The role of capnography in esophagogastroduodenoscopy (EGD) is controversial. Simultaneous supplemental
oxygen, position of patient, open
mouth breathing pattern, and anatomy of the oral and nasal cavity can influence capnography accuracy. This study first measured capnographic data via the nasal or oral cavity during sedated EGD. Secondly, we 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 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.