1. Disorders of Potassium Balance

Question 1

What are the points of regulation of potassium?

Answer 1

Intake
Cellular distribution
Renal excretion

Question 2

What mediators affect the cellular distribution of potassium?

Answer 2

Insulin and catecholamines
pH
Cell turnover
Osmolality

Question 3

How do insulin and catecholamines affect the cellular distribution of potassium?

Answer 3

Stimulate Na/K to reduce serum K+

Question 4

What affect does pH have on the cellular distribution of potassium?

Answer 4

H/K pump means that when a drop in pH increases K+
Acidosis= high potassium
Alkalosis= low potassium

Question 5

How does cell turnover affect K+ levels?

Answer 5

Vast majority of K+ is intracellular: released when cells are broken and taken up when new cells created

Question 6

Which cells excrete K+ in the distal tubule?

Answer 6

Principal cells

Question 7

Which cells excrete H+ in the distal tubule?

Answer 7

Intercalated cells

Question 8

Describe how principal cells excrete potassium

Answer 8

Na+ in from tubule from eNAC
3Na+ swapped for 2K+ and Na resorbed
K+ follows negative gradient (HCO3-) to be excreted into the tubule

Question 9

What is hypokalaemia defined as?

Answer 9

<3.5mmol/L

Question 10

What are the intracellular shift causes of hypokalaemia?

Answer 10

Cell growth
Due to insulin or catecholamines
-B-agonists in asthma, COPD and pre-term labour
-Refeeding syndrome

Question 11

What B-agonist is given in pre-term labour?

Answer 11

Tocolytics

Question 12

Classify renal causes of hypokalaemia

Answer 12

Due to aldosterone

K+ wasting nephropathies

Question 13

What are the aldosterone related reasons for excess K+ secretion?

Answer 13

Diuretics: increase Na+ excretion and switch on aldosterone
Vomiting: metabolic acidosis
Salt wasting nephropathies
Conn’s syndrome

Question 14

What are the causes of K+ wasting nephropathies?

Answer 14

Low Mg
Drug toxicity
Renal tubular acidosis
Polyuria

Question 15

What are the consequences of hypokalaemia?

Answer 15

Muscle weakness/paralysis
ECG changes and arrhythmia
Urinary concentration deficits
Hypertension and stroke

Question 16

What are the problems with giving potassium IV?

Answer 16

Concentrated causes phlebitis
Dextrose increases insulin which will lower K+
Saline results in volume overload

Question 17

Define hyperkalaemia

Answer 17

> 5.4 mmol/L

Question 18

What are the causes of hyperkalaemia due to increased intake?

Answer 18

Blood transfusion
Penicillin and dialysate
TPN

Question 19

What are the causes of extracellular shift of K+?

Answer 19

Hyperosmolarity: DKA, hyperglycaemia
Cell destruction: rhabdomyolysis and tumour lysis syndrome
Drugs: beta blockers, digoxin, succinylcholine
Acidaemia

Question 20

What are the causes of reduced renal excretion of K+?

Answer 20

Renal failure
Hypoaldosteronism
Drugs
Gordon’s syndrome

Question 21

What is Gordon’s syndrome?

Answer 21

Cl- shunt so less negative charge in lumen

Question 22

What are the causes of hypoaldosteronism?

Answer 22

Addison’s disease
Diabetes: reduced renin
ACE/aldosterone/renin inhibitors
Spironolactone

Question 23

What are the consequences of hyperkalaemia?

Answer 23

Muscle weakness/paralysis

ECG changes and arrhythmia

Question 24

What changes are seen on the ECG in hyperkalaemia?

Answer 24

Peaked T wave and long QRS

Question 25

What is the treatment for high K+?

Answer 25

Prevent arrhythmia: calcium gluconate protects cardiac membranes
Stop all sources of K+
Insulin and albuterol to promote intracellular shift
Promote renal excretion

Question 26

What can be used to increase renal excretion of K+?

Answer 26

Diuretics, 
fludrocortisone, 
polystyrene, 
resins 
dialysis