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|Newsletters: Tube Feeding Associated Diarrhea|
Tube Feeding Associated Diarrhea
Hamish D Duncan, MD, MRCP, Gastroenterologist, Queen Alexandra Hospital, Portsmouth, UK; and David B. A. Silk, MD, FRCS, Gastroenterologist, Central Middlesex Hospital, London, UK
We are grateful to the authors, and Greenwich Medical Media Limited, for allowing us to reprint this condensed version of a chapter that appears in Intestinal Failure ©2001, edited by Jeremy Nightingale, MD. Please note much of the data used in the article is based on in-hospital studies completed in Europe, thus some sections may not match the US homeEN consumer’s experience.
The most commonly reported complication of enteral tube feeding (EN) is diarrhea, which occurs in up to 30% of patients on general medical and surgical wards and up to 68% of patients on intensive care units. Diarrhea is distressing for patients and their relatives, time consuming for nursing staff and can add to potential problems such as infected pressure sores and altered fluid and electrolyte balance. Diarrhea, defined as an increase in bowel frequency and/or fluid content of the stool, can result in nutrient and electrolyte loss in patients being tube fed. The complication of diarrhea may also delay patient discharge and increase hospital costs. If diarrhea is severe, it may be necessary to stop enteral feeding and institute parenteral nutrition (PN) with its associated risks and costs.
There is considerable variability in the reported incidence of tube feeding related diarrhea (from as low as 2.3% to as much as 68%), which is due in part to differences in the definition of diarrhea used by investigators, and the ability to collect and measure every stool sample, which is often not a feasible proposition. Diarrhea has been defined empirically as an increase in the frequency and/or volume of stool, or a decrease in the consistency of stool and quantitatively as an increase in stool weight of more than 200 gm per 24 hours, or as an increase in stool water of more than 500 ml per 24 hours, or has simply been a function of the investigator or patients’ subjective assessment. These definitions are further confounded because they do not take into account the patient’s usual bowel habit and stool consistency. Diarrhea usually occurs when the capacity of the colon to absorb fluid is exceeded or altered for whatever reason.
Diarrhea may result from a variety of causes including bacterial or viral infection, use of hyper-osmolar formula, lactose intolerance, antibiotic treatment, magnesium containing antacids, drug side-effects (e.g. digoxin and propanolol) and so called inert fillers of drugs which can include magnesium stearate, docusate sodium and sorbitol. In patients with a short bowel and no colon, additional factors contribute to the development of diarrhea, including loss of the daily intestinal secretions produced in response to food, and rapid gastric emptying and small bowel transit. A lack of peptide YY, which is known to delay gastric emptying and small intestinal motility, and is found in the highest concentration in the colon, may be responsible for this.
Etiology of EN Related Diarrhea
Several mechanisms have been proposed as contributing towards the development of enteral tube feeding associated diarrhea, which are discussed below.
Temperature of liquid EN diet: There is little conclusive evidence that either refrigeration or warming of the liquid feed have clinically important effects on gastrointestinal complications including diarrhea or abdominal cramps.
Enteral diet osmolality: Likewise, there is little conclusive evidence that diet osmolality (neither diluted formula nor formula infused at a slow rate) plays any significant role in enteral feeding related diarrhea, when the diet is instilled directly into the stomach.
Lactase: Most commercially prepared enteral diets are now clinically lactose free, and thus this potential problem has been removed. However if a patient with diarrhea is taking some oral food, it is important to check that they are not consuming too much milk or milk products. Keep in mind that relative lactase deficiency may develop due to reduced absorptive area (SBS patients) and/or to reduced transit time, resulting in diarrhea when the patient is fed milk or milk-based foods.
Fat malabsorption: Problems with fat absorption can cause diarrhea in tube fed patients. Patients with severe pancreatic disease may have a deficiency of lipase necessary to hydrolyze triglycerides, and gastric surgery may prevent adequate mixing of lipase with luminal contents. Patients with biliary obstruction, ileectomy or ileitis, may have insufficient bile salts for adequate fat absorption, resulting in diarrhea and abdominal discomfort. Medium chain triglycerides can also cause diarrhea, flatulence and abdominal pain in patients intolerant to them. Patients with a jejunostomy do not need to reduce their fat intake, but if the colon remains in continuity with the shortened small bowel, then steatorrhoea may develop. Using a formula with a lower fat content (and thus lower energy density) may alleviate diarrhea due to fat malabsorption in patients with a short bowel and retained colon.
Hypoalbuminaemia: The role that hypoalbuminaemia (low albumin level) may play in causing enteral feeding related diarrhea is so far inconclusive. Hypoalbuminaemia is more likely to be a marker of disease severity and degree of undernutrition rather than a direct cause of enteral feeding associated diarrhea, with changes in bowel structure and function due to starvation contributing to the risk of developing tube feeding associated diarrhea.
Drugs and antibiotics, Major Contributors: Diarrhea is a common complication associated with drugs and antibiotics. Many drugs contain so called ‘inert carriers’ for the active compound, however they are osmotically active and the inert carrier may cause diarrhea. For example, some drugs such as acetaminophen (Tylenol®) contains sorbitol, and others such as antacids contain magnesium or docusate sodium. Sorbitol, magnesium and docusate sodium can all cause diarrhea in their own right. Other drugs may cause diarrhea as a result of recognized side effects, such as H2 blockers, anti-arrhythmics, anti-hypertensives, and non-steroidal drug, or because they are designed to encourage bowel movements, such as laxatives.
