Sodium and Calcium Homeostasis

Question 1

What stimuli increase to production of ADH?

Answer 1

Decreased plasma volume sensed by baroreceptors

Increased plasma osmolality sensed by osmoreceptors in the hypothalamus

Question 2

Osmolality is mainly determined by the amount of extracellular water. What are the main mechanisms which regulate water status?

Answer 2

ADH

Thirst

Question 3

How is hyponatraemia defined?

Answer 3

serum sodium <135mmol/l

Question 4

Hyponatraemia is the most common disorder of electrolyte balance in clinical practice. T/F?

Answer 4

True

Question 5

How are hyponatraemia and ADH related?

Answer 5

Hyponatraemia is almost always due to a disorder of water balance as a result of an inability to suppress ADH release resulting in inappropriate retention of water

Question 6

Extrarenal losses of water and sodium can result in hyponatraemia and hypovolaemia. What might result in extra renal losses?

Answer 6

Vomiting
Diarrhoea
Burns
Pancreatitis
Traumatised muscle

Question 7

What might cause hyponatraemia when there is normal sodium but excess water in the body?

Answer 7

Hypothyroidism
Glucocorticoid deficiency
pain
psychiatric disorders
drugs
syndrome of inappropriate ADH secretion

Question 8

What can cause syndrome of inappropriate ADH?

Answer 8

Cancer (lung, leukaemia, lymphoma)
chest disease (pneumonia)
CNS disorders (infections, injury or drugs)

Question 9

A sudden decrease in sodium concentration can cause cerebral oedema. How does this happen?

Answer 9

The decrease in sodium concentration means that water moves out of the blood and into the cells to increase the plasma osmolality and this causes swelling of the cells

Question 10

What change is serum sodium concentration can result is osmotic demyelination syndrome?

Answer 10

Increase in sodium

Question 11

Hyponatraemia is often asymptomatic. T/F?

Answer 11

True

Question 12

What are the symptoms of hyponatraemia?

Answer 12

Mild confusion
Gait instability
Marked confusion
Drowsiness
Seizures

Question 13

Severe and acute hyponatraemia can present with unconsciousness or seizures. How is this treated?

Answer 13

Infusion of hypertonic (4%) saline

Question 14

How is less severe or chronic hyponatraemia managed?

Answer 14

Fluid restriction

Question 15

What is the controversial second line treatment of mild or chronic hyponatraemia?

Answer 15

AVPR2 antagonists

Question 16

What are the most common causes of hypernatraemia?

Answer 16

Loss of water through sweat losses (burns, sepsis), Gi losses, diabetes insidious and osmotic diuresis
inability to access water

Question 17

How can the water deficit in patients with hypernatraemia be calculated?

Answer 17

water deficit - current total body water (50-60% of lean body weight) x ((serum sodium/140)-1)

Question 18

A fluid regime to treat a water deficit causing hypernatraemia should be done gradually. You should aim for a decrease of 10mmol/l of sodium every how many hours?

Answer 18

24 hours

Question 19

What fluid is used when treating a water deficit in a hypernatraemic patient?

Answer 19

IV 5% dextrose

Question 20

What percentage of calcium is reabsorbed in the kidney?

Answer 20

97-99%

Question 21

What affects does vitamin D have on serum calcium levels and how does it achieve this?

Answer 21

Increases Gi absorption of calcium, increases bone resorption and increases renal reabsorption which leads to an overall increase in serum calcium

Question 22

Which hormone is the main regulator of calcium homeostasis?

Answer 22

PTH

Question 23

Bone acts as a reservoir for which mineral?

Answer 23

Calcium

Question 24

What percentage of serum calcium is free or ionised?

Answer 24

45%

Question 25

To which protein is calcium bound in the blood?

Answer 25

Albumin

Question 26

What are the clinical features of hypercalcaemia?

Answer 26

``` Polyuria Polydipsia Nephrolithiasis Nephrocalcinosis Distal renal tubular acidosis Nephrogenic diabetes insipidus anorexia nausea vomiting pancreatitis peptic ulcer disease muscle weakness bone pain osteopenia oestoporosis decreased concentration confusion fatigue ```

Question 27

What affect does hypercalcaemia have on heart rate?

Answer 27

Slows heart rate

Question 28

What can cause hypercalcaemia?

Answer 28

``` Primary hyperparathyroidism (usually single parathyroid adenoma) Malignancy where the tumour is secreting PTH-related peptide ```

Question 29

How can PTH measurement help to determine to cause of hypercalcaemia?

Answer 29

PTH is decreased then malignancy most likely | PTH normal or increased the primary hyperparathyroidism most likely

Question 30

What is classified as mild hypercalcaemia?

Answer 30

<3mmol/l

Question 31

What is classified as moderate hypercalcaemia?

Answer 31

3-3.5mmol/l

Question 32

What is classified as severe hypercalcaemia?

Answer 32

>3.5mmol/l

Question 33

Patients with hyperclacaemia are often hypovolaemia and this impairs renal clearance of calcium. How is this hypovolaemia treated?

Answer 33

0.9% IV saline

Question 34

What drugs are most commonly used when treating hypercalaemia as a result of malignancy?

Answer 34

Bisphosphonates

Question 35

Calcitonin can be given in the treatment of hypercalcaemia. How does this work?

Answer 35

Increases renal calcium excretion and decreases bone resorption

Question 36

Bisphosphonates can be given in the treatment of hypercalcaemia. How does this work?

Answer 36

Inhibit osteoclasts to inhibit bone resorption

Question 37

Glucocorticoids can be given in the treatment of hypercalcaemia. How does this work?

Answer 37

Vitamin D production

Question 38

In some cases parathyroidectomy may be used to treat hypercalcaemia. T/F?

Answer 38

True

Question 39

What are the clinical features of hypocalcaemia?

Answer 39

``` Tetany Peri-orbital numbness Muscle cramps Tingling of the hands and feet Caropedal spasm Laryngospasm Seizures ```

Question 40

What are the possible causes of hypocalcaemia?

Answer 40

Low PTH (following surgery or autoimmune) High PTH due to vitamin D deficiency, chronic renal failure or loss of calcium Drug use Hypomagnesaemia (leading to PTH resistance)

Question 41

How is chronic hypocalcaemia managed?

Answer 41

Vitamin D supplementation and calcium salts

Question 42

How is acute hypocalcaemia treted?

Answer 42

IV calcium replacement possibly alongside magnesium replacement