[A clinical study of impedance graph in verifying tracheal intubation]

To evaluate the clinical usefulness of impedance pneumography in determining the tube placement during endotracheal intubation.

Thirty-six endotracheally-intubated patients for elective operations underwent general anesthesia and endotracheal intubation, and then a second identical tube was inserted into the esophagus under laryngoscopic control. The ventilation circuit was then attached either to tracheal or esophageal tube. The tube position was determined by 2 blinded examiners, one experienced and the other inexperienced, using three methods: impedance pneumography, capnography, and auscultation. The order of the tubes tested and the order of the methods used were randomized. The observation results and the time needed to determine were recorded by another assistant.

Of the 216 tests conducted, both examiners correctly diagnosed the position of the tube using impedance pneumography and capnography. In the auscultation method there were two false-negative results (with the tracheal tube identified as esophageal) and one false-positive (with the esophageal tube identified as tracheal) by the experienced examiner, while five false-negative results (with the tracheal tube identified as esophageal) and nine false-positive (with the esophageal tube identified as tracheal) by the inexperienced examiner. With the sensitivity and specificity of impedance pneumography as standards (100%), the sensitivity and specificity of the capnography were both 100% too, and the sensitivity and specificity of the auscultation method were 90% and 86% respectively, both significantly lower than those of the other 2 methods (all P<0.01). Capnography needed 3.4 s+/-1.3 s and 3.7 s+/-1.4 s to verify tracheal intubation and esophageal intubation respectively, both significantly longer than those of the auscultation methods (1.7 s+/-0.7 s and 2.5 s+/-1.7 s) and impedance pneumography (1.6+/-0.3 and 2.1+/-1.1s, all P<0.01). It took less time for impedance pneumography and auscultation to verify the tracheal intubation than to verify esophageal intubation (both P<0.01).

Impedance pneumography is one of the reliable methods for diagnosing tracheal tube position.