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Phase 2 1. Gastroenterology > Fluid and electrolyte balance > Flashcards

Fluid and electrolyte balance Flashcards

1
Q

summarise water balance

A

intake = 2000ml

turnover = 9000ml

excretion = 100ml

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2
Q

What are the sites of fluid loss?

A

Fluid loss is not just restricted to the GI tract (colon)
the kidney is also a site of fluid loss. Insensible loss
occurs through the skin

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3
Q

How is the movement of water driven?

A

Through movement of electrolytes

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4
Q

What is the difference between ion channels and transporters?

A

 Ion channels are the fast means of exchanging electrolytes
 Transporters are slower
o These are carriers for drugs
o Drugs target particular transporters

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5
Q

How does sodium enter the intestinal cell?

A

sodium co-transporters transporting amino acids, peptides, bile salts and vitamins in, with sodium.

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6
Q

How is sodium pumped out of the intestinal cell?

A

(active transport)

Sodium is pumped out of the cell and potassium enters
o A gradient forms as there is less sodium in the cell
o Transporters then use this gradient to transport sodium back into the cell via passive diffusion
o Active transport takes sodium out

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7
Q

How is water absorbed in the intestines?

A

NB: Water follows the ions that are entering the cell via passive diffusion

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8
Q

How does glucose influence sodium transport?

A

When glucose is available, then the transport of sodium can happen more efficiently

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9
Q

How does sodium drive nutrient absorption?

A

The sodium gradient (generated by active removal of sodium from cells) provides energy for the active transport of many minerals, vitamins and metabolits

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10
Q

How is ORS used to treat cholera?

A

patients with cholera did
not absorb sodium chloride when salt was provided orally.

 However, if glucose was also given, it was fully absorbed and it enhanced sodium absorption.
 Cholera causes huge loss of water and severe dehydration
 ORS contain sodium, potassium and glucose
o When these were introduced, deaths from cholera dropped by millions

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11
Q

What is the Cystic fibrosis transmembrane conductance regulator

A

(CFTR) is a membrane protein and chloridechannelin
vertebrates that is encoded by theCFTRgene.
 The CFTR channel is present in the intestines, airways and pancreatic duct
 The CFTR gene is not part of cyclic AMP system and therefore can be affected by different substances that
affect the cAMP pathway
 CFTR functions as an ATP-gated anion channel, increasing the conductance for certain anions (e.g. Cl−) to flow down their electrochemical gradient.

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12
Q

How does the Cystic fibrosis transmembrane conductance regulator usually work?

A

 Normally, the protein moves chloride and thiocyanate ions (with a negative charge) out of an epithelial cell to
the covering mucus.
 Positively charged sodium ions follow passively, increasing the total electrolyte concentration in the mucus,
resulting in the movement of water out of the cell via osmosis.
 In the intestines and pancreatic ducts, this forms a layer of water close to the cells, which moistens the
epithelium and enables the pancreatic enzymes to function

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13
Q

What happens when there is a mutation in the Cystic fibrosis transmembrane conductance regulator?

A

A mutation in CFTR = CFTR not working properly (i.e. in cystic fibrosis) which causes problems with the
intestines and airways

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14
Q

What is Secretory diarrhoea?

A

High volume of fluid loss due to decreased absorption and increased secretion

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15
Q

What can cause Secretory diarrhoea?

A 
o Acute infections
o Failure of the bile salt absorption
o Malabsorption of fat
o Laxative abuse
o Carcinoid syndrome
o Zollinger-Ellison syndrome
o Secreted Na+, Cl- K+ HCO3-
o Endocrine is mostly secretory diarrhoea
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16
Q

What is Osmotic (malabsorptive) diarrhoea

A

 Osmotically active substances accumulate in the lumen

 There is a decrease intestinal absorption leading to a high volume of fluid loss

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17
Q

What causes Osmotic (malabsorptive) diarrhoea?

A 
o Laxatives
o Antacids
o Acarbose (alpha-glucosidase inhibitor)
o Orlistat (lipase inhibitor)
o Digestive enzyme deficiencies (lactase) in the intestine and pancreas
o Pancreatic insufficiency
o Inflammatory disease
o Short bowel syndrome
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18
Q

What is Inflammatory diarrhoea

A

 Increased secretion and propulsive activity of the bowel leads to a low volume of fluid loss
 This type of diarrhoea lasts longer than others

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19
Q

What can cause Inflammatory diarrhoea

A 
o Inflammatory bowel disease
o Crohn’s disease
o Ulcerative colitis
o Infectious disease
> Shigella
> Salmonella
o Irritable colon
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20
Q

What are the types of diarrhoea found in children?

A
  • acute watery
  • bloody
  • persistant
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21
Q

What is acute watery diarrhoea?

A

diarrhoea causing dehydration

o V. cholerae, E. coli, Rotavirus

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22
Q

What is bloody diarrhoea?

A

diarrhoea (dysentery) leading to intestinal damage and nutrient loss
o Shigella

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23
Q

What is persistant diarrhoea?

A

diarrhoea (>14 days) particularly in undernourished children or children with concominant diseases
o Campylobacter, Salmonella and Cryptosporidium protozoa (In HIV patients) are all causes of child-
death worldwide due to diarrhoea

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24
Q

How is diarrhoea treated in children?

