The investigators aim to prospectively study the feasibility and clinical impact of
hyperbaric oxygen therapy in acute hospitalized moderate to severe ulcerative colitis flares
as an adjunct to standard medical treatment. Specifically, we will investigate the impact of
hyperbaric oxygen therapy on clinical response/remission and serum and mucosal inflammatory
markers. The investigators expect that hyperbaric oxygen therapy will improve patient
responsiveness to steroids and avoid progression to second line therapy during
hospitalization.