FDA approval has recently been granted for a new drug - Conivaptan - for use in hyponatremic conditions. Conivaptan works by excreting free water from the body and thereby produce concurrent rise in serum sodium concentrations. Conivaptan has not been evaluated specifically in patients with brain injuries. The primary objective of this study is to demonstrate the safety and efficacy of intravenous Conivaptan for the treatment of hyponatremia in patients with brain injury. If effective, Conivaptan may represent a safe treatment option.