Epidural anesthesia and hyperbaric oxygen therapy also have vasodilator effect. Hyperbaric oxygen therapy treatment is used to treat gas gangrene. Patients undergoing hyperbaric oxygen therapy must equalize their ears to avoid barotrauma. The only absolute contraindication to hyperbaric oxygen therapy is untreated pneumothorax. The use of hyperbaric oxygen therapy as an adjunct to antibiotic therapy remains controversial. It also occurs frequently in those undergoing repeated hyperbaric oxygen therapy. Hyperbaric oxygen therapy has been explored as well. Other treatments may include vitamin C, exchange transfusion, and hyperbaric oxygen therapy. Evidence to support the use of hyperbaric oxygen therapy and chiropractic therapy is lacking. There is very tentative evidence for hyperbaric oxygen therapy in severe disease. More research is necessary to confirm the effectiveness of hyperbaric oxygen therapy for treating migraines. Research on hyperbaric oxygen therapy to reduce side effects is also ongoing. In rare instances, people receiving hyperbaric oxygen therapy have had seizures. In certain cases, hyperbaric oxygen therapy may be useful. In 1962 Smith and Sharp reported successful treatment of carbon monoxide poisoning with hyperbaric oxygen.