Potassium Flashcards
What percentage of potassium (K) is intracellular?
90%
A small drop in serum K can represent a large drop in total body potassium.
What is the potassium deficit required to lower serum potassium concentration by 1 mmol/L in chronic hypokalaemia?
200 to 400 mmol (200 to 400 mEq)
This is valid provided there is no concurrent acid-base abnormality.
What can cause a normal or elevated serum potassium concentration despite a marked potassium deficit?
DKA (Diabetic Ketoacidosis)
This occurs due to urinary and GI losses.
What are the serum potassium levels for mild hypokalaemia?
3.0 - 3.5 mmol/l
Usually asymptomatic unless severe drop or potentiating factors.
What symptoms are associated with moderate hypokalaemia (2.5-3.0 mmol/l)?
- Malaise
- Weakness
- Constipation
- Arrhythmias
Arrhythmias can occur if there are underlying cardiac problems.
What are the symptoms of severe hypokalaemia (2.0-2.4 mmol/l)?
- Dizziness
- Muscle weakness
- Rhabdomyolysis
- Hypoflexia
- Cramps
- Tetany
- Palpitations
- Impaired renal function
What are the symptoms when serum potassium is less than 2.0 mmol/l?
- Paralysis
- Respiratory impairment
This includes paralysis of respiratory muscles.
How does hypokalaemia affect digoxin toxicity?
Hypokalaemia increases the risk of digoxin toxicity
Which ECG changes are associated with hypokalaemia?
- Prolonged QT interval
Arrhythmias can occur in the presence of underlying cardiac issues.
What renal profile tests should be included in the initial assessment for hypokalaemia?
- K
- Na
- Cl
- Bicarbonate
- Urea
- Creatinine
- Serum chloride
- Serum magnesium
What urine electrolytes should be measured to evaluate hypokalaemia?
- Urine potassium
- Urine chloride
- Urine creatinine
Urine creatinine is necessary for calculating fractional excretion of potassium.
What can cause spurious hypokalemia?
- Heat
- Drip arm dilution
This can occur if blood is taken and allowed to stand at room temperature.
What urine potassium level indicates extra-renal loss?
Urine K < 20 mmol/l
This is also associated with urine K < 2.5 mmol/mmol creatinine.
What urine potassium level indicates renal loss?
Urine K > 20 mmol/l
This is also associated with urine K > 2.5 mmol/l creatinine.
What are the causes of hypokalemia with a normal acid base and urine K < 20 mmol/l?
- Anorexia
- Decreased K intake
- Laxative use
- Vomiting
- Burns
What is the impact of magnesium depletion on potassium levels?
Mg depletion can increase urinary potassium loss
Mg is required for ATPase function.
What are common drugs that can cause hypokalaemia?
- Thiazides
- Loop diuretics
- Adrenaline
- Laxatives
- Amphotericin B
- High dose penicillin
What is the mechanism by which insulin affects potassium levels?
Insulin promotes uptake of K by skeletal muscle and hepatic cells
This occurs by increasing ATPase activity.
What condition is characterized by flaccid paralysis of limbs and trunk on awakening?
Familial Hypokalaemic Periodic Paralysis (FHPP)
This is due to a mutation in voltage-gated channels in skeletal muscle.
What is causes Bartter’s syndrome?
Defect in Na reabsorption in the thick ascending limb of the loop of Henle
This typically leads to hyperplasia of the juxtaglomerular apparatus.
What is the urine chloride level in chloride-losing diarrhea?
Urine chloride > 10 mmol/l
What are the symptoms of Gitelman’s syndrome?
- Hypomagnesaemia
- Similar to chronic thiazide treatment
This results from a mutation in the NCCT carrier.
What is the expected urine potassium level in upper GI losses?
Urine potassium ~ elevated
This is often associated with metabolic alkalosis.
What are the levels of aldosterone and renin in apparent mineralocorticoid excess?
Low aldosterone, low renin
This condition can occur due to cortisol’s mineralocorticoid effects.
What enzyme is deficient in apparent mineralocorticoid excess?
11-beta hydroxysteroid dehydrogenase 2
This enzyme converts cortisol to cortisone, preventing cortisol from activating mineralocorticoid receptors.
What enzyme does liquorice inhibit?
1-beta hydroxysteroid dehydrogenase 2
Liquorice can lead to symptoms of mineralocorticoid excess by inhibiting this enzyme.
What condition is characterized by hyperactivity of epithelial Na channels?
Liddle’s syndrome
This leads to excessive sodium reabsorption and hypertension.
What is the second most common CAH?
11-beta hydroxylase deficiency
It causes virilisation in females, precocious puberty in males, hypertension, hypokalaemia, and alkalosis.
What is the effect of excess 11-DOC in 11-beta hydroxylase deficiency?
