Electrolyte abnormalities Flashcards
What are the two conditions that account for 90% of cases of hypercalcaemia?
- Primary hyperparathyroidism: commonest cause in non-hospitalised patients
- Malignancy: the commonest cause in hospitalised patients
What is the common cause of malignancy-related hypercalcaemia?
Malignancy may be due to several processes, including:
- PTHrP from the tumour (e.g. squamous cell lung cancer)
- Bone metastases
- Myeloma, due primarily to increased osteoclastic bone resorption caused by local cytokines (e.g. IL-1, tumour necrosis factor) released by the myeloma cells
What is the key investigation for patients with hypercalcaemia?
Measuring parathyroid hormone levels
What are other causes of hypercalcaemia?
- Sarcoidosis
- Other causes of granulomas (e.g. tuberculosis, histoplasmosis)
- Vitamin D intoxication
- Acromegaly
- Thyrotoxicosis
- Milk-alkali syndrome
- Drugs (thiazides, calcium-containing antacids)
- Dehydration
- Addison’s disease
- Paget’s disease of the bone
Is hypercalcaemia common in Paget’s disease of the bone?
Usually normal in this condition, but hypercalcaemia may occur with prolonged immobilisation
What is the mnemonic for the features of hypercalcaemia?
‘bones, stones, groans and psychic moans’
This mnemonic helps to remember the common symptoms associated with hypercalcaemia.
What is a notable ocular feature of hypercalcaemia?
Corneal calcification
Corneal calcification can occur due to elevated calcium levels in the body.
What ECG finding is associated with hypercalcaemia?
Shortened QT interval
A shortened QT interval can be a significant indicator of hypercalcaemia on an ECG.
What cardiovascular condition can occur due to hypercalcaemia?
Hypertension
Elevated calcium levels can lead to increased blood pressure.
What is hyperkalaemia?
A condition characterized by elevated plasma potassium levels
Plasma potassium levels can be influenced by various factors including aldosterone, acid-base balance, and insulin levels.
What is the relationship between metabolic acidosis and hyperkalaemia?
Metabolic acidosis is associated with hyperkalaemia due to competition between hydrogen and potassium ions for exchange with sodium ions
This occurs across cell membranes and in the distal tubule.
List ECG changes seen in hyperkalaemia.
- Tall-tented T waves
- Small P waves
- Widened QRS
- Sinusoidal pattern
- Asystole
These changes indicate cardiac disturbances associated with elevated potassium levels.
What are common causes of hyperkalaemia?
- Acute kidney injury
- Potassium-sparing diuretics
- ACE inhibitors
- Angiotensin 2 receptor blockers
- Spironolactone
- Ciclosporin
- Heparin
- Metabolic acidosis
- Addison’s disease
- Rhabdomyolysis
- Massive blood transfusion
Some medications can inhibit aldosterone secretion, contributing to hyperkalaemia.
Which foods are high in potassium?
- Salt substitutes (potassium-based)
- Bananas
- Oranges
- Kiwi fruit
- Avocado
- Spinach
- Tomatoes
These foods can contribute to increased potassium levels in the body.
True or False: Beta-blockers can potentially cause hyperkalaemia in renal failure patients.
True
Beta-blockers interfere with potassium transport into cells, which can exacerbate hyperkalaemia.
Fill in the blank: Both unfractionated and low-molecular weight _______ can cause hyperkalaemia.
heparin
This effect is thought to be due to the inhibition of aldosterone secretion.
What role does aldosterone play in potassium regulation?
Aldosterone helps regulate plasma potassium levels by promoting potassium excretion
Inhibition of aldosterone can lead to elevated potassium levels.
What is hyperkalaemia?
An electrolyte disturbance characterized by elevated potassium levels in the blood
Untreated hyperkalaemia may cause life-threatening arrhythmias.
What are the classifications of hyperkalaemia according to the European Resuscitation Council?
- Mild: 5.5 - 5.9 mmol/L
- Moderate: 6.0 - 6.4 mmol/L
- Severe: ≥ 6.5 mmol/L
What ECG changes are associated with hyperkalaemia?
- Peaked or ‘tall-tented’ T waves
- Loss of P waves
- Broad QRS complexes
- Sinusoidal wave pattern
What is the first step in managing severe hyperkalaemia?
Stabilisation of the cardiac membrane
Which treatment does NOT lower serum potassium levels?
IV calcium gluconate
What is a short-term method to shift potassium from extracellular to intracellular fluid?
