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Endocrinology > Hyper/Hyponatraemia + SIADH > Flashcards

Hyper/Hyponatraemia + SIADH Flashcards

1
Q

What are the three main types of hyponatraemia?

A
  • Hyponatraemia with hypovolaemia
  • Hyponatraemia with euvolaemia
  • Hyponatraemia with hypervolaemia
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2
Q

What are extrarenal causes of hyponatraemia with hypovolaemia?

A
  • Vomiting
  • Diarrhoea
  • Haemorrhage
  • Burns
  • Pancreatitis
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3
Q

What are renal causes of hyponatraemia with hypovolaemia?

A
  • Osmotic diuresis
  • Diuretics
  • Adrenocortical insufficiency
  • Tubulo-interstitial renal disease
  • Unilateral renal artery stenosis
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4
Q

What are causes of hyponatraemia with increased extracellular volume?

A
  • Heart failure
  • Liver failure
  • Oliguric kidney injury
  • Hypoalbuminaemia
  • Severe hypothyroidism
  • Glucocorticoid deficiency
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5
Q

What are causes of euvolaemic hyponatraemia?

A
  • Vagal neuropathy
  • Addison’s Disease
  • Hypothyroidism
  • SIADH
  • Psychogenic polydipsia
  • Drugs
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7
Q

What are features of hyponatraemia?

A
  • Anorexia
  • Nausea
  • Malaise
  • Headache
  • Irritability
  • Confusion
  • Weakness
  • Decreased GCS/Drowsiness
  • Seizures
  • Encephalopathic
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8
Q

What is regarded biochemically as mild hyponatraemia?

A

Na+ = 130-135 mmol/L

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9
Q

What is regarded biochemically as moderate hyponatraemia?

A

Na+ = 125-130 mmol/L

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10
Q

What is regarded biochemically as profound hyponatraemia?

A

Na+ = < 125 mmol/L

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11
Q

How would you determine if someone had renal or extrarenal hypovolaemic hyponatraemia?

A

Urinary Na+ levels

  • If > 20 mmol/L = Kidney is cause
  • If < 20 mmol/L = Extrarenal
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12
Q

What volume status is SIADH associated with?

A

Euvolaemia

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13
Q

How would you approach establishing the cause of hyponatraemia (history and investigations)?

A
  • Through history - chronicity, med rec
  • Fluid status assessement
  • Bloods - U+E’s, Glucose, lipids, Cortisol, TFTs, LFTs, Plasma osmolality
  • Urine - Osmolality, Na+, K+
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14
Q

What is the general mechanism behind hypovolaemic hyponatraemia?

A

Loss of salt in excess of water loss

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15
Q

Why do extrarenal causes of hypovolaemic hyponatraemia cause urine concentration?

A

Urinary excretion of sodium falls in response to the volume depletion, as does water excretion, leading to concentrated urine containing <10 mmol/L of sodium.

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16
Q

What does a urine Na+ of > 20 mmol/L indicate in someone with hypovolaemic hyponatraemia?

A

Renal cause

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17
Q

What are signs of hypovolaemia?

A
  • Reduced skin tugor
  • Dry mucous membranes
  • Tachycardia
  • Low BP (esp. postural drop)
  • Sunken eyes
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18
Q

What are signs of hypervolaemia?

A
  • Oedema
  • Raised JVP
  • LVF
  • Ascites
19
Q

What would you particularly want to determine if someone had euvolaemic hyponatraemia?

A

If it was hypotonic hyponatraemia i.e.

  • Plasma Osm <275 mOsm/kg
  • Urine Osm > 100 mOsm/kg
20
Q

When determining how to manage someone with hyponatraemia, what would you want to determine first?

A

Are they symptomatic of asymptomatic

21
Q

How would you manage someone with hypovolaemic hypontraemia?

A

IV 0.9% saline

22
Q

How would you manage acute symptomatic hyponatraemia?

A

Move to level 2 care

  • Administer hypertonic saline
    1. 150 ml 3% saline over 15-20 minutes
    2. Check Na+ and Repeat 150 ml after 20 mins if no clinical improvement
    3. Stop hypertonic, administer slow 0.9% saline
    4. Check Na+ every 6 hours - Aim for correction no more than 10 mmol/L in first 24 hours. Thereafter, aim for 8 mmol/L
23
Q

What are causes of SIADH?

