Rapid analysis of exhaled CO2 to assess endotracheal tube placement

Background: assessing proper placement of an endotracheal tube can be difficult. Assessment techniques include visualization of the tube in the larynx, auscultation of the chest and abdomen, assessment of compliance by the 'feel' of the resuscitation bag, assessment of radiographs, and observations related to the presence or absence of (1) humidity in the tube, (2) patient phonation, or (3) gastric contents in the tube. Despite these techniques, tubes can be misplaced. We reasoned as have others that the presence or absence of CO2 might be a more rapid and specific indicator of tube placement. Method and materials: all endotracheal intubation attempts by Respiratory Care Services at Duke University Medical Center from July 1989 to October 1990 were studied. A Biochem 515 portable CO2 monitor was used to detect CO2 in the gas returned through the endotracheal tube. Proper tube position was ultimately confirmed by chest radiograph. Results: we analyzed the 933 patient intubations that occurred during the study period, and found that in 915/925 successful intubations CO2 was present (true positive 99%), and in 8/8 unsuccessful intubations CO2 was absent (true negative 100%). No unsuccessful intubations had CO2 present (false positive 0%) and 10/925 successful intubations had CO2 absent (false negative of 1.1%). Of the 10 successful intubations that did not result in endotracheal CO2, 7 subjects were believed to have had little or no CO2 in the lung due to poor cardiopulmonary perfusion, 1 was associated with a faulty CO2 analyzer, and for 2 there was no explanation for the absence of CO2. Conclusion: Our results confirm the earlier work of Owen and Cheney reported in this journal. Although no one sign is completely conclusive for verification of endotracheal tube placement, CO2 detection is quick and easy, and the presence of CO2 confirms proper intubation.

Duke Scholars

Author Neil Ross MacIntyre Jr. Medicine, Pulmonary, Allergy, and Critical Care Medicine