How stylet use can effect confirmation of endotracheal tube position using ultrasound
Original Contribution
How Stylet use can effect confirmation of endotracheal tube position using ultrasound
Erkan Goksu MD?, Vefa Sayrac MD, Cem Oktay MD, Mutlu Kartal MD, Mehmet Akcimen MD
Department of Emergency Medicine, School of Medicine, Akdeniz University, 07059 Antalya, Turkey
Received 18 July 2008; revised 9 September 2008; accepted 10 September 2008
Abstract
Introduction: None of the techniques used for confirmation of endotracheal tube (ET) placement are proven reliable 100% of the time. The purpose of our study is to determine whether ultrasound can accurately detect the passage of ET through the trachea and esophagus and to see whether this visualization is augmented with the use of a metal stylet.
Methods: A total of 7 physicians made assessments of ET positions using an ultrasound during their passage through the trachea or esophagus. A total of 40 esophageal and 40 tracheal intubations were performed randomly in a blinded fashion on a fresh, unfrozen human cadaver. Half were performed with a metal stylet and the other half without a stylet.
Results: During transtracheal assessment regardless of stylet use, correct identification of ET position was achieved in 275 of 280 Esophageal intubations and 268 of 280 tracheal intubations. The overall sensitivity was 95.7%, and specificity was 98.2%. The presence and the absence of stylet was identified in 109 of 280 and in 155 of 280 attempts, respectively. Correct identification of stylet presence yielded a sensitivity of 38.9% and a specificity of 55.4%.Ultrasound can be used by emergency physicians to accurately detect the passage of ET through the trachea and esophagus; however, stylet use did not augment ET visualization.
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Introduction
Esophageal intubation is more likely to occur in critical care environments such as emergency departments (EDs). It may be rapidly fatal if it is not recognized in a proper and timely manner. The properly placed endotracheal tube (ET) provides a definitive protected airway and is vital for ensuring adequate ventilation in the event of cardiac arrest, respiratory failure, or significant trauma. However, recent studies in an urban emergency medical system found that up
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E-mail address: [email protected] (E. Goksu).
to 25% of medical or pediatric and adult trauma patients had esophageal intubations on presentation to the ED [1-2].
There are numerous methods to confirm the position of the ET as follows: detection of exhaled CO2 by capnography (qualitative/quantitative), direct visualization of the ET passing through the vocal cords, revisualization with direct laryngoscopy, gurgling over the epigastrium, auscultating breath sounds, fogging in the ET, esophageal detection device, visualization of chest movement, pulse oximetry, and chest radiograph [3].
Although numerous techniques have been described to confirm ET placement, there is no perfect confirmation tool, and many methods are less reliable or some are unavailable in the ED. A meta-analysis demonstrated capnography to be
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only 93% sensitive [4]. In addition, detection of end-tidal CO2 by either capnography or colorimetric measurement depends on adequate pulmonary blood flow. Therefore, it is unreliable in patients with cardiac arrest or those in a low- flow state, with a sensitivity of only 72% [5]. Secretions, blood, and anatomical variations can obscure the direct visualization of the trachea and vocal cords. Listening over the epigastrium may be helpful but cannot provide the proper positioning with 100% sensitivity and specificity. Ausculta- tion of lungs to verify for breath sounds may be limited if the patient is an infant or a small child. Fogging in the ET can occur even with esophageal intubation [6]. Esophageal detection device can be misinterpreted in patients with morbid obesity, late pregnancy, Status asthmaticus, or copious tracheal secretions [7].
Ultrasound (US) is being used by the emergency physicians for a variety of conditions. Virtually all foreign bodies are hyperechoic and appear as bright structures that are distinct from their surrounding tissues. Disposable plastic ET and metal stylets produce acoustic shadowing and reverberation or comet-tail artifacts, which can facilitate visualization [8].
In this study, we sought to determine if US can accurately detect the passage of the ET through the trachea or esophagus in real time fresh cadaver model and if this visualization is augmented with the use of a metal stylet.
