1. Disorders of Potassium Balance Flashcards
What are the points of regulation of potassium?
Intake
Cellular distribution
Renal excretion
What mediators affect the cellular distribution of potassium?
Insulin and catecholamines
pH
Cell turnover
Osmolality
How do insulin and catecholamines affect the cellular distribution of potassium?
Stimulate Na/K to reduce serum K+
What affect does pH have on the cellular distribution of potassium?
H/K pump means that when a drop in pH increases K+
Acidosis= high potassium
Alkalosis= low potassium
How does cell turnover affect K+ levels?
Vast majority of K+ is intracellular: released when cells are broken and taken up when new cells created
Which cells excrete K+ in the distal tubule?
Principal cells
Which cells excrete H+ in the distal tubule?
Intercalated cells
Describe how principal cells excrete potassium
Na+ in from tubule from eNAC
3Na+ swapped for 2K+ and Na resorbed
K+ follows negative gradient (HCO3-) to be excreted into the tubule
What is hypokalaemia defined as?
<3.5mmol/L
What are the intracellular shift causes of hypokalaemia?
Cell growth
Due to insulin or catecholamines
-B-agonists in asthma, COPD and pre-term labour
-Refeeding syndrome
What B-agonist is given in pre-term labour?
Tocolytics
Classify renal causes of hypokalaemia
Due to aldosterone
K+ wasting nephropathies
What are the aldosterone related reasons for excess K+ secretion?
Diuretics: increase Na+ excretion and switch on aldosterone
Vomiting: metabolic acidosis
Salt wasting nephropathies
Conn’s syndrome
What are the causes of K+ wasting nephropathies?
Low Mg
Drug toxicity
Renal tubular acidosis
Polyuria
What are the consequences of hypokalaemia?
Muscle weakness/paralysis
ECG changes and arrhythmia
Urinary concentration deficits
Hypertension and stroke
What are the problems with giving potassium IV?
Concentrated causes phlebitis
Dextrose increases insulin which will lower K+
Saline results in volume overload
Define hyperkalaemia
> 5.4 mmol/L
What are the causes of hyperkalaemia due to increased intake?
Blood transfusion
Penicillin and dialysate
TPN
What are the causes of extracellular shift of K+?
Hyperosmolarity: DKA, hyperglycaemia
Cell destruction: rhabdomyolysis and tumour lysis syndrome
Drugs: beta blockers, digoxin, succinylcholine
Acidaemia
What are the causes of reduced renal excretion of K+?
Renal failure
Hypoaldosteronism
Drugs
Gordon’s syndrome
What is Gordon’s syndrome?
Cl- shunt so less negative charge in lumen
What are the causes of hypoaldosteronism?
Addison’s disease
Diabetes: reduced renin
ACE/aldosterone/renin inhibitors
Spironolactone
What are the consequences of hyperkalaemia?
Muscle weakness/paralysis
ECG changes and arrhythmia
What changes are seen on the ECG in hyperkalaemia?
Peaked T wave and long QRS
What is the treatment for high K+?
Prevent arrhythmia: calcium gluconate protects cardiac membranes
Stop all sources of K+
Insulin and albuterol to promote intracellular shift
Promote renal excretion
What can be used to increase renal excretion of K+?
Diuretics, fludrocortisone, polystyrene, resins dialysis
