Transcription
Hello and welcome back to the ICU doc. This is Gabriel Prada, and here is a quick lecture about non-ultrasound for endotracheal intubation.
During intubation, we can use ultrasound to find out whether the tube is in the trachea and mainstem bronchus, or the esophagus. For this purpose, we need to combine simple but accurate trachea and lung ultrasound techniques.
With tracheal ultrasound, we will look for the single or double comet tail images. With lung ultrasound, we will look for lung sliding and lung pulses. That's all we need.
Tracheal ultrasound will tell you if the tube is in the trachea or the esophagus. Ideally, you should start scanning before intubating the patient and maintain a good image during and after intubation. Place the linear high-frequency probe just above the suprasternal notch, perpendicular to the trachea, on a transverse orientation.
Under normal circumstances, say before intubation, this is the image you should get. This curved bright image is the anterior aspect of the trachea with a posterior shadow that extends down to the end of the screen due to the air inside the trachea. This is called the single comet tail artifact. And in case you're part of the 99% of humans who have never seen a comet in real life, it's a picture of one. While we keep waiting for Halley's. Cool, right? Tracheas and comets with the ICU doc.
Now, what do you think happens when you insert a tube inside this trachea? Nothing. Nothing happens. The image does not change at all. Endotracheal intubation looks exactly the same as no intubation at all. You still get the single comet tail artifact. You cannot see the tube inside the trachea because the air inside the trachea prevents you from seeing what's inside, including the tube. Remember that air is the worst enemy of ultrasound.
In contrast, when the tube accidentally goes inside the esophagus, you will see two comet tail images. Do you see them? Let me help you, just in case. Here is one, and here is the other one. The comet on the left corresponds to the trachea, while the comet on the right to the tube inside the esophagus, mimicking a second airway. Remember that normally the esophagus is collapsed without air inside. A collapsed esophagus is indistinguishable from its surrounding soft tissue, so you cannot normally see it. If you see it, it is because there is a tube inside it.
Moving on, lung ultrasound will tell you whether the tube is in the trachea, in the mainstem bronchus (meaning a bronchial or selective intubation), or in the esophagus. But first, let's quickly review the concept of lung sliding. On the left, we have a typical M-mode image of lung sliding or seizure sign, and on the right, an M-mode image of absent lung sliding or barcode sign.
So, what does lung sliding mean? The presence of lung sliding means that that part of the lung you're scanning is moving as a result of air going in and out. The lung is inflating and expanding, then deflating and contracting, and while it does so, the visceral pleura slides back and forth against the static parietal pleura. In mechanically ventilated patients, the presence of lung sliding means that that lung you're scanning is being ventilated.
Now, let's say that you're scanning the lungs of an intubated patient, looking for lung sliding while you ventilate the patient. There are three possible scenarios.
First scenario: Both lungs show lung sliding or seizure sign. Thus, both lungs are being ventilated. The tube is therefore in the trachea.
Second scenario: One lung shows lung sliding or seizure sign, but the other lung shows absent lung sliding or barcode sign, which means that only one lung is being ventilated. The tube must be in the right mainstem bronchus, since only the right lung is being ventilated.
Third scenario: Both lungs show absent lung sliding or barcode sign, meaning that both lungs are not being ventilated. The tube is therefore in the esophagus, sending air to the stomach.
Now, some of you would ask, "Hey, Cade, isn't this barcode sign a sign of pneumothorax?" To which I answer, "Yes." And now, barcode sign by itself does not confirm pneumothorax. Here's where the lung pulse sign comes into play. When scanning over a non-ventilated lung, yes, you will see a barcode sign, but you will also see the lung pulse sign. Look at the image on the right and look at the arrowheads indicating the lung poles. The lung poles is nothing but the lung moving, pulsating due to the beating heart. The movement of the heart is transmitted through the lung tissue, moving the lung parenchyma and the pleura. Lung poles is seen as a barcode sign that is intermittently interrupted by bits of motion that cause a transitory disruption of this barcode pattern. These interruptions are repetitive and in synchrony with the patient's heartbeat.
See, in patients with pneumothorax, if you're scanning over the area with pneumothorax, you will see a barcode sign, but you will not see the lung poles because the lung is compressed, and the air in between the parietal pleura and the visceral pleura does not transmit the motion of the heartbeat, and thus you cannot see the lung pulsating.
Let's summarize everything on this nice table. Findings consistent with endotracheal intubation are: tracheal ultrasound showing a single comet tail artifact and lung ultrasound showing bilateral presence of lung sliding. Within the bronchial or selective intubation: tracheal ultrasound will show a single comet tail artifact, while lung ultrasound will show unilateral absence of lung sliding and presence of lung poles with contralateral presence of lung sliding. And with esophageal intubation: tracheal ultrasound will show a double comet tail artifact, and lung ultrasound will show bilateral absence of lung sliding with presence of lung poles.
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