. 43% respectively (P b .001). Overall, anesthetists performed better than paramedics (P = .009), but also when only pictures of the non-circulated model were taken into account (P = .007). The majority of participants and all staff anesthetists correctly recognized the vocal cords in both the circulated and non- circulated airway.

Conclusions: Pictures of a circulated airway were more often recognized than of a non-circulated airway and per- sonnel with a daily routine in airway management performed better than personnel with less frequent exposure. Future research should determine whether continuous visualization of the airway with a video tube could reduce the number of misplaced tracheal tubes in pre-hospital airway management.

(C) 2016

Introduction

Airway management during cardiopulmonary resuscitation can be challenging [1,2]. Particularly in the pre-hospital setting, failed, esophageal and endobronchial intubations are common complications and all can be rapidly catastrophic [3-6]. Current guidelines advice using waveform capnography to confirm correct tube placement [7]. This gold standard confirmation method is however not universally avail- able and is also frequently misinterpreted in the emergency setting [8].

In order to prevent unrecognized Esophageal intubation, many authors now advocate the use of supraglottic airway devices (SADs) in pre-hospital airway management [1,9-11]. However, these devices do not reliably secure the airway from gastric contents and are not suitable when high inspiratory pressures are required. Therefore, after initial SAD placement, patients who present with cardiopulmonary arrest frequently still need to be intubated [12].

? Funding: This study was supported by departmental funding only.

* Corresponding author at: Department of Anesthesiology, VU University Medical Cen- ter, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands.

E-mail address: [email protected] (E.M. Koopman).

Recently the VivaSight SL(TM) (ET View Ltd., Misgav, Israel) (Fig. 1) be- came available. This is a single use tracheal tube with a high-resolution camera embedded in its tip, which allows continuous visualization of the airway and therefore may serve as an alternative to capnography in confirming correct tube position. This device has also been used to intubate the trachea under continuous visualization through one of various SADs [13-15]. This may be an ideal technique to secure the airway after initial pre-hospital SAD placement. A precondition to this technique is that airway management providers are able to visually recognize different airway structures.

With this study we aimed to evaluate whether medical personnel involved in Emergency airway management was able to recognize different airway structures, both in a circulated and in a non- circulated situation.

Material and methods

Study design

The Institutional Review Board of the VU University Medical Center approved this pilot study. We enrolled ten staff anesthetists, ten trainee anesthetists and ten paramedics as volunteers to compare pictures

http://dx.doi.org/10.1016/j.ajem.2016.03.044

0735-6757/(C) 2016

Fig. 1. VivaSight(TM) Single Lumen tube with an integrated camera in its tip.

obtained with a VivaSight tube in a circulated airway of a healthy patient and in a non-circulated human cadaver. All participants gave written informed consent for participation. The patient gave written informed consent for the publication of the pictures of her airway.

Tube description

The VivaSight is a single use, single lumen tracheal tube with a high- resolution camera embedded in its tip (Fig. 1). This camera is connected to an external monitor with a video cable. An additional sideport at the proximal part of the tube is used to flush the camera lens with saline when secretions block the view. The VivaSight tube is currently

available in sizes 7.0, 7.5 and 8.0. Its outer shape and sizes are similar to other commonly used Endotracheal tubes.

Study setting

After consent we intubated a healthy patient scheduled for elective surgery with a VivaSight size 7.0 and took pictures with the incorporated camera at four characteristic positions. The first image was taken directly above the vocal cords, the second directly below the vocal cords, the third more distal in the patient’s trachea where the carina was visible and one last image was obtained in the patient’s esophagus (Fig. 2).

To simulate a non-circulated airway, we intubated an embalmed human cadaver provided by the Anatomy Department of the VU University. For this intubation we also used a VivaSight 7.0, and took pictures at identical positions as in the patient (Fig. 3).

Study protocol

The pictures of the circulated and of the non-circulated airway were shown to the study participants in a random order. For each picture the participants were asked whether it was taken in the esophagus or in the trachea and in case of the trachea, at what position it was taken.

Data collection

Profession, number of years of airway management experience and number of correct recognitions of tube position were scored.

Data analysis

Results were analyzed using SPSS 22.0 (IBM, Stuttgart, Germany). Data are presented as median (IQR). Kruskal-Wallis test was used to analyze the results and the Mann-Whitney U test when differences between two groups were tested. Pearson’s chi squared test was used

Fig. 2. Four images of a circulated airway obtained with the VivaSight SL tube. A: right in front of the vocal cords B: trachea at subglottic level C: trachea at carina level D: esophagus.

