Brief Report

An assessment of a tracheal tube introducer as an endotracheal tube placement confirmation device

Aaron E. Bair MD^a,*, Erik G. Laurin MD^a, Brandi J. Schmitt MS^b

^aDepartment of Emergency Medicine, University of California, Davis School of Medicine, Sacramento, CA 95817, USA

^bDepartment of Cell Biology and Human Anatomy, University of California, Davis School of Medicine, Sacramento, CA 95817, USA

Accepted 15 February 2005

Abstract

Introduction: Early detection of an inadvertent Esophageal intubation can be particularly challenging in cases when the current standard of care, carbon dioxide detection, is unreliable. We sought to determine the sensitivity and specificity of an inexpensive and portable device, the Gum elastic bougie (Eschmann Tracheal Tube Introducer, SIMS Portex, Inc, Keene, NH), as an endotracheal tube placement confirmation device.

Methods: We conducted a prospective blinded trial in 20 human cadavers. Each cadaver was randomized to a mixed series of 5 esophageal and 5 tracheal intubations. Each intubation was assessed with the bougie twice, once by a novice to the technique, and once by an assessor who was constant through the trial. Assessors used the bougie to bfeelQ for bclicksQ of the tracheal rings and to appreciate bhang upQ of the bougie as it was advanced into the smaller airways. Absence of these findings was presumed to indicate an esophageal intubation. Actual placement was confirmed by bronchoscopy. Each assessor made an independent determination of Tube location. Descriptive statistics were used to summarize the data.

Results: Overall, 93% (95% confidence interval [CI], 86%-97%) of tracheal placements were correctly identified. The constant assessor was able to correctly identify 98% (95% CI, 90%-100%). Tracheal rings were detected in 92% of tracheal placements. Ring clicks were 95% specific for tracheal intubation. Hang up was reported in 100% of tracheal placements with a specificity of 84%. Overall, 95% (95% CI, 88%- 98%) of esophageal intubations were detected. The constant assessor detected 100% of esophageal intubations.

Conclusion: In the cadaver model used in this study, the gum elastic bougie (Eschmann Tracheal Tube Introducer) shows promise as an endotracheal tube confirmation device.

D 2005

Presented in part at the Mediterranean Emergency Medicine Congress, Barcelona, Spain, September 2003.

T Corresponding author.

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

Introduction

Endotracheal tube placement verification is a fundamen- tal component of Emergency airway management. An unrecognized nontracheal intubation can have devastating consequences. End-tidal carbon dioxide detectors and

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various aspirator devices are used commonly for endotra- cheal tube confirmation. Although there are multiple techniques and devices that are commonly used for endotracheal tube confirmation, none of these are perfectly reliable. For example, there are circumstances when carbon dioxide detection is unreliable (ie, low perfusion states). In addition, aspiration techniques have been shown to be unreliable in the setting of obesity, foreign material within the airway, and with prior insufflation of the stomach [1- 4]. Hence, there are commonly encountered circumstances when these techniques of endotracheal tube confirmation may not be dependable. In these potentially difficult cases, there is a need for an additional technique of endotracheal tube confirmation.

The gum elastic bougie (Eschmann Tracheal Tube Introducer, SIMS Portex, Inc, Keene, NH) was originally developed as an endotracheal tube introducer, not as a dilator, as the term bougie might imply. The usual technique for use during intubation relies on the successful placement of the bougie into the trachea followed by passage of an endotra- cheal tube over the bougie. As the bougie is introduced into the trachea, the angled tip slides along the tracheal rings and transmits a palpable series of bclicks.Q Furthermore, if the bougie is successfully placed into the airway, it will hit resistance and bhang upQ as the tip advances into the smaller airways of the bronchial tree. This determination takes only seconds to perform. When used as an adjunct for endotra- cheal tube placement, appreciable clicks and hang up are useful clues when laryngoscopy is limited by anatomy or obscured by foreign material (ie, emesis, blood) [5]. Over the past 40 years since its development, the bougie has become a favored difficult airway adjunct in Britain and is commonly referenced in the anesthesia literature [5-9]. In addition, it has recently been reported as a useful adjunct in the emergency department [10,11].

In addition to the already described use for difficult intubation, the bougie may also be useful for distinguishing endotracheal from esophageal tube placements. Our primary objective in this study was to assess the sensitivity and specificity of the gum elastic bougie (Eschmann Tracheal Tube Introducer) as an endotracheal tube placement confirmation device. In addition, we sought to determine if limited experience with the device and the technique would markedly reduce its utility. We hypothesized that the gum elastic bougie could be used with good sensitivity and specificity, even among novice users, to determine location of tube placement.

Methods

Study design

This was a prospective, blinded, randomized comparative study of bougie sensitivity and specificity as an endotra- cheal tube placement confirmation device.

