This document discusses the diagnosis and treatment of hyponatremia. It defines acute and chronic hyponatremia and outlines their differing risks. For severe symptoms, it recommends rapidly increasing serum sodium with 3% saline to prevent brain herniation. For moderate symptoms, the priority is preventing further sodium decreases rather than increases. Asymptomatic hyponatremia should be treated by optimizing volume status and restricting fluid intake. The risks of unpredictable rapid sodium correction are also covered.

1. Ubaidur Rahaman
Internist and Critical Care Specialist

2. HYPONATREMIA
Defined as serum Na less than 135 mmol/L
Acute Hyponatremia: Existence of less than 48 hours
Chronic Hyponatremia: Existence of more than 48 hours
Severe symptoms: vomiting, seizures, obtundation,
Moderately severe symptoms: headache, confusion, drowsiness
Acute hyponatremia: low serum osmolality exposes risk of cerebral
edema and herniation
Chronic Hyponatremia: Adaptive mechanism obviates risk of cerebral
edema
but at heightened risk of osmotic demyelinationSeverity of symptoms correlate with rate and magnitude of fall in
serum Na
Once treatment is begin unpredictable rapid correction and paradoxical
fall (desalination) in serum sodium concentration should be watched
for and prevented/ corrected

3. SEVERESYMPTOMS Result of cerebral edema and increased intracranial pressure
with impending risk of death due to herniation
Risk of herniation outweighs the risk of osmotic demyelination
Rapidly increasing serum osmolality is an urgency to prevent brain
herniation
Rapid increase of 5 mmol/L of serum sodium in the first hour
may decrease brain edema and risk of herniation
If symptoms does not improve after first hour rule out other causes

4. HYPONATREMIA
SEVERE SYMPTOMS
3% Saline @ 2ml/kg IV over
20 min
REPEAT 3% SALINE TILL
Symptoms improve or
rise in S.Na by 5 mmol/L
in 1 hour
Symptoms
improved
STOP 3% SALINE
Start isotonic saline @
1ml/kg
Evaluate and treat cause
Check S.Na at 6 and 12
hours
Symptoms
persisting
CONTINUE 3% SALINE
@ 1mmol/L/hour rise in S.Na
till symptoms improve or S.Na
rises by 10 mmol/L
Check S.Na every 4 hourly
Evaluate cause and treat
Rule out other causes of
symptoms

5. MODERATELYSEVERE
SYMPTOMS Result of cerebral edema but no threat of herniation
Risk of herniation rises significantly with further fall in serum
sodium level
Weighing the risk of cerebral edema versus ODS in these patients is
tricky, especially if hyponatremia is chronic
Priority is to prevent further fall in serum sodium concentration
rather than increasing it
In acute hyponatremia with a decrease of more than 10 mmol/L,
2 ml/kg of 3% saline may be given over 20 minutes
Hypovolemic hyponatremia: Isotonic saline
Euvolemic or Hypervolemic Hypernatremia: Isotonic saline with
frusemide, fluid restriction

6. ASYMPTOMATIC
HYPONATREMIA
Hypovolemic hyponatremia: Intravascular volume optimization with
isotonic saline
Euvolemic or Hypervolemic hyponatremia: Fluid restriction- daily
fluid intake
500 ml less than urine output
Oral solute like urea
Vaptans- V2 receptor antagonist

7. UNPREDICTABLE
RAPIDCORRECTION
Once treatment begins Renal capacity to excrete electrolyte free water fluctuates markedly
This results in unpredictable rise in serum sodium concentration
Interplay between various factors account for this
Suppression of endogenous vasopressin once intravascular volume is optimized
Removal of other causes of increased vasopressin level like drugs, pain,
anxiety, vomiting, surgery
Resulting diuresis leads to unpredictable rapid increase in serum
sodium concentration
This may be reason why Androgue- Madius formula understimates correction

8. UNPREDICTABLE
RAPIDCORRECTION
Seen in hypovolemic hyponatremia once intravascular volume is optimized
Seen in non vasopressin mediated hyponatremia like psychogenic
polydipsia and bear potomania when water intake is restricted
Seen in glucocorticoid deficient patient, once steroid is restarted
Addition of desmopressin with hypertonic saline makes renal excretion of
electrolyte free water constant
Change in serum sodium concentration becomes predictable
as calculated by Androgue- Madius formula
Increase in urine output (more than 100 ml/hr) is warning sign for this
phenomenon
Desmopressin may be given as 1-2 microgram intravenous every 8 hourly
D5W may be used to replaced urinary free water loss in urine

9. DESALINATION
Worseningof
hyponatremia
Paradoxical fall in serum sodium concentration with infusion of
isotonic saline
Seen in cases with high vasopressin level: Isotonic or Hypertonic
hypernatremia:
SIADH, CHF, cirrhosis, NS
Hypertonic saline should be used instead of isotonic saline along
with intermittent frusemide
Small free water volume in 3% saline and diuresis associated with
frusemide prevents this phenomenon

10. 1 liter isotonic saline containing 154 meq Na
in 1000 ml free water is excreted in urine as
150 meq Na in 300 ml free water,
Retention of 700 ml free water which
further decreases serum sodium concentration
(desalination of 700 ml of isotonic saline)
DESALINATION
Worseningof
hyponatremia

11. RENALREPLACENTTHERPAY
INHYPONATREMIA
Dialysis may rapidly increase serum sodium concentration breaking
the limit
Lowest concentration of commercial dialysate sodium is 135 mmol/L
Fortunately osmotic demyelination is rare after dialysis
Uremia has been shown to be protective against osmotic
demyelination syndrome
However rapid increase in serum sodium must be avoided
Choosing the lowest possible dialysate sodium, hypotonic fluid,
low blood flow and short duration of dialysis may be protective
CRRT with hypotonic replacement fluid would also prevent rapid
change in serum sodium

12. NEVERFORGET
Limit to increase in serum sodium is 10 mmol/L in first 24 hour and
8 mmol/L in each of subsequent 24 hours till it rises to 130 mmol/L
to prevent osmotic demyelination
Osmolality of infusing fluid should be higher than that of urine,
alas paradoxical hyponatremia
may result by desalination phenomenon
Intermittent frusemide may prevent this phenomenon
Severe symptoms are signs of increased intracranial pressure and
herniation, hence urgency to treat by rapidly raising serum
osmolality
Increased urine output (diuresis) during treatment is warning sign
of rapid correction,
Desmopressin and D5W to replace lost volume should be used
If potassium is being replaced, reduce dose of hypertonic saline as
it may lead to rapid correction of sodium as well as osmolality
Infusion of 3% saline @ 1ml/kg/hr will increase serum sodium by 1
mmol/L/hr,
considering 514 meq of sodium in 1000 ml of 3% saline.

13. REFERENCES
Clinical practice guidelines on diagnosis and treatment of
hyponatremia. European Journal of Endocrinology, 2014
Treatment of hyponatremia. Seminars in Nephrology 2009
Management of hyponatremia in the ICU. Chest 2013
Hyponatremia. NEJM 2000