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
Management of hypokalemia
- replace K+
- Mx depends on severity and ECG findings
Causes of hyperkalaemia
Causes of hyperkalaemia
- acute kidney injury
- drugs: potassium sparing diuretics, ACE inhibitors, angiotensin 2 receptor blockers, spironolactone, ciclosporin, heparin
- metabolic acidosis
- Addison’s disease
- rhabdomyolysis
- massive blood transfusion
ECG features associated with hyperkalaemia
ECG findings
- Peaked or ‘tall-tented’ T waves (occurs first)
- Loss of P waves
- Broad QRS complexes
- Sinusoidal wave pattern
- Ventricular fibrillation
Features/symptoms of hyperkalaemia
- weakness
- paraesthesia
- paralysis
- depressed tendon reflexes
Management of hyperkalaemia
Stabilisation of the cardiac membrane
- intravenous calcium gluconate
(does NOT lower serum potassium levels)
Short-term shift in potassium from extracellular to intracellular fluid compartment
- combined insulin/dextrose infusion
- nebulised salbutamol
Removal of potassium from the body
-
calcium resonium (orally or enema)
- enemas are more effective than oral as potassium is secreted by the rectum
- loop diuretics
-
dialysis
- haemofiltration/haemodialysis should be considered for patients with AKI with persistent hyperkalaemia
Definition of hypercalcaemia and hypocalcaemia
Hypercalcaemia → >2.6 mmol/L
Hypocalcaemia → <2.1 mmol/L
Causes of hypocalcaemia
- vitamin D deficiency (osteomalacia)
- chronic kidney disease
- hypoparathyroidism (e.g. post thyroid/parathyroid surgery)
- pseudohypoparathyroidism (target cells insensitive to PTH)
- rhabdomyolysis (initial stages)
- magnesium deficiency (due to end organ PTH resistance)
- massive blood transfusion
Acute pancreatitis may also cause hypocalcaemia. Contamination of blood samples with EDTA may also give falsely low calcium levels
Management of hypocalcaemia
- acute management of severe hypocalcaemia is with intravenous replacement. The preferred method is with intravenous calcium gluconate, 10ml of 10% solution over 10 minutes
- intravenous calcium chloride is more likely to cause local irritation
- ECG monitoring is recommended
- further management depends on the underlying cause
Features/ symptoms/signs of hypocalcaemia
As extracellular calcium concentrations are important for muscle and nerve function many of the features seen in hypocalcaemia seen a result of neuromuscular excitability
Features
- tetany: muscle twitching, cramping and spasm
- perioral paraesthesia
- if chronic: depression, cataracts
- ECG: prolonged QT interval
Trousseau’s sign
- carpal spasm if the brachial artery occluded by inflating the blood pressure cuff and maintaining pressure above systolic
- wrist flexion and fingers drawn together
- seen in around 95% of patients with hypocalcaemia and around 1% of normocalcaemic people
Chvostek’s sign
- tapping over parotid causes facial muscles to twitch
- seen in around 70% of patients with hypocalcaemia and around 10% of normocalcaemic people
ECG features seen in hypocalcaemia
- prolonged QT and PR intervals
- T wave inversion
- heart block
Definition of:
hypermagnesemia
hypomagnesemia
- Hypermagnesemia Mg > 1.1 mmol/L
- Hypomagnesemia Mg <0.6 mmol/L
Causes of hypermagnesemia
- renal failure
- iatrogenic
Features of hypermagnesemia
- confusion
- weakness
- respiratory depression
- AV block
- cardiac arrest
ECG features of hypermagnesemia
- prolonged QT and PR intervals
- T wave peaking
Management of hypermagnesemia
- If Mg >1.75 mmol/L → CaCl IV bolus repeated if needed
- saline diuresis with furosemide
- haemodialysis
Causes of hypomagnesemia
Cause of low magnesium
- drugs: diuretics, proton pump inhibitors
- total parenteral nutrition
- diarrhoea
- alcohol
- hypokalaemia, hypocalcaemia
- conditions causing diarrhoea: Crohn’s, ulcerative colitis
- metabolic disorders: Gitleman’s and Bartter’s
Features of hypomagnesemia
Features may be similar to hypocalcaemia:
- paraesthesia
- tetany
- seizures
- arrhythmias
- decreased PTH secretion → hypocalcaemia
- ECG features similar to those of hypokalaemia
- exacerbates digoxin toxicity
ECG features of hypomagnesemia
- flattened P waves
- increased QRS duration
- torsade de points
Management of hypomagnesemia
<0.4 mmol/l
- IV replacement. An example regime would be 40 mmol of magnesium sulphate over 24 hours
>0.4 mmol/l
- oral magnesium salts (10-20 mmol orally per day)
- diarrhoea can occur with oral magnesium salts
