Hyperbaric Oxygen Therapy for Ulcerative Colitis (HBOT-UC)

Who May Qualify: - Participants with known or newly diagnosed UC who require hospitalization for an acute moderate to severe flare - Age 18-85 - Able to fully participate in all aspects of the trial - Consented and able to receive first HBOT session within first 48 hours of initiation of intravenous steroids - Agreement to not participate in another trial for the duration of the active intervention period Who Should NOT Join This Trial: - Received hyperbaric oxygen therapy either as part of standard of care or through a clinical trial prior to enrollment - Complication requiring urgent surgical intervention - Requirement for new start of a biologic or small molecule during the hospitalization prior to randomization and/or anticipated requirement for rescue medical or surgical therapy within 48 hours of randomization - Toxic megacolon - Inability to receive intravenous steroids - Historically failed or been exposed to 4 or more classes of advanced therapeutic options - Known or suspected diagnosis of Crohn's colitis, indeterminate colitis, ischemic colitis, radiation colitis, diverticular disease associated with colitis, microscopic colitis or infectious colitis - Received any investigational drug within 30 days - Clinically significant cardiac, renal, neurological, endocrine, respiratory or hepatic impairment that increases the risk for HBOT toxicity - Women who are pregnant or nursing - Unwillingness to complete course of HBOT Always talk to your doctor about whether this trial is right for you.