Hyponatremia associated with administration of hypotonic intravenous (IV) fluids may have serious complications. It has recently been suggested that isotonic saline may be a more appropriate choice of maintenance IV fluid. This pilot and feasibility study aims to compare isotonic saline to 0.45% saline in hospitalized children requiring parenteral fluid support in order to:

Aim 1: To determine the feasibility of conducting a double-blind, randomized controlled trial comparing these solutions.

Aim 2a: To compare the rate of change in serum Na (mmol/L/hr) and the incidence of hyponatremia (Na <136 mmol/L) between patients receiving isotonic and hypotonic intravenous fluids at at least 50% of the traditional maintenance rate for an interval of at least 8 hours.

Aim 2b: To compare the incidence of adverse events between the two IV fluid treatment groups.

Inclusion Criteria:

• 1 month to 18 years of age
• Require IV fluids for at least 8 hr.
• Baseline serum sodium >=136 mmol/L & <=145 mmol/L

Exclusion Criteria:

• Baseline serum sodium concentration less than 136 mmol/L or greater than 145 mmol/L
• Renal disease, a history of cardiac dysfunction or evidence of cardiac dysfunction, pre-existing hypertension, diuretic use, edema, or known adrenal dysfunction
• Acute neurological illness such as meningitis or encephalitis
• Severe chronic neurological illnesses (uncontrolled seizure disorders, severe developmental delay)