Discolor Endotrachealtube / Endotracheal tube

Medical personnel carry out the trachea endotracheal intubation from the mouth and an oxidation reaction is produced with the reagent paper agent inside the wall.
When being inserted into the trachea with a high oxygen concentration and high moisture content environment, this makes the endotracheal tube distal end turn red due to oxidation.
If it is mistakenly inserted into the esophagus, it is rendered colorless since it is unable to trigger reactions.