Materials and methods
This prospective randomized trial was done using only one human cadaver model in the Cadaver laboratory of a university hospital. A total of 7 physicians, 1 faculty physician of the Department of Emergency Medicine and 6 residents of various postgraduate years, participated in the study. Two residents from the first and the third years and 1 resident from the second and forth years were recruited. All physicians were experienced with the use of US in daily practice. Participants were given a 15-minute presentation on neck anatomy and how to identify the laryngeal structures with US. A Mysono 201 7.5-MHz curviLinear probe (Medison CO., LTD/South Korea) was placed transversely over the larynx at the trachea over the sternoclavicular notch (Fig. 1). Intubations were performed by a faculty member of the ED and confirmed by another faculty physician. A fresh, unfrozen human cadaver with an approximate weight of 65 kg and a height of 165 cm was used; no neck pathologic condition was noted on examination. In our institution, studies on human cadavers are performed with the approval and the supervision of the Department of Clinical Anatomy, so institutional review board approval is not required.
Physicians made assessments of ET positions during their passage through the trachea or esophagus (Fig. 2). Fig. 2 displays the static images of tracheal and esophageal intubations with or without stylet use. However, confirma-
Fig. 1 Demonstration of probe placement just superior to the Suprasternal notch.
tion of the tube position during intubation with US is a dynamic process. During tracheal intubation, while tube is passing through the tracheal ring, shadowing increases in the trachea. During esophageal intubation, while the tube is passing through the esophagus, a new shadowing appears beside the tracheal ring. A total of 40 esophageal and 40 tracheal intubations were performed. Half were performed with a metal stylet and the other half without a stylet. Endotracheal tube with an ID: internal diameter of 8.0 were used. The order of intubations was previously selected randomly and sealed in envelopes. Physicians performing intubations opened each envelope before performing each attempt. A curtain was also placed just under the mandible of the cadaver to separate the physician performing the intubation and the participants performing US.
Sensitivity, specificity, and positive and negative like- lihood ratios and their 95% confidence intervals (CIs) were calculated for ET placement. Statistical analysis was performed using SPSS 10.0 (SPSS Inc, Chicago, Ill).
Results
In this study, 6 emergency medicine residents (2 first year, 1 second year, 2 third year, and 1 fourth year) and a faculty emergency physician completed 80 (20 esophageal without stylet, 20 tracheal without stylet, 20 tracheal with stylet, 20 esophageal with stylet) assessments of ET placement by placing a probe over the transtracheal region above the sternoclavicular notch.
During transtracheal assessment regardless of stylet use, correct identification of ET position was achieved in 275 of
280 esophageal intubations and 268 of 280 tracheal intubation. The overall sensitivity was 95.7% (95% CI, 93.8-96.8), and the overall specificity was 98.2% (95% CI, 96.3%-99.3%). The positive likelihood ratio was 53.6, and
Fig. 2 A, Ultrasonographic image of esophageal intubation without a stylet. Shadowing can be visualized posterior to the trachea (T), and in the left paratracheal area, esophagus (E) has been opened by the tube. B, Ultrasonographic image of esophageal intubation with a stylet. Shadowing is seen posterior to the trachea (T), and in the left paratracheal area, esophagus (E) has been opened by the tube. Identification of tube position is not affected with stylet use. C, Tracheal intubation without a stylet. Shadowing posterior to the trachea (T) can be visualized. The esophagus is not visualized. D, Tracheal intubation with a stylet. Shadowing posterior to the trachea (T) is seen. The esophagus is not visualized. Identification of tube position is not augmented with use of stylet (Medison Digital Sonoace 5500, Medison America Inc, Cypress, Calif 90630).
negative likelihood ratio was 0.04. During transtracheal assessment, correct identification of ET position was achieved in 135/140 tracheal placements without stylet, 133/140 tracheal placements with stylet, 137/140 esophageal placements with stylet, and 138/140 esophageal placements without stylet. These results yielded a sensitivity of 97.5% (95% CI, 95.5%-98.7.4% ) and a specificity of 96.5% (95%
CI, 94.5%-97.7%).
