Hyper/Hyponatraemia + SIADH Flashcards
What are the three main types of hyponatraemia?
- Hyponatraemia with hypovolaemia
- Hyponatraemia with euvolaemia
- Hyponatraemia with hypervolaemia
What are extrarenal causes of hyponatraemia with hypovolaemia?
- Vomiting
- Diarrhoea
- Haemorrhage
- Burns
- Pancreatitis
What are renal causes of hyponatraemia with hypovolaemia?
- Osmotic diuresis
- Diuretics
- Adrenocortical insufficiency
- Tubulo-interstitial renal disease
- Unilateral renal artery stenosis
What are causes of hyponatraemia with increased extracellular volume?
- Heart failure
- Liver failure
- Oliguric kidney injury
- Hypoalbuminaemia
- Severe hypothyroidism
- Glucocorticoid deficiency
What are causes of euvolaemic hyponatraemia?
- Vagal neuropathy
- Addison’s Disease
- Hypothyroidism
- SIADH
- Psychogenic polydipsia
- Drugs
What are features of hyponatraemia?
- Anorexia
- Nausea
- Malaise
- Headache
- Irritability
- Confusion
- Weakness
- Decreased GCS/Drowsiness
- Seizures
- Encephalopathic
What is regarded biochemically as mild hyponatraemia?
Na+ = 130-135 mmol/L
What is regarded biochemically as moderate hyponatraemia?
Na+ = 125-130 mmol/L
What is regarded biochemically as profound hyponatraemia?
Na+ = < 125 mmol/L
How would you determine if someone had renal or extrarenal hypovolaemic hyponatraemia?
Urinary Na+ levels
- If > 20 mmol/L = Kidney is cause
- If < 20 mmol/L = Extrarenal
What volume status is SIADH associated with?
Euvolaemia
How would you approach establishing the cause of hyponatraemia (history and investigations)?
- Through history - chronicity, med rec
- Fluid status assessement
- Bloods - U+E’s, Glucose, lipids, Cortisol, TFTs, LFTs, Plasma osmolality
- Urine - Osmolality, Na+, K+
What is the general mechanism behind hypovolaemic hyponatraemia?
Loss of salt in excess of water loss
Why do extrarenal causes of hypovolaemic hyponatraemia cause urine concentration?
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.
What does a urine Na+ of > 20 mmol/L indicate in someone with hypovolaemic hyponatraemia?
Renal cause
What are signs of hypovolaemia?
- Reduced skin tugor
- Dry mucous membranes
- Tachycardia
- Low BP (esp. postural drop)
- Sunken eyes
What are signs of hypervolaemia?
- Oedema
- Raised JVP
- LVF
- Ascites
What would you particularly want to determine if someone had euvolaemic hyponatraemia?
If it was hypotonic hyponatraemia i.e.
- Plasma Osm <275 mOsm/kg
- Urine Osm > 100 mOsm/kg
When determining how to manage someone with hyponatraemia, what would you want to determine first?
Are they symptomatic of asymptomatic
How would you manage someone with hypovolaemic hypontraemia?
IV 0.9% saline
How would you manage acute symptomatic hyponatraemia?
Move to level 2 care
- Administer hypertonic saline
- 150 ml 3% saline over 15-20 minutes
- Check Na+ and Repeat 150 ml after 20 mins if no clinical improvement
- Stop hypertonic, administer slow 0.9% saline
- Check Na+ every 6 hours - Aim for correction no more than 10 mmol/L in first 24 hours. Thereafter, aim for 8 mmol/L
What are causes of SIADH?
- 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
What would you consider as the likely cause of euvolaemic hypovolaemia if someone had a urine Na+ > 20 mmol/L?
SIADH likely
What can be a complication of giving sodium too quickly?
Osmotic demyelination syndrome - encompasses central pontine myelinolysis and extrapontine myelinolysis
What is osmotic demyelination syndrome?
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.
What rate should Na+ be corrected in the first 24 hours?
8 mmol/L
What are features of central pontine myelinolysis?
- Dysarthria
- Dysphagia
- Flaccid symmetric quadraparesis
- Locked in syndrome and death if severe
How would you manage someone with an electrolyte free water clearence of < 0.5 who had SIADH?
1 L fluid restriction, and reassess after 24-48 hrs
How would you manage someone with an electrolyte free water clearence of 0.5-1.0 in someone with SIADH?
0.5 L fluid restriction, and reassess after 24-48 hrs
How would you manage someone with a electrolyte free water clearence ratio of >1.0?
No fluid restriction
What are features of extrapontine myelinolysis?
- Tremor
- Ataxia
- Movement disorders
What investigations would you do if you suspected SIADH?
- Investigate underlying causes
- Review medications
- Consider CT head/Chest/Abdo/Pelvis
What criteria are required for the diagnosis of SIADH?
- Euvolaemia
- Hyponatraemia
- Hypotonic hyponatraemia
- High urine osmolarity
- High urine Na+ (>20 mmol/L)
- Normal TFTs, Renal funtion
- No Diuretics
What plasma osmolality is commonly seen in SIADH?
<260 mmol/L
What would you want to calculate before determiningn how to treat SIADH?
Furst formula (electrolyte free water clearence) - Urine Na + K/Serum Na
What other treatments would you consider using for someone with SIADH?
- Tolvaptan
- Demecocycline
What are causes of hypernatraemia?
- Diabetes insipidus
- Iatrogenic - excessive saline
- Osmotic diuresis - e.g. diabetes
- Primary hyperaldosteronism
- Drugs - Lithium, tetracyclines, amphotericin B
What are symptoms of hypernatraemia?
- Lethargy
- Thirst
- Weakness
- Iriitability
- Confusion
- Coma
- Seizures
- Signs of dehydration
What investigations might you consider doing in someone who is hypernatraemic?
- Bloods - U+E’s, Plasma osmolality
- Urine - Na+ and osmolality
- Electrolyte-free water excretion
How would you manage hypernatraemia?
- Treat cause - Desmopressin, withdraw nephrotoxic drugs
- Move to ITU if severe
- Consider IV 0.9% saline if hypovolaemic
What might a electrolyte free water excretion ratio of > 5.0 indicate in someone with hyperntatraemia?
Diabetes insipidus
