Electrolyte Imbalances Flashcards
Hypercalcaemia diagnosis?
Serum calcium concentration of 2.6 mmol/L or higher, on two occasions, following adjustment (correction) for the serum albumin concentration.
- Mild: 2.6-3
- Moderate: 3.01-3.4
- Severe: >3.4
What 2 conditions account for 90% of cases of hypercalcaemia?
- primary hyperparathyroidism
- malignancy e.g. lung, myeloma
How does malignancy cause hypercalcaemia?
- bone mets
- PTHrP from tumour eg. squamous cell lung cancer
- myeloma (increased osteoclastic bone resporption caused by local cytokines eg. IL-1 tumour necrosis factor, released by myeloma cells
Less common causes of hypercalcaemia?
sarcoidosis, vit D intoxication, acromegaly, thyrotoxicosis, milk-alkali syndrome, drugs, dehydration, Addison’s, Paget’s
What drugs can cause hypercalcaemia?
Thiazides, calcium-containing antacids
What is the key diagnostic investigation for hypercalcaemia?
PTH levels
How does hypercalcaemia present?
- bones, stones, groans and psychic moans
- corneal calfication
- HTN
- Bone pain
- Abdominal pain
- Renal stones
- Depression
- Drowsiness
- Confusion
- Muscle weakness
How is hypercalcaemia managed?
- IV Saline (3-4 L/day)
- IV Bisphosphonates
Referral if required. Consider stopping certain causative drugs and monitor response. Monitor symptoms. Lifestyle measures. ?monitor serum Ca, eGFR, creatinine, BMD, renal imaging if specialist advises.
What would you see on blood test results for hypercalcaemia secondary to malignancy?
- Raised calcium
- low PTH
- low phosphate
- raised PTHrP
Most common cause of hypercalcaemia in outpatients?
Primary hyperparathyroidism
What are plasma potassium levels regulated by?
Aldosterone, acid-base balance and insulin levels.
What causes hyperkalaemia?
- AKI
- ACE/Spironolactone
- Addisons
- Rhadbomyolysis
- Massive blood transfusion
- Metabolic acidosis
What drugs cause hyperkalaemia?
Potassium sparing diuretics eg. spironolactone, ACE in, angiotension 2 receptor blockers, ciclosporin, heparin
What can potentially cause hyperkalaemia in renal failure patients?
Beta blocks- interfere with potassium transport into cells.
How does heparin cause hyperkalaemia?
Inhibition of aldosterone secretion
Why is metabolic acidosis associated with hyperkalaemia?
Hydrogen and potassium ions compete with each other for exchange of sodium ions across cell membranes and in the distal tubule.
Foods high in potassium?
Bananas, oranges, kiwi, avocado, spinach, tomatoes. Salt substitutes (contain K instead of Na).
What is the classification for hyperkalaemia?
Plasma potassium level:
Mild - 5.5 - 5.9
Moderate: 6 - 6.4
Severe: >6.5
How does hyperkalaemia show on ECG?
- Tall T waves
- Absent p waves
- broad QRS
- Sinusoidal pattern
Untreated hyperkalaemia may cause what?
Life-threatening arrhythmias.
Precipitating factors eg. AKI and aggravating drugs eg. ACE i should be stopped in what?
Hyperkalaemia
What patients for hyperkalaemia should have emergency treatment?
All patients with severe hyperkalaemia (≥ 6.5 mmol/L) or with ECG changes
Overview of hyperkalaemia management
- Emergency management
- Then further management: TUC, stop exacerbating drugs eg. ACE in
- Then LOWER total body potassium
How is hyperkalaemia managed initially?
- IV Calcium gluconate (stabilise myocardium- does NOT lower K)
- Insulin/Dextrose solution (short term shift in K from ECF to ICF)
- Nebulised salbutamol
Management of hyperkalaemia after initial emergency treatment to actually LOWER total body potassium?
- Calcium resonium -> oral or enema which is more effective
- Loop diuretics
- Dialysis if persistent
Why can hyperkalaemia be associated with acidosis?
Potassium and hydrogen can be thought of as competitors. As potassium levels rise, fewer hydrogen ions can enter the cells.
What are causes of hypernatraemia?
- Dehydration
- Osmotic diuresis (eg. hyperosmolar non-ketotic diabetic coma)
- Diabetes insipidus
- XS IV saline
How is hypernatremia managed?
