ChemPath - Potassium and electrolyte cases Flashcards

1
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the methods of potassium regulation

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the renin-angiotensin-aldosterone system

A
  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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the triggers for aldosterone release from the adrenals

A

Angiotensin II
Potassium (high)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the triggers for renin release

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the causes of hyperkalaemia

A
  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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What ECG changes are seen in hyperkalaemia

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How do you manage hyperkalaemia

A
  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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the causes of hypokalaemia

A
  • 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain why renal losses cause hypokalaemia

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the clinical features of hypokalaemia

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What ECG changes are seen in hypokalaemia

A

ST depression
Flat T-waves
U waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What initial investigation should be done for hypokalaemia

A

Aldosterone:renin ratio

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the management for hypokalaemia

A

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

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the differences between the types of renal tubular acidosis

A

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

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

RTA T4 - hypoaldosteronism, hyperkalaemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

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

A

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

Hypovolaemic → 0.9% saline replacement

17
Q

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

A

Check volume status → hypervolaemic

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

18
Q

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

A

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

19
Q

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

A

Assess volume status → euvolaemic
Ix: TFTs

Management: thyroxine replacement

20
Q

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

A

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

21
Q

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

A

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

22
Q

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

A

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