Acts as a mineralocorticoid causing Na and water retention
This results in high blood pressure and renin suppression.
What hormonal changes occur in CAH due to 17 alpha hydroxylase deficiency?
Reduced cortisol, increased ACTH, and increased sex steroids
This can lead to underdeveloped genitalia in males and delayed puberty in females.
What stimulates renin secretion in the body?
Reduction in intravascular volume
This can be due to conditions like congestive heart failure and liver cirrhosis.
What are common causes of high aldosterone and high renin?
- Congestive heart failure
- Liver cirrhosis
- Nephrotic syndrome
- Renovascular stenosis
- Renin secreting tumors
These conditions can lead to increased renin release due to low blood volume.
What renin and aldosterone results do you expect in primary hyperaldosteronism?
A condition with high aldosterone and low renin
It includes causes such as adrenal adenoma and bilateral adrenal hyperplasia.
What is the mechanism of glucocorticoid-remediable aldosteronism?
Aldosterone is controlled by ACTH due to a fusion of regulatory elements
This results in excess aldosterone production under ACTH influence.
What is a key indicator of intravascular volume depletion?
Chloride levels
Low chloride can indicate a response to hypovolaemia.
What is the treatment for mild hypokalaemia?
- Sando K (oral K)
- Potassium chloride
Monitoring serum potassium levels is essential.
What is the treatment for severe hypokalaemia?
IV potassium infusion
Severe cases require careful monitoring and should not be given as a bolus.
What are symptoms of hyperkalaemia?
- Paraesthesia of extremities
- Muscle weakness
- Paralysis
- Confusion
- Cardiac arrhythmias
- Heart block
- Cardiac arrest
Hyperkalaemia can have serious cardiac implications.
Name a class of diuretics that can increase serum potassium.
Potassium-sparing diuretics
Examples include spironolactone, amiloride, and triamterene.
What are some ACE inhibitors that can affect potassium levels?
- Ramipril
- Lisinopril
These medications can lead to increased serum potassium.
What immunosuppressants can lead to hypokalaemia?
- Tacrolimus
- Ciclosporin
These drugs can affect renal potassium handling.
What tests should be requested to investigate hypokalemia?
Urine potassium
Urine Chloride
Urine creatine (K: Cr ratio)
Serum Bicarbonate
Magnesium
Renin and Aldosterone
Urine pH (RTA)
Urinary free cortisol / salivary cortisol/ dex suppression test
What are the causes of hypokalaemia if Ur K >20 mmol/l or >2.5 mmol/l creatinine and bicarbonate < 22 mmol/l?
RTA 1 or 2
DKA
Acetazolamide
What are the causes of hypokalaemia if Ur K > 20 (or < 2.5 mmol/l creatinine) and variable acid base?
Hypomagnesaemia
Penicillins
Aminoglycosides
Leukaemia
What are the causes of hypokalaemia if:
Ur K < 20
or Ur K < 2.5 mmol/l creatinine
bicarbonate < 22mmol/l?
Prolonged Diarrhoea*
Villous adenoma
VIPoma
Laxative use*
What are the causes of hypokalaemia if:
Ur K < 20
or Ur K < 2.5 mmol/l creatinine
bicarbonate 22-29 mmol/l?
Anorexia*
Decreased K intake
Laxative use*
Vomiting
Burns
What are the causes of hypokalaemia if:
bicarbonate > 29 mmol/l
Urine Chloride < 10 mmol/l?
Normotensive
Volume contraction:
Vomiting
Diuretics* – late effect
Chloride losing diarrhoea
What assessment is required to investigate the causes of hypokalaemia if:
bicarbonate > 29 mmol/l
Urine Chloride > 10 mmol/l?
Blood pressure
If a patient is hypertensive with hypokalaemia with a raised renin and aldosterone what are the possible causes?
1) Renin-secreting tumour
2) Renal artery stenosis
↑ beta-adrenergic receptor activity:
3) Phaeochromocytoma
4) Hyperthyroidism
5) Beta-agonists
If a patient is hypertensive with hypokalaemia with a low renin but raised aldosterone what are the possible causes?
1°hyperaldosteronism*- (Adrenal hyperplasia, Adrenal adenoma)
Glucocorticoid-suppressible hyperaldosteronism
If a patient is hypertensive with hypokalaemia with a low / normal renin but normal aldosterone what are the possible causes?
Cushings
If a patient is hypertensive with hypokalaemia with a low renin but low aldosterone what are the possible causes?
1) Liddles syndrome
2) CAH – 11B-hydroxylase deficiency
3) Apparent mineralocorticoid excess – Liquorice, carbenoxalone treatment.
↑ beta-adrenergic receptor activity
4) Phaeochromocytoma
5) Hyperthyroidism
6) Beta-agonists
