Use of Conivaptan (Vaprisol) for Hyponatremic Neuro-ICU Patients

Inclusion Criteria: * severe hyponatremia (Na \< 130 mmol/L) or * symptomatic hyponatremia - Na \< 135 mmol/L for at least six hours with Glasgow Coma Scale \< 15 Exclusion Criteria: * Enrollment in the NMH high-risk spine protocol. These patients receive large amounts of fluids, have rapid changes in electrolytes, and are typically corrected in 48 hours * Expected death from any cause * Known sensitivity or allergy to conivaptan * Renal failure (baseline creatinine \> 1.5 mg/dL) * Clinical diagnosis of hypovolemia, or by central venous pressure (CVP) \< 5 mm Hg if a central venous catheter is in place * Concomitant use of potent inhibitors of cytochrome P-450 isoenzyme 3A4 (e.g., ketoconazole, itraconazole, clarithromycin, ritonavir, indinavir). These agents are not commonly used in the Neuro-ICU * Clinical diagnosis of liver failure or insufficiency * Pregnancy (must be excluded before entry) * Lack of informed consent from the patient or a legally authorized representative (LAR) * Use of intra-arterial vasodilators (e.g. verapamil, nicardipine) within 24 hours (e.g. for vasospasm after SAH) * Concern by the Neuro-ICU pharmacist of a drug-drug interaction that would meaningfully impact care (the Neuro-ICU pharmacist will review the medication regimen before recruitment) * Patients with a diagnosis of diabetes insipidus or treated with vasopressin, since these patients are already treated for abnormal free water balance * Patients with congestive heart failure, since this is an approved use of the drug (these patients are typically not cared for in the Neuro-ICU) * Age\<18 years (these patients are not cared for at NMH) * Inclusion declined by the attending physician or consulting study nephrologist