Chem Path: Potassium and electrolytes

Question 1

What is the serum level for K+

Answer 1

3.5 to 5

Question 2

Explain how the RAAS system works

Answer 2

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

Question 3

What does aldosterone do

Answer 3

Increased Na channels in the kidneys to reabsorb water and Na and excrete K via ROMK channels

Question 4

What receptor does aldosterone work on

Answer 4

Mineralocortocid receptor

Question 5

How can you classify the reasons for hyperK

Answer 5

Renal
Reduced Renin
Drugs
Cellular secretion 
Low aldosterone

Question 6

Explain the renal causes of hyperK

Answer 6

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.

Question 7

Why can you have reduced renin?

Answer 7

Type 4 renal tubular acidosis seen in diabetic nephropathy

Question 8

Name which drugs can cause hyperK

Answer 8

NSAIDS, ACEi, ARB, Aldosterone antagonists

Question 9

How does NSAID cause it

Answer 9

Chronic NSAID use reduces renin and aldosterone

Question 10

Name some ACEi

Answer 10

Ramipril and lisinopril

Question 11

Name some ARBs

Answer 11

Losartan and candesartan

Question 12

Name some aldosterone rec blockers

Answer 12

Spironolactone

Question 13

What causes low aldosterone?

Answer 13

Addison’s

Question 14

How does Addison’s present in terms of symptoms?

Answer 14

Dizziness and nausea, tanned and postural hypotension

Question 15

How is Addisons diagnosed

Answer 15

Short synthacten test

Question 16

How is Addisons treated?

Answer 16

Hydrocortisone and fludrocortisone

Question 17

When is K released from cells?

Answer 17

Rhabdomyosis and in acidotic states

Question 18

What are the ecg changes you can see in hyperK

Answer 18

Peaked T waves

Question 19

How is hyperK managed?

Answer 19

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

Question 20

What are the causes of hypoK+

Answer 20

GI Loss due to D&V
Renal
Cells (HypoMg and alkalosis)
Excess cortisol 
Thiazide and loop diuretics

Question 21

Which drugs cause hypoK

Answer 21

Thiazide diuretics and loop diuretics

Question 22

How do the diuretics cause hypoK?

Answer 22

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.

Question 23

What are the 2 syndromes that also prevent Na reabsorption at the loop?

Answer 23

Gitelman and Bartter

Question 24

How does excess cortisol cause hypoK

Answer 24

It binds to the MR receptors, mimicing aldosterone

Question 25

What are the cellular/metabolic causes of hypo K

Answer 25

Alkalosis and hypoMg

Question 26

Symptoms of hypoK+

Answer 26

Muscle weakness, cardiac arryhtmias, polyurea and polkydipsia

Question 27

What are the ecg changes of hypoK

Answer 27

U waves, torsades de pointes and increased risk of VT

Question 28

Why is there polyurea and polydipsia?

Answer 28

HypoK can cause nephrogenic DI due to resistance to ADH

Question 29

How to test for hypoK with hypertension

Answer 29

Aldosterone:renin ratio

Question 30

How to manage hypoK?

Answer 30

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

Question 31

How do you manage hypovolaemic hypoNa

Answer 31

Volume replacement with 0.9% saline

Question 32

What are the features of hypervolaemia

Answer 32

Raised JVP, odoema

Question 33

What can cause hypervolaemia?

Answer 33

Heart failure, nephrotic syndrome, cirrhosis

Question 34

Why does heart failure cause low Na?

Answer 34

In HF there is low CO, so BP is low, this stimulates osmorecetpors which in turn increases ADH production, which retains more water

Question 35

How do you manage hypercvolaemia?

Answer 35

Fluid restrict

Question 36

How does cirrhosis cause hypervolaemia?

Answer 36

In cirrhosis, there is vasodilation due to disrupted NO action escpecially in the splachnic circulation. So BP drops and the osmoreceptors cause ADH release.

Question 37

What can cause SIADH?

Answer 37

Lung cancer releasing ADH

Question 38

How do you diagnose SIADH and what are the parameters?

Answer 38

Measure plasma and urine osmolality. There will be reduced plasma osmolality and increased urine osmolality

Question 39

What do you do before diagnosing SIADH?

Answer 39

Rule out hypovolaemia, hypothyroid and adrenal insufficiency (check cortisol)

Question 40

What drugs can cause SIADH

Answer 40

SSRIs, TCA, opiates, PPIs, carbamazepine

Question 41

What are features of central DI

Answer 41

Polyuria, polydipsia and may have bitemporal hemianopia

Question 42

How is DI diagnosed?

Answer 42

High plasma osmolality and reduced urine osmolality (opposite to SIADH)

Question 43

What would you exclude before DI?

Answer 43

Diabetes, hypoK, hyperCa,