Combined insulin/dextrose infusion
What is an effective method for removing potassium from the body?
- Calcium resonium (orally or enema)
- Loop diuretics
- Dialysis
True or False: Nebulised salbutamol can be used to temporarily lower serum potassium.
True
Fill in the blank: All patients with severe hyperkalaemia (≥ 6.5 mmol/L) or with ECG changes should have _______.
emergency treatment
What should be done with exacerbating drugs such as ACE inhibitors in the context of hyperkalaemia?
They should be stopped
What should be treated in addition to hyperkalaemia itself?
Any underlying cause
What are the aims of hyperkalaemia management?
- Stabilisation of the cardiac membrane
- Short-term shift in potassium
- Removal of potassium from the body
What is more effective for potassium removal: enemas or oral calcium resonium?
Enemas
What should be considered for patients with acute kidney injury (AKI) and persistent hyperkalaemia?
Haemofiltration/haemodialysis
What is hypernatraemia?
An elevated sodium level in the blood
Name one cause of hypernatraemia.
- Dehydration
- Osmotic diuresis (e.g., hyperosmolar non-ketotic diabetic coma)
- Diabetes insipidus
- Excess IV saline
True or False: Hypernatraemia should be corrected quickly.
False
What is a potential consequence of rapidly correcting hypernatraemia?
Cerebral oedema, resulting in seizures, coma, and death
What is the generally accepted rate for correcting hypernatraemia?
No greater than 0.5 mmol/hour
Fill in the blank: Hypernatraemia can be caused by _______.
[dehydration]
What is a serious risk associated with cerebral oedema due to hypernatraemia correction?
Seizures, coma, and death
Name two conditions that can lead to osmotic diuresis.
- Hyperosmolar non-ketotic diabetic coma
- Diabetes insipidus
What happens to brain tissue when sodium and potassium levels drop rapidly?
It can lead to cerebral oedema
What organizations currently do not have clinical guidelines for hypernatraemia correction?
- NICE
- Royal College of Physicians
What is hypocalcaemia?
A condition characterized by low calcium levels in the blood.
What can reveal the cause of hypocalcaemia?
The clinical history combined with parathyroid hormone levels.
What are some 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
What can contaminate blood samples and affect calcium levels?
Contamination with EDTA may give falsely low calcium levels.
What is the management for severe hypocalcaemia?
IV calcium replacement is required.
What is the preferred method for IV calcium replacement?
Intravenous calcium gluconate, 10ml of 10% solution over 10 minutes.
What is a drawback of intravenous calcium chloride?
It is more likely to cause local irritation.
What monitoring is recommended during management of severe hypocalcaemia?
ECG monitoring is recommended.
What does further management of hypocalcaemia depend on?
It depends on the underlying cause.
What is hypocalcaemia?
A condition characterized by low extracellular calcium concentrations, affecting muscle and nerve function.
What are common features of hypocalcaemia?
Tetany, perioral paraesthesia, depression, cataracts, and prolonged QT interval on ECG.
What is tetany?
Muscle twitching, cramping, and spasm.
What is Trousseau’s sign?
Carpal spasm when the brachial artery is occluded by inflating a blood pressure cuff above systolic pressure.
Seen in around 95% of patients with hypocalcaemia and around 1% of normocalcaemic people.
What is Chvostek’s sign?
Twitching of facial muscles when tapping over the parotid gland.
Seen in around 70% of patients with hypocalcaemia and around 10% of normocalcaemic people.
What is hypokalaemia?
A condition characterized by low potassium levels in the blood.
What can potassium and hydrogen be thought of as?
Competitors.
What is hyperkalaemia associated with?
Acidosis, because as potassium levels rise, fewer hydrogen ions can enter the cells.
What are some causes of hypokalaemia with alkalosis?
Vomiting, thiazide and loop diuretics, Cushing’s syndrome, Conn’s syndrome (primary hyperaldosteronism).
What are some causes of hypokalaemia with acidosis?
Diarrhoea, renal tubular acidosis, acetazolamide, partially treated diabetic ketoacidosis.
What deficiency may also cause hypokalaemia?
Magnesium deficiency.
What may be difficult until magnesium deficiency is corrected?
Normalizing the potassium level.
What are some causes of hypomagnesaemia?
Causes include drugs (diuretics, proton pump inhibitors), total parenteral nutrition, diarrhoea, alcohol, hypokalaemia, hypercalcaemia, and metabolic disorders (Gitleman’s and Bartter’s).
What are the features of hypomagnesaemia?