A
  • Malignancy - SCLC, thyroid, prostate
  • ADH secretion (ectopic
  • Drugs - SSRIs, ecstasy
  • CNS disease - meningencephalitis, abscess, subdural/subarachnoid, head injury, neurosurgery, Guillain barre
  • Hormone deficiency - hypothyroidism, adrenal insufficiency
  • Other - porphyria, trauma, major abdo/thoracic surgery, HIV
  • Pulmonary - TB, pneumonia, abscess, aspergillosis, SCLC
28
Q

What would you consider as the likely cause of euvolaemic hypovolaemia if someone had a urine Na+ > 20 mmol/L?

A

SIADH likely

29
Q

What can be a complication of giving sodium too quickly?

A

Osmotic demyelination syndrome - encompasses central pontine myelinolysis and extrapontine myelinolysis

30
Q

What is osmotic demyelination syndrome?

A

Neurones reclaim organic osmolytes slowly in the phase of rapid correction of hyponatraemia, resulting in a hypo-osmolar intracellular compartment and lead to shrinkage of cerebral vascular endothelial cells.

Consequently the blood–brain barrier is functionally impaired, allowing lymphocytes, complement, and cytokines to enter the brain, damage oligodendrocytes, activate microglial cells and cause demyelination.

31
Q

What rate should Na+ be corrected in the first 24 hours?

A

8 mmol/L

32
Q

What are features of central pontine myelinolysis?

A
  • Dysarthria
  • Dysphagia
  • Flaccid symmetric quadraparesis
  • Locked in syndrome and death if severe
33
Q

How would you manage someone with an electrolyte free water clearence of < 0.5 who had SIADH?

A

1 L fluid restriction, and reassess after 24-48 hrs

34
Q

How would you manage someone with an electrolyte free water clearence of 0.5-1.0 in someone with SIADH?

A

0.5 L fluid restriction, and reassess after 24-48 hrs

35
Q

How would you manage someone with a electrolyte free water clearence ratio of >1.0?

A

No fluid restriction

36
Q

What are features of extrapontine myelinolysis?

A
  • Tremor
  • Ataxia
  • Movement disorders
38
Q

What investigations would you do if you suspected SIADH?

A
  • Investigate underlying causes
  • Review medications
  • Consider CT head/Chest/Abdo/Pelvis
39
Q

What criteria are required for the diagnosis of SIADH?

A
  1. Euvolaemia
  2. Hyponatraemia
  3. Hypotonic hyponatraemia
  4. High urine osmolarity
  5. High urine Na+ (>20 mmol/L)
  6. Normal TFTs, Renal funtion
  7. No Diuretics
40
Q

What plasma osmolality is commonly seen in SIADH?

A

<260 mmol/L

41
Q

What would you want to calculate before determiningn how to treat SIADH?

A

Furst formula (electrolyte free water clearence) - Urine Na + K/Serum Na

45
Q

What other treatments would you consider using for someone with SIADH?

A
  • Tolvaptan
  • Demecocycline
46
Q

What are causes of hypernatraemia?

A
  • Diabetes insipidus
  • Iatrogenic - excessive saline
  • Osmotic diuresis - e.g. diabetes
  • Primary hyperaldosteronism
  • Drugs - Lithium, tetracyclines, amphotericin B
47
Q

What are symptoms of hypernatraemia?

A
  • Lethargy
  • Thirst
  • Weakness
  • Iriitability
  • Confusion
  • Coma
  • Seizures
  • Signs of dehydration
48
Q

What investigations might you consider doing in someone who is hypernatraemic?

A
  • Bloods - U+E’s, Plasma osmolality
  • Urine - Na+ and osmolality
  • Electrolyte-free water excretion
49
Q

How would you manage hypernatraemia?

A
  • Treat cause - Desmopressin, withdraw nephrotoxic drugs
  • Move to ITU if severe
  • Consider IV 0.9% saline if hypovolaemic
50
Q

What might a electrolyte free water excretion ratio of > 5.0 indicate in someone with hyperntatraemia?

A

Diabetes insipidus

Endocrinology (17 decks)

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