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Airway Management in Children: Ultrasonography Assessment of Tracheal Intubation in Real Time?

Marciniak, Bruno MD*; Fayoux, Pierre MD†‡; Hébrard, Anne MD*; Krivosic-Horber, Renée MD*; Engelhardt, Thomas MD, PhD§; Bissonnette, Bruno BSc, MD, FRCPC

doi: 10.1213/ane.0b013e31819240f5
Pediatric Anesthesiology: Research Reports
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BACKGROUND: Pediatric tracheal intubation requires considerable expertise and can represent a challenge to many anesthesiologists. Confirmation of correct tracheal tube position relies on direct visualization or indirect measures, such as auscultation and capnography. These methods have varying sensitivity and specificity, especially in the infant and young child. Ultrasonography is noninvasive and is becoming more readily available to the anesthesiologist. In this study, we investigated the characteristic real-time ultrasonographic findings of the normal pediatric airway during tracheal intubation and its suitability for clinical use.

METHODS: Thirty healthy children with normal airways requiring tracheal intubation were studied. Ultrasonographic measurements of the pediatric airway during tracheal intubation under deep inhaled anesthesia were performed using a Sonosite Titan® (Sonosite, Bothell, WA) scanner while recording characteristic images during this process. Correct tracheal tube placement was further confirmed using auscultation and satisfactory end-tidal capnography.

RESULTS: The mean (± sd) age of studied patients was 48 ± 37 mo, weight was 19.7. ± 8.6 kg and the sex ratio (m/f) was 1:2. Successful tracheal intubation was verified using the following criteria: 1) identification of the trachea and tracheal rings, 2) visualization of vocal cords, 3) widening of glottis as the tracheal tube passes through, and 4) tracheal tube position above carina and demonstration of movement of the chest wall visceroparietal pleural interface (i.e., sliding sign) after manual ventilation of the lungs. One esophageal intubation was readily recognized by visualization of the tube in the left paratracheal space.

CONCLUSION: This study describes characteristic ultrasonographic findings of the pediatric airway during tracheal intubation. It suggests that ultrasonography may be useful for airway management in children.

IMPLICATIONS: This study describes the ultrasonic visualization of tracheal intubation and demonstrates that ultrasound scanning may be a suitable method to confirm tracheal tube position in young children.

From the *Pôle d’Anesthésie Réanimation, Hôpital Jeanne de Flandre, CHRU, Rue Eugène Aviné, 59037 Lille Cedex France; †UPRES JE2490, Preclinical research group in perinatal medicine, Lille 2 University, Lille, France; ‡U.F. d’ORL pédiatrique, Pôle d’ORL Hôpital Claude Huriez. CHRU Lille, France; §Royal Aberdeen Children’s Hospital, Foresterhill, Aberdeen, UK; and ‖Department of Anesthesia, Hospital Sick Children, Toronto, Canada.

Accepted for publication October 7, 2008.

Reprints will not be available from the author.

Address correspondence to Dr. Bruno Marciniak, UF Anesthesie de l’enfant, Pôle d’Anesthesie Reanimation de l’Hopital Jeanne de Flandre, CHRU Lille, Rue Eugene Avine, 59037 Lille Cedex France. Address e-mail to bmarciniak@chru-lille.fr.

Securing the airway by tracheal intubation in children requires skill and experience. Direct visualization of the glottis and passing the tracheal tube under direct vision is considered the “gold standard”1 but is not a guarantee of correct placement,2–4 especially in the infant and young child. Nonrecognized esophageal intubation or bronchial intubation can result in significant morbidity and mortality3 and is more likely to occur in critical care environments or in small children. Other contributing factors, such as unfavorable conditions in unfamiliar environment and inexperienced personnel, are confounding problems with tracheal intubation in children.

