Chem Path: Potassium and electrolytes Flashcards
What is the serum level for K+
3.5 to 5
Explain how the RAAS system works
Low perfusion pressure or low serum sodium triggers renin release from JGA, which in turn converts angiotensinogen from the liver to angio 1, which is converted to angio 2 in the lungs via ACE. This triggers aldosterone release from the adrenals
What does aldosterone do
Increased Na channels in the kidneys to reabsorb water and Na and excrete K via ROMK channels
What receptor does aldosterone work on
Mineralocortocid receptor
How can you classify the reasons for hyperK
Renal Reduced Renin Drugs Cellular secretion Low aldosterone
Explain the renal causes of hyperK
Due to low egfr (low gradient between efferent and afferent), there is need to increase the gradient between the afferent and efferent arterioles. Therefore, you need to dilate afferent. This is done by reducing the angio 2 as it is a vasoconstrictor.
Why can you have reduced renin?
Type 4 renal tubular acidosis seen in diabetic nephropathy
Name which drugs can cause hyperK
NSAIDS, ACEi, ARB, Aldosterone antagonists
How does NSAID cause it
Chronic NSAID use reduces renin and aldosterone
Name some ACEi
Ramipril and lisinopril
Name some ARBs
Losartan and candesartan
Name some aldosterone rec blockers
Spironolactone
What causes low aldosterone?
Addison’s
How does Addison’s present in terms of symptoms?
Dizziness and nausea, tanned and postural hypotension
How is Addisons diagnosed
Short synthacten test
How is Addisons treated?
Hydrocortisone and fludrocortisone
When is K released from cells?
Rhabdomyosis and in acidotic states
What are the ecg changes you can see in hyperK
Peaked T waves
How is hyperK managed?
First, 10ml 10% calcium gluconate. Next 100ml 20% dextrose with 10 units of insulin and insulin drives K+ into cells. Next nebulised salbutamol. Treat underlying cause
What are the causes of hypoK+
GI Loss due to D&V Renal Cells (HypoMg and alkalosis) Excess cortisol Thiazide and loop diuretics
Which drugs cause hypoK
Thiazide diuretics and loop diuretics
How do the diuretics cause hypoK?
Prevents reabsorption of Na at the loop, therefor more Na reaches the distal nephron, this means more Na is crossing the channels, and more K+ is being lost.
What are the 2 syndromes that also prevent Na reabsorption at the loop?
Gitelman and Bartter
How does excess cortisol cause hypoK
It binds to the MR receptors, mimicing aldosterone
What are the cellular/metabolic causes of hypo K
Alkalosis and hypoMg
Symptoms of hypoK+
Muscle weakness, cardiac arryhtmias, polyurea and polkydipsia
What are the ecg changes of hypoK
U waves, torsades de pointes and increased risk of VT
Why is there polyurea and polydipsia?
HypoK can cause nephrogenic DI due to resistance to ADH
How to test for hypoK with hypertension
Aldosterone:renin ratio
How to manage hypoK?
Depends on K+ levels,
If between 3 and 3.5 - PO KCL (2 sandoK tables TDS for 48 hours)
If less than 3 - IV KCL max 10mmol per hour
How do you manage hypovolaemic hypoNa
Volume replacement with 0.9% saline
What are the features of hypervolaemia
Raised JVP, odoema
What can cause hypervolaemia?
Heart failure, nephrotic syndrome, cirrhosis
Why does heart failure cause low Na?
In HF there is low CO, so BP is low, this stimulates osmorecetpors which in turn increases ADH production, which retains more water
How do you manage hypercvolaemia?
Fluid restrict
How does cirrhosis cause hypervolaemia?
In cirrhosis, there is vasodilation due to disrupted NO action escpecially in the splachnic circulation. So BP drops and the osmoreceptors cause ADH release.
What can cause SIADH?
Lung cancer releasing ADH
How do you diagnose SIADH and what are the parameters?
Measure plasma and urine osmolality. There will be reduced plasma osmolality and increased urine osmolality
What do you do before diagnosing SIADH?
Rule out hypovolaemia, hypothyroid and adrenal insufficiency (check cortisol)
What drugs can cause SIADH
SSRIs, TCA, opiates, PPIs, carbamazepine
What are features of central DI
Polyuria, polydipsia and may have bitemporal hemianopia
How is DI diagnosed?
High plasma osmolality and reduced urine osmolality (opposite to SIADH)
What would you exclude before DI?
Diabetes, hypoK, hyperCa,
