The incidence of esophageal intubations in the acute setting is reported to be 6-16%. Capnography is the gold standard of care for detecting failed intubations. Cardiac arrest studies showed 100% sensitivity and specificity with ETCO2 for verifying tube position.
During the last five years or so, several studies have demonstrated how tracheal ultrasound is as good or nearly as good for verifying tube position. In the systems and hospitals I have worked in access to capnography is almost global so tracheal ultrasound for tube verification seemed to me to be of purely academic interest. Then, recently the service I work for had numerous incidents where the capnography curve didn’t come up at all on our monitors. We still have no explanation for why this happened and are looking into it.
The inclusion criteriae included any patient that was intubated in the ED durign the time period no matter the cause. Patients with distorted anatomy were excluded. Ultrasound was compared against capnography.
Ultrasound confirmation was achieved by simply placing a linear probe across the trachea, sliding it downwards until the ETT was seen.
The linear probe was then slid laterally to visualize the esophagus to confirm at was empty and collapsed.
Results were in concordance with previous studies. Sensitivity for ultrasound in confirming tube position in oesophagus, with capnography as gold standard, was 98% and specificity was 100%. In two, out of 99, instances the ultrasonographer decided the tube was in the oesophagus when it was in fact in the right place. All six esophageal intubations were identified by ultrasound. Mean confirmation time was 16,4s.
Study lives here:
Crit Ultrasound J. 2013 Jul 4;5(1):7. doi: 10.1186/2036-7902-5-7. A feasibility study on bedside upper airway ultrasonography compared to waveform capnography for verifying endotracheal tube location after intubation.Adi O, Chuan TW, Rishya M.
Additional reference added 16th dec 2013:
Here’s a study on real-life endotracheal intubations verified by ultrasound in a CPR setting (thanks to @fayazg99 for the link). It is interesting to note how capnography sometimes was interpreted as if the tube was esophageal, while the ultrasound correctly saw the tube in the trachea:
“The misdiagnosis of endotracheal tube placement involves two scenarios: esophageal intubations that are incorrectly identified as tracheal; and tracheal intubations that are incorrectly identified as esophageal. For cardiac arrest patients, both situations can cause morbidity and mortality. Waveform capnography is the current preferred method of confirming tracheal intubation, and has thus far been the optimal screening tool to exclude esophageal intubation. However, in 5 of our study patients, endotracheal intubations were incorrectly identified as esophageal with waveform capnography. By contrast, tracheal ultrasonography correctly identified endotracheal positioning in all these patients. These false results may in turn lead to unnecessary re-intubation, causing undue interruption of chest compressions during cardiopulmonary resuscitation. We recognize the limitations of tracheal ultrasonography in some situations. However, with near-perfect negative likelihood ratios in assessing endotracheal tube position, tracheal ultrasonography not only excludes esophageal intubation, but also provides definite confirmation of correct endotracheal intubation that can complement the weakness of capnography in cardiac arrest patients.
Therefore, we are convinced that tracheal ultrasonography has a niche role to play in airway management during resuscitation. The combination of tracheal ultrasonography and capnography has the potential to achieve the optimal sensitivity and specificity to confirm endotracheal tube placement in critical patients.”
Also check out this article by the same Taiwanese team on an ultrasound ETT position protocol – T.R.U.E:
Tracheal rapid ultrasound exam (T.R.U.E.) for confirming endotracheal tube placement during emergency intubation, Resuscitation, 2011.