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FINALS > Electrolyte Imbalances > Flashcards

Electrolyte Imbalances Flashcards

1
Q

Hypercalcaemia diagnosis?

A

Serum calcium concentration of 2.6 mmol/L or higher, on two occasions, following adjustment (correction) for the serum albumin concentration.
- Mild: 2.6-3
- Moderate: 3.01-3.4
- Severe: >3.4

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2
Q

What 2 conditions account for 90% of cases of hypercalcaemia?

A
  • primary hyperparathyroidism
  • malignancy e.g. lung, myeloma
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3
Q

How does malignancy cause hypercalcaemia?

A
  • bone mets
  • PTHrP from tumour eg. squamous cell lung cancer
  • myeloma (increased osteoclastic bone resporption caused by local cytokines eg. IL-1 tumour necrosis factor, released by myeloma cells
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4
Q

Less common causes of hypercalcaemia?

A

sarcoidosis, vit D intoxication, acromegaly, thyrotoxicosis, milk-alkali syndrome, drugs, dehydration, Addison’s, Paget’s

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5
Q

What drugs can cause hypercalcaemia?

A

Thiazides, calcium-containing antacids

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6
Q

What is the key diagnostic investigation for hypercalcaemia?

A

PTH levels

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7
Q

How does hypercalcaemia present?

A
  • bones, stones, groans and psychic moans
  • corneal calfication
  • HTN
  • Bone pain
  • Abdominal pain
  • Renal stones
  • Depression
  • Drowsiness
  • Confusion
  • Muscle weakness
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8
Q

How is hypercalcaemia managed?

A
  • IV Saline (3-4 L/day)
  • IV Bisphosphonates

Referral if required. Consider stopping certain causative drugs and monitor response. Monitor symptoms. Lifestyle measures. ?monitor serum Ca, eGFR, creatinine, BMD, renal imaging if specialist advises.

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9
Q

What would you see on blood test results for hypercalcaemia secondary to malignancy?

A
  • Raised calcium
  • low PTH
  • low phosphate
  • raised PTHrP
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10
Q

Most common cause of hypercalcaemia in outpatients?

A

Primary hyperparathyroidism

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11
Q

What are plasma potassium levels regulated by?

A

Aldosterone, acid-base balance and insulin levels.

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12
Q

What causes hyperkalaemia?

A
  • AKI
  • ACE/Spironolactone
  • Addisons
  • Rhadbomyolysis
  • Massive blood transfusion
  • Metabolic acidosis
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13
Q

What drugs cause hyperkalaemia?

A

Potassium sparing diuretics eg. spironolactone, ACE in, angiotension 2 receptor blockers, ciclosporin, heparin

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14
Q

What can potentially cause hyperkalaemia in renal failure patients?

A

Beta blocks- interfere with potassium transport into cells.

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15
Q

How does heparin cause hyperkalaemia?

A

Inhibition of aldosterone secretion

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16
Q

Why is metabolic acidosis associated with hyperkalaemia?

A

Hydrogen and potassium ions compete with each other for exchange of sodium ions across cell membranes and in the distal tubule.

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17
Q

Foods high in potassium?

A

Bananas, oranges, kiwi, avocado, spinach, tomatoes. Salt substitutes (contain K instead of Na).

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18
Q

What is the classification for hyperkalaemia?

A

Plasma potassium level:
Mild - 5.5 - 5.9
Moderate: 6 - 6.4
Severe: >6.5

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19
Q

How does hyperkalaemia show on ECG?

A
  • Tall T waves
  • Absent p waves
  • broad QRS
  • Sinusoidal pattern
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20
Q

Untreated hyperkalaemia may cause what?

A

Life-threatening arrhythmias.

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21
Q

Precipitating factors eg. AKI and aggravating drugs eg. ACE i should be stopped in what?

A

Hyperkalaemia

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22
Q

What patients for hyperkalaemia should have emergency treatment?

A

All patients with severe hyperkalaemia (≥ 6.5 mmol/L) or with ECG changes

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23
Q

Overview of hyperkalaemia management

A
  • Emergency management
  • Then further management: TUC, stop exacerbating drugs eg. ACE in
  • Then LOWER total body potassium
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24
Q

How is hyperkalaemia managed initially?

A
  • IV Calcium gluconate (stabilise myocardium- does NOT lower K)
  • Insulin/Dextrose solution (short term shift in K from ECF to ICF)
  • Nebulised salbutamol
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25
Q

Management of hyperkalaemia after initial emergency treatment to actually LOWER total body potassium?

A
  • Calcium resonium -> oral or enema which is more effective
  • Loop diuretics
  • Dialysis if persistent
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26
Q

Why can hyperkalaemia be associated with acidosis?

A

Potassium and hydrogen can be thought of as competitors. As potassium levels rise, fewer hydrogen ions can enter the cells.

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27
Q

What are causes of hypernatraemia?

