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What is gastroenteritis?

  • Gastroenteritis is a medical condition, characterized by inflammation of the GI tract (bacteria, parasites, viruses)
    • The primary manifestation of gastroenteritis is diarrhoea, but it may also be accompanied by nausea, vomiting, abdominal pain and cramp,as well as fever

Causes of vomiting and diarrhoea


  • Gastrointestinal: obstruction, dysmotility, malabsorption, lactose intolerance
  • AIDs-related complex
  • Specific disease: inflammatory bowel disease, GI bleeding
  • Tumours: gastrinoma, colon cancer, villous adenoma
  • Rx (prescription): drug induced: antibiotics, laxatives , chemotherapy
  • Obstetrics and gynaecology: pregnancy, preeclampsia etc
  • Endocrine and metabolic: diabetes, hyperthyroidism etc
  • Neurological: migraine, motion sickness, vestibular disorders
  • Topical GI irritants: alcohol, NSAIDs etc
  • Environmental: food poisoning, high altitude, acute radiation
  • Renal: obstructive uropathy, renal colic
  • Infection: gastroenteritis, hepatitis, meningitis etc
  • Trauma
  • Ischemia: mesenteric ischemia, ischemia colitis
  • Stress, anxiety, bulimia etc (Psychogenic)

Definition of diarrhoea

  • Diarrhoea
    1. passage of unusually loose or liquid stools 3 times or more per day
    2. recent change in consistency



  • Acute diarrhoea:
    • Sudden onset
    • Lasts for < 2 weeks
    • Self-limiting, resolves without sequelae (need hydration)
  • Chronic diarrhoea:
    • Lasts for > 3 weeks
    • Associated with recurring diarrhoea, fever, nausea, vomiting, weight loss, and chronic weakness, dehydration, anaemia

Causes of Diarrhoea

Acute Diarrhoea

  • Infection
    • Non-inflammatory: large amount, watery ; diarrhoea;often associated with nausea & vomiting. Caused by toxin-producing bacteria or viruses that disrupt small intestinal absorption and secretion. Main danger: dehydration (doesn't damage the structure of the intestine, but reverses absorption direction causing very large amount of watery diarrhoea, very dangerous)
    • Inflammatory (dysentery): bloody diarrhea; small amount; colonic tissue damage caused by bacteria invasion or toxin. Main dangers: damage to intestinal mucosa, sepsis and malnutrition (not necessarily cause dehydration, but affects nutrient absorption due to damage of villi; or sepsis)
  • Drug induced: antibiotics, laxatives, cholinergic drugs
  • Anxiety or emotional stress (either constipation or diarrhoea)

Chronic Diarrhoea

  • Inflammatory bowel disease: (either constipation or diarrhoea)
    • Ulcerative colitis and Crohn’s disease
  • Irritable bowel syndrome
  • Lactose intolerance
  • Cancer: bowel cancer
  • Hormone disorders: diabetes, hyperthyroidism

Diarrhoea facts

  • World-wide:
    • Morbidity
      • 4 billion episodes/yr
      • Each child average 1-3 episodes /yr
    • Mortality
      • 3 M die /yr
      • 99% in developing countries (one of the leading causes of death)
      • 84% among children< 5 y/o
  • Australia:
    • kills 120 Australians/yr
    • most common reason for work/school absenteeism
    • each year, 1.2 million visits to the doctor, and 2.1 million days of lost work
    • costs $1.25 billion/yr to the Australian economy

Why is diarrhoea dangerous?