Successful tracheal tube placement is generally realized by auscultation and/or end-tidal capnography. However, none of these methods are absolutely reliable and both require ventilation of the lungs.2,3

Ultrasonography (US) is becoming more commonly available to anesthesiologists due to its success in identifying vascular structures.5 The use of US to confirm tracheal intubation has been described in adults reporting either direct visualization of the tracheal tube or indirect signs of ventilation.6 In neonates, a sonographic approach has been used to confirm endotracheal tube tip position.7

This study was designed to assess the suitability of US to confirm tracheal intubation in a clinical setting in children and to provide a description of US findings of pediatric tracheal intubation.

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METHODS

After receiving approval from the Ethics Committee of our institution and parental consent, 30 healthy children ASA I or II, with normal airways and requiring tracheal intubation, were enrolled in this prospective study. Patients with anticipated difficult airway management were excluded. Induction of anesthesia was achieved with spontaneous ventilation using a sevoflurane -nitrous oxide-oxygen mixture with an inspired concentration of 50%.

US measurements were performed using a Sonosite Titan (Sonosite, Bothell, WA) using a 5- to 10-MHz linear transducer probe. The probe was placed transversally on the anterior neck just superior to the suprasternal notch and moved cranially to the level of the glottis. The location of the true vocal folds was confirmed by the visualization of paired hyperechoic linear structures with respiratory and swallowing mobility. Direct laryngoscopy and tracheal intubation were performed under deep inhaled anesthesia and after the injection of propofol (3 mg/kg) in 100% oxygen. Changes in anatomical appearance were noted and recorded during intubation. The probe was moved caudally to visualize the tube within the trachea.

Tracheal intubation was further confirmed using auscultation and satisfactory end-tidal capnography tracing. The probe was moved to the thorax, below and perpendicular to the clavicles. Movements of the chest wall visceral-parietal pleural interface (VPPI) were recorded.

Successful US visualization of tracheal intubations was defined by instantaneous modification of the glottis plane when the tracheal tube passed through it and an enhancement of the tracheal posterior shadow. Signs of potential esophageal intubation as well as VPPI movements were recorded and characterized.

Time to confirm tracheal intubation and correct tube placement over the carina were recorded.

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RESULTS

Thirty patients were studied. The mean (± sd) age and weight were 48 ± 37 mo and 19.7 ± 8.6 kg, respectively. The trachea was immediately identified by visualization of the tracheal rings in all children (Fig. 1). The depth of the trachea was always under 1 cm. The glottis was characterized by the visualization of the vocal cords and was easily seen (Fig. 2). Vocal cord movements during spontaneous respiration or intermittent positive pressure ventilation were readily observed. Tracheal intubation was confirmed by watching the modification of the glottis plane when the tracheal tube passed through the glottis. The vocal cords were always visible but not the tracheal tube. The passing of the tracheal tube was characterized by the widening of the vocal cords at the base of the glottis. These changes were visible instantaneously, even though the tube itself was not always directly visualized. A posterior shadow to the tracheal ring may have provided indirect evidence of tracheal intubation (Fig. 3) but was not always easily visible and depended on the depth of the structures and the size chosen for the window of the US machine. The esophagus was never visible. One case of esophageal intubation was readily detected by visualization of the tube in the left paratracheal space (Fig. 4).

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

Direct US confirmation of the position of the tracheal tube tip was not possible. Confirmation of the correct position of the tube within the trachea and over the carina was obtained in all cases during intermittent positive pressure ventilation. Movements of the chest wall determined by the VPPI were observed during ventilation, the Doppler effect enhancing the movement of the pleural interface (Fig. 5). Visualization of vocal cord movements during tracheal intubation was instantaneous and confirmation of tracheal tube placement over the carina by observation of the sliding sign took <5 s. A suggested sequence of characteristic US findings is summarized in Table 1.

Figure 5

Figure 5

Table 1

Table 1

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DISCUSSION

Tracheal intubation in children requires expertise to prevent inadvertent esophageal or bronchial intubation. This is particularly true in the child requiring cardiopulmonary resuscitation, presenting with a difficult airway anatomy and in small children in whom tracheal intubation is more delicate. Numerous devices have been described to verify tracheal tube position with the vast majority relying on indirect measurements.8–13

Auscultation is commonly considered the first step to confirm tracheal intubation. Sensitivity and specificity are variable and lower in tracheal tubes with a Murphy eye.2 Auscultation may also be misleading in patients with low lung compliance or cases of severe bronchospasm.

