Electrolytes

Question 1

What are the renal causes of hyperkalaemia?

Answer 1

• AKI
• CKD
• hyperkalaemic renal tubular acidosis

Question 2

List drugs which can directly or indirectly cause hyperkalaemia

Answer 2

ACE inhibitors 
ARBS
Potassium sparing diuretics 
NSAIDS
Digoxin (toxic levels)
Trimethoprim 
Heparin 
Ciclosporins 
Tacrolimus 
Nicorandil

Question 3

In DKA, what happens to potassium levels and why?

Answer 3

Increase. There is a lack of insulin causing potassium to shift from intracellular to extracellular space.

Question 4

Why might Addison’s disease cause hyperkalaemia?

Answer 4

Aldosterone promotes excretion of potassium from the kidney. In Addison’s disease, the adrenal glands are unable to produce adequate levels of aldosterone. This results in reduced renal excretion of potassium.

Question 5

What would warrant URGENT treatment for hyperkalaemia?

Answer 5

A potassium level of 6.5 mmol/L or above and/or hyperkalaemia associated ECG changes. (All patients with high potassium will require some further management and monitoring)

Question 6

What drug can be given to stabilise the myocardium if there are hyperkalaemia associated ECG changes?

Answer 6

calcium gluconate 10% - will help to stabilise for 30-60 minutes and reduce risk of fatal arrhythmia. You can give further doses if ECG changes persist.

Question 7

If a patient has a potassium of 7.5 mmol/L, what can be administered to shift potassium from the extracellular to intracellular space?

Answer 7

IV soluble insulin (5-10 units) with 50 mL glucose 50% given over 5-15 minutes. Can repeat if necessary or start continuous infusion.
Salbutamol by slow injection or nebulisers (use with caution in patients with CVD).

Question 8

How can we remove potassium from the body?

Answer 8

Calcium resonium - removal via GI tract
Correct the underlying cause i.e kidney function
Haemodialysis - last resort for resistant hyperkalaemia which has failed to respond to all other therapies.

Question 9

You suspect a hyponatraemic patient could have SIADH, why would you run a serum cortisol?

Answer 9

To rule out Addison’s disease as a potential cause. The serum cortisol will be reduced in Addison’s disease.

Question 10

You suspect a patient has SIADH, why would you check TFTs?

Answer 10

Hypothyriodism is a potential cause of SIADH. Look for low T3 and high TSH.

Question 11

In a healthy individual with a low serum sodium osmolality, what would you expect the urine osmolality to be?

Answer 11

Also low, the kidneys should be working hard to retain sodium.

Question 12

In a patient with SIADH, what happens with water balance?

Answer 12

the excess of ADH causes water retention.

Question 13

In SIADH, what happens with sodium/solute balance at the kidney?

Answer 13

Although excess ADH causes water retention, it does not cause solute retention, therefore urine osmolality will be high (concentrated with sodium) despite a low serum sodium.

Question 14

What imaging will you order when trying to establish the cause of SIADH?

Answer 14

Chest x-ray
CT chest
You are looking for small cell lung cancer

Question 15

In SIADH, would you expect the patient to be hypervolaemic, euvolaemic or hypovolaemic?

Answer 15

Likely to be euvolaemic

Question 16

If a patient has a diagnosis of SIADH and has a urine osmolality of >20, what would an appropriate management plan?

Answer 16

Fluid restriction (the fluid restriction volume will depend on the electrolyte free water clearance - called by Furst formula)

Question 17

Name drugs which can cause hyponatramia.

Answer 17

Thiazide diuretics (cause inhibition of sodium chloride reabsorption at the distal tubules)
Loop diuretics (more likely if taken with ACE or spironolactone) - they inhibit sodium chloride reabsorption at the ascending loop of Henle.
SSRI’s (especially citalopram) - usually develops within first few weeks of taking these drugs
Antipsychotics i.e. haloperidol and phenothiazines
Carbamazepines

Question 18

Explain water/sodium balance leading to hyponatraemia in hypervolaemic patients.

Answer 18

Both total body water AND sodium content increase BUT the relative increase in total body water is greater than the increase in total body sodium, resulting in oedema.

Question 19

List some causes of hypervolaemia potentially leading to hyponatramia.

Answer 19

Congestive heart failure
Liver disease (cirrhosis with ascites) 
Kidney disease (AKI, CKD, nephrotic syndrome)

Question 20

Describe the fluid status of a patient who is euvolaemic but hyponatraemic.

Answer 20

The total body water increases but total sodium content remains unchanged thereby producing a dilutional effect.

Question 21

Describe the water/sodium balance in a patient who is hypovolaemic and hyponatraemic

Answer 21

The total body water and sodium content are Bothe reduced but the relative decrease in total body sodium is greater than the decrease in total body water.