  • Diarrhoea may lead to dehydration and malnutrition
    • Risk is in elderly and young
    • In adults, it's just embarrassing

Common infectious organisms

  • Non-invasive infection (enterotoxic syndromes)
    • Bacteria:: Enterotoxigenic E. coli, Vibrio cholera
    • Viruses: Noroviruses, rotavirus
    • Parasites: Cryptosporidium, Giardia
  • Invasive infection(bloody diarrhoea, dysentery)
    • Bacteria: Enterohemorrhagic E. coli,
    • Enteroinvasive E. coli, Salmonella,; Shigella; Campylobacter
    • Viruses: Cytomegalovirus
    • Parasites: Amoeba

High-risk groups for infectious diarrhoea

  • Travelers: 40% developed: traveler's disease
  • Food or water contamination
  • Immunodeficient persons
  • Daycare attendees and their family members
  • Institutionalised persons

  • Traveller's disease
  • Food borne illness (FBI)

Water balance

  • See diagram
  • 9L secreted and absorbed inside gut per day (excluding drinking/pooping)
  • If you reduce absorption or increase secretion, or increase motility, then diarrhoea will occur

Intestinal mucosa

Mechanisms of diarrhoea

  • increased intestinal secretion
    • Bacterial or viral toxins, inflammatory cytokines and prostaglandins as secretagogues
  • decreased intestinal absorption
    • Intestinal villi absorption is diminished due to damage of villi structure by toxin, bacteria invasion, inflammation
  • increased osmotic load:
    • Laxative results in the collection of osmotically active, nondigestible agents within the intestinal lumen, drawing fluid into the lumen.
  • increased intestinal motility
    • Colon motility: irritable bowel syndrome
    • Small bowel motility: hyperthyroidism

Treatment of diarrhoea

  • Treatment of specific aetiology
    • (mesalamine, balsalazide, infliximab for IBD)
    • Antimicrobials
  • Non-specific treatment
    • Diet
    • Rehydration
    • Adsorbents
    • Bismuth subsalicylate
    • Antimotility drugs


  • Take adequate oral fluids
  • Frequent feedings of tea, "flat" carbonated beverages, and soft, easily digested foods (eg, soups, crackers, bananas, rice, toast)
  • Chinese congee (rice soup)
  • Avoid high-fiber foods, fats, milk products, caffeine, and alcohol
  • Lactose free


  • Oral rehydration salts (ORS)
  • A convenient mixture: ½ tsp salt (3.5 g), 1 tsp baking soda (2.5 g NaHCO3), 8 tsp sugar (40 g), and 8 oz orange juice (1.5 g KCl), diluted to 1 L with water

This gives you sodium, potassium, glucose to get the water into cells (sodium-glucose cotransporter from lumen into enterocyte - increase osmolarity of cells, build up osmotic gradient)

Rehydration is recommended for diarrhea of all aetiologies and in all age group

Sodium and water absorption


  • Bind to bacteria and toxins, so they are eliminated in the stool
  • Examples:
    • Activated charcoal
    • Kaolin
    • Attapulgite
    • 12 yrs over: 1.2 to 1.5g/dose, up to 9g/day
    • 6 to 12 yrs: 600 to 750 mg after each loose bowel movement and up to 4.5 g/day
    • 3 to 6 yrs: 300 to 375 mg after each loose bowel movement up to 7 doses/da
  • Mechanisms of action:
    • Coat the walls of the GI tract or
    • Bind to the bacteria or toxin, which is then eliminated through the stool
    • Make stools look firmer, but no correction of dehydration

Bismuth subsalicylate (BSS)

  • Bismuth subsalicylate (Pepto Bismol)
    • 30 mL or 2 tablets every 30 min for 8 doses; repeat on day 2
    • Highly insoluble, limited to the lumen
    • Salicylate toxicity may occur with excessive dosing
  • Mechanisms of action:
    • has a direct mucosal protective effect (coating)
    • inhibits prostaglandin synthesis (by salicylic acid)
      • Salicylic acid is COX inhibitor
    • has anti infective actions

Antimotility drugs – opioids

Medicinal Uses

  • Mechanisms:
    • Decrease bowel motility and relieve bowel spasms
    • Prolong transit time through the bowel to allow more time for water and electrolytes absorption


