Teng WN, Ting CK, Wang YT, Hou MC, Tsou MY, Chiang H, Lin CL.

J Clin Monit Comput. 2017 May 24. doi: 10.1007/s10877-017-0029-8. [Epub ahead of print

The authors evaluated the role of capnography in esophagogastroduodenoscopy (EGD). Simultaneous supplemental oxygen, position of patient, open mouth breathing pattern, and anatomy of the oral and nasal cavity  influences capnography accuracy. This study first measured capnographic data via the nasal or oral cavity during sedated EGD. Secondly, the authors investigated the influence of supplementary oxygen through the oral cavity on the capnographic reading. Patients with ASA class I or II status admitted for routine EGD exams were enrolled. End-tidal carbon dioxide measurements were performed simultaneously via nasal catheter and oral catheter with standard oral bite and nasal cannula supplementary oxygen when the patient is awake, during sedation and during sedation with endoscopy. The influence of oral supplementary oxygen, oral capnography were recorded using a mandibular advancement bite block. One hundred and four patients were enrolled. Breathing in the conscious patient is conducted primarily via the nostrils (95%). When sedated with endoscope placement, the percentage of nasal breathing decreased significantly to 47% and oral capnography sufficiently captured data in 100% of patients. Supplementary oral oxygen decreased oral capnographic measurement significantly (38.89 ± 7.148 vs. 30.73 ± 7.84, p < 0.001). However, the measurements using the MA bite block did not differ from oral cavity catheter (28.86 ± 8.51 vs. 30.73 ± 7.839, p = 0.321). The authors concluded that the conscious patient breathes mostly nasally while the sedated patient breathes mostly orally during EGD when an oral bite is in place. Capnography measurement via oral cannula increases the measurement accuracy and efficacy. Oral supplementary oxygen may decrease capnographic measurement but still provide sufficient reading for interpretation.

Comment Bhavani shankar Kodali MD

This study demonstrates that capnography can be used in endoscopic procedures. There are many devices in the market to facilitate nasal or oral sampling of carbon dioxide.  A change in CO2 values from pre-sedation to intra-sedation is more important than absolute values of CO2.  Every effort should be made to improve the sampling of expired gases and authors describe one method.