Introduction: Middle ear barotrauma is the most common side effect of hyperbaric oxygen therapy. Knowledge and understanding of its pathophysiology are crucial for an accurate diagnosis and proper decision making about treatment and prevention.

Objective: Describe up-to-date information on pathophysiology of middle ear barotrauma after hyperbaric oxygen therapy considering the physiology of pressure variation of the middle ear.

Data Synthesis: Middle ear barotrauma occurs especially during the compression phase of hyperbaric oxygen therapy. The hyperoxic environment in hyperbaric oxygen therapy leads to ventilatory dysfunction of the eustachian tube, especially in monoplace chambers, where the patients are pressurized with 100% O2, favoring middle ear barotrauma.

Conclusion: The eustachian tube, the tympanic cavity, and mastoid work together in a neural controlled feedback system in which various mechanisms concur for middle ear pressure regulation.