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Gastrointestinal > Water/Electrolyte Balance and Diarrhoea > Flashcards

Water/Electrolyte Balance and Diarrhoea Flashcards

1
Q

In a healthy person how much water is absorbed through the GI tract every day?

A

9L

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2
Q

In a healthy person how much water is expelled in faeces every day?

A

100-200ml

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3
Q

What is the approximate value of daily insensible loss?

A

800ml

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4
Q

2L of the 9L of fluid that are absorbed every day by the GI tract are from dietary intake. Where does the remaining 7L come from?

A

Salivary, gastric, pancreatic, biliary and intestinal secretions

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5
Q

How does increase fluid lead to a self perpetuating cycle that presents as diarrhoea?

A

Increased fluid causes more rapid propulsion of the intestine which decreases the amount of absorption which can take place and leads to further fluid accumulation. This is a self perpetuating cycle which results in diarrhoea

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6
Q

Give example of drugs and conditions which can lead to osmotic diarrhoea?

A 
Laxatives
Antacids
Acarbkse
Orlistat
Digestive enzyme deficiencies
Pancreatic insufficiency
Inflammatory disease
Short bowel syndrome
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7
Q

What is osmotic diarrhoea?

A

Diarrhoea which results from either the accumulation of non absorbable solutes or a failure to digest or absorb nutrients

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8
Q

What molecules are absorbed in the large intestine?

A

Water
Electrolytes
Short chain fatty acids

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9
Q

Which transporter protein is responsible for the cotransport of sodium and glucose?

A

SGLT1

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10
Q

Once sodium and glucose have been absorbed into the enterocyte, how do they e it the enterocyte?

A

Glucose moves out via facilitated diffusion with a GLUT2 transporter in the basolateral membrane
Sodium is actively pumped out of the cell at the basolateral membrane via the sodium potassium pump

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11
Q

Why are low osmolality oral rehydration salts preferable than isoosmotc ORS in the treatment of diarrhoea?

A

These further reduce the need for IV fluid use as the low osmolality prevents any unwanted secretion of water into the intestinal lumen

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12
Q

List some of the causes of secretory diarrhoea?

A

Infections such as rotavirus, e.coli, shigella, campylobacter, salmonella and v cholerae
Carcinoid syndrome
Zollinger ellison syndrome

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13
Q

How can inflammation cause diarrhoea?

A

This can damage the epithelium and impair its ability to absorb water and electrolytes

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14
Q

Infection with which bacterium commonly causes bloody diarrhoea?

A

Shigella

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15
Q

Describe how diarrhoeal disease might be prevented

A

Vaccinations against organisms such as rotavirus and measles which can cause diarrhoea
Good hand washing
Improved sanitation

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16
Q

What are the differences between colloid and crystalloid IV fluids?

A

Colloids are large molecular weight molecules which act to increase blood volume
Crystalloids contain water and electrolytes and restore water homeostasis in tissues - these include saline and dextrose solutions

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17
Q

What percentage of saline solution will remain intravascular after infusion?

A

25%

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18
Q

What percentage of dextrose solution will remain intravascular after infusion?

A

10%

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19
Q

Describe the situations in which you would choose to use IV saline or IV dextrose solutions to treat diarrhoea

A

Saline is used when the patient has lost both water and electrolytes
Dextrose is used when the patient has only lost water

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20
Q

0.9% saline is most commonly used, why is this?

A

Because this is closest to the physiological level of sodium

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21
Q

Which IV fluid may be used to treat metabolic acidosis and why?

A

Ringer lactate solution as the lactate in this solution is readily metabolised and will produce bicarbonate ions

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22
Q

What ratio of saline:dextrose is most commonly given as a postoperative regimen?

A

2:1

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23
Q

What patient factors will influence the rate of fluid replacement?

A 
Age
Cardiovascular status
Renal function
Severity of dehydration
Length of time it took to become rehydrated
24
Q

What volume of fluid is contained in a standard IV fluid bag?

A

500ml

25
Q

Why prescribing IV fluids, how is the dose commonly written?

A

As time of infusion of a standard 500ml bag e.g. 4hr bag

26
Q

Why is it important to check the patients cardiovascular status before giving IV fluids?

A

Because if a patient has a weak CV system them given too much fluid too quickly will overload the heart leading to heart failure and pulmonary oedema

27
Q

Potassium is often supplemented in IV fluids. What is the maximum rate of infusion of potassium and the maximum concentration per bag?

A

10mmol/h

20mmol

28
Q

In diarrhoea it is common to lose electrolytes. Why is hypokalaemia so dangerous?

A

It can lead to arrythmias

29
Q

What factor determines whether fluid and electrolytes will be absorbed paracellularly or cellularly?

A

The permeability of tight junctions in the intestinal epithelium

30
Q

What water and electrolyte transporters are contained in the apical membrane of epithelial cells of the jejunum?

