Diarrhea and Constipation Flashcards
What are some definitions of Diarrhea? What is the pathophys?
Increased stool fluidity (frequent patient definition)
Three or more stools per day
Stool weight ≥ 200 gm per day
Normally the gut absorbs most of the fluid it secretes
The small and large intestine absorb 99% of oral intake and endogenous secretions: a total fluid load of 9 to 10 L daily.
When infections, toxins or other noxious substances are present, secretion and motility are altered to expel the unwanted material, and diarrhea results.
Water moves across the intestinal mucosa secondary to osmotic forces generated by the transport of solutes (electrolytes and nutrients).
A decrease in absorption or increase in secretion lead to additional fluid within the lumen and diarrhea.
What is osmotic diarrhea? What is secretory diarrhea? How can you determine which kind of diarrhea predominates?
Osmotic diarrhea results from the malabsorption of ingested non-electrolytes. These substances retain fluid osmotically within the gut lumen, reducing water absorption.
Secretory diarrhea (more common) results from either malabsorption (most commonly) or secretion of electrolytes. Many bacterial toxins interfere with ion
transport in the gut, inducing a secretory diarrhea.
Rarely are the etiologies of diarrhea are purely osmotic or purely secretory, but determining which mechanism predominates can be useful.
Stool osmotic gap:
290 - 2 ([stool Na+] + [stool K+]) = stool osmotic gap
Gap < 50 secretory diarrhea
Gap >100 osmotic diarrhea
What are some etiologies of osmotic diarrhea? What improves it?
Results from ingestion of poorly absorbed items such as mannitol, sorbitol,magnesium, sulfate.
Disaccharides cannot be absorbed without the appropriate disaccharidase
o Most common disaccharidase deficiency is lactase deficiency.
o Lactase is present on the brush border cells of the small intestine in young mammals, but disappears in adults.
Osmotic diarrhea disappears with fasting, or with stopping ingestion of the inciting agent.
What is the mechanism of secretory diarrhea? Describe some common causes?
Mechanism is always:
o Net secretion of anions (chloride or bicarbonate) –or-
o Inhibition of net sodium absorption (more common)
Common causes:
o Infection (enterotoxins- See Chapter 32)
o Neuroendocrine tumors that produce peptides that stimulate secretion by epithelial cells
o Endogenous neurotransmitters and other modulators
Acetylcholine, serotonin, histamine, inflammatory cytokines
Work by altering intracellular messengers (cAMP, calcium, etc.)
o Exogenous compounds such as drugs and poisons
o Epithelial injury or decreased absorptive surface area, resulting in abnormal absorption
Viral gastroenteritis
Celiac sprue
Inflammatory bowel disease
Intestinal resection
o “Intestinal hurry”
Rapid transit
Prevents adequate time for absorption
The malabsorption of electrolytes also can produce a component of osmotic diarrhea
Examples: diabetes mellitus, post-vagotomy diarrhea
Compare and contrast acute and chronic diarrheas and their causes?
Acute diarrheas (< 4 weeks) are usually caused by infection, and are usually self-limited and/or easily treated.
Some pathogens can cause chronic diarrhea, even in immunocompetent patients.
Examples are Giardia lamblia or Yersinia species.
What is the difference between the etiologies of large and small volume diarrheas?
The recto-sigmoid region of the colon acts as a storage reservoir. When there is inflammation in this area, frequent, small-volume stools are the result.
If this area is intact, and the source of inflammation is the right colon or small bowel, stools will be less frequent, but high volume.
Simply, small, frequent, painful stools often result of inflammation in the distal GI tract, and painless large-volume, watery stools are often the result of right colon or small bowel disease.
Describe the differences between watery and inflammatory diarrheas?
Watery: implies a defect in water absorption, either secretory (increased electrolyte secretion or decreased electrolyte absorption ) or osmotic (ingestion of
poorly absorbed substance)
Inflammatory: often associated with signs/symptoms of inflammation such as blood in stool, fever, cramping
What is the differential diagnosis of acute diarrhea?
Acute Diarrhea
Infection (bacteria, viruses, protozoa, parasites)
Food poisoning
Food allergies
Medications
Early onset of chronic diarrhea
What is the differential diagnosis of chronic diarrhea?
