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