ELECTROLYTE DISORDERS Flashcards
What abnormality does this ECG indicate? Point out the three main abnormalities. Which muscular symptoms would you expect in this patient?
Displays many of features of hyperkalaemia:
- Prolonged PR
- Broad, bizarre QRS complexes: merge with preceding P and subsequent T waves
- Peaked T waves
Hyperkalaemia causes muscle paralysis: starts at lower extremities then trunk then upper extremities. Note that very wide QRS complexes are almost always due to hyperkalaemia
What is the most common cause of hyperkalaemia?
Acute and chronic kidney disease
Explain the mechanism by which insulin Deficiency and beta-blockers both cause hyperkalaemia
Sodium/potassium ATPase is activated by adrenaline and insulin
When there is lack of insulin or during beta-blockade the pump is less active → more potassium outside cells
How does digoxin affect potassium levels? Explain why
Blocks sodium/potassium ATPase: causes hyperkalaemia
Explain why tumour lysis syndrome causes hyperkalaemia. Explain why hyperosmolarity causes hyperkalaemia
- Tumour lysis syndrome: cell contents released
- Hyperosmolarity: water driven out of cells, potassium follows
What does this ECG show? What muscle symptoms would you expect in a patient with this ECG?
- ST depression
- T wave inversion
- U waves
- Long QU interval
Indicative of hypokalaemia: expect muscle weakness/paralysis (lower extremities then trunk then upper extremities)
What is the origin of the U wave?
Origin unclear
May represent repolarisation of Purkinje fibres but can be normal
What are the two most common causes of hypokalaemia?
- Increased renal losses: diuretics, types 1 and 2 renal tubular acidosis
- Increased GI losses: vomiting, diarrhoea
A patient with hypokalaemia that does not respond to potassium therapy is likely to have which electrolyte imbalance?
Hypomagnesaemia: cannot correct potassium until magnesium is corrected!
Magnesium promotes urinary potassium loss
Acute hypercalcaemia is often caused by what? What is the main symptom? Explain why this occurs
Malignancy
Polyuria + polydipsia
High calcium ⇒ loss of ability to concentrate urine due to down regulation of aquaporins → AKI. Calcium also acts like loop diuretic
What are the four main symptoms of chronic hypercalcaemia? How do you remember them? Why is this no longer seen?
- Stones: kidney
- Bones: increased calcium resorption, bone pain
- Groans: abdominal pain, constipation
- Psychiatric overtones: anxiety, altered mental status
What are the two most common causes of hypercalcaemia?
- Hyperparathyroidism
- Malignancy
Somebody presents with twitching of the face. Exhibit the following sign on tapping of facial nerve. What is likely diagnosis and what is the sign? Explain why this occurs
Hypocalcaemia
Chvostek’s sign: facial contraction tetany on tapping of the nerve
♦ Calcium blocks sodium channels in neurons: low calcium causes easy depolarisation and spontaneous contractions
You noticed a patient hand spasms on inflation of the blood pressure cuff. What is the sign called and what is it indicative of?
Trousseau’s sign: indicative of hypocalcaemia
♦ Calcium blocks sodium channels in neurons: low calcium causes easy depolarisation and spontaneous contractions
Most common cause of hyperphosphataemia and symptoms
Acute and chronic kidney disease
Mostly asymptomatic: symptoms usually from hypocalcaemia caused by phosphate precipitating serum calcium
How does hypoparathyroidism affect phosphate levels?
- PTH inhibits sodium/phosphate co-transporter in PCT → increased phosphate excretion
- Hypoparathyroidism increases levels as transporter will be more active
What can long-standing untreated hyperphosphataemia cause?
Calciphylaxis AKA calcific uremic arteriolopathy (CUA)
- phosphate deposition & calcification of small blood vessels in fat, skin
- associated with kidney disease
- results in non-healing wounds
- usually fatal
Describe and explain how diabetic ketoacidosis affects phosphate levels
Affected much the same way as potassium (extracellular shift but depleted total body levels)
What electrolyte imbalance should you consider in an alcoholic who is malnourished and in hospital and starts experiencing hypoventilation and respiratory muscle weakness?
Hypophosphataemia caused by refeeding syndrome (increased food intake causes increased metabolism and a further decrease in phosphate levels)
Main symptom of low phosphate is weakness due to ATP depletion, often presents as respiratory muscle weakness
Magnesium blocks the channels of which 2 electrolytes? What then are the symptoms of high magnesium? What is the main cause of hypermagnesaemia?
Calcium and potassium channels
Raise magnesium will cause the symptoms of decreased calcium and potassium
main cause: renal insufficiency
Hypomagnesaemia will cause a reduction in which 2 electrolytes?
List some causes of low magnesium
- Calcium
- Potassium
♦ GI losses, pancreatitis, renal losses, alcohol induced tubular dysfunction, drugs e.g. omeprazole (impaired absorption)
Most common cause of hypercalcaemia in outpatients
Primary hyperparathyroidism
Which anti-viral drug is famous for causing a high number of electrolyte imbalances including renal wasting of magnesium?
Foscarnet
