Potassium

Question 1

What is potassium important?

Answer 1

strict regulation is crucial for vital physiologic processes:

• resting membrane potenital
• propagation of AP
• hormone secretion and action
• vascular tone
• systemic blood pressure control
• acid-base homeostasis
• gastrointestinal motility
• glucose and insulin metabolism
• mineralocorticoid action
• renal concentrating ability
• fluid and electrolyte balance

Question 2

Why is maintaining potassium levels at the correct level important?

Answer 2

hypokalaemia or hyperkalaemia patients have an increased rate of death from any cause
- deranged potassium levels are associated with progression of cardiac and kidney disease and interstitial fibrosis

Question 3

In a healthy individual how is potassium lost?

Answer 3

via kidneys 90%

via gut and skin 10%

Question 4

What is the reference serum potassium concentration?

Answer 4

3.5-5.3 mmol/L

Question 5

Why is potassium relevant in terms of food?

Answer 5

approximate levels of extracellular K in an adult are 60-80 mmol total extracellular potassium and 20-25mmol of total plasma potassium

meals may contain more potassium than the total plasma potassium content
rapid clearance by renal and extra-renal mechanisms reduce variation in plasma potassium to no more than 10%

Question 6

What are examples of high potassium foods?

Answer 6

medium banana (110)
1/2 papaya (100)
1/2 cup prune juice (95)
1/4 cup of raisins (69)
medium mango (84) or kiwi (62)
1/2 cup of cubed cantaloupe (55) or diced honeydew melon (5)
medium pear (50)

Question 7

What does potassium stimulate in the serum and in the urine?

Answer 7

serum
- K stimulates ATPase which increases hormone release (insulin, catecholamines, aldosterone)

urine
- K stimulates renal cell uptake and secretion of K

Question 8

What is the main regulator of K?

Answer 8

kidney = main regulator of total body K

Question 9

When K is taken in how it redistributed between ECF and ICF?

Answer 9

through hormones, acid base status, plasma osmolarity and potassium sequestration into liver and muscle

Question 10

Within the kidney which regions filter K?

Answer 10

PCT - 60-70%
Ascending loop = 20-30%
Dct - 10% = Fine tuning by aldosterone K+/H+ for Na

of 600mmol/day filter, about 100 is excreted

Question 11

When K levels are too high how are they returned to normal levels?

Answer 11

insulin and catecholamines act to increase K uptake into cells
Aldosterone acts on the kidney to increase its excretion

Question 12

What is the effect of aldosterone ?

Answer 12

exchange of Na for H+ or K+
net loss of K
net gain of sodium

Question 13

What are the causes of an overactive RAS system and what does it lead to ?

Answer 13

Hypokalaemia

• Conn’s = aldosterone
• Cushings= cortisol
• Renal artery stenosis = renin

Question 14

What are the causes of an underactive RAS system and what does it lead to/

Answer 14

hyperkalaemia

• adrenal insufficiency
• ACE inhibitors
• Spironolactone

Question 15

How are insulin and catecholamines involved in regulating K?

Answer 15

Drive cellular uptake of K via activation of Na/K ATPase

occurs in the liver, skeletal muscle (catecholamines), adipose tissue (insulin)

Question 16

What does metabolic acidosis cause in relation to K?

Answer 16

increases plasma K

• inhibition of renal tubular K secretion
• shift of K from ICF to ECF

MOA:
- inter-relationship between ECF H+ and K+
- ECF H+ affects K+ entry into cells
therefore if H enters cells (ICF) instead of K the K in the ECF rises => hyperkalaemia

Question 17

What does metabolic alkalosis cause in relation to K?

Answer 17

reduced plasma K

Question 18

In terms of acidosis what happens at the kidneys in relation to K?

Answer 18

H+ load blocks K excretion therefore you get hyperkalaemia

• with increased H+ (low pH more H+ is exchanged for Na
• consequence of this is loss of H+ rather than K+

Question 19

What happens to K in terms of an acidosis being caused by hyper-cholaemia?

