Hypo- and hypernatraemia Flashcards
What is hyponatraemia?
A low serum sodium level, defined as serum sodium < 135mmol/l
Normal serum sodium levels range from 135-145mmol/l.
Why is hyponatraemia important?
It is the commonest electrolyte abnormality seen in hospital admissions and can be life-threatening.
What are the common causes of hyponatraemia?
Sodium loss and water gain.
What is the normal range for serum sodium?
135-145mmol/l.
What percentage of total body water do men and women have?
Men: 60% (42 litres), Women: 55% (38 litres).
What are the main compartments of total body water?
- Intracellular: ~30 litres
- Interstitial: ~9 litres
- Vascular: 3 litres
What is the significance of sodium in the body?
Sodium is the primary extracellular cation and osmole, critical for water balance.
What happens if we lose salt?
We will lose water, leading to hypovolaemia.
What happens if we gain water?
We will dilute our sodium, potentially leading to hyponatraemia.
What are the volume states associated with hyponatraemia?
- Normovolaemic hyponatraemia
- Hypovolaemic hyponatraemia
- Hypervolaemic hyponatraemia
What is pure water gain associated with in terms of volume status?
Normovolaemic or mild hypervolaemia.
What clinical scenario can lead to normovolaemic hyponatraemia?
SIADH, hypothyroidism, or iatrogenic causes.
What is hypovolaemic hyponatraemia?
Occurs when both salt and water loss happen, but water loss is insufficient to concentrate sodium.
What is hypervolaemic hyponatraemia?
Occurs when water gains exceed sodium gains.
What physiological responses occur in cardiac failure?
- Reduced cardiac output
- Reduced effective circulating volume
- Stimulation of renin/angiotensin/aldosterone and ADH
What can cause confusion in patients with hyponatraemia?
Hypotonic fluids diluting the extracellular space and causing cerebral oedema.
What are common clinical scenarios for fluid loss?
- Haemorrhage
- Vomiting
- Diarrhoea
- Burns
- Diuretic states
- Sequestration
- Iatrogenic causes (e.g., diuretics, stomas)
What are common clinical scenarios for fluid gain?
- Heart failure
- Liver failure
- Renal failure
- Hypothyroidism
- Psychogenic causes
- ADH excess
What is the vicious cycle in cardiac failure related to hyponatraemia?
Fluid overload worsens left ventricular function, leading to worsening hyponatraemia.
What is the key takeaway regarding salt and water balance?
Hyponatraemia is common and usually reflects water movement rather than sodium movement.
Fill in the blank: Sodium is the primary _______ cation.
extracellular
True or False: Water movement is passive, while sodium movement requires energy.
True
What is hypernatraemia?
A condition characterized by elevated sodium levels in the blood
Major cause is concentration by water loss.
What is the major cause of hyponatraemia?
Dilution by water gain
This occurs when water intake exceeds sodium intake.
What are the important terms related to sodium and water homeostasis?
- Hyponatraemia
- Hypernatraemia
- Normo (or eu-) volaemia
- Hypovolaemia
- Hypervolaemia
These terms describe various states of sodium and fluid balance in the body.
What are the common clinical signs of hypernatraemia?
Signs include confusion, weakness, and thirst
Symptoms may vary based on severity and rapidity of onset.
Fill in the blank: The major cause of hypernatraemia is _______.
concentration by water loss.
What are the common clinical scenarios leading to water loss?
- Haemorrhage
- Vomiting
- Diarrhoea
- Burns
- Diuretic states
- Sequestration
- Miscellaneous renal diseases
These conditions can cause significant fluid loss leading to hypernatraemia.
True or False: Hypervolaemia is commonly associated with hypernatraemia.
False
Hypernatraemia is almost always associated with hypovolaemia.
What specific causes can lead to hypernatraemia?
- Pure water loss
- Reduced water intake
- High sodium intake
This includes conditions like diabetes insipidus and excessive sweating.
What is the role of ADH in water homeostasis?
ADH regulates water reabsorption in the kidneys
Abnormalities in ADH secretion can lead to disorders like SIADH and diabetes insipidus.
What does SIADH stand for?
Syndrome of Inappropriate Antidiuretic Hormone secretion
It leads to excessive water reabsorption and dilutional hyponatraemia.
What are the specific tests for investigating altered sodium and water homeostasis?
- Plasma osmolality
- Urine osmolality
- Urine sodium concentration
These tests help differentiate between causes of sodium imbalance.
What is the recommended rate of correction for asymptomatic hyponatraemia?
4-10 mmol/l/day
Rapid correction can lead to complications like central pontine myelinolysis.
What are the clinical features of volume depletion?
- Postural hypotension
- Tachycardia
- Absence of JVP
- Reduced skin turgor
Symptoms include thirst, dizziness, weakness, and confusion.
What are the clinical features of volume excess?
- Hypertension
- Tachycardia
- Raised JVP
- Oedema
Symptoms may include nausea, dyspnoea, and confusion.
How is hyponatraemia managed?
Restrict water intake
Treatment focuses on correcting the underlying water imbalance.
How is hypernatraemia managed?
Administer water
Oral intake is preferred, but IV fluids like 5% dextrose can be used.
What is the significance of urine osmolality in diagnosing diabetes insipidus?
Urine osmolality is usually low in diabetes insipidus
This reflects the kidneys’ inability to concentrate urine due to insufficient ADH.
What are the causes of cranial diabetes insipidus?
- Pituitary tumor
- Head injury
- Meningitis
- Genetic factors
These conditions can affect ADH production.
What is nephrogenic diabetes insipidus?
A condition where there is reduced tubular response to ADH
Causes include genetic factors and certain medications like lithium.
