Review Question - QID 108761

A 72-year-old woman presents to the emergency department complaining of severe abdominal pain and several days of bloody diarrhea. Her symptoms began with intermittent bloody diarrhea 5 days ago and worsened steadily. For the last 24 hours, she has complained of fevers, chills, and abdominal pain. She has a history of ulcerative colitis, idiopathic hypertension, and hypothyroidism. Her medications include hydrochlorothiazide, levothyroxine, and sulfasalazine. Her temperature is 39.1°C (102.4°F), pulse is 120/min, blood pressure is 90/60 mmHg, and respirations are 20/min. The patient is alert and oriented to person and place, but does not know the day. Her mucus membranes are dry. Heart and lung exam are not revealing. Her abdomen is distended with marked tenderness without rebound. Bowel sounds are hyperactive. Laboratory tests are obtained and the results are shown below:

Serum:
Na+: 142 mEq/L
Cl-: 107 mEq/L
K+: 3.3 mEq/L
HCO3-: 20 mEq/L
BUN: 15 mg/dL
Glucose: 92 mg/dL
Creatinine: 1.2 mg/dL
Calcium: 10.1 mg/dL

Hemoglobin: 11.2 g/dL
Hematocrit: 30%
Leukocyte count: 14,600/mm^3 with normal differential
Platelet count: 405,000/mm^3

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