A
  • Dehydration
  • Osmotic diuresis (eg. hyperosmolar non-ketotic diabetic coma)
  • Diabetes insipidus
  • XS IV saline
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28
Q

How is hypernatremia managed?

A

Rehydration with IV Saline/Hartmann’s

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29
Q

Rate to correct hypernatraemia with 0.9% saline or Hartmann’s?

A

No greater than 0.5mmol/hour (10mmol/24 hours)

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30
Q

Why should you not correct serum sodium conc too rapidly?

A

Risk of cerebral oedema- seizure, coma, death.

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31
Q

What are causes of hypocalcaemia?

A
  • Vit D deficiency
  • CKD
  • Acute pancreatitis
  • hypoparathyroidism (post thyroid/parathyroid surgery)
  • magnesium def (due to end organ PTH resistance)
  • massive blood transfusion
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32
Q

What normally will reveal the cause of hypocalcaemia?

A

Parathyroid hormone levels and clinical history

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33
Q

How is hypocalcaemia managed?

A
  • Oral calcium carbonate if mild
  • IV calcium gluconate when severe eg. tetany (10ml of 10% solution over 10mins)
  • ECG monitoring
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34
Q

What may give falsely low calcium levels?

A

Contamination of blood samples with EDTA

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35
Q

How does hypocalcaemia present?

A
  • dry skin, brittle nails, coarse hair
  • Tetany: Muscle twitching, cramps and spasms
  • perioral paraesthesia
  • seizures
  • Prolonged QT inverval
  • Trousseau sign
  • Chvostek sign
36
Q

Trousseau sign? (hypocalcaemia)

A

Carpal spasm when the brachial artery is occluded by inflating BP cuff and maintaining above systolic. Wrist flexion and fingers drawn together. (95% pts)

37
Q

Chvostek sign? (hypocalcaemia)

A

Tapping over parotid causes facial twitch. (70% pts)

38
Q

What causes hypokalaemia?

A
  • Diuretics
  • Renal tubular acidosis
  • Cushings/Conns
  • Diarrhoea/vomiting
39
Q

What may also cause hypokalaemia?

A

Magnesium deficiency

40
Q

How does hypokalaemia present?

A
  • Muscle weakness
  • Hypotonia
  • ECG changes
41
Q

How is hypokalaemia managed?

A
  • Treat cause
  • Oral supplementation if mild
  • IV fluid if severe with cardiac monitoring
42
Q

Why might sometimes it be difficult to normalise potassium levels?

A

Difficult until magnesium deficiency has been corrected

43
Q

Hypokalaemia with causes alkalosis?

A
  • vomiting
  • thiazide and loop diuretics
  • Cushing’s
  • Conn’s (primary hyperaldosteronism)
44
Q

Hypokalaemia with acidosis causes?

A
  • diarrhoea
  • renal tubular acidosis
  • acetazolamide
  • partially treated diabetic ketoacidosis
45
Q

Causes of low magnesium?

A
  • drugs
  • total parenteral nutrition
  • diarrhoea (acute or chronic)
  • alcohol
  • hypokalaemia
  • hypercalcaemia
  • metabolic disorders eg. Gitleman’s and Bartter’s
46
Q

What drugs can cause hypomagnesaemia?

A

Diuretics and PPI

47
Q

How can hypercalcaemia cause hypomagnesaemia?

A

Eg. secondary to hyperparathyroidism.
Ca and Mg functionally compete for transport in the thick ascending limb of the loop of Henle

48
Q

Clinical presentation of hypomagnesaemia?

A

May be similar to hypocalcaemia:
- paraesthesia
- tetany
- arrhythmias
- decreased PTH secretion= hypocalcaemia
- ECG features

49
Q

What does hypomagnesaemia exacerbate?

A

Digoxin toxicity

50
Q

Mx of hypomagnesaemia if <0.4mmol/L or tetany, arrhythmias or seizures

A
  • IV magnesium replacement eg. 40mmol magnesium sulfate over 24hrs
51
Q

Mx of hypomagnesaemia if >0.4mmol/L

A

oral magnesium salts (10-20mmol oral per day in divided doses)

52
Q

What can occur with oral magnesium salts?

A

Diarrhoea

53
Q

Hyponatraemia may be caused by either what 2 things?

A

water XS or sodium depletion

54
Q

Causes of psuedohyponatraemia

A

hyperlipidaemia (increase in serum volume) or taking blood from a drip arm

55
Q

What aid making a diagnosis of hyponatraemia?

A

Urinary sodium and osmolarity levels

56
Q

Definition of hyponatraemia

A

serum sodium conc of <135mmol/L
usually incidental finding on routine bloods.

57
Q

Severity of hyponatraemia?

A
  • Mild: serum sodium conc 130-135mmol/L
  • Moderate: 125-129
  • Severe: <125

Acute= onset <48hrs
Chronic= onset >48hrs

58
Q

What causes hyponatraemia?

A
  • SIADH
  • Hypothyroidism
  • Thiazides
  • Diarrhoea/Vomiting
  • Psychogenic polydipsia
59
Q

Causes of hypovolemic/clinically dehydrated hyponatraemia?

