Malabsorption after Small Bowel Resection: Complications

The following are the most important diseases or complications that may be contributed to by small bowel resection (partial small bowel resection):

Respiratory system (J00-J99)

  • Pneumonia (inflammation of the lungs)

Endocrine, nutritional, and metabolic diseases (E00-E99).

  • Malnutrition (malnutrition)

Infectious and parasitic diseases (A00-B99).

  • Infections

Circulatory system (I00-I99)

Mouth, esophagus (food pipe), stomach, and intestines (K00-K67; K90-K93).

  • Bleeding, unspecified
  • Dysbiosis (imbalance of intestinal flora).
  • Short bowel syndrome (see below)
  • Incisional hernia – abdominal wall hernia in the area of the surgical scar.

More

  • Anastomotic stenosis – narrowing of the connecting suture.
  • Suture insufficiency – inability of the suture to adapt the tissues.
  • Wound healing disorders

When the small intestine of adults is resected up to 50%, it is still possible to meet energy, nutrient and vital substance requirements, so that no malabsorption (“poor absorption“) results – provided that the duodenum (duodenum), ileum (ileum) and the valve-like ileocecal valve (valve at the junction between the colon and the appendix) are preserved. Under these circumstances, the loss of absorptive capacity can be compensated for by the considerable reserve capacity of the small intestine – by adaptation (adjustment) of the rest of the intestine. Adaptation is made possible by increased enzyme activity in the mucosa of the small intestine and increase in size of the mucosal protrusions (villi) as well as the mucosal invaginations (crypts). However, as the extent of resection increases, the area of resorption decreases, and with it the coverage of nutrient and vital substance, energy, and water requirements. If more than 50% of the small intestine is removed, absorption of essential nutrients and vital substances is compromised. Resection over 75% of the total length results in marked malabsorption and malnutrition (malnutrition). Underutilization of:

Clinical symptoms, absorption of nutrients and vital substances and the resulting deficiency symptoms, in addition to the remaining intestinal length, are largely dependent on whether the scrotum, jejunum or ileocecal valve is preserved. If partial or total removal of the colon occurs simultaneously with small bowel resection, absorption may also be significantly impaired and symptoms may be exacerbated.

Resection of the terminal ileum

The lower part of the small intestine – ileum (scimitar), terminal ileum is the site of vitamin B12 absorption and bile salt reabsorption. Vitamin B12 and bile salts are subject to the intestinal-liver (enterohepatic) circulation. This is essential for the regulation of vitamin B12 as well as bile acid balance.

Consequences – Resection of the terminal ileum

After surgical resection of the terminal ileum – of approximately 100 cm – the enterohepatic circulation is interrupted. As a result, vitamin B12 absorption is impaired – vitamin B12 deficiency – and nonphysiologic amounts of bile salts pass into the colon because of the lack of reabsorption. There they increase the contraction waves of the smooth muscles (peristalsis) and reduce the reabsorption of water. In this way, the bile acids cause chologenic diarrhea (diarrhea) with high losses of fluid, electrolytes, and water-soluble vitamins. The bile salts are eventually excreted in the stool. The liver is unable to compensate for the loss of bile acids by increasing synthesis, resulting in a decrease in bile salt concentration in the bile fluid. As a result of the loss, bile salts are no longer available for micelle formation. The critical micellar concentration leads to reduced utilization of dietary fat and fat-soluble vitamins A, D, E, and K.Since dietary fats cannot be sufficiently absorbed, the unabsorbed fats and fatty lipid products reach deeper parts of the intestine. There they accelerate the intestinal passage by stimulating peristalsis and finally – as a result of the increase in fecal fat excretion (steatorrhea; chologenic fatty stool). By also promoting contraction waves and inhibiting water reabsorption from the intestine, bile salts in the colon exacerbate fatty diarrhea Increased losses of fat through the stool also result in increased losses of fat-soluble vitamins A, D, E, and K, as well as essential fatty acids. Depending on the extent of the fat absorption disturbance, a negative energy balance occurs, resulting in weight loss [4.2]. The bile acids produced in the large intestine bind calcium, as a result of which the essential mineral is increasingly excreted together with the bile acids. Calcium deficiencies can rapidly develop as a result. Hypocalcemia (calcium deficiency) is also favored by the unabsorbed fatty acids, because these combine with calcium to form insoluble calcium soaps and thus inhibit calcium absorption. Furthermore, the loss of bile acid promotes the excretion of oxalic acid in the urine (hyperoxaluria) and thus increases the risk of kidney stone formation. Patients with a resected ileum should therefore avoid foods containing oxalic acid, such as beet, parsley, rhubarb, spinach, chard as well as nuts. Causes of increased oxalic acid – oxaluria:

  • High amounts of glycine enter the colon with bile salts, where it is converted to glyoxalate by bacteria. Glyoxalate is converted to oxalic acid after absorption in the liver
  • High bile salt concentration in the colon increases the permeability of the mucosa to oxalate ions
  • Low bile salt concentration delays the absorption of fatty acids, allowing fatty acids to combine with calcium to form insoluble calcium soaps. Thus, oxalic acid can no longer be bound by calcium to form calcium oxalate, resulting in increased absorption of free oxalic acid ingested from food and excretion in the urine