Chronic Diarrhea
Watery diarrhea
o Osmotic diarrhea
Osmotic laxatives
Carbohydrate malabsorption
o Secretory diarrhea
Bacterial toxins
Inflammatory bowel disease
Diverticulitis
Vasculitis
Medications and toxins
Stimulant laxative abuse
Disordered gut motility
Endocrinopathies (hyperthyroidism, neuroendocrine tumors)
Neoplasia (colon cancer, lymphoma, villous adenoma)
o Inflammatory diarrhea
Inflammatory bowel disease
Infectious diseases
Diverticulitis
Neoplasia
Ischemic colitis
o Fatty diarrhea
Malabsorption
Maldigestion
Celiac sprue
Short bowel syndrome after surgical resection
See Chapter 15, pages 15-20
Pancreatic exocrine insufficiency
Lack of adequate luminal bile acids
How is chronic diarrhea treated?
Supportive Care- replacement of fluid and electrolyte deficits
Oral rehydration solutions (if not vomiting) containing glucose or amino acids will accelerate sodium and fluid absorption
Rehydration solutions do not decrease stool output, in fact, stool weight may increase
Empiric therapy with antibiotics for acute infectious diarrhea, depending on prevalence of infectious agent, severity of illness, and suspected etiology.
How do fiber supplements help diarrhea? Examples?
Fiber supplements
o Alter stool consistency but do not reduce stool weight
o Can be helpful in fecal incontinence by bulkening stool
o Can help delay stool transit, increasing stool form
o Examples: psyllium, guar gum
How do opiates help with diarrhea? What are some examples? Which is the preferred? WhY?
Opiates
o Decrease intestinal motor activity, slowing colonic transit time
o Decrease fluid secretion
o Enhance fluid transport
o Ameliorate abdominal cramping
o Increase anal sphincter tone
o Examples loperamide, diphenoxylate, codeine, morphine, tincture of
opium
Loperamide is particularly preferred.
Loperamide does not cross the blood-brain barrier (reducing risk for habituation or other CNS side effects)
o Avoid opiates in patients with severe acute colitis.
When are somatostatin analogs used?
Somatostatin analogs (octreotide)
o Improves diarrhea in specific conditions such as carcinoid syndrome, other endocrinopathies, AIDS-associated diarrhea.
Which adrenergic agonist is used? How does it help diarrhea? When can it be used? Side effects?
Adrenergic agonist (clonidine)
o Affects motility and intestinal transport
o Potentially useful in diabetic patients with diarrhea
o Can cause hypotension, limiting its usefulness in some patients
What does bismuth subsalicylate do?
Bismuth subsalicylate
o Antisecretory agent with rare side effects
o Decreases stool frequency and improves form
o Has antimicrobial (bismuth) and antisecretory (salicylate) properties
What do probiotics do? Examples?
Probiotics
o Modify colonic flora
o May stimulate microenvironment immunity and speed recovery of traveler’s diarrhea or anti-biotic-associated diarrhea
o Examples include Lactobacillus, Bifantis, Saccarhomyces boulardii,
What are some definitions for constipation?
It is important to understand how patients define constipation (e.g., hard stool, straining, inability to have bowel movements)
Traditional medical definition is 3 for fewer bowel movements per week, but reports of stool frequency do not correlate well with complaints of constipation.
Rome III Criteria for functional constipation (2006):
o Must include ≥ 2 of the following:
Straining
Lumpy or hard stools
Feeling of incomplete evacuation
Use of manual maneuvers to facilitate defecation (digital
evacuation, support of pelvic floor)
Less than 3 bowel movements per week
o Rarely have loose stools unless using a laxative
o Insufficient criteria for constipation-predominant irritable bowel syndrome
o Symptoms must be present for ≥ 3 months
What are some risk factors for constipation?
Female gender (clear reason unknown)
Age (decreased food intake, reduced mobility, weakening of abdominal and pelvic wall muscles, chronic illness, medications)
Ethnicity (non-whites vs. whites in North America)
Lower socio-economic class and education level
Low fiber diet (suggested by observational studies)
Physical inactivity (suggested by observational studies)
Medication use
o Opioids
o Diuretics
o Antidepressants
o Antihistamines
o Antispasmodics
o Anticonvulsants
o Aluminum antacids
o NSAIDS in the elderly
Describe 3 types of constipation.
Normal-transit constipation
o Incomplete evacuation
o Abdominal pain can be present but isn’t a prevailing feature
o Normal physiologic testing
Slow-transit constipation
o Infrequent stools (e.g., less than once a week)
o Lack of urge to defecate
o Poor response to fiber and laxatives
o Associated with generalized symptoms such as malaise, fatigue
o More prevalent in young women
o Physiologic testing reveals delayed motility
Defecatory disorders
o Frequent straining
o Incomplete evacuation
o Need for specific maneuvers, such as digital evacuation, to produce a bowel movement
o E.g., pelvic floor dysfunction, rectal prolapsed
What are some possible causes of secondary constipation?
