FIGURE 1. The extent of surgery score (ESS) is based on the number of abdominal regions involved in the operative procedure. Abdominal regions 0 to 8 are associated with specific anatomic structures located within the abdomen and pelvis. The small bowel is defined sequentially in a proximal to distal direction: region 9 is upper jejunum, region 10 is lower jejunum, region 11 is upper ileum, and region 12 is lower ileum.