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Stage 2: Supporting Life > Fluid and Electrolyte Balance > Flashcards

Fluid and Electrolyte Balance Flashcards

1
Q

Describe TBW in different groups of people

A
  • 60% ideal weight of man
  • 50-55% ideal weight of woman
  • 70% of weight in infants
  • 65% of weight in children
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2
Q

Why are infants more vulnerable to dehydration?

A

Bc they don’t have as much protective non-water areas

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3
Q

What causes worse outcomes, fluid overload or dehydration?

A

Fluid overload

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4
Q

What is the relationship between fat and water?

A

The more fat you have, the less water you have

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5
Q

Which is the only area of fluid we can access and therefore directly affect?

A

Plasma

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6
Q

What is the normal blood volume?

A

2.5L (65ml/kg in females and 75ml/kg in males)

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7
Q

Describe water loss

A
  • Generate fluid through metabolism
  • Normally 500ml/day loss (but no absolute amount)
  • Skin and lungs = insensible losses
  • Urine is a measure of water loss however skin, lungs and faeces is not easily measurable
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8
Q

Describe fluid loss in most people?

A

Most people are euvolaemic → in balance, generally controlled by the amount of urine passed

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9
Q

Describe net charge in body fluid

A
  • In any fluid, the total cations = total anions bc we do not have a net charge
  • The anion gap is just based on what we choose to measure
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10
Q

Describe how different ions are kept in balance

A
  • Sodium and potassium gradient is maintained by Na-K ATPase
  • Calcium → intracellular calcium has peaks and troughs all the time, but is high locally where it is having an effect
  • Chloride is driven by sodium → high sodium levels = high chloride levels
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11
Q

What is the normal range for plasma sodium?

A

135-145 mmol/L (reflects body water content)

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12
Q

Describe sodium in the body

A
  • 25% non-exchangeable in tissues e.g. bones (slow turnover)
  • 75% exchangeable in solution in ECF
  • Sodium consumption variable 110-220 mmol/day
  • ~ 5-10mmol loss in sweat and faeces
  • Sodium drives water reabsorption
  • Total body exchangeable sodium content reflects TBW
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13
Q

What is sodium excretion regulated by?

A

1) RAA
2) Natriuretic peptides → increase sodium excretion in the kidneys
3) Intrinsic renal mechanisms

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14
Q

What is natriuresis?

A

Excretion of sodium in the urine

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15
Q

If you’re dehydrated or hypovolaemic what are your sodium levels like?

A

Low

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16
Q

Where are the juxtaglomerular cells?

A

In macula densa on the DCT but close to the glomerulus

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17
Q

Where is ACE?

A

In lungs and endothelial cells

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18
Q

What is the effect of aldosterone?

A

Increased sodium reabsorption in the DCT

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19
Q

What happens to osmolarity when you are water deficient?

A

It increases

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20
Q

What is the action of ADH?

A

Acts on the collecting duct to reabsorb water

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21
Q

When do natriuretic peptides act?

A

When there is fluid overload

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22
Q

What is fluid overload caused by?

A

1) Kidney failure
2) Heart failure → LH = lung, RH = periphery
3) Liver failure → fluid build up in abdomen

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23
Q

What does increased GFR lead to?

A

Less sodium reabsorption and more sodium secretion → natriuresis

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24
Q

What causes the heart to release ANP and BNP?

A

Cardiac distension, sympathetic stimulation and angiotensin II

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25
Q

What are the actions of ANP and BNP?

A

Vasodilation, decrease renin and decrease GFR

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26
Q

What is involved in a fluid balance examination

A

Limbs, head and neck, chest, abdomen, fluid balance chart, weight chart

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27
Q

What are you looking for in the limbs part of a fluid balance examination?

A

1) Temperature, pulse (volume and rate), BP sitting and standing
2) Skin turgor → if dehydrated will be decreased (but look at context of age), pitting oedema is newly acquired

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28
Q

What are you looking for in the head and neck part of a fluid balance examination?

A

1) Sunken eyes → if losing fluid from eyes, quite significant dehydration
2) Dry mucous membranes → not necessarily dehydrated but def not fluid overloaded (can’t be dehydrated without dry mucous membranes)
3) JVP and carotid pulse

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29
Q

What are you looking for in the chest part of a fluid balance examination?

A

1) Capillary refill

2) Lung auscultation for pulmonary oedema

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30
Q

What are you looking for in the abdomen part of a fluid balance examination?

A

Ascites → might be fluid overloaded by TBW still isn’t high, just fluid in wrong place

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31
Q

What are 6 symptoms/history in people with hypovolaemia?

