Week 4: Electrolyte disturbances

Question 1

Normal sodium range

Answer 1

135-145 mmol/L

Question 2

Normal potassium range

Answer 2

3.5-5.5 mmol/L

Question 3

Normal calcium range

Answer 3

2.2-2.6 mmol/L

Question 4

How are calcium and phosphate levels affected in chronic renal impairment

Answer 4

Low calcium

High phosphate

Question 5

Causes of low potassium

Answer 5

K+ entering cell:

• metabolic alkalosis
• insulin
• adrenergics

K+ can’t come out of cell:
-low magnesium

Loss:

• V and D, osmotic diuresis, diuretics
• Cushing’s

Insufficient dietary intake

Question 6

Causes of high potassium

Answer 6

K+ leaving cell:
-cell lysis (eg chemotherapy, burns, haemolysis)

K+ not entering cell:

• metabolic acidosis
• low insulin
• B blockers

Low renin, aldosterone

Question 7

Why does low magnesium cause hypokalemia

Answer 7

Low magnesium inhibits K from crossing cell membrane

Question 8

Why does Cushing’s cause hypokalemia

Answer 8

Excess cortisol acts like aldosterone and binds to Na/K pump

Question 9

Hyper/hypotension is caused by high/low potassium

Answer 9

Hypertension: high potassium

Hypotension: low potassium

Question 10

Diarrhoea/constipation is caused by high/low potassium

Answer 10

Diarrhoea: high potassium

Constipation: low potassium

Question 11

How do potassium imbalances affect reflexes and muscle strength

Answer 11

BOTH:

• flaccid paralysis
• decreased reflexes

Question 12

Drugs that should be avoided in low potassium

Answer 12

• Insulin
• Adrenergic agonists
• Steroids
• Anything that causes more GI loss eg laxatives, diuretics

Question 13

Drugs that should be avoided in high potassium

Answer 13

• Beta blockers, digoxin
• ACEi (leads to less aldosterone)
• Heparin (blocks synthesis of aldosterone)
• NSAIDs (reduce renin release so less K+ excreted)

Question 14

What drugs/ compounds cause potassium to LEAVE a cell

Answer 14

1. Metabolic acidosis

2. Rhabdomyolysis

Question 15

What drugs/ compounds cause potassium to ENTER a cell

Answer 15

1. Insulin
2. Adrenergics
3. Metabolic alkalosis

Question 16

How do thiazide diuretics and lithium affect calcium levels

Answer 16

Both cause reduced excretion of calcium from kidney

HYPERCALCAEMIA

Question 17

How are sodium and potassium levels affected in chronic renal impairment

Answer 17

Less renin produced

HYPERKALEMIA
HYPONATREMIA

Question 18

How does cortisol affect calcium levels

Answer 18

Inhibits calcium absorption

HYPOCALCAEMIA

(so Cushing’s causes hypocalcaemia and Addison’s causes hypercalcaemia)

Question 19

How does phaeochromocytoma affect calcium levels

Answer 19

HYPERCALCAEMIA

Question 20

How does hyperthyroidism affect calcium levels

Answer 20

HYPERCALCAEMIA

Question 21

How does Addison’s affect sodium levels

Answer 21

HYPONATREMIA

Low aldosterone, less reabsorption of Na

Question 22

How does Conn’s affect sodium levels

Answer 22

HYPERNATREMIA

More aldosterone, more reabsorption of Na

Question 23

How does Cushing’s affect sodium levels

Answer 23

HYPERNATREMIA

More cortisol, similar effect to high aldosterone, more reabsorption of Na

Question 24

How does SIADH affect sodium levels

Answer 24

HYPONATREMIA

More ADH, More Na lost in urine

Question 25

How does Diabetes insipidus affect sodium levels

Answer 25

HYPERNATREMIA Less ADH, less NA lost in urine

Question 26

Management of hypernatremia

Answer 26

IV dextrose

Question 27

Management of hyponatremia

Answer 27

IV sodium Water restriction (caution not to overcorrect or this will cause cerebral oedema

Question 28

Management of hyperkalemia (with specific doses)

Answer 28

1. Calcium gluconate (10%, 5-10ml IV) 2. Insulin (Novorapid 10-20units, IV) 3. Sabutamol (10-20mg, nebuliser) 4. GI cation exchangers 5. Dialysis

Question 29

Management of hypokalemia

Answer 29

IV potassium | IV magnesium if this is also low

Question 30

Management of hypercalcaemia

Answer 30

1. IV fluids (do this first!) | 2. IV bisphosphonates

Question 31

Management of hypocalcaemia

Answer 31

IV calcium

Question 32

Why are pts at risk of electrolyte imbalance after a bladder obstruction

Answer 32

Relief of obstruction leads to post obstruction diuresis Will lose lots of salt and water

Question 33

Signs of hyperkalemia on ECG | state in order at which they appear

Answer 33

1. Tall T wave 2. Widened flattened T wave 3. Prolonged PR interval 4. Widened QRS 5. Loss of P waves 6. Sine wave Also bradycardia at any point

Question 34

Signs of hypokalemia on ECG | state in order at which they appear

Answer 34

1. Flat/ inverted T wave 2. Prominent U waves 3. ST depression 4. Prolonged QU interval (>500ms) 5. Torsade des pointes

Question 35

Signs of hypercalcaemia on ECG | state in order at which they appear

Answer 35

1. Shortened QT interval | 2. J waves (curve on the downward point of the QRS complex)

Question 36

Signs of hypocalcaemia on ECG | state in order at which they appear

Answer 36

Prolonged ST segment leading to QTc prolongation | this is the only change

Question 37

Most common cause of primary hyperparathyroidism

Answer 37

Solitary parathyroid adenoma | Multiple adenomas, parathyroid hyperplasia, parathyroid carcinoma are also causes, but rarer