ChemPath - Potassium and electrolyte cases

Question 1

What are the normal reference ranges for sodium, potassium, urea, and creatinine (and which is the most abundant intracellular cation)

Answer 1

Sodium = 135-145
Potassium = 3.5-5.3 (most abundant intracellular cation)
Urea = 2.5-6.7
Creatinine = 70-100

Question 2

What are the methods of potassium regulation

Answer 2

Loss through the GI tract
Renal regulation and secretion (Angiotensin II and aldosterone)
Movement from intracellular to extracellular

Question 3

Describe the renin-angiotensin-aldosterone system

Answer 3

1. Angiotensinogen is produced by the liver
2. Renin (kidney) converts angiotensinogen → angiotensin I
3. Angiotensin-converting-enzyme (ACE) (lung) converts angiotensin I → angiotensin II
4. Angiotensin II stimulates the adrenal gland to produce aldosterone (zona glomerulosa)
5. Aldosterone stimulates sodium reabsorption by increasing the no. of Na channels in the luminal membrane
6. This creates a negative electrical gradient in the lumen
7. Potassium is secreted into the lumen
8. As sodium is retained, water is also retained

Question 4

What are the triggers for aldosterone release from the adrenals

Answer 4

Angiotensin II
Potassium (high)

Question 5

What are the triggers for renin release

Answer 5

Low BP In the renal artery
Low sodium in the macular densa by the JGA
SNS beta-1 receptor activation

Question 6

What are the causes of hyperkalaemia

Answer 6

1. Renal impairment (reduced GFR)
2. Renin
   - T4 Renal tubular acidosis (diabetic nephropathy)
   - NSAIDs
3. Drugs - ACEi, ARBs, spironolactone
4. Addison’s disease
5. release from cells - rhabdomyolysis (muscle death), acidosis (H+/K+ exchange)

Question 7

What ECG changes are seen in hyperkalaemia

Answer 7

Peaked T wave (early)
Broad QRS
Flat P-wave
Prolonged PR (and bradycardia)
Sine wave (latest)

Question 8

How do you manage hyperkalaemia

Answer 8

1. 10ml 10% calcium gluconate (stabilise)
2. 100ml of 20% dextrose
3. 10U insulin (must be given together)
4. Nebulised salbutamol - drives potassium into the cell
5. Treat the underlying cause

Question 9

What are the causes of hypokalaemia

Answer 9

• GI losses (diarrhoea, vomiting, fistulas)
• Renal loss
  - Conn’s (Hyperaldosteronism), Cushing’s
  - Bartter syndrome, thiazide/loop diuretics (increased Na+ delivery to DCT)
  - Hyperglycaemia (osmotic diuresis)
• Redistribution into cells
  - Insulin/insulinomas
  - beta-agonists
  - Alkalosis
  Rare causes
  - Hypomagnesaemia
  - Renal tubular acidosis T1, T2

Question 10

Explain why renal losses cause hypokalaemia

Answer 10

The triple (loop)/co (thiazides)-transporter is blocked → less Na absorbed in the ascending loop → more sodium is transported to the distal convoluted tubule → nephron cortex is more electronegative → more Na is reabsorbed in the distal convoluted tubules → lumen is negative → potassium moves down the gradient through ROMK channels

Question 11

What are the clinical features of hypokalaemia

Answer 11

Muscle weakness
Cardiac arrhythmias
Polyuria and polydipsia (nephrogenic DI from low K+ or a high Ca2+)

Question 12

What ECG changes are seen in hypokalaemia

Answer 12

ST depression
Flat T-waves
U waves

Question 13

What initial investigation should be done for hypokalaemia

Answer 13

Aldosterone:renin ratio

Will differentiate between aldosterone excess (Conn’s) and other causes
Conn’s - A:R ratio will be HIGH (renin very low)

Question 14

What is the management for hypokalaemia

Answer 14

3-3.5
Oral KCL (2 SandoK tablets, TDS) + recheck K+

<3
IV KCL (max rate 10mmol/h)
Treat the underlying cause

Question 15

What are the differences between the types of renal tubular acidosis

Answer 15

RTA T1 - distal RTA, less H+ excretion, hypokalaemia

RTA T2 - proximal distal RTA, less HCO3 reabsorption, hypokalaemia

RTA T4 - hypoaldosteronism, hyperkalaemia

Question 16

A 67-year-old man was started on bendroflumethiazide for hypertension 2 weeks ago. He has had D& V for 2 days. He has dry mucous membranes and decreased skin turgor. Urea & electrolytes:
- Na+: 129 mmol/L
- K+: 3.5 mmol/L
- Ur: 8.0 mmol/L
- Cr: 100 μmol/L

How do you manage this patient

Answer 16

Check volume status (eyes, skin turgor, mucous membranes)

Hypovolaemic → 0.9% saline replacement

Question 17

A 57yo woman has breathlessness worse on lying flat. Her past medical history includes a Non-STEMI. She is on ramipril, bisoprolol, aspirin and simvastatin. She has elevated JVP, bi-basal crackles and bilateral leg oedema. Urea & electrolytes:
○ Na+: 128 mmol/L
○ K+: 4.5 mmol/L
○ Ur: 8.0 mmol/L
○ Cr: 100 μmol/L

How do you manage this patient

Answer 17

Check volume status → hypervolaemic

Fluid restrict to 1L/1.5L
Treat the underlying cause (heart failure)

Question 18

A 55-year-old man has jaundice. He has a past history of excessive alcohol intake. He has multiple spider naevi, shifting dullness and splenomegaly. Urea & electrolytes:
○ Na+: 122 mmol/L
○ K+: 3.5 mmol/L
○ Ur: 2.0 mmol/L
○ Cr: 80 μmol/L

How do you manage this patient

Answer 18

Assess volume status → hypervolaemia
Ix: LFTs
Fluid restriction
Treat the underlying cause (cirrhosis)

Question 19

A 40yo woman presents with fatigue, weight gain, dry skin and cold intolerance. O/E she looks pale. Urea & electrolytes:
○ Na+: 130 mmol/L
○ K+: 4.2 mmol/L
○ Ur: 5.0 mmol/L
○ Cr: 65 μmol/L

How do you manage this patient

Answer 19

Assess volume status → euvolaemic
Ix: TFTs

Management: thyroxine replacement

Question 20

A 45-year-old woman presents with dizziness and nausea. On examination she looks tanned and has postural hypotension. Urea & electrolytes:
○ Na+: 128 mmol/L
○ K+: 5.5 mmol/L
○ Ur: 9.0 mmol/L
○ Cr: 110 μmol/L

How do you manage this patient

Answer 20

Assess volume status → euvolaemic
Ix: short synACTHen test
Management: hydrocortisone + fludrocortisone

Question 21

A 62-year-old man has chest pain, cough and weight loss. He looks cachectic. He has a 30-pack-year smoking history. Urea & electrolytes:
○ Na+: 125 mmol/L
○ K+: 3.5 mmol/L
○ Ur: 7.0 mmol/L
○ Cr: 85 μmol/L

How do you manage this patient

Answer 21

Assess volume status → euvolaemic
Ix: Plasma and urine osmolarity, CXR
Management: Fluid restrict

Question 22

What features in this patient predisposes them to hyperkalaemia

A 65-year-old man with type 2 diabetes mellitus and hypertension presents with malaise and drowsiness. He is on a basal bolus insulin regimen, ramipril, amlodipine, simvastatin and aspirin

Answer 22

Reduced GFR from DM and HTN
ACEi
Adrenal insufficiency
Diabetic renal acidosis