A

Diuretic stage of renal failure, diuretics, Addisonian crisis

60
Q

Causes of euvolaemic hyponatraemia?

A

SIADH

61
Q

Causes of hypervolaemic hyponatraemia?

A

HF, liver failure, nephrotic syndrome

62
Q

Clinical presentation of hyponatraemia?

A
  • most asymptomatic (esp if mild and chronic)
  • Early symptoms: headache, lethargy, nausea, confusion, muscle cramps
  • Late: seizures, coma, resp arrest
  • rapid changes or severe: vomiting, headaches, drowsiness, seizures, coma, cardio-resp arrest
63
Q

Consequences of chronic hyponatraemia?

A

Increased risk of falls, bone fractures, osteoporosis, gait instability, concentration and cognitive deficits

64
Q

Ix for hyponatraemia?

A
  • History & pt volume status
  • Serum and urine osmolality and urinary sodium conc
  • After initial identification of hyponatraemia measure serum Na again to exclude rapid decreasing Na conc
65
Q

Hyponatraemia inital Mx in all patients?

A

Exclude a spurious result (eg. blood taken from drip arm) and review any meds that may cause hyponatraemia

66
Q

Mx of hyponatraemia if hypovolemic cause suspected?

A

Normal (isotonic) saline (0.9% NaCl). If serum Na rises then supports diagnosis, if falls then consider SIADH.

67
Q

Mx of hyponatraemia if euvolemic cause is suspected? eg. secondary to SIADH

A
  • fluid restrict (500-1000ml/day)
  • Consider Tolvaptan (vasopressin V2-receptor antagonist)
68
Q

Mx of hyponatraemia if hypervolemic cause suspected?

A
  • Fluid restrict (500-1000ml/day)
  • Consider loop diuretis
69
Q

Mx of acute, severe (<120) or symptomatic hyponatraemia?

A
  • Close monitoring, preferably in HDU
  • Hypertonic saline (3% NaCl) used to correct levels more quickly than in chronic pts
70
Q

Mx of acute hyponatraemia with mild or no symptoms?

A

Non-essential parenteral fluids and meds stopped if provoking

71
Q

Mx of Chronic hyponatraemia without moderate or severe symptoms?

A

Non-essential parenteral fluids and meds stopped if provoking

72
Q

Summary of hyponatraemia management?

A

If hypovalaemia: 0.9% isotonic saline
If euvolaemic: Treat underlying cause e.g SIADH by fluid restriction
If acute: 3% hypertonic saline

73
Q

What is the big risk with severe hyponatraemia?

A

cerebral odema= brain herniation

74
Q

Over-rapid correction of hyponatraemia may lead to what?

A

Osmotic demyelination syndrome (Central pontine myelinolysis)

75
Q

What is the pathophysiology behind osmotic demyelination syndrome?

A
  • Develop secondary to astrocyte and ?oligodendrocyte apoptosis.
  • These cells of the glial syncytium are crucial for myelination.
  • Chronic hypon= loss of osmotically active osmolytes eg. glutamate from astrocytes
  • These provide protection against cerebral oedema
  • Organic osmolytes can’t be replaced quick enough when brain vol shrinks in response to correction of hypona
  • dehydrated astrocytes and oligod undergo apoptosis= demyelination
76
Q

Avoid osmotic demyelination syndrome when correcting hyponatraemia?

A

Raise Na+ levels by only 4-6mmol/l in 24hrs

77
Q

Symptoms of osmotic demyelination syndrome?

A

After 2 days and irreversible.
Dysarthria, dysphagia, paraparesis/quadriparesis, seizures, confusion, coma. Locked in syndrome.

78
Q

How do vaptans (vasopressin-ADH receptor antagonists) eg. Tolvaptan work?

A

Act on V2 receptors. Antagonism of V2 receptors results in selctive water diuresis, sparing the electrolytes. Can stimulate thirst receptors leading to the desire to drink free water.

79
Q

What should be avoided in patients who have hypovolemic hyponatremia?

A

Vasopressin/ADH receptor antagonists (vaptans). Also can be hepatotoxic in pts with liver disease.

80
Q

Management of severe hyponatraemia (<120)

A

Hypertonic saline (3% NaCl)

81
Q

What are signs of hypercalcaemia on ECG?

A

Short QT interval, J waves

82
Q

What are signs of hyperkalaemia on ECG?

A

Tall-tented T waves, small P waves, widened QRS.
Leading to a sinusoidal pattern and asystole

83
Q

What are the signs of hypocalcaemia on ECG?

A

Prolonged QT interval

84
Q

What are the signs of hypokalaemia on ECG?

A

U waves, small t waves, prolonged PR, ST depression

85
Q

What are the signs of hypomagnesaemia on ECG?

A

Similar to hypokalaemia: prolonged PR, prolonged QT, ST depression

FINALS (36 decks)

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