A 7-day-old premature infant (gestational age 28 weeks, birth weight 1100 g) born to a mother with inadequate antenatal steroids presents with feeding intolerance, abdominal distension, and grossly bloody stools. Abdominal X-ray shows the finding marked **A** in the diagram—bubbly and linear lucencies within the bowel wall, most prominent in the right lower quadrant. Which of the following is the most appropriate IMMEDIATE management for this infant?