The presence and the absence of stylet was identified in 109 of 280 and in 155 of 280 attempts, respectively. Correct identification of stylet presence yielded a sensitivity of 38.9% (95% CI, 34.7%-43.2% ) and a specificity of 55.4% (95% CI, 51.1%-59.6%). The positive likelihood ratio was 0.872, and negative likelihood ratio was 1.103.
Sensitivities and specificities of ET position and stylet presence by the participants are displayed in Table 1.
Discussion
None of the techniques used for confirmation of ET placement is proven reliable 100% of the time. Although the direct visualization of the ET passing through the vocal cords is said to be the gold standard, it still requires firm evidence of correct placement and needs to be verified with other techniques. The American College of Emergency Physicians Policy Statement recommends the confirmation of ET position with additional techniques before securing the airway [3]. These techniques can be divided as traditional and secondary confirmation methods. Traditional methods such as the observation of chest movement, auscultation of the epigastrium, and fogging in the tube are all operator dependent and prone to mistake. Secondary confirmation methods routinely used are capnography and
esophageal detection device. Result of a meta-analysis found continuous capnography to have an aggregate sensitivity of 93% (95% CI, 92%-94%) and an aggregate
specificity of 97% (95% CI, 93%-99%) [4]. Despite normal capnograms, there are reports of esophageal intubations. Mask ventilation, presence of CO2 in the stomach, ingestion of antacids, and low cardiac output states with low pCO2 may result in improper esophageal intubation [4]. Esophageal detection device, as used as another secondary confirmation method, may give false-positive results in the setting of endobronchial intubation, asthmatic patients, airway obstruction, tracheomalacia, and may be obstructed with blood, vomitus, and mucosal contact.
Ultrasound is a promising additional tool of confirma- tion. Ultrasound reveals the anatomy of the larynx and trachea independent of patient physiology, and it is not affected like capnography.
In a cadaver model, Ma et al [7] performed dynamic and static assessments of ET position using a 7.5-MHz curvi- linear probe placed longitudinally over the Cricothyroid membrane. Dynamic assessment resulted in 97% sensitivity and 100% specificity for detecting esophageal ET placement. Static assessment resulted in only 51% sensitivity and 91% specificity. In our study, we placed the 7.5-MHz linear probe transversely on the anterior neck just superior to the suprasternal notch and performed a dynamic assessment. The reason to choose this position was to avoid placing unintentional pressure on the cricothyroid membrane, and a previous study found increased accuracy in detection of ET placement with the transducer positioned at the suprasternal notch [9]. Although the sensitivity and specificity of determining the ET position was high, it was still not correct 100% of the time.
The second objective of our study was to assess if physicians benefit through the use of a metal stylet. Physicians’ identification with the use of a stylet had poor sensitivity and specificity, and the overall agreement between physicians was poor. These results revealed that identification of tube position was not affected with stylet use.
In a prospective study [8] with live human participants, they found a sensitivity of 100% and a specificity of 97% for esophageal intubations. Limitations of this study were its
small sample size and that it used a selected group of patients undergoing elective surgery.
In a pilot study [9] including 33 patients, the sensitivity for identifying the first intubation as tracheal was 100% (95% CI, 77%-100%) with a specificity of 100% (95% CI,
82%-100%).
The study has several limitations that may overestimate its accuracy in the ED setting. We used only one human cadaver in a highly controlled environment. However, we suggest that there was no significant difference in the anatomy when compared with a living human model, intubation of a living might reduce the accuracy of the US. anatomical differences of human with age, height, weight, neck anatomy, or the specific conditions such as a trauma patient with a hematoma in neck or previous neck surgery may complicate the visualization.
Ultrasound may be a rapid and accurate method of confirming ET position during the intubation procedure. This technique provides a rapid and cost-effective approach of verification and precludes unnecessary insufflation of the stomach with use of capnography and decreases the risk of aspiration. To date, all articles published use a cadaver model or small sample size, and all were performed in a highly controlled environment. A prospective study in the chaotic environment of the ED should thus be performed.
In conclusion, our study demonstrated that emergency physicians could accurately detect passage of the ET through the trachea and esophagus, and this situation was not affected using a metal stylet.
Acknowledgment
This study was supported by Akdeniz University Foundation.
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