Fig. 3. Four images of a non-circulated airway obtained with the VivaSight SLtube. A: right in front of the vocal cords B: trachea at subglottic level C: trachea at carina level D: esophagus.

to compare frequencies. A p-value b 0.05 was considered statistically significant.

Results

The main results of this study are summarized in Table 1.

The median (IQR) years of airway management experience of the staff anesthetists, trainees and paramedics was 12 (8-26), 3 (1-4) and 16 (7-20) respectively.

Airway structures in the circulated model were more often recognized than in the non-circulated model, 90% vs. 43% respectively (P b .001).

Overall there was a significant difference in the number of correctly recognized pictures between the staff anesthetist group, the trainee group and the paramedic group (P = .013). Staff anesthetists performed better than paramedics (P = .009), but not when compared to the trainees (P = .17). Staff anesthetists also performed better than para- medics when only pictures of the non-circulated model were taken into account (P = .007).

Both in the circulated and in the non-circulated airway, the picture of the vocal cords was the one most often recognized. The majority of

participants, and in particular all staff anesthetists, were able to recog- nize this picture in both conditions.

Discussion

We believe this is the first study to report on visual recognition of airway structures in both a circulated and a non-circulated model by different groups of airway management providers. It demonstrates that anatomical structures are more often recognized in a circulated than in a non-circulated model. Furthermore professionals with a daily experience in airway management (anesthetists) perform better in recognizing airway structures than professionals with less frequent experience (paramedics). It also shows that anatomical structures in a non-circulated model are infrequently recognized by all airway management providers, but still more often by anesthetists than by paramedics.

As mentioned before, failed, esophageal and endobronchial intubations are common complications in airway management during cardiopulmonary resuscitation, particularly in the pre-hospital setting. There may be a number of reasons for this high incidence of incorrect tube placements. First, the vast majority of pre-hospital airway manage- ment providers consist of paramedics with less training in and less

Table 1

Total number (percentage) of correctly recognized pictures at the four different positions in the circulated and non-circulated airway by the three groups of participants

Circulated airway Non-circulated airway

	Vocal cords	Subglottic level	Carina level	Esophagus		Vocal cords	Subglottic level	Carina level	Esophagus
Staff Anesthetists	10	10	10	8		10	3	3	8
	(100%)	(100%)	(100%)	(80%)		(100%)	(30%)	(30%)	(80%)
Trainee Anesthetists	10	10	10	9		5	2	1	8
	(100%)	(100%)	(100%)	(90%)		(50%)	(20%)	(10%)	(80%)
Paramedics	10	8	8	5		4	0	3	8
	(100%)	(80%)	(80%)	(50%)		(40%)	(0%)	(30%)	(80%)

exposure to airway management compared to anesthetists who intubate patients in the operating theater on a daily basis [9,16]. Furthermore, the circumstances in which pre-hospital airway manage- ment is done are far less ideal than the controlled setting in an operating theater. In general the choice of equipment is different and the teams are smaller. It is not uncommon for blood, secretions and gastric contents to impair clear visualization of the airway and patients cannot always be placed in an ideal ‘sniffing’ intubation position [17]. Last, after intubation has been performed, confirming correct tube position can be challenging, as not one single confirmation method is completely reliable. The current gold standard to confirm correct tube placement, as also recommended by the 2015 CPR guidelines, is waveform capnography [7]. But as mentioned in the 4th National Audit Project of the UK Royal College of Anesthetists and the Difficult Airway Society (NAP4), capnography is not universally used and can easily be misinterpreted during a cardiac arrest [8].

The camera in the VivaSight tube may serve as an alternative method of confirming correct tube position. On the monitor one can see the tube entering the trachea in real time and subsequently observe the correct position of the tube, that is, in front of the carina.

