Week 4: Electrolyte disturbances Flashcards
Normal sodium range
135-145 mmol/L
Normal potassium range
3.5-5.5 mmol/L
Normal calcium range
2.2-2.6 mmol/L
How are calcium and phosphate levels affected in chronic renal impairment
Low calcium
High phosphate
Causes of low potassium
K+ entering cell:
- metabolic alkalosis
- insulin
- adrenergics
K+ can’t come out of cell:
-low magnesium
Loss:
- V and D, osmotic diuresis, diuretics
- Cushing’s
Insufficient dietary intake
Causes of high potassium
K+ leaving cell:
-cell lysis (eg chemotherapy, burns, haemolysis)
K+ not entering cell:
- metabolic acidosis
- low insulin
- B blockers
Low renin, aldosterone
Why does low magnesium cause hypokalemia
Low magnesium inhibits K from crossing cell membrane
Why does Cushing’s cause hypokalemia
Excess cortisol acts like aldosterone and binds to Na/K pump
Hyper/hypotension is caused by high/low potassium
Hypertension: high potassium
Hypotension: low potassium
Diarrhoea/constipation is caused by high/low potassium
Diarrhoea: high potassium
Constipation: low potassium
How do potassium imbalances affect reflexes and muscle strength
BOTH:
- flaccid paralysis
- decreased reflexes
Drugs that should be avoided in low potassium
- Insulin
- Adrenergic agonists
- Steroids
- Anything that causes more GI loss eg laxatives, diuretics
Drugs that should be avoided in high potassium
- Beta blockers, digoxin
- ACEi (leads to less aldosterone)
- Heparin (blocks synthesis of aldosterone)
- NSAIDs (reduce renin release so less K+ excreted)
What drugs/ compounds cause potassium to LEAVE a cell
- Metabolic acidosis
2. Rhabdomyolysis
What drugs/ compounds cause potassium to ENTER a cell
- Insulin
- Adrenergics
- Metabolic alkalosis
How do thiazide diuretics and lithium affect calcium levels
Both cause reduced excretion of calcium from kidney
HYPERCALCAEMIA
How are sodium and potassium levels affected in chronic renal impairment
Less renin produced
HYPERKALEMIA
HYPONATREMIA
How does cortisol affect calcium levels
Inhibits calcium absorption
HYPOCALCAEMIA
(so Cushing’s causes hypocalcaemia and Addison’s causes hypercalcaemia)
How does phaeochromocytoma affect calcium levels
HYPERCALCAEMIA
How does hyperthyroidism affect calcium levels
HYPERCALCAEMIA
How does Addison’s affect sodium levels
HYPONATREMIA
Low aldosterone, less reabsorption of Na
How does Conn’s affect sodium levels
HYPERNATREMIA
More aldosterone, more reabsorption of Na
How does Cushing’s affect sodium levels
HYPERNATREMIA
More cortisol, similar effect to high aldosterone, more reabsorption of Na
How does SIADH affect sodium levels
HYPONATREMIA
More ADH, More Na lost in urine
How does Diabetes insipidus affect sodium levels
HYPERNATREMIA
Less ADH, less NA lost in urine
Management of hypernatremia
IV dextrose
Management of hyponatremia
IV sodium
Water restriction
(caution not to overcorrect or this will cause cerebral oedema
Management of hyperkalemia (with specific doses)
- Calcium gluconate (10%, 5-10ml IV)
- Insulin (Novorapid 10-20units, IV)
- Sabutamol (10-20mg, nebuliser)
- GI cation exchangers
- Dialysis
Management of hypokalemia
IV potassium
IV magnesium if this is also low
Management of hypercalcaemia
- IV fluids (do this first!)
2. IV bisphosphonates
Management of hypocalcaemia
IV calcium
Why are pts at risk of electrolyte imbalance after a bladder obstruction
Relief of obstruction leads to post obstruction diuresis
Will lose lots of salt and water
Signs of hyperkalemia on ECG
state in order at which they appear
- Tall T wave
- Widened flattened T wave
- Prolonged PR interval
- Widened QRS
- Loss of P waves
- Sine wave
Also bradycardia at any point
Signs of hypokalemia on ECG
state in order at which they appear
- Flat/ inverted T wave
- Prominent U waves
- ST depression
- Prolonged QU interval (>500ms)
- Torsade des pointes
Signs of hypercalcaemia on ECG
state in order at which they appear
- Shortened QT interval
2. J waves (curve on the downward point of the QRS complex)
Signs of hypocalcaemia on ECG
state in order at which they appear
Prolonged ST segment leading to QTc prolongation
this is the only change
Most common cause of primary hyperparathyroidism
Solitary parathyroid adenoma
Multiple adenomas, parathyroid hyperplasia, parathyroid carcinoma are also causes, but rarer
