DIARRHOEAL DISEASES

Question 1

What is the result of diarrhoea on electrolytes?

Answer 1

Diarrhoea can result in the excessive loss of sodium, chloride, water, potassium, bicarbonate and
magnesium.

Question 2

Explain why urea rises in diarrhoea

Answer 2

 Loss of sodium chloride and water can result in dehydration and thus volume depletion.
 This leads to hypotension
o NB: to determine that hypotension is due to volume depletion you must check both lying and
standing blood pressure.
o A drop >20 systolic will be observed on standing
 Patient also becomes tachycardic (pulse >100(])
 As a consequence of volume depletion, the glomerular filtration rate and tubular luminal flow rate are
reduced.
 This reduced luminal flow rate allows increased tubular urea reabsorption.
 Thus serum urea rises.
o NB: There is a proportionately bigger increase in urea than creatinine

Question 3

Explain the effect of diarrhoea on creatinine

Answer 3

 Creatinineis a break-down product ofcreatinephosphate in muscle, and is usually produced at a fairly
constant rate by the body (depending on muscle mass).
 Creatinineand its clearance are the main measures of kidney function
 When a significant reduction in extracellular fluid volume occurs and glomerular filtration is reduced,
serum creatinine can rise, but to a lesser extent than serum urea.
 The pattern of an increase in the ratio of urea to creatinine is consistent with dehydration.

Question 4

Explain the effect of diarrhoea on potassium

Answer 4

 Loss of potassium can result in hypokalaemia.
 Increased faecal loss of potassium with diarrhoea
 Only 2% of total body potassium is in the extracellular compartment, yet this amount is very important as
potassium ions in plasma determine the resting membrane potential of cells, such as the muscle and
nerve cells of the heart.
 Thus very high or low potassium levels can precipitate life-threatening cardiac arrhythmias such as
ventricular fibrillation and asystole.
 Extracellular K + levels are therefore very tightly controlled

Question 5

Explain the effect of diarrhoea on bicarbonate

Answer 5

Loss of bicarbonate can result in a metabolic acidosis.

Question 6

Explain the effect of diarrhoea on magnesium

Answer 6

 Loss of magnesium can cause low potassium and low calcium level
 Magnesium functions as a co-factor for many biological reactions, including:
o Na + -K + -ATPase in the kidneys => Mg 2+ is required for K + reabsorption
o PTH release => affects Ca 2+ levels

Question 7

What factors should be considered before prescribing/calculating fluids?

Answer 7

always ask the patient if they have a history of cardiac disease

1. Measured losses (ML)
2. Insensible losses (IL)
3. Previous day’s deficit (PDD)

Question 8

What are measured losses?

Answer 8

 Measured losses include urine, vomit, diarrhoea and surgical drains, fistulae and stomas.
 These volumes are recorded by the nurses on the patient’s fluid balance chart.
 The previous day’s measured losses are used as a guide to estimate the predicted losses for the next day.
 NB: normal urine output is ~0.5ml/kg/hour (30-35 ml/hour in the average adult)

Question 9

What are insensible losses?

Answer 9

 These include fluid loss via the skin and respiratory tract, around 800 ml daily in normal individuals.
 These losses cannot be measured routinely.
 Insensible losses are increased due to increased sweating from any cause and in patients being
ventilated.
 Also increased in patients with:
o Burns
o Sepsis

Question 10

What is the previous days deficit?

Answer 10

 This is calculated by subtracting the previous day’s fluid intake (oral and IV) from the sum of measured
losses (total output) and insensible losses.

PDD = (previous day’s ML + IL) – previous day’s intake (oral and IV)

 NB: if the patient has cardiac disease (or may have cardiac disease - elderly) the PDD does not have to be
replaced over the next 24 hours, it can be replaced over 2 to 3 days.

Question 11

How are fluids calculated?

Answer 11

Fluid required = ML + IL + PDD

perform regular clinical examinations measuring blood pressure, pulse rate and checking for signs of cardiac failure and take into account repeat u&e results.

Question 12

When is saline used?

Answer 12

o used when there is sodium and water depletion.

Question 13

When is dextrose used?

