Chempath - Sodium Flashcards
When is the hyponatraemia, rather than the underlying cause treated?
When Na+ <125mmol/L and symptomatic
(Even if Na+ levels really low eg. 110 but they’re asymptomatic, it’s more dangerous to correct too quickly than leave the patient at that level - compensated hyponatraemia rarely an emergency)
When is hyponatraemia a medical emergency?
When it’s symptomatic
What are the symptoms of hyponatraemia?
- Nausea and vomiting (<134mmol/L)
- Confusion (<131mmol/L)
- Seizures, non-cardiogenic pulmonary oedema (<125mmol/L)
- Coma (<117mmol/L)
What is true hyponatraemia?
Low serum Na+ levels and low plasma osmolality
What can cause low serum Na+ but high plasma osmolality?
Glucose/ mannitol infusion
What can cause low Na+ but normal serum osmolality?
- False result
- Drip arm sample
- Pseudohyponatraemia (due to hyperlipidaemia/ paraproteinaemia)
What is TURP syndrome?
Hyponatraemia from irrigation absorbed through the damaged prostate
What is used to irrigate during TURP?
Glycine 1.5%
What is the clinical presentation of TURP syndrome due to?
Metabolism of glycine and hyponatraemia caused by dilution
Why do the lab tests show hyperlipidaemia or hyperparaproteinaemia as pseudohyponatraemia?
Because the lab measures Na+/plasma volume rather than Na+/water, therefore proteins and lipids will be included in plasma volume making Na+ appear lower
Why does glucose/ mannitol cause false hyponatraemia?
Osmotically active solutes, therefore draw water from the cells into the plasma, diluting the Na+ concentration
(technically a true hyponatraemia)
What are the causes of hypovolaemic hyponatraemia?
Urine Na <20
- Diarrhea
- Vomiting
- Skin losses eg. burns, sweat
- Third space losses eg. burns, ascites
Urine Na >20
- Adrenocortical insufficiency (Addison’s)
- Renal failure/ disease
- Diuretics
- Cerebral salt wasting
What is the management of hypovolaemic hyponatraemia?
Fluid replacement with 0.9% NaCl
What are the causes of euvolaemic hyponatraemia?
Urine Na <40 and urine osmolality <100
- Acute water load
- Psychogenic polydipsia
- Tea and toast/ beer diet
Urine Na >40 and urine osmolality >100
- SIADH
- Glucocorticoid deficiency
- Chronic hypothyroidism
- Acute water load
What is the management of euvolaemic hyponatraemia?
Treat the cause
What are the causes of hypervolaemic hyponatraemia?
Urine Na <20
- Heart failure
- Cirrhosis
- Inappropriate IV fluid
Urine Na >20
- Renal failure (AKI, CKD)
What is the managment of hypervolaemic hyponatraemia?
Fluid restrict and correct the cause
What should be stopped before measuring urinary sodium?
Diuretics
How can cirrhosis lead to hyponatraemia?
- Poor breakdown of vasodilators like NO
- Vasodilation and decreased blood pressure
- Increased release of ADH
- Increased plasma Na+ dilution
What is the management of Addison’s?
Hydrocortisone +- Fludrocortisone
What is the recommended Na+ increase in hyponatraemia?
No more than 8-10mmol/L per 24 hours
What can cause hyponatraemia post surgery?
- SIADH
- Over hydration with hypotonic IV fluids
- Transient increase in ADH due to stress of surgery
What investigations are needed to confirm SIADH?
- Normal 9am cortisol
- Normal TFTs
Diagnosis of exclusion
What are the causes of SIADH?
- Malignancy (SCLC most common)
- CNS disorders
- Chest disease (TB, pneumonia, abscess)
- Drugs (opiates, SSRIs, TCAs, carbamazepine, PPIs)
What is the management for SIADH?
- Fluid restrict
- Demeclocycline (increases ADH resistance)
- Tolvaptan (blocks the V2 receptor)
If severe, consider giving slow IV hypertonic 3% saline
Why can chronic hypothyroidism lead to euvolaemic hyponatraemia?
Reduced CO and renal blood flow –> decreased GFR and water retention
What is the best investigation for volume status (after bedside examination)?
Paired urine and serum osmolalities/ urinary sodium
At what value is hypernatraemia clinically significant?
> 148mmol/L
What are the symptoms of hypernatraemia?
- Thirst
- Confusion
- Seizures and ataxia
- Coma
What can rapid correction of hypernatraemia lead to?
Cerebral oedema
What are the causes of hypovolaemic hypernatraemia?
Urinary Na <20
- GI losses: D&V
- Skin losses: sweating, burns
Urine Na >20
- Loop diuretics
- Osmotic diuresis
- Renal disease
What are the causes of euvolaemic hypernatraemia?
- Resp (tachypnoea)
- Skin (sweating, fever)
- Argenine vasopressin resistance/ deficiency
What are the causes of hypervolaemic hypernatraemia?
- Mineralocorticoid excess (Conn’s)
- Inappropriate saline
What is the managment for hypernatraemia?
Fluids (most causes are hypovolaemic)
- Fluid choice not important, deciding quickly is important
- Regular NaCl will work (will induce initial hypernatraemia then hyponatraemia)
- Don’t correct too quickly (cerebral oedema)
- Encourage PO fluids
What are the causes of argenine vasopressin deficiency?
- Surgery
- Trauma
- Tumours (craniopharyngioma)
- Autoimmune hypophysitis
What is the managment of AVP D?
Desmopressin
What are the causes of AVP R?
- Inherited channelopathies
- Drugs: lithium, demeclocycline
- Electrolyte disturbances: hypokalaemia, hypercalcaemia
What is the treatment for AVP R?
Thiazide diuretics
What are the investigations for AVP D/R?
- Serum glucose (exclude DM)
- Serum K+ (exclude hypokalaemia)
- Serum Ca2+ (exclude hypercalcaemia)
- Plasma and urine osmolalities
- 8-hour water deprivation test
Why can reduced glucocorticoids lead to euvolaemic hyponatraemia?
- Disrupts the feedback loop for aldosterone (same feedback loop)
- Cortisol regulates renal sensitivity to ADH, therefore reduced cortisol increases ADH activity