The incidence of diarrhea associated with antibiotics varies (clindamycin, 7 to 26% and ampicillin, 5 to 10%), depending on how diarrhea is defined. Diarrhea can result from primary structural or functional damage to the small or large intestine. However if this was the only reason, then the incidence of diarrhea in EN patients on antibiotics should be similar to that of patients on antibiotics who are eating normally, which is not the case. Thus there appears to be a synergistic effect of tube feeding and antibiotic usage, resulting in the high incidence of diarrhea in tube fed patients.
The reasons why antibiotics may cause diarrhea are not entirely clear, although it is thought that antibiotics alter the normal intestinal flora, allowing bacterial overgrowth of pathogenic (so called "bad”) bacteria such as Klebsiella, Proteus and E. coli. Antibiotic usage is associated with Clostridium difficile and its toxin in some patients with diarrhea. Clostridium difficile has been found in 20 to 50% of patients with antibiotic related diarrhea and in 95% of cases of pseudomembranous colitis. The presence of Clostridium difficile does not necessarily confirm that this organism is the cause of diarrhea, however, since up to 25% of patients receiving antibiotics have tested positive for Clostridium difficile toxin but have no diarrhea, and Clostridium is found in about 4% of healthy adults. Thus, Clostridium difficile is likely to contribute to some cases of EN feeding related diarrhea, but certainly not all.
Antibiotics could also increase the likelihood of diarrhea developing, by reducing the production of colonic short chain fatty acids (which promote the absorption of water and electrolytes in the colon), and increasing the risk of overgrowth of potentially pathogenic bacteria.
Contaminated formula and feeding equipment: EN formula provides an excellent growth medium for a variety of micro-organisms, and once contaminated they will rapidly multiply. Although formulas are sterile, as soon as the bottles or cans are opened, there is a risk of contamination from handling, the delivery system, prolonged hanging time and spread of bacteria up the administration set. Contaminated feeds may cause diarrhea, sepsis, pneumonia and urinary tract infections.
Bacterial contamination of enteral feed can be a major problem, with up to 36% of enteral diet fed by a continuous drip method being contaminated. A drip chamber may prevent the backwards spread of organisms from the patient to the sterile feed chamber, by interrupting continuity in the column of feed. (Editor’s note: In the US we are increasingly using a "closed” system which prevents this type of contamination.) Because of the high incidence of bacterial contamination in the enteral bag and feeding system found with continuous tube feeding, feeding bags and administration sets should be changed every 24 hours.
Allowing breaks in continuous feedings may also help by allowing the pH of the stomach to fall between feeds. When the stomach is functioning normally and is acidic, most bacteria are killed. Continuous infusion of enteral feed, however, raises gastric pH, (as does H2 antagonists or other antisecretory drugs) which allows bacterial overgrowth in the stomach.
Fiber in tube feeds: Many commercially produced liquid EN tube feeds are low in fiber (poorly metabolized carbohydrate). The ingestion of fiber has been found to slow intestinal transit time and therefore may produce a more regular bowel habit; However, the addition of fiber to enteral diets has not been uniformly successful in preventing development of enteral tube feeding related diarrhea. The reason for this apparent lack of an effect by fiber on bowel function may lie in the small particle size of soy polysaccharide in enteral formula, which is necessary to help reduce viscosity of the feed. Reducing particle size reduces the amount of undigested fiber available to hold water and diminishes it’s ability to bulk the feces. There is thus currently little evidence to suggest that the addition of fiber to enteral diets can overcome the diarrhea associated with tube feeding.
Bolus versus continuous feeds: The method of ‘bolus feeding’ is frequently reported to be associated with a high incidence of complications such as nausea, bloating and diarrhea, although there has previously been little scientific substantiation of this statement. (Editor’s note: Drip feedings are needed if gastroparesis is a serious issue.) It has been suggested that continuous intragastric feeding is generally better tolerated than intermittent feedings although this too has been disputed. We have recently shown that there is little evidence that small volume bolus feeding causes diarrhea more frequently than continuous nasogastric tube feeding. Continuous nasogastric enteral tube feeding may, in fact, cause diarrhea because it fails to provoke a normal postprandial response, suppresses distal colonic segmenting motor activity, and causes an abnormal secretory response in the ascending colon.
Tube feeding related diarrhea is unlikely to be due to the enteral diet itself, and other reasons must be sought — especially the use of antibiotics and other drugs (such as those with sorbitol, magnesium and docusate sodium). Other tips that may be helpful in controlling enteral related diarrhea, although many of them only under specific circumstances, include switching to a lower-fat formula, changing the bags and administration sets every 24 hours, allowing breaks in continuous feeds, using a drip chamber, minimizing the amount of milk and milk products eaten orally, and using bolus feeds. If diarrhea is a problem despite attention to possible causes as discussed, then loperamide (or codeine phosphate) can be instituted to control symptoms and there are anecdotal reports of live yogurt being helpful. Regular monitoring and early involvement of nutrition teams should result in early recognition and treatment of enteral related diarrhea, and thus prevent it from progressing into further complications.
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