Features may include paraesthesia, tetany, seizures, arrhythmias, and decreased PTH secretion leading to hypocalcaemia.
How does hypomagnesaemia affect ECG?
ECG features are similar to those of hypokalaemia and it can exacerbate digoxin toxicity.
What is the treatment for severe hypomagnesaemia (<0.4 mmol/L)?
Intravenous magnesium replacement is commonly given.
An example regime would be 40 mmol of magnesium sulphate over 24 hours.
What is the treatment for mild hypomagnesaemia (>0.4 mmol/L)?
Oral magnesium salts (10-20 mmol orally per day in divided doses) are recommended.
Diarrhoea can occur with oral magnesium salts.
What is hyponatraemia?
Hyponatraemia may be caused by water excess or sodium depletion.
What are causes of pseudohyponatraemia?
Causes of pseudohyponatraemia include hyperlipidaemia or taking blood from a drip arm.
What tests aid in diagnosing hyponatraemia?
Urinary sodium and osmolarity levels aid in making a diagnosis.
What does urinary sodium > 20 mmol/l indicate?
Indicates sodium depletion, renal loss; patient often hypovolaemic.
Causes include diuretics (thiazides, loop diuretics), Addison’s disease, and diuretic stage of renal failure.
What does urinary sodium < 20 mmol/l indicate?
Indicates sodium depletion, extra-renal loss; causes include diarrhoea, vomiting, and sweating.
Other causes include burns and adenoma of the rectum.
What conditions are associated with water excess?
Conditions include secondary hyperaldosteronism, heart failure, liver cirrhosis, nephrotic syndrome, IV dextrose, and psychogenic polydipsia.
Patient is often hypervolaemic and oedematous.
What is the urine osmolality in SIADH?
In SIADH, urine osmolality is > 500 mmol/kg.
Patient is often euvolaemic.
What is a common cause of hyponatraemia in hypothyroidism?
Hypothyroidism can cause hyponatraemia.
What is hyponatraemia?
Hyponatraemia is a condition characterized by low sodium levels in the blood.
What can untreated severe hyponatraemia lead to?
Untreated severe hyponatraemia may result in cerebral oedema and brain herniation.
What are the principles of managing hyponatraemia?
Management is based on the duration, severity, symptoms, and suspected aetiology of hyponatraemia.
What is considered acute hyponatraemia?
Acute hyponatraemia develops over a period of less than 48 hours.
What is considered chronic hyponatraemia?
Chronic hyponatraemia develops over a period greater than 48 hours.
What are the sodium level categories for hyponatraemia?
Mild: 130-134 mmol/L, Moderate: 120-129 mmol/L, Severe: < 120 mmol/L.
What are early symptoms of hyponatraemia?
Early symptoms may include headache, lethargy, nausea, vomiting, dizziness, confusion, and muscle cramps.
What are late symptoms of hyponatraemia?
Late symptoms may include seizures, coma, and respiratory arrest.
What are the suspected aetiologies of hyponatraemia?
Hypovolemic, euvolemic, and hypervolemic causes.
What initial steps should be taken in all patients with hyponatraemia?
Exclude a spurious result and review medications that may cause hyponatraemia.
What is the management for chronic hyponatraemia without severe symptoms if hypovolemic cause is suspected?
Administer normal saline (0.9% NaCl) and monitor serum sodium levels.
What is the management for euvolemic hyponatraemia?
Fluid restrict to 500-1000 mL/day and consider medications like demeclocycline or vaptans.
What is the management for hypervolemic hyponatraemia?
Fluid restrict to 500-1000 mL/day and consider loop diuretics and vaptans.
What is the management for acute hyponatraemia with severe symptoms?
Close monitoring in an HDU or above setting and use hypertonic saline (typically 3% NaCl) for correction.
What are vaptans?
Vaptans are vasopressin/ADH receptor antagonists that act primarily on V2 receptors, causing selective water diuresis.
What complications can arise from treating hyponatraemia?
Osmotic demyelination syndrome can occur due to over-correction of severe hyponatraemia.
What is the pathophysiology of osmotic demyelination syndrome?
It is thought to develop secondary to astrocyte and possibly oligodendrocyte apoptosis due to rapid correction of sodium levels.
What are the symptoms of osmotic demyelination syndrome?
Symptoms include dysarthria, dysphagia, paraparesis or quadriparesis, seizures, confusion, and coma.
What is the recommended rate of sodium level correction?
Na+ levels should only be raised by 4 to 6 mmol/L in a 24-hour period.