Rehydration with IV Saline/Hartmann’s
Rate to correct hypernatraemia with 0.9% saline or Hartmann’s?
No greater than 0.5mmol/hour (10mmol/24 hours)
Why should you not correct serum sodium conc too rapidly?
Risk of cerebral oedema- seizure, coma, death.
What are causes of hypocalcaemia?
- Vit D deficiency
- CKD
- Acute pancreatitis
- hypoparathyroidism (post thyroid/parathyroid surgery)
- magnesium def (due to end organ PTH resistance)
- massive blood transfusion
What normally will reveal the cause of hypocalcaemia?
Parathyroid hormone levels and clinical history
How is hypocalcaemia managed?
- Oral calcium carbonate if mild
- IV calcium gluconate when severe eg. tetany (10ml of 10% solution over 10mins)
- ECG monitoring
What may give falsely low calcium levels?
Contamination of blood samples with EDTA
How does hypocalcaemia present?
- dry skin, brittle nails, coarse hair
- Tetany: Muscle twitching, cramps and spasms
- perioral paraesthesia
- seizures
- Prolonged QT inverval
- Trousseau sign
- Chvostek sign
Trousseau sign? (hypocalcaemia)
Carpal spasm when the brachial artery is occluded by inflating BP cuff and maintaining above systolic. Wrist flexion and fingers drawn together. (95% pts)
Chvostek sign? (hypocalcaemia)
Tapping over parotid causes facial twitch. (70% pts)
What causes hypokalaemia?
- Diuretics
- Renal tubular acidosis
- Cushings/Conns
- Diarrhoea/vomiting
What may also cause hypokalaemia?
Magnesium deficiency
How does hypokalaemia present?
- Muscle weakness
- Hypotonia
- ECG changes
How is hypokalaemia managed?
- Treat cause
- Oral supplementation if mild
- IV fluid if severe with cardiac monitoring
Why might sometimes it be difficult to normalise potassium levels?
Difficult until magnesium deficiency has been corrected
Hypokalaemia with causes alkalosis?
- vomiting
- thiazide and loop diuretics
- Cushing’s
- Conn’s (primary hyperaldosteronism)
Hypokalaemia with acidosis causes?
- diarrhoea
- renal tubular acidosis
- acetazolamide
- partially treated diabetic ketoacidosis
Causes of low magnesium?
- drugs
- total parenteral nutrition
- diarrhoea (acute or chronic)
- alcohol
- hypokalaemia
- hypercalcaemia
- metabolic disorders eg. Gitleman’s and Bartter’s
What drugs can cause hypomagnesaemia?
Diuretics and PPI
How can hypercalcaemia cause hypomagnesaemia?
Eg. secondary to hyperparathyroidism.
Ca and Mg functionally compete for transport in the thick ascending limb of the loop of Henle
Clinical presentation of hypomagnesaemia?
May be similar to hypocalcaemia:
- paraesthesia
- tetany
- arrhythmias
- decreased PTH secretion= hypocalcaemia
- ECG features
What does hypomagnesaemia exacerbate?
Digoxin toxicity
Mx of hypomagnesaemia if <0.4mmol/L or tetany, arrhythmias or seizures
- IV magnesium replacement eg. 40mmol magnesium sulfate over 24hrs
Mx of hypomagnesaemia if >0.4mmol/L
oral magnesium salts (10-20mmol oral per day in divided doses)
What can occur with oral magnesium salts?
Diarrhoea
Hyponatraemia may be caused by either what 2 things?
water XS or sodium depletion
Causes of psuedohyponatraemia
hyperlipidaemia (increase in serum volume) or taking blood from a drip arm
What aid making a diagnosis of hyponatraemia?
Urinary sodium and osmolarity levels
Definition of hyponatraemia
serum sodium conc of <135mmol/L
usually incidental finding on routine bloods.
Severity of hyponatraemia?
- Mild: serum sodium conc 130-135mmol/L
- Moderate: 125-129
- Severe: <125
Acute= onset <48hrs
Chronic= onset >48hrs
What causes hyponatraemia?
- SIADH
- Hypothyroidism
- Thiazides
- Diarrhoea/Vomiting
- Psychogenic polydipsia
Causes of hypovolemic/clinically dehydrated hyponatraemia?
