Short bowel syndrome (SBS), also known as short gut, is broadly described as a condition in which nutrients are not properly absorbed because a large part of the small bowel is missing. This is most often due to defects existing at birth (congenital), or surgical removal of part of the small bowel. There may not be enough functioning bowel or surface area left in the remaining bowel to absorb needed water and nutrients from food. Sometimes, loss of normal function may occur even when the bowel length is intact. Typically, a loss of half or more of the small bowel will result in SBS.
Short bowel syndrome is a condition characterized by malabsorption – difficulties absorbing both nutrients and fluids. Each year, many patients undergo surgical removal (resections) of large segments of their intestinal tract due to diseases, injuries, or congenital defects. Those patients can be left with too little intestinal absorptive surface areas. This then may lead to malabsorption and resulting malnutrition, diarrhea, and fluid and electrolyte imbalances.
The severity of short bowel syndrome in an individual depends on several factors, including:
- length of the remaining bowel,
- site of the resection,
- presence of the muscle that separates the small intestine and the large intestine (ileocecal valve),
- presence of the colon,
- health of the remaining bowel, and
- ability of the remaining bowel to compensate (adapt).
Symptoms of SBS
Symptoms of SBS result when fluids and nutrients are not properly absorbed. These will vary from person to person. Symptoms often include:
- pale greasy stools (steatorrhea)
- swelling of lower extremities (edema)
- foul smelling stools
- weight loss
- electrolyte losses
Vitamin and mineral losses can lead to some symptoms. Depending on which vitamin or mineral is deficient, symptom examples include:
- visual disturbances
- excessive dryness of the eyes
- prickling or tingling feeling on the skin
- muscle spasms
- loss of coordination
- loss of bone mass
- easy bruising and/or prolonged bleeding
- lack of energy (lethargy)
- difficulty breathing on exertion
The small bowel (small intestine) has 3 segments:
- duodenum: digest fats and fat-soluble vitamins (Vitamin A, D, E, and K carbohydrates, and fats)
- jejunum: About 90% of nutrient absorption occurs here. They include proteins, carbohydrates, vitamins, and minerals.
- ileum: absorbs water, bile salts, and vitamin B12
Depending on what parts of the small bowel are removed or not functioning properly, deficiencies of certain nutrients will result. These deficiencies can be many and complex. Examples include:
- Iron deficiency (duodenum)
- Vitamin and mineral deficiency; and malabsorption of carbohydrates, proteins, and fats (jejunum)
- Vitamin B12 deficiency and malabsorption of bile acids (ileum)
- Small intestinal bacterial overgrowth (SIBO) and increased fluid losses (ileocecal valve)
What Happens when SBS Develops?
Immediately following surgical resection of the small bowel, the bowel begins to compensate on its own for the loss of absorptive surface area. 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 and maintenance phase.
The acute phase occurs immediately after bowel resection and may last 3–4 months. Patients will often suffer from large fluid shifts. This occurs when fluids in the body move from one place to another. In SBS this is due to malabsorption which leads to fluctuations in electrolytes. This phase is associated with malnutrition, and fluid and electrolyte losses as high as 6–8 liters/quarts per day. Enteral nutrition (delivery of liquid food to the stomach or small intestine through a feeding tube) may be needed during this phase. If a more significant length of small bowel is removed, then parenteral nutrition (delivery of fluids, electrolytes, and liquid nutrients into the bloodstream through a tube placed in a vein) is required.
Next, the adaptation phase begins. This phase can last 12–24 months. During this phase, the remaining small bowel begins to compensate for its short length by trying to increase its absorptive capacity and slow down the gut’s motility. 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 where 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
Types of Short Bowel Syndrome (SBS)
The result of the adaptive period and the remaining small bowel’s ability to compensate determines the “type” of short bowel syndrome a person has. This can be either Intestinal Insufficiency or Intestinal Failure. Intestinal Insufficiency is when a patient has a reduced length of small bowel remaining but does NOT require IV nutrition or fluids. Those that do require such supportive measures are termed as having Intestinal Failure.
Short bowel syndrome 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.
The Gutsy Perspective
The Gutsy Perspective is a short bowel syndrome (SBS) research-project that that investigates the quality of life of children, adults, and families that have been impacted by pediatric SBS
Adapted from IFFGD publication #290 “What is Short Bowel Syndrome” Contributors: Evelin Eichler RD LD, Clinical Dietitian, University Medical Center Texas Tech University; Richard McCallum MD, Professor of Medicine and Founding Chair and Chief of Gastroenterology, Texas Tech University; Harold J. Boutté Jr. MD, Assistant Professor of Medicine, Northwestern University Feinberg School of Medicine