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Y2 MECHANISMS OF DISEASE > Electrolyte Disorders 👩🏼‍🔬 > Flashcards

Electrolyte Disorders 👩🏼‍🔬 Flashcards

1
Q

What are the 6 measured electrolytes?

A
  1. sodium
  2. potassium
  3. (chloride)
  4. (bicarbonate)
  5. urea
  6. creatinine
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2
Q

What are the estimated electrolytes in the body?

A

water

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3
Q

Why are abnormal electrolytes so clinically important?

A
  1. it can be a primary disease state
  2. it can be a secondary consequence of many diseases
  3. iatrogenic problems are common
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4
Q

What are the 4 main important functions of electrolytes?

A
  1. maintenance of cellular homeostasis
  2. cardiovascular physiology - BP
  3. renal physiology - GFR
  4. electrophysiology - heart & CNS
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5
Q

What are the most common clinical examples of electrolyte disorders?

A
  1. haemorrhage
  2. poor intake in the elderly
  3. diabetes insipidus
  4. diabetes mellitus
  5. diuretic therapy
  6. endocrine disorders involving ADH, aldosterone
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6
Q

What five interconnecting concepts are measured in the lab?

What is the main one that is measured?

A
  1. concentrations
  2. compartments
  3. contents
  4. volumes
  5. rates of gain and loss

In the lab, concentration is measured

The other factors are deduced

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7
Q

What are the missing components of this important concept?

A
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8
Q

What is the normal intracellular fluid (ICF) and extracellular fluid (ECF) volume?

A

ICF - 23 L

ECF - plasma + interstitial 19 L

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9
Q

What is normal cellular sodium concentration?

How can a change in the body affect this?

A

Normal Na conc is 140 mmol/L

Normally the system is maintained in equilibrium

changing any factor causes a new steady state to be reached

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10
Q

How does decreasing the volume of fluid in the body affect ECF, ICF and Na concentration?

A

Decreasing the volume will raise the concentration of any solute

ICF - 20L

ECF - plasma + interstitial 18 L

Na - 148 mmol/L

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11
Q
A
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12
Q

How does increasing the excretion of a solute affect solute concentration?

A

Increasing excretion decreases solute concentration

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13
Q

Fill in the body fluid distribution table

A
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14
Q

How does haemorrhage affect electrolyte concentrations?

A

it leads to loss of isotonic solutions

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15
Q

If 2 L of isotonic fluid is lost from the body, how does this affect ECF, ICF and [Na]?

Why?

A

ECF = plasma and interstitial 17 L

ICF = 23 L

Na - 140 mmol/L

the loss is from the ECF ONLY

there is no change in [Na} and no fluid redistribution

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16
Q

What is the difference between isotonic and hypotonic?

A

an isotonic solution has the same particulate concentration as the blood

a hypotonic solution is less concentrated than the blood

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17
Q

What tends to lead to loss of hypotonic solutions?

A

dehydration

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18
Q

How would loss of 3L of hypotonic fluid affect ECF, ICF and [Na]?

Why?

A

ECF = plasma + interstitial 18 L

ICF = 21 L

[Na] = 148 mmol/L

Greater loss from ICF than ECF

Small increase in [Na]

Fluid redistribution between ECF and ICF

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19
Q

How can isotonic solutions be gained?

A

through administration of saline

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20
Q

How does gain of 2L of isotonic fluid through saline drip affect ECF, ICF and [Na]?

A

ECF = plasma + interstitial 21 L

ICF = 23 L

[Na] = 140 mmol/L

Gain is to ECF ONLY

There is no change in [Na] and no fluid redistribution

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21
Q

How may hypotonic solutions be gained?

A

through giving water

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22
Q

What would happen to ECF, ICF and [Na} if there was gain of 3L of hypotonic fluid?

A

ECF = plasma + interstitial 20L

ICF - 25L

[Na] = 133 mmol/L

greater gain to ICF than to ECF

small decrease in [Na}

fluid redistribution between ECF and ICF

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23
Q

What are examples of physiological compensatory mechanisms?

A
  1. thirst
  2. ADH
  3. renin/angiotensin system
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24
Q

What are examples of therapeutic compensatory mechanisms?

A
  1. intravenous therapy
  2. diuretics
  3. dialysis
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25
Q

Where is ADH produced and when is it released?

What effects does it have?

A

it is produced by the median eminence

it increases when osmolality rises

it decreases renal water loss and increases thirst

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26
Q

What is the median eminence?

A

a part of the hypothalamus from which regulatory hormones are released

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27
Q

What are the 2 simple tests to ascertain ADH status?

What do the results show?

A

measure plasma & urine osmolality:

if urine > plasma, this suggests that ADH is active

measure plasma & urine urea:

if urine is much greater than plasma, this suggests water retention

28
Q

What activates the renin-angiotensin system?

What does it cause?

A

it is activated by reduced IVV caused by Na depletion or haemorrhage

it causes renal Na retention

29
Q

What is the simple test to ascertain renin-angiotensin status?

A

measure plasma and urine [Na]

if urine [Na] < 10 mmol/L, this suggests that RAAS is active

30
Q

What will happen to ECF, ICF and [Na] if 2L of isotonic fluid loss is replaced by isotonic and hypotonic fluids?

A

isotonic fluid:

ECF = plasma + interstitial 19L

ICF = 23 L

Na = 140 mmol/L

This is NORMAL - no change in [Na] and no fluid redistribution

hypotonic fluid:

ECF = plasma + interstitial 18 L

ICF = 24 L

[Na] = 132 mmol/L

There is a fall in [Na] and fluid redistribution

31
Q

What will happen to ECF, ICF and [Na] if loss of 3 L of hypotonic fluid is replaced by isotonic and hypotonic fluid?

