A new method for identifying the depth of insertion of tracheal tubes

When a patient's lungs require mechanical ventilation, a plastic breathing tube (tracheal tube, TT) must be inserted through the vocal cords and into the trachea. Although insertion of the TT is a routine procedure, determining the correct depth of insertion is difficult clinically, and may require a chest radiograph. We investigated the accuracy of a simple clinical method for inserting a TT to the correct depth. Typically, an inflatable cuff surrounds the distal circumference of the TT to occlude the gap between TT and tracheal wall. Our technique involves pressing gently with one finger on the front of the lower part of the neck to locate the center of the cuff. We hypothesized that a) a palpating finger can identify the cuff through the tracheal wall, and b) if placed using this technique, the TT will be correctly positioned in the trachea. We studied 79 patients in whom TTs were inserted for general anesthesia. TTs were inserted to a depth determined by the palpation technique. We developed a stylet incorporating a magnetic reed switch which could be inserted through the TT. A magnet with specific field characteristics was passed along the front of the neck to locate the reed switch and confirm the location of the cuff. The TT position in the trachea was then examined with a fiberoptic scope. The palpation technique resulted in optimal positioning of the TT in all subjects and could save approximately $14,268/year in chest radiograph costs in our institution.