Hyponatraemia

Hyponatraema is a common finding, especially within our elderly population. However, its significance is is not a simple numbers game, and needs senior input. Prior to treatment the following need to be considered and balanced.

  1. Symptoms Severity – these are not exclusive to hyponatraemia and may be due to other disease processes (esp. if the low sodium is long-term)
  2. Sodium Level – the sodium concentration doesn’t always correlate to the clinical picture, and is dependant on speed of change, and co-morbidities
  3. Rate of Drop – the faster sodium levels drop the more symptomatic the patient often is (i.e. with long term hyponatraema the patient may be profoundly hyponatraemic but asymptomatic)
  4. Co-morbidities – Increasing sodium too quickly risks osmotic demyelination. How well will the patient cope with treatment?

Emergency treatment (hypertonic saline) is generally indicated in those with Severe Symptoms ONLY

1. Symptom Severity

  • Severe: Cardiorespiratory arrest, Seizures, Reduced Conscious level, Vomiting (sodium typically <130mmol/l)
  • Moderately Severe: Confusion, Headache, Nausea
  • Mild/None

2. Sodium Level

  • Profound: <125mmol/l
  • Moderate: 129-125mmol/l
  • Mild: 135-130mmol/l

3. Rate of Drop

Look at the patients previous blood results, if the hyponatraemia has been a long term issue, but the symptoms have just started, is there something else going on?

 

Emergency Treatment

  • In general hypertonic saline treatment should be reserved for those with Severe Symptoms ONLY + [Na] <130mmol/l
    • Less severely symptomatic patients would generally be better treated in a more planned manner, either under medicine or GP management but senior input will be important in striking the right balance
  • Aim to increase [Na] by 5mmol/l within 1 hour
  • If symptoms do not improve with Step 1 you may consider progressing to Step 2

Step 1

  1. 150ml 3% Sodium Chloride, 20min – this must be done in Resus with close monitoring
  2. Recheck [Na] – use iStat for quick result (if using lab proceed to 3. as results will have approx. 1hr delay) – Stop if [Na] increased by ≥5mmol/l
  3. 150ml 3% Sodium Chloride, 20min – if [Na] not increased sufficiently this may be repeated twice more (but keep checking [Na])
  4. Stop Hypertonic Sodium Chloride –  commence 0.9% NaCl start disease specific treatments and investigation, repeat U&E @ 6+12hr

Step 2 – consider if Step 1 has failed to increase [Na] by 5mmol/l

  1. 150ml 3% Sodium Chloride, 20min – this must be done in Resus with close monitoring, aiming to increase [Na] by 1mmol/l
  2. Indications to stop hypertonic saline
    • Symptomatic improvement
    • [Na] – Rise of 10mmol/l OR Reaches 130mmol/l (whichever happens first)

Urine Osmolality

If you get the chance – send a urine sample for osmolality as this can help the diagnostic process for medicine.

  • <100mOsm/kg – Primary polydipsia, Inappropriate IV fluid
  • >100mOsm/kg
    • Urine [Na] <30mmol/l – Heart Failure, GI losses, Diuretics, Portal hypertension, Low Albumin, 3rd Space loss
    • Urine [Na] >30mmol/l – Vomiting, SIADH, Addisons, Salt wasting, NSAID, AVP like drugs, (if on ACEi/ or diuretic consider the causes in [Na]<30mmol/l differentials)

 

Society of Endocrinology – Guide

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