A

 Fluid replacement to prevent dehydration (ORS)
 Zinc supplements (decrease the severity and duration)
 Continue feeding
 Use appropriate fluids available at home and increased fluids in general

25
Q

Why is zinc supplementation important in treating children with diarrhoea

A

vital micronutrient essential for protein synthesis, cell growth and differentiation, immune function,
and intestinal transport of water and electrolytes

26
Q

What is the public health implication of diarrhoea?

A

88% of worldwide deaths from diarrhoea are attributable to unsafe water, poor sanitation and poor hygiene.

27
Q

What preventative measures are in place to lessen the public health burden of diarrhoea?

A
  • Rotavirus and measles vaccinations
  • Early breastfeeding and vitamin A supplementation
  • Handwashing with soap
  • Improved water quality
  • Community-wide sanitation promotion
28
Q

What key steps should be taken in managing diarrhoea?

A

 Assess the patients clinical state. Are they severely ill or is it a mild issue? (Unconscious/too severely dehydrated, people cannot take fluids orally)
 Fluid balance chart - assess what the patient took in and what came out
 Check for and be aware of fluid shifts
 Modify treatment to the condition of patient and renal function

29
Q

What factors influence the speed of fluid replacement?

A
  • age
  • renal function
  • cardiovascular status
  • severity of existing dehydration
  • time it took to develop
30
Q

Describe the influence low osmolality has on water movement

A

 If there is too much salt in the gut/circulation, the water will come out the cell, causing cell dehydration.
 This means the cell will shrink

31
Q

Describe the influence high osmolality has on water movement

A

 Fluid enters the cell and the cell expands
 Brain expanding cells is not good
o Hyponatraemia leads to brain oedema

32
Q

What influences osmolality?

A

Less sodium, less chloride - less osmolality

33
Q

What is the difference is osmolality in the gut?

A

Gut has lower osmolality than the enterocyte, so more water will enter the cell and cause cells to expand
o This is good in diarrhoea

34
Q

What effect does reduced osmolality ORS have?

A
  • decreases stool output and dehydration by 20-30% compared to the original formula

= decreases need for TV therapy

35
Q

What are the different types of intravenous solutions?

A
  • colloids

- crystalloids

36
Q

What are colloids?

A

large molecular weight, e.g:

  • albumin
  • hydroxyethyl starch (HES)
  • Haemaccel
37
Q

What is the effect of colloids?

A

should theoretically preferentially increase the intravascular volume

38
Q

What are crystalloids

A

water plus elctrolytes, e.g:

  • saline
  • dextrose
  • ringer’s-lactate (Hartmanns)
39
Q

What is the effect of crystaloids

A

should theoretically increase the intravascular volume, interstitial volume and intracellular volume.

40
Q

What is isosmotic?

A

having the same osmotic pressure

An iso-osmotic solution is the preferred solution given, as you do not want to cause too much of a shift

41
Q

Which fluids are isosmotic?

A
  • saline 0.9%
  • dextrose 5%
  • sodium bicarbonate 1.96%
42
Q

Which fluids are hypoosmostic

A
  • saline 0.45%
43
Q

Which fluids are hyperosmotic

A

sodium bircarbonate 8.4% (extremely hyperosmotic)

44
Q

When should hyperosmotic fluids be given?

A 
Acidosis Emergency (caridac arrest)
Use sodium bicarbonate 8.4%
45
Q

When should colloids be used?

A

used in acute circulatory shock when wanting to restore the volume as Colloids are given IV and they stay in the IV bed

46
Q

What is the benefit of saline as a universal hydration solution?

A

 Only 25% will stay in the vascular bed
 Used as a universal rehydration solution (middle of the road)
o Also rehydrates tissues and stays in vascular bed

47
Q

What is the effect of dextrose on hydration?

A

o Very quickly goes into cells
o Glucose and dextrose are similar
o Glucose will be quickly metabolised by the cells and therefore water will follow and enter the cells

48
Q

What is the post-operative fluid regimen of a normal patient

A

involves saline and dextrose 2:1

49
Q

Why do some crystalloids contain lactate?

A

substantial amount of bicarbonate is produced during lactate metabolism

This is good to use in those with chronic acidosis i.e. those who have lost bicarbonate.

50
Q

How is rate of fluid replacement measured?

A

Based on time of infusion of a standard 500mL bag

51
Q

What is the use of 2-hourly infusion and how much fluid would be infused over 24 hours

A

emergency rehydration

6 litres

52
Q

What is the use of 4-hourly infusion and how much fluid would be infused over 24 hours

A

3 litres

53
Q

What is the use of 6-hourly infusion and how much fluid would be infused over 24 hours

A

standard regimen

2 litres

54
Q

What is the use of 8-hourly infusion and how much fluid would be infused over 24 hours

A

slow rehydration

1.5 litres

55
Q

Why does potassium need to be tightly regulated?

A

It is extremely dangerous when potassium levels are too high/too low
o Low is around 2.5-3mmol/L
o High is around 6mmol/L

56
Q

What is the maximum concentration of potassium for peripheral administration?

A

40mmol/L

57
Q

What is the maximum rate of potassium administration?

A

10mmol/h:

faster only if cardiac monitoring/ central line are available (up to 20 mmol/h)

58
Q

Describe the cardiac monitoring required during potassium supplementation

A

 Baseline ECG required if K <3 mmol/l
 Cardiac monitoring if K <2.5 mmol/L
 Or if K is given faster than 10 mmol/h

Phase 2 1. Gastroenterology (20 decks)

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