Hyponatremia

Question 1

Investigations to do in Hyponatremia

Answer 1

Blood: Na, K, urine, creatinine, osmolality

Urine: Na, creat, osmolality

Monitor urine output

Monitor serum sodium

Depending on history and examination: LFT, TSH, Cortisol, uric acid

Consider neuroimaging if other cause of obtundation/seizures anticipated

South African setting – consider tuberculosis

Question 2

Approach to Hyponatremia in EC

Answer 2

Aggressively treat the following (UpToDate):

Severe symptoms: obtunded, seizures
Acute hyponatremia with symptoms, even if mild
Hyperacute hyponatraemia (primary polydipsia, MDMA intoxication)
With:

100ml Hypertonic Saline 3% over 5-10 minutes (Paeds: 3ml/kg of 3% hypertonic saline)

Can be repeated x 1 if still seizing

Stop hypertonic saline administration thereafter

*note: hypertonic saline can be given safely via peripheral iv

*note: sodium bicarbonate 8.5% can be given in place of hypertonic saline if no hypertonic saline available

Give 1-2 ml of 8.4% NaHCO3 iv.

Question 3

Normal serum osmolality

Answer 3

Normal serum osmolality = 275-295 mOsm/l

Question 4

Calculate osmolality and osmolar gap

Answer 4

Calculated osmolality = 2x Na (mmol/l) + Glucose (mmol/l) + urea (mmol/l) (2 salts, a sugar and bun!)

Osmol gap = Measured osmolality – calculated osmolality. If osmol gap >10 – look for exogenous substances!

Question 5

How does the busy respond to decreased effective circulating volume

Answer 5

Carotid and aortic arch receptors: symphathetic activity increases, ADH release
Atri and ventricles: release natriuretic peptides
Glomerular afferent arterioles: activate RAA system

Question 6

Management of Hyponatremia

Answer 6

Emergency
-if severe symptoms (seizures, coma), acute Hyponatremia even if mild
1. 100ml Hypertonic saline 3% over 5-1min (kids 3ml/kg 3% ) repeat if still seizing
2. NaHCO3 8.5% can be used in place of hypertonic saline

Non urgent
Fluid restriction to 50-60% of daily maintenance requirements
-hypovolemia: 250-500ml isotonic blouses
-hypervolemia: consider loop diuretics
Prevent worsening Hyponatremia -help lock Iv
-water intake restriction
Treat the cause

Question 7

Complications of overtreating Hyponatremia

Answer 7

Osmotic demyelination syndrome

Sx include ataxia, Neuro deficits and locked in syndrome

Question 8

How to prevent overcorrection

Answer 8

Monitor serum sodium after each dose of hypertonic saline, hourly for 6 hours after that, and regularly for the next 24 hours

Strictly monitor intake and output

Administer DDAVP (Desmopressin) if:
- Urine output suddenly increases (i.e. > 100ml/hour)
-Urine osmolality > 100mmol/l

Question 10

In what scenarios does over correction of Hyponatremia occur?

Answer 10

Hypovolaemic hyponatraemia – kidneys are keeping water back appropriately (ADH). As soon as the volume status improves, the kidneys allow more water to pass, and the sodium levels increase quickly.

Treating the cause. As drugs that can cause hyponatraemia (thiazides, SSRIs) are discontinued, or alcohol intake is stopped (beer potomania), the sodium levels will rapidly increase faster than expected.

Not taking additional potassium supplementation into account. In the hyponatraemic hypokalemic patient, giving IV potassium will cause more potassium to be taken up into the cells, resulting in more sodium into the extracellular/intravascular space.

Question 11

How to prevent overcorrection

Question 12

How to treat overcorrection of Hyponatremia

Answer 12

DDAVP

Consider 5% dextrose water to lower sodium concentrations

Consult with a specialist nephrologist