Hyperkalaemia

Question 1

What is the normal range of potassium?

Answer 1

3.5 - 5.5 mmol/L

Some sources put the upper limit at 5.3 or even 5.0

Question 2

What counts as:
- Mild
- Moderate
- Severe 
Hyperkalaemia?

Answer 2

Mild: >5.5
Moderate: >6.0
Severe: >7.0

Question 3

What are the main clinical manifestations of hyperkalaemia?

Answer 3

Very similar to hypokalaemia:

• weakness in legs, then arms
• cardiac conduction abnormalities: ECG changes and arrhythmias

Question 4

What are the classic ECG changes associated with hyperkalaemia?

Answer 4

ECG changes follow a discernable stage-like pattern:

First; tall, tented T waves, then

QRS complex widening; bundle branch blocks; AV blocks, then

P wave flattening (and subsequent disappearance), then

Sine wave (as QRS complex blends with T wave)

Question 5

What other conditions can cause tall tented T-waves?

Answer 5

Early stages of MI

Rarely, a normal variant

Question 6

Causes of hyperkalaemia

Answer 6

Reduced renal excretion (usually due to severe renal impairment)

Low aldosterone (aldosterone usually blocks renal reabsorption of K; when aldosterone is low, less K is resorbed, and more of it instead lost in the urine)

Release of K from cells (either trans-membrane shift, or cell lysis)

Question 7

Which of the mechanisms of hyperkalaemia is the most common aetiology?

Answer 7

Impaired renal excretion is by far the most common aetiology of clinically relevant hypokalaemia.

Question 8

What are the main causes of impaired urinary excretion?

Answer 8

Renal failure

Hypoaldosteronism (aldosterone’s job is to retain Na, and get rid of K. If there is insufficient aldosterone, more K gets retained).

Question 9

What are the main aetiologies of internal redistribution.

Answer 9

Cell lysis (tumour lysis syndrome, rhabdomyolysis)

Medications (B-blockers, digoxin toxicity)

Insulin deficiency

Acidosis

Exercise

Question 10

What is pseudohyperkalaemia?

Answer 10

When K moves out of cells during blood drawing.

Mechanical trauma can cause hemolysis of the sample

Question 11

Outline the diagnostic evaluation of hyperkalaemia:

Answer 11

1. Exclude pseudohyperkalaemia
2. Evaluate renal function and medication list
3. Evaluate for hypoaldosteronism: check renin, aldosterone, and cortisol.

Question 12

How do you treat hyperkalaemia?

Answer 12

1. Treat underlying cause
2. Buy time with rapid-acting (but transient measures), if there are ECG changes or if K is >6.5.
3. Therapies that remove K from the body

Question 13

Identify some rapidly-acting (but transient) measures to control hyperkalaemia:

Answer 13

IV calcium (antagonises action of K at cell membrane, so stabilises cardiac function)

Insulin (drives K into cells) (given with glucose to prevent hypoglycaemia)

B2-agonist, such as nebulised salbutamol

Question 14

How quickly does IV calcium take to work, and how long does it last?

Answer 14

Time to onset: <5 minutes

Duration: 10-30 minutes

Question 15

How quickly does insulin work (when being used to treat hyperkalaemia)?

Answer 15

Time to onset 15 minutes

Duration: 2 hours

Question 16

How quickly does salbutamol work (when being used to treat hyperkalaemia)?

Answer 16

Time to onset: 15 minutes

Duration: 2 hours

Question 17

What does a patient’s acid-base status have to do with their K levels?

Answer 17

In response to alkalosis, the body shifts K into the cells, in exchange for H+ ions into the blood. This regulates the alkalosis, but results in hypokalaemia.

Question 18

What therapies remove K from the body?

Answer 18

Kayexalate (polysterene polymer bound to sodium. The Na is off-loaded in the intestine in exchange for K which is excreted in the faeces).

Diuretics (loop / thiazide) (with or without saline hydration).

Haemodyalisis

Question 19

When should diuresis be used as a treatment for hyperkalaemia?

Answer 19

Patient must have ALL of the following:

Mild to moderate hyperkalaemia

Renal function not severely impaired (otherwise, diuretics would have limited action)

Patient has other indications for diuresis

Question 20

When is dialysis appropriate treatment for hyperkalaemia?

Answer 20

End stage renal disease
Severe ECG changes
Arrhythmias