Question

A $52$-year-old man is evaluated in the intensive care unit on the third day of hospitalization for severe acute pancreatitis. The patient was initially admitted with severe epigastric pain and a serum lipase level of $3,500\text{ U/L}$. Over the first $48\text{ hours}$, he received aggressive fluid resuscitation with $12\text{ L}$ of intravenous lactated Ringer solution. Today, the nursing staff reports that he appears increasingly lethargic. His temperature is $38.7^\circ\text{C}$ ($101.7^\circ\text{F}$), blood pressure is $108/65\text{ mmHg}$, pulse is $118/\text{min}$, and respirations are $24/\text{min}$. Physical examination shows generalized pitting edema and clear lungs bilaterally. The abdomen is significantly distended and diffusely tender to palpation without rigidity or guarding. Bowel sounds are absent.

Laboratory results are as follows:
Leukocyte count: $18,500/\text{mm}^3$
Blood urea nitrogen: $32\text{ mg/dL}$ (was $18\text{ mg/dL}$ on admission)
Serum creatinine: $1.9\text{ mg/dL}$ (was $0.9\text{ mg/dL}$ on admission)
Serum sodium: $138\text{ mEq/L}$
Serum potassium: $4.1\text{ mEq/L}$
Serum chloride: $104\text{ mEq/L}$
Serum bicarbonate: $16\text{ mEq/L}$

Arterial blood gas analysis on room air shows a pH of $7.32$, $\text{PaCO}_2$ of $30\text{ mmHg}$, and $\text{PaO}_2$ of $78\text{ mmHg}$.

A contrast-enhanced CT scan of the abdomen reveals diffuse enlargement of the pancreas with non-enhancement of approximately $50\%$ of the parenchyma, consistent with severe pancreatic necrosis. There are large peripancreatic fluid collections but no retroperitoneal gas is visualized.

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