There have been numerous studies in adults and children which have established the safety of Hyperbaric oxygen therapy (HBOT) that is given in hyperbaric chambers. The most common side effect of HBOT is middle ear barotrauma where the ear drum gets irritated, bleeds or even ruptures. This occurs in approximately 2% of patients. The incidence of this is decreased with pseudoephedrine treatment before HBOT.
Less common side effects Hyperbaric oxygen therapy in descending order include sinus squeeze which is a sharp pain in the sinus, serous otitis which is fluid build-up behind the eardrum, claustrophobia, and reversible myopia which is nearsightedness.
Seizures may occur infrequently in about 1-3 out of 10,000 patients. Higher pressures especially over 2-3 ATA have a higher incidence of side effects.
We need to remember that oxygen is a drug. And just like any drug, it has beneficial effects at a certain dose, but too high of a dose can increase side effects.