Capnography is routinely used in the operating room in adults and children.14 Portable devices, such as the STATCAP and Pedi-Cap (Nellcor, Hayward, CA), are available for out-of-operating-room environments, but capnography requires spontaneous or manual ventilation as well as good pulmonary blood flow. Leaks around pediatric noncuffed tubes may also lead to diagnostic errors. False positive and false negative cases have been reported. Li15 performed a meta-analysis of end-tidal CO2 and intubation during cardiac arrest in adults and found a sensitivity from 0.78 to 0.99 and a specificity from 0.92 to 1. In a neonatal intensive care unit, Roberts et al.16 found sensitivity at 0.98 and specificity at 100%.

Transmission of light through the tissues of the neck has also relied on an intense and circumscribed midline glow of light in the region of the anterior neck, just below the thyroid prominence. However, these devices are not suitable for tracheal tube size with an inner diameter of 6 and 4.5 mm for Trachlight (Laerdal Medical, Armonk, NY) and SURCH-LITE (AARON Medical Industries, St. Petersburg, FL), respectively. Alternative methods, such as aspiration of air from the lungs (TubeChek: Ambu, Linthicum, MD) and acoustic reflectometry, are currently not widely used12,17 or are unsuitable in small children.18

Direct visualization of the glottis and passing the tracheal tube under direct vision is not always possible in cases of difficult intubation in a child with distorted anatomy or pathological conditions.

Fiberoptic control of tube placement is generally considered by anesthesiologists and intensivists to be the gold standard for confirmation of correct tube placement. Observation of the tracheal rings and carina is generally easy and unmistakable but requires availability of a fiberscope and may be complicated by misting, blood and secretions. The use of the fiberscope may also be limited by the inner diameter of the tracheal tube.

A standard chest radiograph is commonly used to determine tube position in intensive care patients, but it is time consuming and therefore not realistic in the operating room environment. It may be only suitable for follow-up in intensive care.19

US has been reported to be reliable to assess laryngeal structures in adults20 and has been used to determine the tracheal diameter in children.21 Confirmation of correct tracheal tube position has been reported in adults6 and neonates,7,22 but it was suggested that physicians required considerable experience in US. Indirect signs of ventilation such as diaphragmatic movement in ordinary two-dimensional sector images and M-mode immediately before and after tracheal intubation23 as well as the sliding sign (the back and forth sliding of visceral and parietal pleura past each other) to assess ventilation, have been reported.24,25

In contrast to previous studies, Rosenstein et al.26 reported that personnel less experienced in US were able to differentiate between tracheal and esophageal intubation and one report in adults suggested a sensitivity and specificity of 100%.27

No studies are available assessing the use of US imaging for real-time confirmation of tracheal tube position in children. This current study demonstrates that US readily detected tracheal intubation in all but one patient in whom esophageal intubation was diagnosed immediately upon insertion of the tube into the esophagus. This study reports characteristic US findings suggesting a set of criteria for confirming tracheal intubation in children. However, it must be remembered that all clinicians involved in this study were experienced in US and none of the studied children presented with difficult airway management. The addition of an indirect sign, such as movement of the chest wall VPPI, may also be useful to confirm successful ventilation. This sign is more easily observed in the apneic or paralyzed patients.

This technique is likely to be used for routine tracheal intubation. However, US confirmation of correct tracheal tube placement may be beneficial for circumstances in which capnography is unreliable, such as cardiac arrest. Other situations include airway trauma or difficult intubation. In these situations, it might be useful to be able to confirm passing of the tracheal tube through the vocal cords and correct tracheal tube placement in real-time. However, this will need to be confirmed in future studies.

US is now more commonly available in the operating room due to its increased use for securing vascular access. The place for its use in real-time airway management has yet to be established in adults and children, and further studies are required to assess sensitivity and specificity of this technique based on the suggested US criteria.

We conclude that US of the pediatric airway can be easily used to assess correct tracheal tube position and to detect esophageal intubation.

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