Participants

• • 1. Novice assessors

For purposes of this study, we sought a population of providers who were unfamiliar with use of the bougie. Flight nurses from the university-associated air medical transport service were recruited to participate in this study. The flight nurses, although skilled in airway management, had no prior training in the study technique. The goal was to have each nurse participate only once to limit the influence of experience. Each nurse was given a brief (approximately 5 minutes) descriptive overview of the use of the bougie for endotracheal tube confirmation. This overview consisted of a verbal description immediately before the actual demonstra- tion of a single endotracheal tube placement. For training purposes, a single endotracheal tube placement was used to demonstrate the tactile concepts of clicks and hang up.

• • 1. Experienced assessor

For purposes of this study, we sought an individual who would be available for assessment of each of the specimens during the study period. This person was trained and practiced in the bougie technique before the initiation of the study. Our intention was that the technical performance of this individual would be analogous to that of the experienced and skilled provider. The individual selected was a regular employee of the laboratory and not trained as a medical provider. In contrast to the novice assessors, this assessor had no prior airway management training before the trial. This individual assessed every specimen enrolled in this trial.

Interventions and measurements

• • 1. Specimens

Access to 20 nonfixed, nonfrozen human cadavers was obtained through the Donated Body Program at the affiliated medical school. Over a period of approximately 4 months, as the cadaver specimens became available, the study team was assembled to perform the requisite intervention and data gathering. The Human Subjects Institutional Review Board granted approval for this study.

• • 1. Bougie confirmation technique

The bougie product used consistently in this trial was the Eschmann Tracheal Tube Introducer, a flexible intubating stylet measuring 60 cm by 5 mm. An 8.0-mm Hi-Lo cuffed endotracheal tube (Mallinkrodt, Tyco Health- care, Mansfield, MA) was placed in either the trachea or the esophagus according to randomization. To maximize the number of tracheal rings accessible to the bougie, the Endotracheal tubes were placed in the trachea with the balloon cuff just past the vocal cords. The esophageal tubes were placed under direct visualization at a corresponding depth. After intubation, placement was confirmed with bronchoscopy. The participants, who were blinded to placement, were instructed to orient the direction of the bougie tip anteriorly and insert it into the tube. Tube lengths and bougie lengths were then

Table 2 The sensitivity and specificity of key tactile features used to distinguish a tracheal intubation
	n (%)	Sensitivity	Specificity
Clicks detected	94 (92)	92	95
(overall)
Experienced assessor	50/51 (98)	98	100
Novice assessor	44/51 (86)	86	90
Hang up detected	102 (100)	100	84
(overall)
Experienced assessor	51/51 (100)	100	84
Novice assessor	51/51 (100)	100	67

Fig. 1 The passage of the tip of the bougie distal to the endotracheal tube. As the tip passes over the tracheal rings, the assessor feels the clicks.

thyroid cartilage

Bougie tip

Endotracheal tube

aligned and the lubricated bougie was then passed out of the tip of the tube in an effort to feel clicks (Fig. 1). Subsequently, the bougie was advanced and the presence or absence of terminal resistance (ie, hang up) was noted. As the study was designed as a preliminary analysis of the technique and generally only takes a matter of seconds to perform, no time limit was imposed on the participants.

• • 1. Study protocol

All cadaver specimens were randomized to a mixed series of 5 esophageal and 5 tracheal intubations. The order of either esophageal or tracheal intubation and the propor- tion of each were determined in advance by a computer- generated randomization scheme. The study participants were blinded to tube placement and to each other’s questionnaire responses. The 2 different participants then assessed each intubation independently. The participants were then asked to respond in writing to questions on a structured data-gathering form. The participants responded byesQ or bnoQ to whether clicks and hang up were appreciable. Ultimately, they had to decide whether the tube had been placed in the trachea or esophagus.

• • 1. Data analysis

Descriptive statistics were used to analyze the data. We performed all statistical analyses using Stata 7.0 for

Table 1 The accuracy of performance of the bougie technique overall, as well as the relative performances of the novice assessors and the experienced assessor
	Tracheal n (%)	95% CI		Esophageal n (%)	95% CI
Experienced	50/51 (98)	90-100		49/49 (100)	93-100
Novice	45/51 (88)	76-96		44/49 (90)	78-97
Overall	95/102 (93)	86-97		93/98 (95)	88-98

Windows (Stata Corp, College Station, Tex). Data were summarized as percentage frequency occurrence for cate- gorical variables. When appropriate, 95% confidence intervals (CIs) were calculated. Our sample size was limited by cadaver availability over a finite period and, as such, an a priori sample size calculation was not performed.

Results

Twenty human cadavers were used to perform 200 as- sessments in this trial. Of these, 102 were randomized to a tracheal placement. Thirteen (65%) of the cadavers used in this study were male. None of the cadavers in this trial had evidence of prior tracheal or laryngeal surgery.

