Nitrous TRD Bipolar Depression

Investigators will study approximately 64 patients with Treatment-Resistant Bipolar Depressive Disorder, defined as a failure of at least 1 antidepressants in the current depressive episode and 2 lifetime medication failures. The study will last approximately 6 to 8 weeks, involving randomization into one of two treatment groups receiving 3 one hour long inhalation treatments over a week. Post-treatment assessments follow each inhalation treatment and are conducted 1 week and 2 weeks following the final inhalation treatment. Patients are then randomized again into the Second Stage of the study, involving the same treatment and post-treatment schedule as the First Stage detailed above.