Question: How does one best verify that the endotracheal tube is in correct position after intubation?
Answer: Over the years, many techniques have been used to verify proper placement of the endotrachal tube. In the past, verification relied on visual confirmation of bilateral movement of the chest during positive pressure ventilation, on auscultation of the chest with a stethoscope, and on the appearance of vapor in the endotracheal tube on exhalation. Some have been known to press on the chest and listen for expulsion of air; others have actually attached whistles to the endotracheal tube.
Of these techniques, the most reliable is bilateral auscultation of the chest. However, one can be misled, particularly with a small child, in whom sounds are readily transmitted, or with an extremely obese person, in whom breath sounds may be very difficult to hear adequately. For reliable auscultation, I recommend that the chest be auscultated in at least two places bilaterally, one of which should be the midaxillary line. Also, one should listen over the epigastrium.
Newly introduced equipment that gives breath-by-breath analysis of carbon dioxide tension gives certainty that the endotracheal tube is in the trachea, as opposed to the esophagus, by detecting an appropriate level of end-tidal carbon dioxide with each breath. This can be done with a dedicated carbon dioxide analyzer or with a mass spectrometer. If carbon dioxide is not detected on exhalation and the equipment is working properly, the endotracheal tube is certainly misplaced or totally obstructed.
End-tidal carbon dioxide monitoring does not readily detect endobronchial intubation. An endobronchial intubation frequently can be detected by recognizing a difference in the breath sounds transmitted from the two sides of the chest by auscultation or, more accurately, by roentgenogram. Unfortunately, the latter is not readily available for routine use during anesthesia.
Monitoring the patient’s oxygenation with an oximeter can detect when the endotracheal tube is not in the trachea and may suggest when a tube is placed in one or the other main stem bronchi. However, particularly after the patient has been preoxygenated, oximetry may delay the detection of a faulty intubation because oxygen desaturation does not occur instantly.
My recommendation is that, after endotracheal intubation, bilateral auscultation of the chest in at least two places and auscultation over the epigastrium be done routinely. If the capability exists to measure end-tidal carbon dioxide tension, then this should be done on a routine basis. Further, patients in whom endotracheal tubes are placed for long-term ventilation, such as those in the intensive care unit, should have a follow-up chest roentgenogram.
Response by: Jerome H. Modell, M.D., Professor and Chairman, Dept. of Anesthesiology, University of Florida.