A

1) Thirst
2) Lethargy
3) Postural dizziness
4) Confusion
5) GI losses
6) Reduced urine volume

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32
Q

What 5 things might you see in an examination of someone with hypovolaemia?

A

1) Fast and weak pulse
2) BP postural drop of > 20 mmHg OR low BP
3) Loss of skin turgor
4) Sunken eyes
5) Dry mucous membranes

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33
Q

What are 5 symptoms/history in people with hypervolaemia?

A

1) Breathlessness
2) Confusion
3) Abdominal bloating
4) Peripheral oedema
5) Weight gain

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34
Q

What 6 things might you see in an examination of someone with hypervolaemia?

A

1) Fast and bounding pulse
2) BP can be high or low
3) Skin turgor generally maintained
4) Peripheral oedema
5) Elevated JVP
6) Ascites

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35
Q

What is hyponatraemia?

A

Na < 135 mmol/L

36
Q

What does hyponatraemia result from?

A

1) The intake and subsequent retention of water → excess of water in relation to sodium
2) The depletion of total body sodium in excess of concurrent body water losses

37
Q

What is the key feature of hyponatraemia?

A

Volume status of the patient

38
Q

What are the 3 classifications of hyponatraemia?

A

1) Hypovolaemia
2) Euvolaemia
3) Hypervolaemia

39
Q

What are the two types of causes of hypovolaemia leading to hyponatraemia?

A

1) Extra-renal losses

2) Renal losses

40
Q

What are causes of extra-renal losses leading to hypovolaemia and hyponatraemia?

A

1) Dermal losses → burns
2) GI losses → vomiting, diarrhoea
3) 3rd space → pancreatitis

41
Q

What is urine sodium like in extra-renal losses leading to hypovolaemia and hyponatraemia?

A

< 25 mmol/L

42
Q

What is urine sodium like in renal losses leading to hypovolaemia and hyponatraemia?

A

> 30mmol/L

43
Q

What are causes of renal losses leading to hypovolaemia and hyponatraemia?

A

1) Diuretic therapy
2) Cerebral salt wasting
3) Primary adrenal insufficiency → lack of aldosterone

44
Q

What is urine sodium like in euvolaemia causing hyponatraemia?

A

> 30 mmol/L

45
Q

What are causes of euvolaemia leading to hyponatraemia?

A

1) Water intoxication → primary polydipsia, excess IV hypotonic fluids
2) Hypothyroidism
3) Hypopituitarism → glucocorticoid deficiency
4) Pregnancy
5) SIADH (evaluate underlying aetiology)

46
Q

Generally what causes hypervolaemia leading to hyponatraemia?

A

The failures

47
Q

What causes hypervolaemia leading to hyponatraemia with urine sodium < 25?

A

1) Congestive cardiac dysfunction
2) Cirrhosis with ascites
3) Nephrotic syndrome

48
Q

What causes hypervolaemia leading to hyponatraemia with urine sodium >30?

A

CKD

49
Q

What is SIADH?

A

Syndrome of inappropriate ADH secretion

50
Q

What are the types of causes of SIADH?

A

1) Neoplastic
2) Pulmonary
3) CNS
4) Drugs
5) Other

51
Q

What are neoplastic (cancer) causes of SIADH?

A

1) Lung → small cell, mesothelioma
2) GI → stomach, pancreas
3) GU → bladder, prostate, endometrium
4) Thymoma
5) Leukaemia
6) Lymphoma
7) Sarcoma

52
Q

What are pulmonary causes of SIADH?

A

1) Infection → pneumonia, abscess, TB, aspergillosis
2) Asthma
3) CF
4) PPV (positive pressure ventilation)

53
Q

What are CNS causes of SIADH?

A

1) Infection → abscess, meningitis, AIDS
2) Bleeds → subdural, SAH
3) CVA
4) Head trauma
5) MS, GBS
6) Shy-Drager

54
Q

What are drugs causes of SIADH?

A

1) AVP analogues → desmopressin, oxytocin, vasopressin

2) Stimulate AVP release/action → SSRIs, antipsychotics, anti-epileptics, NSAIDs, MDMA

55
Q

What are other causes of SIADH?

A

1) Idiopathic

2) Hereditary (V2 receptor)

56
Q

When are you more likely to have symptoms in hyponatraemia?

A

If it comes on more rapidly

57
Q

What do the symptoms of hyponatraemia depend on?

A

Severity of hyponatraemia

58
Q

What are symptoms in mild hyponatraemia (130-135)?

A

Asymptomatic

59
Q

What are symptoms in moderate hyponatraemia (121-129)?

A

Cramps, weakness, nausea

60
Q

What are symptoms in severe hyponatraemia (<120)?

A

Lethargy, headache, confusion

61
Q

What are symptoms in severe and rapidly evolving hyponatraemia?

