Hyperbaric Oxygen Therapy for Perianal Fistulizing Crohn's Disease Not Responsive or Intolerant to Conventional Care: HYPNOTIC Pilot Study

Inclusion Criteria:

• Adults (\>19 years old)
• Diagnosis of Crohn's disease based on standard endoscopic, radiologic and/or histologic criteria.
• One or more perianal fistula tract connecting the rectum and the perianal skin. Patients must have active fistula drainage and/or a recurrent perianal abscess within the past month.
• Failure or intolerance of conventional therapy (imuran, methotrexate, anti-TNF therapies, vedolizumab and/or ustekinumab). Failure is defined as persistent perianal drainage or recurrent abscesses after a minimum of 3 months of therapy.
• Standard or care treatment has been stable (dose and treatment interval) for at least 3 months.
• Able to provide written consent to participate

Exclusion Criteria:

• Fistulas not believed to be due to Crohn's disease (examples include, obstetrical complications, tuberculosis, anorectal cancer or diverticular fistula).
• Rectovaginal fistulas.
• Undrained perianal abscesses on pelvic MRI exams (abscesses will require successful drainage by an exam under anaesthesia with or without seton prior to study inclusion).
• Surgical procedure such as an advancement flap, fistula plug, fistula glue or ligation of intersphincteric fistula tract (LIFT) procedure within the past 6 months.
• Diverting ostomies or ileal pouch anal anastomosis.
• Current or planned pregnancy or lactation during the study treatment period.
• Contraindications to HBOT (claustrophobia, incompatible implanted medical device, and other conditions) based on the discretion of our HBOT clinicians.