By Alice Chao, MD and Laleh Gharahbaghian, MD
In recent years, the use of ultrasound (US) for confirmation of endotracheal tube (ETT) placement has gained increasing popularity. Several techniques already exist to confirm endotracheal tube placement. However, every tool has its limitations, and some are not always available in the emergency department (ED). The likely reason that airway US has gained attention is the ease at which images can be obtained. Airway US for ETT confirmation is best used when the end-tidal CO2 monitor is not accurate, radiology is unavailable, the patient arrives intubated and requires airway confirmation, or the patient does not respond as expected after intubation. There are some tips and tricks that can assist in obtaining the best view.
There have been several studies investigating the sensitivity and specificity of ultrasound in confirmation of ETT placement, both in live and cadaveric models. In a systematic review and meta-analysis by Chou et al, a pooled sensitivity of 93% and specificity of 97% was determined for detection of esophageal intubations in adult patients and cadaveric models.1 Gottlieb reported a pooled sensitivity of 98% and specificity of 98% in a snapshot summary of a systematic review of live adult patients.2 Therefore, it has been concluded that transtracheal US can be used to evaluate for proper ETT placement during emergency intubations.
1. Use the high frequency linear probe. The curvilinear probe has also been used in some studies, though less commonly.
2. Place the probe in a transverse orientation just above the suprasternal notch. Be careful not to apply too much pressure as this may displace anatomical location of underlying structures (Image 1) Normal Airway Anatomy:
a. The trachea will appear as a hyperechoic curvilinear structure with comet-tail artifact and shadowing. (Image 2)
b. The esophagus is usually seen more distally and to the right side of the screen as an oval structure with a hyperechoic wall and hypoechoic center.
c. TIP: Prior to intubation, if time permits, view the regional anatomy to anticipate post-intubation imaging CLICK HERE FOR VIDEO.
d. Tracheal US can be performed in real-time as the endotracheal tube is passed, but is not necessary for ETT confirmation
3. Successful endotracheal intubation will demonstrate an increase in artifact and shadowing in the region of the trachea only
a. TIP: Performing a slight shaking of the ET tube will only show movement of the trachea. If color Doppler is used during the movement of the tube, a color ray will come from the trachea. CLICK HERE FOR VIDEO.
b. Esophageal intubation will reveal an adjacent hyperechoic curvilinear structure with shadowing and comet-tail artifact posterolateral to the trachea, consistent with the ET tube location within the esophagus. CLICK HERE FOR VIDEO. This has been referred to as the “double tract sign”
i. It should be noted that if the esophagus is located directly posterior to the trachea, an esophageal intubation may be missed by US as this second hyperechoic structure will be obscured by the shadowing from the trachea
ii. TIP: Ensure adequate depth to visualize location of the esophagus and perform a slight shaking of the ET tube will show movement lateral to the trachea. If color Doppler is used during the movement of the tube, a color ray will come from the esophagus.
c. An additional sonographic way to identify ETT confirmation includes visualizing bilateral lung sliding while bagging the paralyzed patient.
The 2010 ACLS guidelines recommend quantitative capnography as the most reliable method for confirming ETT placement.4 However, this comes with its limitations, such as limited availability in some EDs, potentially false readings in cases of decreased pulmonary flow such as in cardiac arrest, and necessity of ventilation to obtain a reading which may be accompanied by significant complications in the setting of esophageal intubation. Ultrasound is portable, widely available in many EDs, and used by many emergency physicians. It is not limited by pulmonary blood flow in the case of cardiac arrest. In addition, esophageal intubation can be identified immediately upon placement, avoiding the need for ventilation of the stomach in these situations. Airway US is gaining popularity amongst emergency physicians and should be considered for confirmation of endotracheal tube placement in emergent intubations.