After intubation, a low ETCO2 reading is most likely due to which issue?

A low ETCO2 reading after intubation is most commonly associated with the endotracheal (ET) tube being incorrectly placed in the esophagus rather than the trachea. When the tube is positioned in the esophagus, the ventilation primarily affects the stomach rather than efficiently entering the lungs. As a result, carbon dioxide (CO2), which is a byproduct of respiration mainly produced in the lungs, cannot be adequately exhaled, leading to lower levels of ETCO2 detected.

In contrast, a correctly placed ET tube in the trachea allows for proper ventilation and gas exchange, leading to a more expected range of CO2 levels. Therefore, if the measurement is low, it raises the question of tube placement and suggests checking for esophageal intubation.

Other conditions such as severe respiratory distress, bronchospasm, or complaints related to the airways might influence gas exchange and ETCO2 readings, but they are less likely to cause such a drastic reduction as incorrect tube placement.