Potassium and Electrolytes Flashcards
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 micromol/L
Management?
Clinical assessment = hypovolaemic
DD: diarrhoea, vomiting, diuretics, salt
Management: Volume replacement with 0.9% saline
A 57-year-old 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, bibasal crackles and bilateral leg oedema. Urea & electrolytes: Na+: 128 mmol/L K+: 4.5 mmol/L Ur: 8.0 mmol/L Cr: 100 micromol/L
Management?
Clinical assessment = hypervolaemic
DD: cardiac failure
Management: fluid restriction and treat the underlying cause
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 micromol/L
Management?
Clinical assessment = hypervolaemic
DD: Cirrhosis
Management: fluid restriction, treat the underlying cause
A 40-year-old woman presents with fatigue, weight gain, dry skin and cold intolerance. On examination she looks pale.
Urea & electrolytes: Na+: 130 mmol/L K+: 4.2 mmol/L Ur: 5.0 mmol/L Cr: 65 micromol/L
Management?
Clinical assessment = euvolaemia
DD: hypothyroidism
Management: TFTs, treat the underlying cause (thyroxine replacement)
A 45-yeard-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 micromol/L
Management?
Clinical assessment = euvolaemia
DD: Adrenal insufficiency
Management: Short synacthen test, treat the underlying cause (hydrocostisone and fludrocortisone)
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 micromol/L
Management?
Clinical assessment = euvolaemic
DD: SIADH
Management: Plasma and urine osmolality, treat the underlying cause
A 20-year-old man presents with polyuria and polydipsia. On examination he has bitemporal hemianopia.
Urea & electrolytes: Na+: 150 mmol/L K+: 4.0 mmol/L Ur: 5.0 mmol/L Cr: 70 micromol/L
Management?
Clinical assessment = Hypernatraemia
DD: DI
Management: Serum glucose (exclude diabetes mellitus) Serum potassium (exclude hypokalaemia) Serum calcium (exclude hypercalcaemia) Plasma & urine osmolality Water deprivation test
Causes of hyperkalaemia
Renal impairment: reduced renal excretion
Drugs: ACE inhibitors, ARBs, spironolactone
Low aldosterone (Addison’s disease, type 4 renal tubular acidosis - low renin, low aldosterone)
Released from cells: rhabdomyelosis, acidosis
ECG in hyperkalaemia
Peaked T wave
Management of hyperkalaemia
10ml 10% calcium gluconate
50ml 50% dextrose + 10 units of insulin
Nebulized salbutamol
Treat the underlying cause
Initial investigation in hypertension with hypokalaemia
Aldosterone: Renin ratio
Normal serum concentration of potassium
Potassium is the most abundant intracellular cation
Serum concentrations: 3.5-5mmol/L
Which hormones are involved in renal regulation of potassium
Angiotensin II
Aldosterone
Renin-angiotensin-aldosterone system
Angiotensinogen (from liver) –> angiotensin I (renin from JGA)
Angiotensin I –> angiotensin II (ACE) (in lungs)
Angiotensin II –> aldosterone (from adrenal)
Aldosterone increases secretion of renin from JGA
What stimulates renin secretion in the kidney
Na+ and H2O retention
Increased blood volume/pressure
What drives potassium secretion due to aldosterone actions
Sodium reabsorption through epithelial sodium channels leads to tubular lumen negative electrical potential, driving potassium secretion
MOA aldosterone
Aldosterone increases number of open sodium channels in the luminal membrane
Increased sodium reabsorption
Makes the lumen electronegative and creates an electrical gradient
Potassium is secreted into the lumen
What are the stimuli for aldosterone secretion
Angiotensin II
Potassium
Main causes of hyperkalaemia
Reduced GFR Reduced renin (type 4 renal tubular acidosis i.e. diabetic nephropathy, NSAIDs) ACE inhibitors Angiotensin II receptor blocker Addison's disease Aldosterone antagonist Rhabdomyelosis, acidosis
What stimulates renin secretion
Aldosterone
Causes of hypokalaemia
GI loss Renal loss (hyperaldosteroinism, excess cortisol, increased sodium delivery to distal nephron, osmotic diuresis) Redistribution into the cells (insulin, beta-agonists, alkalosis) Rare causes: renal tubular acidosis types 1 and 2, hypomagnesaemia
What are the renal causes of potassium loss
Loop diuretics, Bartter syndrome in collecting duct.
Thiazide diuretics and Gitelman syndrome in distal collecting tubule
Principal cells involved in potassium absorption in the kidney
Cortical collecting tubule
Clinical features of hypokalaemia
Muscle weakness
cardiac arrhythmia
Polyuria and polydipsia (nephrogenic DI)
Screening test in a patient with hypokalaemia and hypertension
Aldosterone: renin ratio
Management of a patient with hypokalaemia
Serum potassium 3-3.5mmol/L: oral potassium chloride (two SandoK tablets TDS for 48 hours), recheck serum potassium
Serum potassium <3mmol/L: IV potassium choloride, maximum rate 10mmol/hour, rates >20mmol/hour are highly irritating to peripheral veins
Treat underlying cause (e.g. spirinolactone)