A

Seizures, coma, respiratory arest

62
Q

Why can hyponatraemia cause neurological symptoms?

A

1) Water moves into cells bc of the osmotic gradient between ECF and ICF within the brain
2) This leads to raised ICP due to oedema → neurological symptoms

63
Q

What is hypernatraemia?

A

Na > 145 mmol/L

64
Q

How does hypernatraemia occur?

A
  • Net water loss or hypertonic sodium gain

- The increase in plasma tonicity pulls water out the cells, resulting in a decrease in intracellular volume

65
Q

What classifies as severe hypernatraemia?

A

If Na > 158 mmol/L

66
Q

What are symptoms of hypernatraemia?

A

Thirst, anorexia, weakness, stupor, seizures, coma

67
Q

What are the two types of hypernatraemia?

A

1) Unreplaced water loss

2) Sodium overload

68
Q

What causes unreplaced water loss leading to hypernatraemia?

A

1) Insensible and sweat losses
2) GI losses
3) Central diabetes insipidus (lack of ADH)
4) Nephrogenic diabetes insipidus
5) Osmotic diuresis → high glucose in uncontrolled diabetes mellitus
6) Poor water intake → elderly, impaired thirst or osmoregulation (hypothalamus)

69
Q

What causes sodium overload leading hypernatraemia?

A

1) Administration of high salt load → hypertonic sodium solutions
2) Hyperaldosteronism

70
Q

What is hypokalaemia?

A

K < 3.5 mmol/L

71
Q

Describe potassium in the body

A

Potassium enters the body via oral intake or IV, is largely stored in the cells, then excreted in the urine

72
Q

What is severity proportionate to?

A

Rate of onset

73
Q

What are symptoms of hypokalaemia (proportionate to severity)?

A

1) If K < 2.5 → muscle weakness which progresses from lower extremities
2) ECG changes and arrhythmias
3) If chronic → renal abnormalities e.g. impaired concentrating ability, raised BP

74
Q

What are the 4 causes of hypokalaemia?

A

1) Increased entry into cells
2) Increased GI losses
3) Increased urine losses
4) Other

75
Q

What causes increased entry into cells, leading to hypokalaemia?

A

1) Extracellular pH rise
2) Increased insulin
3) Elevated beta-adrenergic activity
4) Hypothermia
5) Drugs e.g. antipsychotics

76
Q

What causes increase GI losses, leading to hypokalaemia?

A

1) Vomiting
2) Diarrhoea
3) Laxative abuse

77
Q

What causes increased urine losses, leading to hypokalaemia?

A

1) Diuretics
2) Primary mineralocorticoid excess
3) Renal tubular acidosis
4) Drugs e.g. amphotericin B
5) Salt-wasting nephropathies e.g. Bartter’s, Gitelman’s
6) Hypomagnasaemia

78
Q

What are other causes leading to hypokalaemia?

A

1) Reduced intake (rare)

2) Increased sweat losses

79
Q

What will urine potassium be in the case of increased GI losses?

A

< 20

80
Q

What will urine potassium be in the case of increased urine losses?

A

> 40

81
Q

What ECG changes do you see with hypokalaemia?

A

Opposite to hyperkalaemia

1) Flat T wave
2) U waves (in between T an P wave)
3) ST depression
4) PR interval prolonged
5) Prolonged QT interval

82
Q

What is hyperkalaemia?

A

K > 5.5 mmol/L

83
Q

What are the 2 types of causes of hyperkalaemia?

A

1) Increased release from cells

2) Reduced urinary excretion

84
Q

What causes increased release of K from cells leading to hyperkalaemia?

A

1) Metabolic acidosis
2) Pseudohyperkalaemia (K movement out of cells after blood is drawn)
3) Insulin deficiency, hyperglycaemia and hyperosmolarity
4) Increased tissue catabolism → trauma, cytotoxic drugs
5) Beta blockers
6) Exercise
7) Hyperkalaemic periodic paralysis
8) Other e.g. digoxin toxicity, blood transfusions

85
Q

What causes reduced urinary excretion leading to hyperkalaemia?

A

1) Acute and chronic kidney disease
2) Reduced aldosterone secretion
3) Reduced response to aldosterone
4) Drugs e.g. K sparing diuretics, ACE inhibitors,
5) Type IV renal tubular acidosis

86
Q

What are symptoms of hyperkalaemia?

A

1) Paresthesia
2) Muscle weakness → paralysis
3) Arrhythmias

87
Q

What ECG changes occur in hyperkalaemia?

A

1) Tall peaked T waves
2) Shortened QT interval
3) PR interval lengthening
4) QRS widening
5) P waves disappear → sine wave

Stage 2: Supporting Life (30 decks)

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