  1. Morphine
  2. Codeine
  3. Diphenoxylate
  4. Loperamide
  • 1-3 have CNS effects (cross BBB), NOT very useful for diarrhoea treatment
  • Loperamide - trade name: Imodium (2mg caplets/capsules)


  • a μ-opioid receptor agonist
  • inhibits intestinal motility and secretion by depressing ACh release from enteric plexuses --> prolonged transit time
  • does not produce CNS effects, no analgesic or euphoric properties
  • first choice of antidiarrheal opioid
  • Uses/Indications:
    • acute nonspecific diarrhoea
    • chronic diarrhoea
    • reduce discharge in patients with intestinal resection
  • Contraindications:
    • Constipation; abdominal distension; children < 2 years
    • Not as primary therapy in: acute dysentery ulcerative colitis, Crohn's disease, bacterial enterocolitis with invasive organisms

Side effects of Opioids

  • Drowsiness, sedation, dizziness, lethargy
  • Constipation
  • Respiratory depression
  • Bradycardia, hypotension
  • Urinary retention
  • Flushing, rash, urticaria

Antimotility drugs - anticholinergics

  • Examples: atropine, hyoscine, Scopolamine
  • Mechanisms
    • Muscarinic receptor antagonists; block the action of ACh
    • Decrease intestinal muscle tone and peristalsis, resulting in a slow movement of fecal matter through the GI tract
    • Relieve tummy spasms and cramping

Side effects of anticholinergics

  • Dry mouth
  • Urinary retention, impotence
  • Headache, dizziness, drowsiness
  • Blurred vision, photophobia
  • Tachycardia
  • Constipation
  • Fatigue


  • Supportive therapy is usually sufficient for most patients with viral or bacterial diarrhoea
  • Indications for use of antibiotics:
    • Bloody diarrhea – shigella, amoeba
    • Severe cholera cases
    • Giardiasis
    • Diarrhea associated with serious non-intestinal infections
Cause Antimicrobials of choice
  • Doxycycline
  • Tetracycline
Shigella dysentery
  • Ciprofloxacin
Amoebiasis/Giardiasis Metronidazole
Traveller's diarrhoea Norfloxacin

Why not treat every patient with antimicrobials

  • Treatment may not change disease duration or it severity
  • May cause unwanted effects such as:
    • Suppression of gut flora
    • Development of drug resistance
    • Prolongation of the Salmonella carrier state
    • Production of complications, eg. Haemorrhagic Uraemic Syndrome (HUS) toxic megacolon

Prevention of traveller's diarrhoea

  • It is better to follow the Mexican proverb “boil it, bottle it, peel it, cook it .... or forget it.
  • Wash hands
  • Lighten the diet, avoid milk products
  • Avoid fruit which has not been cleaned or peeled
  • Safe water: boil water, or drink bottled beverages
  • Avoid cold meats, seafood or reheated food
  • Avoid swimming in local water supply - unless you know it has been correctly treated

“Travel expands the mind.... but loosens the bowels!”

Vomiting – Antiemetics

  • The chemoreceptor trigger zone (CTZ) and the vomiting centre both cause vomiting when stimulated
  • The CTZ receives impulses from drugs, toxins, and the vestibular center and stimulates the vomiting center, which triggers motor response
  • This causes forceful contractions of diaphragm, abdominal muscles, and the stomach, thus vomiting occurs
  • Bismuth subsalicylate (Pepto Bismol)
  • Anticholinergics
  • Ondansetron, granisetron – serotonin 5HT3 receptor antagonists
    • Action: inhibit 5HT3 receptor in the CTZ & afferent vagal nerve terminals in upper GI tract
    • Indication: chemo induce emesis
    • Side effects: headache, diarrhoea, dizziness, fatigue
  • Antiemetics can mask the cause
    • They should not be used until cause is determined
    • Unless vomiting is severe enough to cause dehydration and electrolyte imbalance