Another potential advantage of using the VivaSight during cardio- pulmonary resuscitation is its ease of insertion through an SAD. These devices are used increasingly often during cardiopulmonary resuscita- tion, because they are easy to insert and there is no risk of esophageal intubation [1,18]. However, despite their life-saving capabilities during Initial resuscitation, SADs need to be replaced by a tracheal tube at some point, since they do not reliably protect the airway from aspiration of gastric contents [19]. Some modern SADs, such as the intubating la- ryngeal mask airway ILMA(TM) (Intavent; Orthofix Ltd., Maidenhead, Berkshire, UK) and Air-Q, also known as the Intubating Laryngeal Airway(TM) (ILA; Cook-gas, St Louis, MO, USA) are specifically designed to serve as a conduit for tracheal intubation. However blind intubation success rate through these SADs is generally disappointing and fiberoptical guidance should always be considered [20-22]. In a previous study we found that intubation with a VivaSight through an SAD, is easy to learn and has a high success rate [13]. We believe this intubating technique can be particularly useful for health care professionals with a limited exposure to airway management, such as paramedics and emergency physicians. However, in order to use this technique, one needs to be able to recognize airway structures.

In the present study we found that anesthetists performed better than paramedics in recognizing airway structures. This is not surprising, since the first group has a daily routine and many years of training in examining airway structures both in easy and Difficult airways, while the latter group only occasionally requires participating in airway man- agement. Furthermore, all anesthetists in our institute have experience in examining the airway beyond the glottic level with a fiberoptic bronchoscope, while most paramedics will not have this experience. Therefore we believe that visual recognition of airway structures and subsequently intubation with a VivaSight tube through an SAD is a technique that can be trained. In previous studies it was found that the learning curve to reach a 90% success rate in tracheal intubation by direct laryngoscopy required 47 to 57 patients [23,24]. Airway management with a videolaryngoscope or an SAD requires far less training [25,26]. In our own experience, intubation with a VivaSight through an SAD is easy to learn. A biomedical student without any previous experience in airway management was able to repeatedly intubate a manikin in our simulation room successfully with this tech- nique after verbal instructions and a short demonstration [13].

We also found that airway structures were more often recognized in the circulated than in the non-circulated model. The pictures of the cir- culated airway in our study show a much sharper visual contrast be- tween the pink mucosa and the more pale cartilage structures such as the epiglottis and the tracheal rings, than the pictures of the cadaveric airway. To our knowledge no studies have been published describing airway structures in a cadaver or during cardiac arrest, but we believe

lack of mucosa perfusion will impair recognition of airway structures during resuscitation. Nonetheless, again anesthetists performed better than paramedics, suggesting that also in a non-circulated airway, train- ing will improve correct recognition.

A limitation of this study is that we used an embalmed cadaver to simulate a non-circulated airway instead of a real patient in cardiac arrest. We decided to do this since it is obviously difficult to obtain informed consent from a patient or a relative during or directly after cardiopulmonary resuscitation. Furthermore, in the cadaver we had time to take pictures at the exact same locations in the airway as we previously obtained in the well-circulated patient.

Another limitation is that the participants were asked to determine what they recognized on static images while in reality the process of ad- vancing the tube through the SAD and into the glottis is obviously a con- tinuous process. Secretions then may temporarily impair visualization. Similar to advancing a fiberoptic bronchoscope in the airway, it is usual- ly not problematic when vision of the VivaSight camera is temporarily blocked. However it is important to be able to recognize certain key an- atomic structures such as the vocal cords, tracheal rings and carina in order to be certain that the tube has entered the trachea and not the esophagus. With this study we wanted to investigate whether airway management providers were able to recognize these specific anatomical structures and in order to compare recognition between different groups and between a circulated and non-circulated airway, we decided to use non-moving images. The vast majority of participants and in par- ticular, all staff anesthetists, were able to correctly recognize the pic- tures of the vocal cords, both in the circulated and non-circulated airway. Therefore we believe that real-time imaging of the airway during intubation may be a useful new method of confirming tracheal tube position, also during cardiopulmonary arrest.

One final limitation is that we used a small number of participants and pictures of a single cadaver. We accept this limitation since we consider this a pilot study, which should be used to guide future research in emergency airway management.

Conclusion

This study demonstrates that staff anesthetists, trainee anesthetists and paramedics are better in recognizing anatomical airway structures in a circulated airway than in a non-circulated airway. It also shows that staff anesthetists perform better than paramedics. In particular all staff anesthetists were able to recognize the vocal cords both in the circulated and non-circulated airway. Future research should focus on whether real time visualization of the airway with a VivaSight tube could reduce the number of misplaced tracheal tubes during cardiopulmonary resuscitation.

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