A

Sodium glucose cotransporters
Sodium amino acid cotransporters
Sodium hydrogen antiporters

31
Q

In the jejunum, hydrogen is secreted into the lumen of the intestine in order to absorb sodium. Where does this hydrogen come from?

A

The breakdown of carbon dioxide and water to hydrogen ions and bicarbonate ions by carbonic anhydrase

32
Q

When should handwashing be carried out when dealing with patients with diarrhoea, disease?

A

After handling the patient, their bedding or clothing or sick room equipment and before preparing or serving food

33
Q

What is diarrhoea defined as?

A

Frequency if stool passage of more than three times a day with decreased stool consistency and a stool weight of greater than 250g per day

34
Q

What is dysmotility diarrhoea?

A

Diarrhoea resulting fro abnormal gut motility where decreased transit times allow insufficient time for fluid absorption

35
Q

Use of which antibiotics is particularly associated with c.difficile infection?

A

Clindamycin
Celhalosporins
Ampicillin
Amoxicillin

36
Q

Describe how toxins from vibrio cholerae can result in secretory diarrhoea?

A

Chloride ions enter enterocytes from the bloodstream via cotransport with sodium or potassium and cause an increase in intracellular cAMP activity by activating adenylyl cyclase. This activates cystic fibrosis transmembrane conductance regulator (CFTR) to pump out the chloride ions into the lumen of the small intestine. This secretion of negative ions into the lumen draws sodium ions into the lumen through tight junctions between enterocytes. This leads to the movement of water into the intestinal lumen by osmosis. This is the normal physiology. When infected with vibrio cholerae, toxins from the bacteria cause an inappropriate increase in intracellular cAMP, which activates CFTR to secrete chloride ions and therefore water into the lumen.

37
Q

What is the result of the loss of bicarbonate ions due to diarrhoea?

A

Metabolic acidosis

38
Q

What is the result of the loss of potassium ions due to diarrhoea?

A

Arrythmias

39
Q

Which serum blood test is often used to assess diarrhoea?

A

Urea and electrolytes test

40
Q

An increase in urea and creatinine serum concentration indicates clinical dehydration. Why do these molecules increase in concentration in patients with diarrhoea?

A

Urea is the waste product of protein metabolism and creatinine is a muscle waste product - these are both excreted in urine by the kidneys. Diarrhoea causes a large loss of fluid leading to decreased blood volume and this causes slower movement of blood through the kidneys. This leads to a decreased glomerular filtration rate which allows for increased reabsorption of urea and creatinine and therefore explains the rise in their serum concentrations

41
Q

When prescribing IV fluid how is the fluid required calculated?

A

Fluid required = sum of previous days measured losses + insensible loss + previous days deficit (previous days measured losses + insensible loss - previous days intake)

42
Q

What fluids can be measured to calculate the measured losses for the day in a patient with diarrhoea?

A

Urine output
Facal output
Vomit
Fluid from surgical drains

43
Q

All strains of E.coli are pathogenic. T/F?

A

False - some E.coli strains exist as commensal organisms

44
Q

Cryptosporidium and giardia are protozoa which can cause diarrhoea and are endemic in Scotland. T/F?

A

True

45
Q

What age group is particularly affected by norovirus?

A

Elderly people

46
Q

What host factors can determine the likelihood of enteric infection?

A 
Age
Genotype
Personal hygiene
Gastric acidity
Intestinal motility
Enteric microflora
Immunity
Intestinal receptors
47
Q

What microbial factors can determine the likelihood of enteric infection?

A

Toxins
Attachment
Invasiveness
Infectious doses

48
Q

Which four antibiotics can particularly affect the bowel flora to cause c.difficle infection?

A

clindomycin
coamoxyclav
cephalosporins
ciprofloxacin

49
Q

What is tenesmus?

A

The feeling of incomplete emptying after defecation

50
Q

Why is a follow up stool sample required when a patient has been infected with salmonella typhi?

A

Because they could still be carrying the bacteria in the dormant state and this has implications on their occupation if, for example, the work handling food or in healthcare

51
Q

What is meant by growing an organism on selective culture media?

A

The organism is grown on an agar plate that is designed to only be able to grow one specific bacterium

52
Q

What is meant by growing an organism on a differential culture media?

A

The organism is grown on an agar plate which contains specific chemicals which cause specific bacterial strains to exhibit a specific colour change reaction in order to identify the organism

53
Q

What common test is used to look for specific viruses in a stool sample?

A

PCR

54
Q

Which part of the GI tract absorbs the most water?

A

Small intestine

55
Q

Which part of the GI tract has the most net absorption of water?

A

Large intestine

56
Q

In the colon, sodium can be absorbed through a sodium channel. Which hormone stimulates this?

A

Aldosterone

57
Q

What is the name for the combination of crypt cell secretion and villous cells absorption that occurs in the small intestine?

A

Fluid circuit hypothesis

Gastrointestinal (22 decks)

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