Diuretic stage of renal failure, diuretics, Addisonian crisis
Causes of euvolaemic hyponatraemia?
SIADH
Causes of hypervolaemic hyponatraemia?
HF, liver failure, nephrotic syndrome
Clinical presentation of hyponatraemia?
- most asymptomatic (esp if mild and chronic)
- Early symptoms: headache, lethargy, nausea, confusion, muscle cramps
- Late: seizures, coma, resp arrest
- rapid changes or severe: vomiting, headaches, drowsiness, seizures, coma, cardio-resp arrest
Consequences of chronic hyponatraemia?
Increased risk of falls, bone fractures, osteoporosis, gait instability, concentration and cognitive deficits
Ix for hyponatraemia?
- History & pt volume status
- Serum and urine osmolality and urinary sodium conc
- After initial identification of hyponatraemia measure serum Na again to exclude rapid decreasing Na conc
Hyponatraemia inital Mx in all patients?
Exclude a spurious result (eg. blood taken from drip arm) and review any meds that may cause hyponatraemia
Mx of hyponatraemia if hypovolemic cause suspected?
Normal (isotonic) saline (0.9% NaCl). If serum Na rises then supports diagnosis, if falls then consider SIADH.
Mx of hyponatraemia if euvolemic cause is suspected? eg. secondary to SIADH
- fluid restrict (500-1000ml/day)
- Consider Tolvaptan (vasopressin V2-receptor antagonist)
Mx of hyponatraemia if hypervolemic cause suspected?
- Fluid restrict (500-1000ml/day)
- Consider loop diuretis
Mx of acute, severe (<120) or symptomatic hyponatraemia?
- Close monitoring, preferably in HDU
- Hypertonic saline (3% NaCl) used to correct levels more quickly than in chronic pts
Mx of acute hyponatraemia with mild or no symptoms?
Non-essential parenteral fluids and meds stopped if provoking
Mx of Chronic hyponatraemia without moderate or severe symptoms?
Non-essential parenteral fluids and meds stopped if provoking
Summary of hyponatraemia management?
If hypovalaemia: 0.9% isotonic saline
If euvolaemic: Treat underlying cause e.g SIADH by fluid restriction
If acute: 3% hypertonic saline
What is the big risk with severe hyponatraemia?
cerebral odema= brain herniation
Over-rapid correction of hyponatraemia may lead to what?
Osmotic demyelination syndrome (Central pontine myelinolysis)
What is the pathophysiology behind osmotic demyelination syndrome?
- Develop secondary to astrocyte and ?oligodendrocyte apoptosis.
- These cells of the glial syncytium are crucial for myelination.
- Chronic hypon= loss of osmotically active osmolytes eg. glutamate from astrocytes
- These provide protection against cerebral oedema
- Organic osmolytes can’t be replaced quick enough when brain vol shrinks in response to correction of hypona
- dehydrated astrocytes and oligod undergo apoptosis= demyelination
Avoid osmotic demyelination syndrome when correcting hyponatraemia?
Raise Na+ levels by only 4-6mmol/l in 24hrs
Symptoms of osmotic demyelination syndrome?
After 2 days and irreversible.
Dysarthria, dysphagia, paraparesis/quadriparesis, seizures, confusion, coma. Locked in syndrome.
How do vaptans (vasopressin-ADH receptor antagonists) eg. Tolvaptan work?
Act on V2 receptors. Antagonism of V2 receptors results in selctive water diuresis, sparing the electrolytes. Can stimulate thirst receptors leading to the desire to drink free water.
What should be avoided in patients who have hypovolemic hyponatremia?
Vasopressin/ADH receptor antagonists (vaptans). Also can be hepatotoxic in pts with liver disease.
Management of severe hyponatraemia (<120)
Hypertonic saline (3% NaCl)
What are signs of hypercalcaemia on ECG?
Short QT interval, J waves
What are signs of hyperkalaemia on ECG?
Tall-tented T waves, small P waves, widened QRS.
Leading to a sinusoidal pattern and asystole
What are the signs of hypocalcaemia on ECG?
Prolonged QT interval
What are the signs of hypokalaemia on ECG?
U waves, small t waves, prolonged PR, ST depression
What are the signs of hypomagnesaemia on ECG?
Similar to hypokalaemia: prolonged PR, prolonged QT, ST depression
