| Stage I | Abdominal distension or abdominal x ray showing gaseous distension or frothy appearance of bowel lumen (or both); blood in stool; hypotonia, apnoea, or bradycardia (or combination of these) |
| Stage II | Abdominal tenderness or rigidity; absent bowel sounds; tissue in stool; abdominal x ray showing gas in the bowel wall or portal tree; abnormal bleeding with trauma; thrombocytopenia; lymphocytopenia |
| Stage III | Marked abdominal distension or rigidity; free gas in the peritoneum; spontaneous bleeding; coagulopathy; severe metabolic acidosis |