A

isotonic fluid:

ECF = plasma + interstitial 21L

ICF = 21L

[Na] = 146 mmol/L

[Na] is slightly increased but there is NO fluid redistribution

hypotonic fluid:

ECF = plasma + interstitial 19L

ICF = 23L

[Na] = 140 mmol/L

[Na is restored and there is fluid redistribution

32
Q

What 2 factors can lead to hyponatraemia?

A
  • too little Na in ECF
  • excess water in ECF
33
Q

What 2 factors can lead to hypernatraemia?

A
  • too little water in ECF
  • too much Na in ECF
34
Q

What 2 factors can lead to dehydration?

A
  • water deficiency
  • fluid (Na and water) depletion
35
Q

Fill in the blanks in the tree for diagnosing hyponatraemia

A
36
Q

How will the following features change in hyponatraemia due to diuretics?

A
37
Q

How are the following factors changed in hyponatraemia due to Syndrome of inappropriate antidiuretic hormone secretion (SIADH)?

A
38
Q

How are the following factors changed in hypernatraemia due to decreased water intake?

A
39
Q

How do the following factors change in hypernatraemia due to osmotic diuresis?

A
40
Q

What is the potassium reference range?

Which values are dangerous and why?

A

3.6 - 5.0 mmol/L

Values < 3.0 or > 6.0 are potentially dangerous

They can cause cardiac conduction defects or abnormal neuromuscular excitability

41
Q

How is potassium measured?

How is this used to calculate total body potassium?

A

serum potassium concentration is measured

this is a small proportion of the total potassium in the plasma

total body potassium is determined by total cell mass

42
Q

What conditions can significantly affect plasma [K] and why?

A
  1. acidosis
  2. insulin/glucose therapy
  3. adrenaline
  4. rapid cellular incorportation - TPN, leukaemia

This is because exchange between ICF and ECF significantly affects plasma [K]

43
Q

Fill in the potassium distribution table

A
44
Q

What is the effect of K+ redistribution?

A
45
Q

What is the relationship between K+ and H+ ions?

A

They exchange across the cell membrane

They both bind to negatively charged proteins (e.g. Hb)

46
Q

How do changes in pH affect the K+ and H+ equilibrium?

A

acidosis:

potassium moves out of cells, leading to hyperkalaemia

alkalosis:

potassium moves into cells, leading to hypokalaemia

47
Q

What is the movement of H+ and K+ like in acidosis?

A

H+ moves into cells

K+ moves out of cells

this leads to hyperkalaemia

48
Q

What are the 5 causes of hyperkalaemia?

A
  1. artefactual
  2. renal
  3. acidosis (intracellular exchange)
  4. mineralocorticoid dysfunction
  5. cell death
49
Q

What are examples of artefactual causes of hyperkalaemia?

A
  1. delay in sample analysis
  2. haemolysis
  3. drug therapy - excess intake
50
Q

What are examples of renal and ‘cell death’ causes of hyperkalaemia?

A

renal:

  1. acute renal failure
  2. chronic renal failure

cell death:

  1. cytotoxic therapy
51
Q

What are examples of mineralocorticoid dysfunction causes of hyperkalaemia?

A
  1. adrenocortical failure
  2. mineralocorticoid resistance - e.g. spironolactone
52
Q

What are the 5 treatments for hyperkalaemia?

A
  1. correct acidosis if this is the cause
  2. stop unnecessary supplements/intake
  3. give glucose and insulin to drive K into cells
  4. ion exchange resins encourage GIT K binding
  5. short and long-term dialysis
53
Q

What are the 4 causes of potassium depletion?

A
  1. low intake
  2. increased urine loss
  3. gastrointestinal losses
  4. hypokalaemia without depletion
54
Q

What may cause increased urine loss leading to potassium depletion?

A
  1. diuretics/osmotic diuresis
  2. tubular dysfunction
  3. mineralocorticoid excess
55
Q

What may cause gastrointestinal losses leading to potassium depletion?

A
  1. vomiting
  2. diarrhoea
  3. fistulae
56
Q

What may cause hypokalaemia without depletion?

A
  1. alkalosis
  2. insulin/glucose therapy
57
Q

What concentration must there be for it to be classified as potassium depletion?

A

< 2.5 mmol/L

58
Q

What are the effects of potassium depletion due to acute changes in ICF/ECF ratios?

A

neuromuscular changes:

  1. lethargy
  2. muscle weakness
  3. heart arrhythmias
59
Q

what are the effects of potassium depletion due to chronic losses from the ICF?

A

neuromuscular:

  • lethargy
  • muscle weakness
  • heart arrhythmias

kidney

  • polyuria
  • alkalosis due to increase in renal bicarbonate production

also affects vasculature and the gut

60
Q

How may potassium depletion be detected when taking a history from a patient?

A
  1. diarrhoea, vomiting, drugs (diuretics, digoxin)
  2. symptoms of lethargy/weakness
  3. cardiac arrthymias
61
Q

What electrolyte tests would be done in potassium depletion and what results obtained?

A
  1. hypokalaemia
  2. alkalosis due to raised bicarbonate
62
Q

How can potassium depletion be prevented?

A

through giving adequate supplementation

63
Q

How can potassium depletion be treated through replacement of deficit?

A

oral:

46 mmol/day + diet

IV

< 20 mmol/L

64
Q

In what conditions should plasma potassium be monitored regularly?

A
  1. diuretic therapy
  2. digoxin use
  3. compromised renal function
  4. in support of IV resuscitation
65
Q

How will the following factors be changed in hypernatraemia due to aldosterone?

A

Y2 MECHANISMS OF DISEASE (36 decks)

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