Chemical Pathology - Potassium

Question 1

What are some ECG features of hypokalaemia?

Answer 1

• Flattened/inveretd T wave
• Prominent U wave
• Prolonged PR interval
• ST depression

Question 2

What is the breakdown of potassium in the body?

Answer 2

• 90% freely exchangeable
• Rest bound in RBCs, bone and brain tissue

Question 3

What are some causes of hypokalaemia?

Answer 3

Either depletion of shift into cells
- GI loss: vomiting, diarrhoea
- Renal loss: hyperaldosterism (e.g. Conn’s), increased sodium delivery to distal nephron (thiazide + loop diuretics), osmotic diuresis
- Redistribution into cells: insulin, β-agonists, metabolic alkalosis
- rare causes: hypomagnesaemia, rare tubular acidosis type 1 + 2

Question 4

What are the different types of renal tubular acidosis, and some features of them?

Answer 4

Type 1: Most severe, distal failure of H+ excretion + subsequent acidosis + hypokalaemia
Type 2: Milder, proximal failure to reabsorb bicarbonate, leads to acidosis + hypokalaemia
Type 4: aldosterone deficiency or resistance (acidosis + hypokalaemia)

Question 5

What are some clinical features of hypokalaemia?

Answer 5

• Muscle weakness
• Cardiac arrhythmias
• Polyuria
• Polydipsia

Question 6

What is the management of hypokalaemia?

Answer 6

Correct Mg if low
1. K+ 3-3.5 = Oral KCl
2. K+ <3 = IV KCl (max. rate 10mmol/hr)

Treat underlying cause

Question 7

What is a complication of low, untreated hypokalaemia?

Answer 7

Cardiac arrest

Question 8

Which hormone regulates potassium in the body and where?

Answer 8

• Aldosterone
• Cortical Collecting Tubule

Question 9

Which is more common out of hypokalaemia and hyperkalaemia?

Answer 9

Hypokalaemia

Question 10

Which is more dangerous out of hypokalaemia and hyperkalaemia?

Answer 10

Hyperkalaemia

Question 11

What are some causes of hyperkalaemia?

Answer 11

Artefact: Haemolysis, EDTA contamination

Excessive intake: oral (fasting), parenteral, stored blood transfusion

Trascellular movement: acidosis, insuline shortage (DKA), tissue damage/catabolic state (rhabdomyolysis)

Decreased excretion: Acute renal failure, CRF (late), Drugs (K-sparing diuretics/aldosterone antagonists - spironolactone, NSAIDs, ACEi, ARBs), mineralocorticoid deficiency (Addison’s), Type 4 renal tubular acidosis

Question 12

What are some ECG changes associated with hyperkalaemia?

Answer 12

• Loss of p waves
• Tall, tented T waves
• Widened QRS complex
• Prolonged PR interval

Question 13

What ECG abnormality is seen in severe, untreated hyperkalaemia?

Answer 13

Sine wave

Question 14

When should a hyperkalaemic patient be treated?

Answer 14

1. Potassium >5.5 + ECG changes
2. Potassium >6.5, regardless of ECG changes

Question 15

What is the management of a hyperkalaemic patient?

Answer 15

Repeat bloods if K+ >6.5 (possible haemolysis)
1. 10ml 10% calcium gluconate
2. 100ml 20% dextrose + 10IU short-acting insulin
3. ?Nebulised salbutamol
4. ?Calcium resonium
5. Treat underlying cause

Question 16

What is the first-line treatment for a hyperkalaemic patient?

Answer 16

100ml 20% dextrose

Question 17

What are the roles of dextrose and insulin in treating a hyperkalaemic patient

Answer 17

Insulin: drives potassium back into cells
Dextrose: prevents hypoglycaemia

Question 18

What monitoring is required for a hyperkalaemic patient taking digoxin, when and why?

Answer 18

• Cardiac monitoring
• Arrhythmia risk when administering IV calcium gluconate