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Path > Chempath - Sodium > Flashcards

Chempath - Sodium Flashcards

1
Q

When is the hyponatraemia, rather than the underlying cause treated?

A

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)

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2
Q

When is hyponatraemia a medical emergency?

A

When it’s symptomatic

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3
Q

What are the symptoms of hyponatraemia?

A
  • Nausea and vomiting (<134mmol/L)
  • Confusion (<131mmol/L)
  • Seizures, non-cardiogenic pulmonary oedema (<125mmol/L)
  • Coma (<117mmol/L)
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4
Q

What is true hyponatraemia?

A

Low serum Na+ levels and low plasma osmolality

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5
Q

What can cause low serum Na+ but high plasma osmolality?

A

Glucose/ mannitol infusion

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6
Q

What can cause low Na+ but normal serum osmolality?

A
  • False result
  • Drip arm sample
  • Pseudohyponatraemia (due to hyperlipidaemia/ paraproteinaemia)
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7
Q

What is TURP syndrome?

A

Hyponatraemia from irrigation absorbed through the damaged prostate

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8
Q

What is used to irrigate during TURP?

A

Glycine 1.5%

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9
Q

What is the clinical presentation of TURP syndrome due to?

A

Metabolism of glycine and hyponatraemia caused by dilution

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10
Q

Why do the lab tests show hyperlipidaemia or hyperparaproteinaemia as pseudohyponatraemia?

A

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

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11
Q

Why does glucose/ mannitol cause false hyponatraemia?

A

Osmotically active solutes, therefore draw water from the cells into the plasma, diluting the Na+ concentration

(technically a true hyponatraemia)

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12
Q

What are the causes of hypovolaemic hyponatraemia?

A

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

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13
Q

What is the management of hypovolaemic hyponatraemia?

A

Fluid replacement with 0.9% NaCl

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14
Q

What are the causes of euvolaemic hyponatraemia?

A

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

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15
Q

What is the management of euvolaemic hyponatraemia?

A

Treat the cause

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16
Q

What are the causes of hypervolaemic hyponatraemia?

A

Urine Na <20
- Heart failure
- Cirrhosis
- Inappropriate IV fluid

Urine Na >20
- Renal failure (AKI, CKD)

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17
Q

What is the managment of hypervolaemic hyponatraemia?

A

Fluid restrict and correct the cause

18
Q

What should be stopped before measuring urinary sodium?

A

Diuretics

19
Q

How can cirrhosis lead to hyponatraemia?

A
  • Poor breakdown of vasodilators like NO
  • Vasodilation and decreased blood pressure
  • Increased release of ADH
  • Increased plasma Na+ dilution
20
Q

What is the management of Addison’s?

A

Hydrocortisone +- Fludrocortisone

21
Q

What is the recommended Na+ increase in hyponatraemia?

A

No more than 8-10mmol/L per 24 hours

22
Q

What can cause hyponatraemia post surgery?

A
  • SIADH
  • Over hydration with hypotonic IV fluids
  • Transient increase in ADH due to stress of surgery
23
Q

What investigations are needed to confirm SIADH?

A
  • Normal 9am cortisol
  • Normal TFTs

Diagnosis of exclusion

24
Q

What are the causes of SIADH?

A
  • Malignancy (SCLC most common)
  • CNS disorders
  • Chest disease (TB, pneumonia, abscess)
  • Drugs (opiates, SSRIs, TCAs, carbamazepine, PPIs)
25
Q

What is the management for SIADH?

A
  • Fluid restrict
  • Demeclocycline (increases ADH resistance)
  • Tolvaptan (blocks the V2 receptor)

If severe, consider giving slow IV hypertonic 3% saline

26
Q

Why can chronic hypothyroidism lead to euvolaemic hyponatraemia?

A

Reduced CO and renal blood flow –> decreased GFR and water retention

27
Q

What is the best investigation for volume status (after bedside examination)?

A

Paired urine and serum osmolalities/ urinary sodium

28
Q

At what value is hypernatraemia clinically significant?

A

> 148mmol/L

29
Q

What are the symptoms of hypernatraemia?

A
  • Thirst
  • Confusion
  • Seizures and ataxia
  • Coma
30
Q

What can rapid correction of hypernatraemia lead to?

A

Cerebral oedema

31
Q

What are the causes of hypovolaemic hypernatraemia?

A

Urinary Na <20
- GI losses: D&V
- Skin losses: sweating, burns

Urine Na >20
- Loop diuretics
- Osmotic diuresis
- Renal disease

32
Q

What are the causes of euvolaemic hypernatraemia?

A
  • Resp (tachypnoea)
  • Skin (sweating, fever)
  • Argenine vasopressin resistance/ deficiency
33
Q

What are the causes of hypervolaemic hypernatraemia?

A
  • Mineralocorticoid excess (Conn’s)
  • Inappropriate saline
34
Q

What is the managment for hypernatraemia?

A

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

35
Q

What are the causes of argenine vasopressin deficiency?

A
  • Surgery
  • Trauma
  • Tumours (craniopharyngioma)
  • Autoimmune hypophysitis
36
Q

What is the managment of AVP D?

A

Desmopressin

37
Q

What are the causes of AVP R?

A
  • Inherited channelopathies
  • Drugs: lithium, demeclocycline
  • Electrolyte disturbances: hypokalaemia, hypercalcaemia
38
Q

What is the treatment for AVP R?

A

Thiazide diuretics

39
Q

What are the investigations for AVP D/R?

A
  1. Serum glucose (exclude DM)
  2. Serum K+ (exclude hypokalaemia)
  3. Serum Ca2+ (exclude hypercalcaemia)
  4. Plasma and urine osmolalities
  5. 8-hour water deprivation test
40
Q

Why can reduced glucocorticoids lead to euvolaemic hyponatraemia?

A
  • Disrupts the feedback loop for aldosterone (same feedback loop)
  • Cortisol regulates renal sensitivity to ADH, therefore reduced cortisol increases ADH activity

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