Sodium Flashcards
What are the biochemical findings in Addison’s disease?
High potassium, low sodium, normal osmolality.
What is the clinical presentation of an Addisonian crisis?
Nausea and shock.
What are the biochemical findings in Conn’s syndrome?
Low potassium, high sodium, hypertension.
What is the primary cause of Conn’s syndrome?
Primary hyperaldosteronism.
What are the biochemical findings in SIADH?
High urinary sodium,
high urine osmolality,
low plasma osmolality.
What are the common causes of SIADH? (4)
Intracerebral
Alveolar
Drugs
Hormones
How is SIADH managed? (3)
Fluid restriction
Demeclocycline
Tolvaptan
What are the biochemical findings in psychogenic polydipsia? (4)
Low sodium
Low potassium
Low urine osmolality
Low plasma osmolality
What is the key differentiation between psychogenic polydipsia and DI? (1)
Polydipsia: Low sodium, low K⁺
DI: High sodium, hypovolaemic
What are the biochemical findings in DI? (3)
High sodium
Low urine osmolality
Hypovolaemia
What is the difference between cranial and nephrogenic DI? (2)
Cranial DI: Urine concentrates after desmopressin → managed with replacement DDAVP
Nephrogenic DI: No change in urine after desmopressin → causes include genetics, drugs (e.g., lithium) → managed with thiazide diuretics
What is the most common cause of sudden-onset DI? (1)
Pituitary metastases
What is the investigation of choice for DI due to pituitary metastases? (1)
MRI
What are the biochemical findings in HONK? (4) (Hyperosmolar Hyperglycaemic state)
Low potassium
High glucose
High serum osmolality (>320)
High bicarbonate (>15 mmol/L)
How can diabetes mellitus affect sodium levels? (1)
High lipids create pseudohyponatraemia with normal osmolality
What are the biochemical findings 3 days post-prostatectomy? (3)
Low sodium
Normal potassium
Normal volume
What causes hyponatraemia post-prostatectomy? (1)
Fluid overload (plain water given in TURP)
What are the biochemical findings in CAH? (4)
Hyponatraemia
Hyperkalaemia
Inadequate aldosterone synthesis
Hyperandrogenism
What is the main driving force behind hyponatraemia?
Water problem! (Not a sodium issue), due to excess extracellular water
What are the two stimulants of ADH secretion? (2)
High osmolality (detected by osmoreceptors in the hypothalamus).
Low blood pressure or blood volume (detected by baroreceptors in the aorta/atria/carotids).
What is the only exception where hyponatraemia is not caused by ADH excess?
Psychogenic polydipsia.
What is the maximum sodium correction rate per hour to prevent central pontine myelinolysis (CPM)?
No more than 8–10 mmol/L in the first 24 hours.
What should you measure after diagnosing hyponatraemia to determine its type? (2)
Serum osmolality.
Urine osmolality.
What are the signs of hyponatraemia? (3)
Confusion.
Seizures.
Reduced GCS.
What are the signs of hypovolaemia? (3)
Reduced skin turgor.
Dry mucous membranes.
Postural hypotension.
What is the most reliable marker of hypovolaemia?
Urine sodium concentration (< 20 mmol/L).
How do you manage hypovolaemic hyponatraemia?
0.9% saline volume replacement.
What are the causes of euvolaemic hyponatraemia? (2)
Hypothyroidism (check TFTs).
SIADH (serum and urine osmolality).
How do you diagnose SIADH? (3)
Serum osmolality is low.
Urine sodium and osmolality are high.
Exclude hypothyroidism and adrenal insufficiency.
What is the treatment for SIADH? (2)
Fluid restriction.
Additional drugs such as demeclocycline or tolvaptan (V2 receptor antagonist).
What are the signs of hypervolaemia? (3)
Raised JVP.
Peripheral oedema.
Pulmonary oedema.
What are two possible urine sodium levels and their causes in hypervolaemic hyponatraemia? (2)
Urine sodium > 20 mmol/L: renal causes (e.g., nephrotic syndrome, renal failure).
Urine sodium < 20 mmol/L: cardiac failure or cirrhosis.
What is the treatment for hypervolaemic hyponatraemia?
Fluid restriction and treat the underlying cause.
What is pseudohyponatraemia, and what causes it? (2)
Hyponatraemia with normal plasma osmolality.
Causes: Increased protein or lipids (e.g., multiple myeloma, diabetes mellitus).
How do you manage severe hyponatraemia (e.g., coma, seizures)?
Hypertonic 3% saline.
What is the primary cause of hypernatraemia?
Unreplaced water loss.
What are the causes of hypernatraemia? (3)
GI losses (e.g., diarrhoea).
Sweat losses.
Renal losses (e.g., osmotic diuresis in diabetes mellitus, diabetes insipidus).
What investigations help diagnose diabetes insipidus? (4)
Blood glucose (to rule out diabetes mellitus).
Plasma osmolality (high).
Urine osmolality (low).
Water deprivation test.
How do you manage hypernatraemia? (2)
Correct water deficit with 5% dextrose.
Correct extracellular fluid volume with 0.9% saline.
