Electrolyte imblance (shortly from Dr Ifrah) Flashcards
Causes of hyponatraemia
Hyponatraemia is overall due to water excess or sodium depletion:
- fluid loss
- renal disease
- SIADH
- head trauma
- hyperglycaemia
- heart failure
- drugs: IV dextrose, thiazides, loop diuretics
Presentation of hyponatraemia
- anorexia
- headache
- irritability
- low GCS
- seizures
- increased risk of falls
Investigations
- serum osmolarity
- urine osmolarity
- urine Na
Management of hyponatraemia
- chronic
- acute
- correct underlying cause
Chronic /asymptomatic:
- fluid restriction
- demeclocycline → used when SIADH is a cause (MoA: increased urine volume, decreased urine osmolality, and reverted hyponatremia)
Acute /symptomatic:
- replace Na → max rise 4-6 mmol/l in 24 hrs
- in emergency: hypertonic saline, furosemide
A possible complication of too quick treatment of hyponatraemia and how to avoid it
Osmotic demyelination syndrome (central pontine myelinolysis):
- can occur due to over-correction of severe hyponatremia
- To avoid this, Na+ levels are only raised by 4 to 6 mmol/l in a 24-hour period
- Symptoms usually occur after 2 days and are usually irreversible. Dysarthria, dysphagia, paraparesis or quadriparesis, seizures, confusion, and coma. Patients are awake but are unable to move or verbally communicate, also called ‘Locked-in syndrome’
Management of hypercalcaemia
- fluids → rehydration with normal saline(3-4 litres/day)
- bisphosphonates →take 2-3 days to work with the maximal effect being seen at 7 days
- calcitonin - quicker effect than bisphosphonates
- steroids in sarcoidosis
- Loop diuretics (furosemide) → sometimes used in patients who cannot tolerate aggressive fluid rehydration
*diuretics should be used with caution as they may worsen electrolyte derangement and volume depletion
Features of hypercalcamia
- ‘bones, stones, groans and psychic moans’
- corneal calcification
- shortened QT interval on ECG
- hypertension
Causes of hypercalcaemia
Two conditions account for 90% of cases of hypercalcaemia:
- 1. Primary hyperparathyroidism: commonest cause in non-hospitalised patients
- 2. Malignancy: the commonest cause in hospitalised patients. This may be due to number of processes, including; bone metastases, myeloma, PTHrP from squamous cell lung cancer
Other causes include
- sarcoidosis
- vitamin D intoxication
- acromegaly
- thyrotoxicosis
- Milk-alkali syndrome
- drugs: thiazides, calcium containing antacids
- dehydration
- Addison’s disease
- Paget’s disease of the bone
Causes of hypernatraemia
- dehydration
- osmotic diuresis e.g. hyperosmolar non-ketotic diabetic coma
- diabetes insipidus
- excess IV saline
Features/presentation of hypernatraemia
- thirst
- lethargy
- weakness
- confusion
- come
- seizures
Investigations in hypernatraemia
- serum and urine osmolarity
- urine Na
Management of hypernatraemia
- encourage PO water
- glucose 5%
*avoid hypertonic solutions
Hypernatraemia should be corrected with great caution. Although brain tissue can lose sodium and potassium rapidly, lowering of other osmolytes (and importantly water) occurs at a slower rate, predisposing to cerebral oedema, resulting in seizures, coma and death
- rate of no greater than 0.5 mmol/hour correction is appropriate
Causes of hypokalaemia
Hypokalaemia with alkalosis
- vomiting
- thiazide and loop diuretics
- Cushing’s syndrome
- Conn’s syndrome (primary hyperaldosteronism)
Hypokalaemia with acidosis
- diarrhoea
- renal tubular acidosis
- acetazolamide
- partially treated diabetic ketoacidosis
- Magnesium deficiency may also cause hypokalaemia →normalizing the potassium level may be difficult until the magnesium deficiency has been corrected
Features of hypokalaemia
Features
- muscle weakness, hypotonia
- hypokalaemia predisposes patients to digoxin toxicity - care should be taken if patients are also on diuretics
ECG features
- U waves
- small or absent T waves
- prolonged PR interval
- ST depression
ECG features of hypokalaemia
ECG features
- U waves
- small or absent T waves
- prolonged PR interval
- ST depression
