Hyponatraemia

Causes:

Hypovoaemic:

·      Vomiting

·      Addison’s disease

Euvolaemic (ie. SIADH)

·      Major surgery

·      Meningitis

·      Subarachnoid

·      Head injury

·      Pneumonia

·      Drugs

Hpervolaemiac

·      CCF

·      Cirrhosis

·      Nephrotic syndrome

·      Myxoedema

[Gloucester Hospital guidelines]

Na < 130mmol/L is significant

Symptoms usually occur when <125 mmol/L

General steps:

–       Clinical assessment

–       Bloods to include

o   Renal function

o   Serum osmolality

o   Glucose

o   Cortisol 9am

o   TFTs

o   LFTs

–       Urine osmolality and urine Na

–       Review drug charts and stop contributing meds

–       Review fluid charts – stop use of dextrose infusions

Acute Hyponatreaemia:

Acute symptoms: CNS disturbance, confusion, headache, drowsiness, reduced GCS, seizures, encephalopathic

Treatment:

–       Ideally move to a level 2 monitored bed

–       If Na<120 mmol/L AND no other cause identified,

o   Administer 1.8% hypertonic saline 150ml iv over 15 minutes

o   Aim to improve symptoms rather than correct Na

o   Repeat VBG after 20mins and if no change in Na, give further bolus

–       Re-check Na at 6, 12, 24 and 48 hours

o   Na should not rise > 6mmol/L in first 6 hours or > 10mmol/L in first 24 hours

o   If rapid overcorrection, use IV dextrose or consider desmopressin

Chronic hyponatraemia

Assess hydration status: hypovolamic, euvolaemic or hypervolaemic

Hypovolamic:

o   Treat with 0.9% saline

Hypervolaemic:

–       Treat underlying cause eg. CCF, renal failure, liver failure

Normovolaemic:

–       Check plasma and urine osmolalities

o   Plasma <275 mOsm/kg AND Urine >100 mOsm/kg = Hypotonic Hyponatraemia

§  Check urine Na+

·      Urine Na>20 = Likely SIADH

·      Urine Na<20 = Re-consider hypo/hypervolaemia

o   Plasma >275 mOsm/kg = Hypertonic hyponatraemia

§  Consider hyperglycaemia (eg.HHS), mannitol infusion

o   Urine Osm < 100 = consider primary polydipsia

Safe limit of correction is 10mmol/L in first 24hours and then 8 mmol/L in subsequent days.

Groups more at risk of osmotic demyelination are elderly patients, children <16, malnourished, alcoholics, CNS disease and post operative patients. Have a lower rate of correction in this group.