Review Question - QID 109950

A 23-year-old man presents to the emergency department for altered mental status after a finishing a marathon. He has a medical history of obesity and anxiety and is not currently taking any medications. His temperature is 104°F (40°C), blood pressure is 147/88 mmHg, pulse is 200/min, respirations are 33/min, and oxygen saturation is 99% on room air. Physical exam reveals dry mucous membranes, hot flushed skin, and inappropriate responses to the physician's questions. Laboratory values are ordered as seen below.

Hemoglobin: 15 g/dL
Hematocrit: 44%
Leukocyte count: 8,500/mm^3 with normal differential
Platelet count: 199,000/mm^3

Serum:
Na+: 165 mEq/L
Cl-: 110 mEq/L
K+: 4.0 mEq/L
HCO3-: 20 mEq/L
BUN: 30 mg/dL
Glucose: 133 mg/dL
Creatinine: 1.5 mg/dL
Ca2+: 10.2 mg/dL
AST: 12 U/L
ALT: 10 U/L

Which of the following is the most appropriate next step in management?