Table 1 describes the proportion of endotracheal and esophageal intubations, as well as the relative performance of the novice assessors and the experienced assessor. Of note, the experienced assessor was able to detect 100% (95% CI, 93%-100%) of the esophageal intubations in this trial. As a group, the novice assessors identified 90% (95% CI, 78%-97%) of the esophageal intubations. Overall, 95% of esophageal intubations were identified.

Among tracheal intubations, 93% (95% CI, 86%-97%) were correctly identified overall. The experienced assessor tended to be more accurate and was able to correctly identify 98% (95% CI, 90%-100%) of the tracheal place- ments. In contrast, the novice assessors identified 88% (95% CI, 76%-96%) of the tracheal placements. Tracheal rings were detected in 92% of tracheal placements overall (Table 2). Ring clicks were 95% specific for tracheal intubation. Hang up was detected in 100% of tracheal placements with a specificity of 84%.

Discussion

In this study, we evaluated the use of the gum elastic bougie or Eschmann Tracheal Tube Introducer as an endotracheal tube confirmation device. The device itself consists of a 60-cm, resin-coated rod with a woven Dacron polyester core. The tip is a 2-cm segment that is angled approximately 308. The leading tip of the device is designed to improve ease of insertion into a partially

visualized glottis by allowing a variable angle of approach into the trachea [12]. In addition, the angled tip has the potential to provide rapid feedback to the intubator regarding the location of the tip. This tactile feedback could be useful for intubation, as well as endotracheal placement confirmation.

The importance of accurate endotracheal tube placement confirmation is well known, as an unrecognized esophageal intubation can be life-threatening. Although multiple devi- ces currently exist for esophageal intubation detection, they each have limitations [1,3,13-15]. Likewise, clinical indica- tors such as bdirect visualizationQ of the glottis during intubation attempts and bbreath soundQ assessment after tube placement are known to lack adequate sensitivity for detecting inadvertent esophageal intubation [16-18]. Thus, additional objective information is advised to confirm tube placement. For example, end-tidal carbon dioxide is commonly used in addition to other clinical indicators to confirm placement. However, end-tidal carbon dioxide detection is limited in low perfusion states such as cardiac arrest [19]. Likewise, the use of bulb or syringe aspiration techniques is limited by matter in the airway or morbid obesity [3]. In contrast, the use of the bougie method for tube placement determination would theoretically not have those same limitations because it relies only on the presence or absence of palpable clicks and bhang upQ of the bougie within the airway. The use of a bougie is independent of expired carbon dioxide and could possibly perform well in situations that would otherwise limit bulb techniques such as obesity and the presence of airway secretions.

We have found no literature that addresses the use of the bougie as an endotracheal tube confirmation device for use in the manner that we have described here. There has been, however, a report in the literature to suggest that the bougie is reliable at detecting tracheal placement in the setting of difficult airway management [5]. To our knowledge, however, there has been no trial assessing this technique to differentiate endotracheal from esophageal intubations. In our study using cadavers, we found that the bougie technique was 95% sensitive and 93% specific for correctly identifying tracheal intubations. In addition, our data show that even minimal training in this technique results in high success rates.

Limitations

This study has multiple limitations. There are inherent limitations in a study involving cadaver specimens. In particular, we found that because of the stiffening of the tissues, there was a significant amount of resistance to the bougie in the esophagus of some specimens. It appears that among the novice assessors, this was confused as tracheal hang up and this resulted in several esophageal placements being misidentified as tracheal. In retrospect, it might have been better to include both a tracheal and an esophageal placement in the training phase for the novice assessors. In a

living subject, with normal tissue distensibility, we predict that the performance of the novice assessors would be improved as they would be less likely to encounter esophageal resistance and to confuse it with tracheal hang up. If this were the case, then the sensitivity and specificity would be improved over what we have reported. In addition, this study did not evaluate the bougie technique in specimens with particulate matter in their airways nor those that were morbidly obese. These are 2 groups in which the syringe aspiration technique has a higher error rate. It remains unclear how the bougie would perform in such conditions. Furthermore, for this study, all endotracheal tubes were placed relatively high in the trachea. In actual clinical practice, main-stem intubations occur. In such cases, the clicks would likely not be felt. However, the hang-up would still be readily apparent. Finally, as this study was designed as a preliminary study to analyze sensitivity and specificity, no time limits were imposed on the participants of this trial. As such, this limits the applicability of our findings to clinical practice. However, it merits noting that during the development phase of this study, the use of the bougie was observed to require only approximately 5 seconds to use.

Conclusions

In a cadaver model, we found that the bougie technique could be both sensitive and specific in correctly differenti- ating tracheal from esophageal intubations. It performed well when used by those with little experience in the technique but better by an individual with more experience. The bougie technique has potential to be a useful diagnostic adjunct for endotracheal tube placement confirmation in selected difficult patients and merits further study.

Acknowledgments

The authors thank Dr Nathan Kuppermann, MD, MPH, and Dr Edward Panacek, MD, MPH, for their insights and assistance with manuscript preparation.

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