Ultrasound Exam to Confirm ET Tube Position
Endotracheal intubation is one of the commonest procedures done in the emergency and critical care departments. Wrong placement of the ET tube into the esophagus occurs rarely. With the widespread use of videolaryngoscopy the vocal cords are easily visualized and the possibility of wrong placement is limited. But the frequency of the wrong placement increases with inadequate operator expertise, difficult upper airway anatomy, difficult visualization of the upper airway due to fluid, blood or vomitus, lack of support personnel and instruments, out of hospital locations and in rapidly deteriorating patients requiring emergency intubations etc. Not recognizing esophageal intubations early enough may result in the death of the patient.
Hence after every intubation, the health personnel routinely confirm if the ET tube is placed in the trachea. The methods available include
- Five point Auscultation
- Trans-tracheal illumination
- Esophageal detector devices
Of the methods mentioned above, the five point auscultation is the commonest technique used for the confirmation of the ET tube. But studies have shown it to be unreliable in certain situations.
Capnography which measures the end tidal CO2 is a better alternative. The limitation of capnography include lower sensitivity when used as a tool to confirm ET tube placement in patients intubated after cardiac arrest. The inadequate cardiac output grossly affects the physiological mechanisms of CO2 elimination and the end tidal CO2 is decreased drastically. Similar false negative results are obtained when upper airway obstruction occurs with blood, secretions or fluid.
The trans tracheal and the esophageal detector devices have poor sensitivity and are not widely used.
Ultrasound which has found increasing applications in critical care can be used as an modality in confirming the ET tube placement. The following can be noted in the lung ultrasound exam
- Lung Sliding
- Diaphragmatic Movements
- Scanning anterior neck between cricoid and suprasternal notch
Of these the lung sliding or pleural sliding has the highest sensitivity of 95% and a specificity of 100%. When the lung expands, the visceral and the parietal pleura slide past each other. This can be detected in the ultrasound image as bright lines (hyperechoic) sliding back and forth upon each other. The pleural line in the above image is watched to see sliding in real time ultrasound images. In addition comet tail artifacts starting from the pleural line and going downwards can be noted along with the lung sliding. Ultrasound images of the diaphragmatic movements can be used as an additional confirmation. Scanning the anterior neck is a less reliable technique and ET tube balloon should be inflated with saline to study the interface.
Limitation of USG confirmation
The lung sliding may be absent or variable in the presence of various pulmonary pathologies including pneumothorax, pneumonia, large bulla, collapsed lung, empyema,pleural effusion, pulmonary edema, pleural fibrosis/thickening, previous thoracic surgeries etc.
Overall the lung ultrasound is a reliable and valuable tool to confirm the endotracheal tube placement. This can be used in addition to the traditional auscultation and capnography.