Answer 19

hypercholaemia due to bicarbonate loss e.g renal tubular acidosis
- the Cl- cannot pass the plasma membrane to maintain neutrality therefore K is lost from cells and loss in urine

Question 20

What happens in the serum and in the urine during alkalosis?

Answer 20

serum

• H+ moves from cells to ECF as buffer
• to preserve electrochemical neutrality K and Na enter the cell therefore ECF K falls

Urine
- alkalosis increases renal K loss

Question 21

What happens to K during insulin deficiency e.g. DKA?

Answer 21

movement of water and K from ICF to ECF
then in the urine the increased fluid delivery to the lumen causes increased K excretion
=> hyperglycaemia, diuretics, poorly absorbed anions

Question 22

What is defined as hyperkalaemia?

Answer 22

K>5mmol/L
if>6.5- 7 =altered electrical excitability
medical emergency at >7.5
=> arrhythmias, cardiac arrests, ECG changes (tall T waves, wide QRS, wide PR)

Question 23

What are the main causes of hyperkalaemia?

Answer 23

increased intake  (oral or IV)
Reduced excretion 
Altered distribution 
Factitious 
Drugs

Question 24

What are the causes of reduced excretion of K?

Answer 24

renal failure 
mineralocorticoid deficiency (Addison's)
Tubular defects

Question 25

What are the causes of altered distribution of K?

Answer 25

acidosis
insulin deficiency
crush injury, haemolysis, tumour lysis
hyperkalaemic periodic paralysis

Question 26

What are the factitious causes of hyperkalaemia?

Answer 26

improper collection

haematological disorders

Question 27

What drugs can cause hyperkalaemia?

Answer 27

ACEI, ARBs
potassium sparing diuretics
potassium supplements

Question 28

What are the commonest causes of hyperkalaemia?

Answer 28

chronic kidney disease

redistribution secondary to acidosis

Question 29

What are the consequences of hyperkalaemia?

Answer 29

neuromuscular - weakness, parasthesia, paralysis
Gastrointestinal - nausea, vomiting, pain, ileus
Cardiovascular - conduction defects, arrhythmias, cardiac arrest

Question 30

How do you treat acute hyperkalaemia >6.5?

Answer 30

Cardioprotection

• calcium gluconate to increase threshold potentials
• ECG monitor
• care with pts on digoxin

Redistribution

• glucose + insulin
• beta agonist
• bicarbonate

removal

• loop diuretic - furosemide, bumetanide
• ion exchange resins
• dialysis /haemofiltration

Question 31

How is chronic hyperkalaemia treated?

Answer 31

commonest cause is chronic kidney disease so its important to treat the underlying cause
low potassium diet
correction of metabolic acidosis

Question 32

What are some common causes of artefactual high k?

Answer 32

overnight storage prior to sample separation

taken from a vein above an IV infusion of potassium/dextrose

blood taken into EDTA anticoagulant

also haematological malignancies with very high WBC or plt

Question 33

What are the main causes of hypokalaemia?

Answer 33

Losses

• GI= fistula, diarrhoea, purgative abuse, villous adenoma
• Renal = loop diuretics, renal tubular acidosis, mineralocorticoid excess

Inadequate intake
- usually only appears if superimposed on other losses - diarrhoea, diuretics

Redistribution
- insulin, alkalosis, salbutamol, hypokalaemia periodic paralysis, familial periodic paralysis

Question 34

What are the consequences of hypokalaemia?

Answer 34

skeletal muscle - weakness, paralysis
GI - paralytic ileus
Kidney - impaired concentrating ability, tubular defects
Cardiac - conduction defects, arrhythmias, digoxin toxicity

Question 35

What ECG changes are apparent in hypokalaemia?

Answer 35

flattened T wave becoming T wave inversion
ST depression
prominent P wave and prolonged PR interval
U waves - V2-4

torsades de point

Question 36

What is the treatment for hypokalaemia?

Answer 36

oral intake - normal intake + 60mmol/day
equivalent - 8 slow K tablets, 10 effervescent K tablets

IV treatment

• 10mmol/hr max
• dilute potassium ampoule - NEVER straight from ampoule >40mmol/L