• S T Sum-Ping, M P Mehta, and J M Anderton.
• Department of Anesthesia, University of Iowa College of Medicine, Iowa City 52242.
• Anesth. Analg. 1989 Nov 1;69(5):627-32.

AbstractThe trachea and esophagus of 21 patients were simultaneously intubated to comparatively evaluate methods for detecting esophageal intubation. In succession, the trachea and esophagus were ventilated with the same inspiratory volume of 621 +/- 45 mL (mean +/- SD). Carbon dioxide (CO2) levels, volumes, and temperatures of expired gas were measured from the tracheal and esophageal tubes. End-expired CO2 levels of gases from the trachea and esophagus were 4.9 +/- 0.7% and 0.6 +/- 0.6%, respectively, with CO2 waveforms observed in 7 (33%) patients with esophageal intubations. Volumes expired from the tracheal tube averaged 615 +/- 64 mL and from the esophageal tube 35 +/- 16 mL (P less than 0.001). Peak temperatures of expired gas recorded from the tracheal tube (32.0 +/- 0.73 degrees C) were higher than those from the esophageal tube (27.3 +/- 1.2 degrees C) (P less than 0.001). The shape of temperature waveforms with a correctly placed tracheal tube remained constant with each ventilation, contrary to that obtained from an esophageal tube. Although the occasional detected of CO2 waveforms from an esophageal tube might lead to an incorrect assessment of tube placement, this limitation of CO2 analyzer can be offset by measurement of volume and temperature of expired gas in identifying placement of an endotracheal tube.

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