Risk Factors and Stages of Short Bowel Syndrome
Short bowel syndrome (SBS) can occur in a person of any age. Risk factors for SBS include defects existing at birth and diseases of the small intestine that require extensive or recurrent surgery such as Crohn’s disease or gastrointestinal cancers. In addition SBS can be caused by loss of function due to injury or disease in a normal length small intestine. Other explanations include emergency situations related to injury or trauma, perforated bowel, or blocked or restricted blood flow to the bowel.
What Happens when SBS Develops
Immediately following surgical resection of the small intestine, with the resulting loss of absorptive surface area, the intestine begins to compensate on its own. It undergoes various phases to increase absorption and maintain balance (homeostasis). This process, known as adaptation, occurs through structural changes that increase surface area in the remaining bowel. These physiological changes and adaptations can be separated into 3 phases:
- Acute phase
- Adaptation phase
- Maintenance phase
The acute phase occurs immediately after bowel resection and may last 3-4 months. This phase is associated with malnutrition, and fluid and electrolyte losses as high as 6-8 liters/quarts per day. Enteral nutrition may be needed during this phase. If a more significant length of small bowel is removed parenteral nutrition is required.
Next, the adaptation phase begins 2-4 days after bowel resection and lasts 12-24 months. During this phase the intestinal villi, the tiny finger-like projections within the small intestine, will grow in length and thickness, which increases surface area. In addition some increase in the diameter (dilation) of the bowel may occur.
The maintenance phase is the last change, and here the absorptive capacity of the remaining bowel will be maximized. Some patients will still have dependence on parenteral or enteral nutrition. Others will meet their nutritional needs with oral meals, nutrition supplements, and vitamins and minerals, with or without supplements delivered enterally or parenterally.