Diarrhea

Criteria

Several criteria diagnose diarrhea:

• 1.

  Abnormal frequency. Normal frequency is one or two bowel movements per day and is influenced by the amount of fiber in the diet. Three or more bowel movements per day is abnormal.

• 2.

  Abnormal consistency. Abnormal consistency is described as either nonformed stool or stool having excessive fluid content that causes inconvenience to the patient, nursing staff, or caregiver. Normal stool water content is 60%–85% of the total weight.

• 3.

  Abnormal amount. Stool amount and volume vary significantly with the amount and type of enteral intake. Insoluble fiber adds a significant amount of bulk volume. A normal amount is approximately 200 grams per day (g/d). Abnormal amounts are greater than 300 g/d or volumes greater than 250 mL/d. ^,

To date, clinicians lack a consistent scale or index that allows a reliable and practical way of measuring stool volume, consistency, and frequency. In its absence, the bedside nurse remains the most reliable person to identify the presence of diarrhea.

Pathophysiology

Bowel movements with normal physiologic volume, consistency, and frequency are the result of a GI tract that integrates motility, secretion, and absorption of fluids and adapts to the quality of the food bolus given. The result is a fecal bolus that is produced once or twice every 24 hours and has normal consistency and fluidity.

Diarrhea results when there is a disorder of GI physiology or when GI tract function is incapable of handling the food bolus ( Fig. 27.1 ). There are several classifications of diarrhea, suggesting that no single classification is ideal for helping the clinician make patient care decisions. Perhaps the most useful approach is to classify diarrhea according to physiology:

• 1.

  Increased fluid secretion that overwhelms absorption. On average, up to 9 L of fluid is secreted into the GI lumen in addition to oral intake. Less than 1% of that fluid is contained in stool because of the amazingly large absorptive capacity of the small and large bowel. Within the intestinal mucosa, passive and active transport of sodium determines the amount of water that is absorbed. Stimulation of the active secretion of fluids into the GI lumen occurs when intracellular levels of the second messenger, cyclic adenosine monophosphate (cAMP), increases within enterocytes. Increased intracellular cAMP concentration promotes chloride secretion. Thus diarrhea caused by excessive secretion of fluids is termed secretory diarrhea . Secretory diarrhea characteristically contains large amounts of fluid and is described as watery. Secretory diarrhea is observed in certain infectious diseases such as cholera and rotavirus infections. Secretory diarrhea also can be observed in endocrine disturbances associated with carcinoid syndrome or vasoactive intestinal peptide (VIP)–secreting tumors.

• 2.

  Gastroenteritis or infectious diarrhea occurs from GI tract inflammation with resultant increase in mucus secretion from the large bowel, leading to development of diarrhea. Excessive mucus secretion is observed in colonic infections such as bacterial ( Clostridium difficile colitis), viral (norovirus), or parasitic (amebiasis). The incidence of infectious diarrhea in the ICU is unknown, but increases with contaminated food products. Of particular concern is the contamination of the food being given in the ICU. Contamination of enteral formulas can occur at multiple levels, including preparation of the enteral product, use of open feeding systems, addition of modular dietary components, and contamination of the enteral access port (i.e., feeding tube, gastrostomy tube). The incidence of diarrhea resulting from contaminated feeding tubes is unknown.

• 3.

  Diarrhea resulting from increased osmotic load. Many substances taken orally are not fully absorbed and exert significant osmotic force, overwhelming the absorptive capacity of the GI tract. Many patients with diarrhea in the ICU fall into this category.

  • A.

    Osmotic diarrhea caused by medications: Sorbitol is frequently and inadvertently given to patients in the ICU as a means of preparing many medications for delivery via feeding tubes and is an often-overlooked culprit causing diarrhea. Other osmotic agents include GoLYTELY and magnesium-containing medications and electrolyte replacement formulations.

  • B.

    Incomplete digestion and malabsorption: The incidence of malabsorption in the ICU is unknown. However, there are many instances where malabsorption should be considered the cause of diarrhea in the critically ill patient. These include:

    • i.

      Incomplete protein digestion (azotorrhea): Protein digestion occurs mainly in the stomach by pepsin (only activated at low pH) and hydrochloric acid. In the ICU, many patients receive medications that raise gastric pH, such as histamine receptor type 2 (H ₂ ) blockers and proton pump inhibitors. ^, In addition, feeding tubes frequently bypass the stomach, eliminating both gastric acid and gastric proteolytic digestion. Less frequent causes of azotorrhea are protein-losing enteropathies resulting from amyloidosis, sarcoidosis, inflammatory bowel disease, neoplasm, Ménétrier disease, and Zollinger-Ellison syndrome, to name a few.

    • ii.

      Undigested carbohydrates: In addition to sorbitol (see earlier discussion), excessive glucose, lactose, or fructose in tube-feeding formulas can overwhelm the absorptive capacity of the small bowel, causing an osmotic influx into the gut lumen.

    • iii.

      Undigested fats: Steatorrhea (diarrhea caused by undigested fats) is characteristically observed in patients with pancreatic insufficiency. Inadvertent lack of mixing pancreatic enzymes with the food bolus can occur in patients with intestinal bypass or pancreatic fistulas or in patients who have large-volume gland necrosis from pancreatitis or a history of pancreatectomy. It is also observed in patients with incomplete bile production, such as patients with a biliary diversion.

    • iv.

      Excessive dietary load: Diarrhea resulting from excessive load (overfeeding) of any of the main dietary components (protein, carbohydrate, or fat) can occur in the ICU. Iatrogenic overfeeding occurs in up to 33% of patients in the ICU and is a result of inappropriate estimations of caloric and protein needs or inadequate metabolic surveillance. Excessive loads of protein, carbohydrate, or fat also occur with specialized formulas that contain altered amounts of one or more of these components. For example, certain diets are high in fat, overwhelming digestive and absorptive processes.

    • v.

      Atrophy of the GI tract: Atrophy of the intestinal brush border is associated with decreased capacity of digestion and absorption. Atrophy occurs in malnourished patients; thus diarrhea commonly occurs in patients with hypoalbuminemia. Atrophy also occurs when enteral intake is interrupted for more than a few days. This is a particular problem in surgical patients when prolonged “bowel rest” results in disuse atrophy. A similar phenomenon occurs distal to an enterocutaneous fistula or ostomy, which, upon reversal, can result in diarrhea that slowly resolves as villous height returns to baseline.

• 4.

  Abnormal motility: Intestinal dysmotility is a frequent problem in the ICU. The use of promotility agents (e.g., erythromycin) can inadvertently cause diarrhea in these patients.

• 5.

  Abnormal gut flora: Normal colonic flora is essential for normal absorption and function of the large bowel. Antibiotics create massive disruptions in colonic flora and can sometimes lead to nosocomial infections with resultant diarrhea. Currently, C. difficile is the leading cause of nosocomial diarrhea, accounting for 30% of all antibiotic-associated diarrhea. The gut microflora can be modulated through the use of probiotic agents, but this topic is under intense investigation, and no current guidelines exist regarding their use to treat or prevent diarrhea in ICU patients.