Answer 13

o Used when only water replacement is required (when there are no electrolyte losses)
o Water loss without electrolyte loss may occur in fever, hyperthyroidism, high blood calcium, or
diabetes insipidus

Question 14

What are the main reasons for the upper gut being almost sterile

Answer 14

The upper gut has very low populations of bacteria due to a range of factors including:
o gastric acidity
o Propulsive motility - prevents bacteria adhering to the epithelium
o Pancreatic enzymes

Question 15

What are the main reasons for the large intestine having a luxuriant bacterial flora?

Answer 15

The large intestine has:
o very stagnant motility, with retropulsive contractions. This keeps the contents in the proximal
colon for long periods.
o The pH of the colon is buffered by bicarbonate secretion. This allows a large and complex
bacterial ecosystem to develop.

 Most of the contents of the colon are actually bacteria.
 There are approx. 10 12 cfu/g (colony-forming unit) which is 75% of the wet weight.
 There are up to 400 different species in the colon and the vast majority (99.9%) are strict anaerobes.

Question 16

What are the main actions of short chain fatty acids in relation to preventing diarrhoea?

Answer 16

 acetate (2C), propionate (3C), and butyrate (4C), are absorbed readily by the colon, stimulating water and
sodium uptake at the same time
 This prevents osmotic diarrhoea

Question 17

What would happen to the normal gut microbiota if a patient was on large doses of broad spectrum
antibiotics?

Answer 17

 Antibiotics may kill some commensal bacteria
 Can impact colonic water reabsorption due to decreased fermentation of SCFA
o Can cause diarrhoea in the absence of infection
 Increases the risk of pathogenic bacteria becoming established within the gut (e.g. C. difficile)

Question 18

Probiotic:

Answer 18

a live microbial food supplement that beneficially affects the host animal by improving its
intestinal microbial balance

Question 19

Prebiotic:

Answer 19

non-digestible food ingredient that beneficially affects the host by stimulating the growth
and/or activity in one or a limited number of bacteria in the colon that can improve human health
o Resistant starch, galacto-oligosaccharides, and fructo-oligosaccharides

Question 20

Synbiotic:

Answer 20

mixture of prebiotics and probiotics that have synergistic effects

Question 21

How may some probiotics influence diarrhoea?

Answer 21

 Can reduce the duration of diarrhoea (although not by much)
 This may be significant for very vulnerable patients, who cannot tolerate diarrhoeal losses
 Faecal transplants are used to treat C. difficile

Question 22

Define diarrhoea

Answer 22

 3 or more loose or watery stools per day
 Occurs by two basic mechanisms: too much secretion or not enough absorption
o Secretory- does not stop when patient fasts
o Osmotic (malabsorptive)- diarrhoea stops when patient fasts

Question 23

Secretory diarrhoea

Answer 23

 Does not stop when the patient fasts
 Caused by:
o Enterotoxin
o Laxatives
o Congenital defects

Question 24

Osmotic (Malabsorptive) diarrhoea

Answer 24

 Improves when patient fasts
 Caused by:
o Lactase deficiency
o Pancreatic enzyme deficiency
o Loss of enterocytes
o Bacterial overgrowth
o Ingestion of nutrient binding substances
o Lymphatic obstruction

Question 25

Other causes of diarrhora

Answer 25

 Motility disorders
o Diabetes mellitus
o Post-surgical
 Inflammatory exudation
o IBD, infections (shigellosis)
 Diarrhoeal disease results from more fluid being presented to the colon by the small intestine than the
colon can cope with.

Question 26

How does Clostridium difficile cause fluid entry into small intestine?

Answer 26

produce enterotoxins

o can cause epithelial cells to fall off the mucosa, leaving spaces through which fluid can be extruded.

Question 27

How does E. coli cause fluid entry into small intestine?

Answer 27

produce heat stable (STa) enterotoxin

o inhibit the enterocyte fluid absorption mechanism

Question 28

How does Vibrio cholerae cause fluid entry into small intestine?

Answer 28

interrupt the fluid uptake mechanism in the same way that E.coli does but also produce an enterotoxin (zona occludens toxin or ZOT)
o ZOT loosens the tight junctions between enterocytes and causes intestinal vasodilatation.
o the catastrophically large fluid losses in cholera are mainly due to a combination of:
 vasodilatation, leading to increased interstitial fluid pressure
 increased passive water permeability because of enhanced conductivity between epithelial cells.