Question

A $68$-year-old woman is admitted to the hospital with a $48$-hour history of colicky abdominal pain, severe nausea, and repeated episodes of bilious vomiting. She has not passed flatus or had a bowel movement for $3$ days. Her past surgical history is significant for an open hysterectomy performed $10$ years ago. On initial evaluation, she was afebrile and hemodynamically stable. Her abdomen was distended and tympanic, with mild diffuse tenderness but no guarding or rebound. An initial plain abdominal radiograph demonstrated multiple dilated loops of small bowel with prominent air-fluid levels and a paucity of gas in the colon. She was admitted for conservative management with intravenous fluid resuscitation, bowel rest, and nasogastric tube decompression.

Twelve hours after admission, the patient reports a sudden worsening of her abdominal pain, which is now constant and severe. Her temperature is $39.1^\circ\text{C}$ ($102.4^\circ\text{F}$), blood pressure is $92/58 \text{ mmHg}$, pulse is $122/\text{min}$, and respiratory rate is $22/\text{min}$. Physical examination now reveals a rigid abdomen with marked diffuse tenderness, involuntary guarding, and rebound tenderness. Bowel sounds are absent. Laboratory studies demonstrate a leukocyte count of $22,000/\text{mm}^3$ with a left shift, and a serum lactate level of $4.2 \text{ mmol/L}$.

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