Tracheoesophageal fistulae (TEF) are difficult to spot and need a high level of suspicion. Researchers predicted that using capnography to detect a rise in end-tidal carbon dioxide (etCO2) during esophagogastroduodenoscopy with carbon dioxide (CO2) insufflation would aid in TEF diagnosis due to gas transfer from the esophagus to the trachea. Medical records were evaluated for 42 consecutive instances with recurrent, acquired, or missing congenital TEF identified between January 2015 and November 2019 that underwent esophagoscopy with CO2 insufflation. A control group of 97 individuals who had been similarly endoscopically examined and had surgical confirmation of the lack of recurrent TEF was also gathered. Pre-operative esophagoscopy, bronchoscopy, and capnography were performed on all patients, and the diagnostic abilities of various combinations of modalities for TEF diagnosis were estimated. The statistical study determined that a maximal intra-esophagoscopy end-tidal CO2 level of 68 mmHg was the best discriminator between cases and controls, although in fact, repeated TEFs frequently enable fast rises of 90 mmHg. Increasing the number of diagnostic modalities enhanced diagnostic sensitivity to detect recurring TEF; the combination of intra-esophageal fluoroscopy with bronchoscopy and capnography 68 mmHg achieved the best diagnostic sensitivity for TEF detection. There were some cases of TEF discovered by capnography that esophagoscopy missed. 

TEF can be detected by paying attention to etCO2 during esophagoscopy with CO2 insufflation. TEF identification remains difficult, despite the fact that combining diagnostic modalities improves diagnostic sensitivity.

Reference: https://journals.lww.com/jpgn/Fulltext/2020/05000/Comparison_of_Detection_Methods_for.7.aspx