Resection of the ileocecal valve

The ileocecal valve and colon serve to stabilize water and electrolyte balance, reduce diarrhea, and optimize meeting energy needs. The ileocecal valve also has the function of preventing the reflux of intestinal contents from the colon, which is heavily colonized with bacteria, into the small intestine, which is poor in bacteria. Extensive failure of the ileocecal valve may result in bacterial overgrowth in the small intestine, as bacteria enter the small intestine without obstruction with the reflux of intestinal contents from the colon. The cellular antigens are able to convert primary bile acids into secondary bile acids in the colon. The primary bile acids are thus no longer available for micelle formation, preventing the absorption of fats in the intestine. High concentrations of secondary bile acids, in turn, increase the risk of cancer by supporting mechanisms that promote tumor development. Furthermore, the utilization of vitamin B12, carbohydrates as well as proteins (protein) is impaired, as bacteria extract high amounts of these vital substances from the diet for their own needs. Because of this, vitamin B12 deficiencies are not uncommon in patients with absent ileocecal valves. In addition, the body is inadequately supplied with carbohydrates and proteins. The increased accumulation of bacteria and bacterial toxins in the small intestine damages the mucosa of the small intestine. As a result of the mucosal inflammatory as well as tumor-like changes, malabsorption of nutrients and vital substances occurs. In particular, essential fatty acids, fat-soluble vitamins, vitamin C, calcium, magnesium, iron, and zinc are insufficiently absorbed [4.2]. Furthermore, the impairment of the intestinal mucosa leads to increased intestinal protein loss, as the leakage of plasma proteins through the intestinal mucosa into the interior of the intestine exceeds the rate of protein (albumen) formation – enteral protein loss syndrome. Decrease in circulating plasma proteins is usually accompanied by severe protein deficiency. In addition, increased intestinal protein loss leads to a decrease in oncotic pressure and thus – depending on the extent of the decreased concentration of plasma proteins (hypoproteinemia) – to the formation of edema.If the ileocecal valve fails, the passage through the small intestine is accelerated [4.2]. As a result, nutrients and vital substances cannot be sufficiently absorbed or decomposed by the mucous membrane of the large intestine – amplification of osmotic diarrhea. Fluids and electrolytes, such as calcium, magnesium, potassium and sodium, are lost in high amounts with the diarrhea [4.2]. Individuals who have had surgical removal of the terminal ileum or ileocecal valve are often deficient in energy and essential nutrients and vital nutrients because of the absorption disturbances and increased losses through the stool.

Importance of the colon

A fully functional large intestine (colon) plays an essential role in short bowel syndrome. Despite very little remaining length of the small intestine, the colon can help maintain energy balance. In addition to absorbing electrolytes and water, the colon has the ability to convert carbohydrates not used by the rest of the intestine, as well as dietary fiber, into short-chain fatty acids, such as n-butyrate, acetate and propionate, through bacterial degradation. These are rapidly and almost completely absorbed by the colon mucosa. Short-chain fatty acids are of considerable importance for the functioning of the colon mucosa. They serve as energy-providing substrates for the microflora of the colon mucosa [4.2]. Butyrate is the most important energy supplier of mucosal cells. Together with propionate, butyrate stimulates physiological new cell formation in the crypts of the colon and maintains the activity of bacterial enzymes and thus the functional processes in the colon. A high intake of dietary fiber thus ensures a high content of short-chain fatty acids in the colon. The resulting lowering of the pH value prevents the colonization of pathogenic germs [4.1]. A high pH value inside the intestine, on the other hand, promotes the conversion of primary to secondary bile acids. High concentrations of secondary bile acids, in turn, increase the risk of colon cancer by supporting mechanisms that promote tumor development. Furthermore, fatty acids promote the absorption of sodium chloride and water in the colon. As a result of the coupled fatty acid, sodium chloride and water reabsorption, solutes – osmotically active molecules, such as dissolved salts and glucose – are increasingly removed from the interior of the intestine. In this way, the tendency to diarrhea is significantly reduced-provided that an intact terminal ileum allows bile acid reabsorption

Consequences of partial and total resection of the colon, respectively

However, when the colon is partially or totally resected in combination with small bowel resection, the high reserve capacity of the colon for water and electrolyte reabsorption is lost. Finally, colectomy (removal of the colon) leads to diarrhea that is difficult to control therapeutically. Similarly, carbohydrates as well as dietary fiber cannot be absorbed in the absence of and are increasingly lost in the stool – development of osmotic diarrhea. As a consequence, the energy balance and thus the nutritional status of the patients are considerably worsened. Loss of the ileocecal valve associated with colectomy further accelerate small bowel passage

Resection of the jejunum

Compared with the terminal ileum, ileocecal valve, and colon, surgical resection of the jejunum (empty bowel) is not of great importance because absorption of nutrients and vital substances is handled by the terminal ileum [4.2].