All patients will be infused intravenously with 100 ml of normal saline with or without ketamine for four hours (25 ml/hr) daily for 10 days. The maximum intravenous ketamine infusion dose for this study will be 0.35 mg/kg/hr, not to exceed 25 mg/hr (100 mg of ketamine over a 4 hour period). On the first day, the intravenous ketamine infusion will be set to 50% of the maximum rate. On the second day, the intravenous ketamine infusion will be increased to 75% of the maximum rate. On the third day, the intravenous ketamine infusion will be increased to the maximum rate. The daily ketamine infusion rate is maintained at this level for the duration of the ten day study.