The investigators hypothesize that hyperventilation will facilitate prolonged seizure duration and faster remission of depressive symptoms. As well there may be significant cerebral desaturation and cardiovascular side effects of ECT therapy following hyperventilation. Lastly, the effect of hyperventilation on the efficacy of ECT therapy may be improved when ketamine anesthesia is used simultaneously. To test this hypothesis this study will compare ketamine anesthesia to etomidate anesthesia. Etomidate is a short acting anesthetic that is commonly used in these procedures.