Mechanical obstruction
o Neoplasm
o Stricture
o Extrinsic compression
Metabolic or endocrine disorders
o Diabetes mellitus
o Hypo/hyper thyroidism
o Hypokalemia
o Hypercalcemia
Medications
Neurologic or myopathic disorders
o Parkinson’s disease
o Multiple sclerosis
o Spinal cord injury
What are some non-pharmacologic strategies that should be used to treat constipation?
Reassurance
Behavioral adjustments
o Set aside regular, unhurried time for defecation
o Respond to the urge to defecate
o Increase activity if sedentary lifestyle
o Avoid constipating drugs if possible
Addressing confounding psychosocial issues
Pelvic floor physical therapy if defecatory disorders are present
Dietary changes
o Increased dietary fiber and fiber supplements can improve mild to moderate constipation.
o Fiber can cause increased bloating, flatulence.
o Instruct patients to increase fiber intake slowly, over weeks, to goal 20 to 25 gm per day.
o Commercially available fiber supplements
Methylcellulose (Citrucel)
Psyllium (Metamucil)
Calcium polycarbophil (FiberCon)
Guar gum (Benefiber)
Describe 3 types of osmotic laxatives.
Poorly absorbed ions
o Magnesium, sulfate, phosphate compounds
Magnesium hydroxide
Fleet phosphosoda
o Create a hyperosmolar environment in the lumen
o Caution use of magnesium and phosphate compounds in those with renal insufficiency
Poorly absorbed sugars
o Lactulose
Non-absorbable synthetic disaccharide (galactose + fructose)
Since not absorbed in the small intestine, undergoes fermentation in colon by bacteria to short chain fatty acids, H2 and CO2
Lowers stool pH
Side effects include abdominal bloating and discomfort
o Sorbitol
Used commercially as an artificial sweetener
Very similar effects and side effects as lactulose, but cheaper
Polyethylene glycol (PEG)
o Metabolically inert
o Binds to water molecules within the lumen, increasing intraluminal water
o Not metabolized by colonic bacteria
o PEG solutions with electrolytes are often use for colonoscopy preparations retention
What do stimulant laxatives do? Describe two examples.
Stimulant Laxatives- stimulate intestinal motility and increase intestinal secretion. Begin working within hours and often cause abdominal cramping.
Anthraquinones (e.g., casarca, senna, aloe)
o Inactive plant glycosides that pass through small intestine unchanged
o Hydrolyzed by bacterial glycosidases in the colon to their active metabolites
o Active metabolites increase transport of electrolytes into the lumen, and increase motility by stimulating the myenteric plexus.
o No clear evidence that long term use causes adverse effects, but is in question
Bisacodyl
o A diphenylmethane compound
o Hydrolyzed by intestinal enzymes, acts both on the small and large bowel
o Effects similar to anthraquinones
o No evidence of adverse events with long term use
Describe 2 stool softeners.
Stool Softeners
Docusate sodium
o A detergent that stimulates fluid secretion by small and large bowel.
o Studies have shown it to be less effective than pysllium.
Mineral oil
o Becomes emulsified into the stool, providing lubrication of the stool for passage
o Long-term use can cause malabsorption of fat-soluble vitamins, anal seepage
Describe 3 types of enemas or suppositories.
Phosphate enemas
o Cause distension and stimulation of rectum
o Cause superficial damage to rectal epithelium
o Can lead to hyperphosphatemia and hypocalcemia in those that can’t evacuate enemas quickly
Saline or tap water enemas
o Distend the rectum and soften the feces
o Does not damage the rectal mucosa, and appears to be as effective as phosphate enemas
Stimulant suppositories
o Glycerin- causes an osmotic effect
o Bisacodyl- stimulates enteric neurons
Which chloride channel activator is used? How does it work?
Chloride Channel Activator
Lubiprostone
o Activates the chloride 2 channel, increasing intestinal secretion and transit
Which guanylate cyclase C agonist is used? How does it work?
Guanylate Cyclase C Agonist
Linaclotide
o Peptide homologue of a heat-stable enterotoxin; activates guanylate cyclase C, leading to increase cGMP
What are the prokinetic medications? How do they work?
Prokinetic Medications
5HT4 agonists
Increase contractility of the intestine
Two previous agents removed from the market
Continuing research is being done on other agents
