Chapter 5 - Hypernatremia

Question 1

Hypernatremia is

Answer 1

Increased in sodium concentration more than 150mEq/l.

Question 2

Causes of hypernatremia

Answer 2

A - Net water loss
1 - pure water loss –> Insensible losses, Diabetes Insipidus (may result from deficiency of ADH or its end organ unresponsiveness)
2 - Hypotonic fluid loss –>
- Renal –> Loop, osmotic diuretics, post obstructive, polyuric phase of acute tubular necrosis
- GI –> vomiting, diarrhea, nasogastric drianage, lactulose

B - Hypertonic sodium gain
1 - Excess sodium intake –> Sodium bicarbonate, saline infusion, hypertonic feeds, boiled skimmed milk, ingestion of sodium chloride, hypertonic dialysis
2 - Endocrine –> Primary hyperaldosteronism, cushing syndrome

Question 3

lack of thirst in mentally alert, hypernatremic child indicates:

Answer 3

defect in either osmoreceptors or cortical thirst center

- presence of intact thirst mechanism, a slight increase in sodium ( 3-4mEq/l) above normal elicits intense thirst.

Question 4

Clinical manifestation of hypernatremia

Answer 4

most objective sign –> lethargy or mental status changes which proceeds to coma and convulsions.

Question 5

effects of hypernatremia on brain

Answer 5

• acute and severe hypernatremia –> osmotic shift of water from neurons leads to shrinkage of brain and tearing of meningeal vessels and intracranial hemorrhage.
• slow developing hypernatremia –>well tolerated, adaptation occur by movement of electrolytes into cells and later by inracellular generation of organic osmolytes.

Question 6

treatment of hypernatremia

Answer 6

1 - Treat hypotension first, regardless of sodium concentration ( normal saline bolus, Ringer’s lactate, 5% albumin)

2 - Correct deficit over 48 to 72 hours. Rapid decline of chronic (>48 hours) is associated with risk of cerebral edema. Recommended rate of drop is 0.5mEq/l/hour ( 10- 12mEq/l/ day)

3 - Oral solutions preferred to parenteral correction.

4 - Generally hypotonic infusates are used ( infusate sodium of ~ 40mEq/l, as N/4 or N/5 salline). Sodium free fluid should be avoided ( except in acute onset, eg: sodium overload)

5 - Decline of sodium can be estimated using Adrogue Madias formula:
▲Na = { (amount of Na in 1 litre of infusate) + (amount of K in 1 litre of infusate) - (serum Na) } / (TBW +1)
TBW = 0.6 x body weight

6 - Seizures due to hypernatremia are treated using hypertonic 3% saline at 5-6ml/kg infusion over 1-2 hour

7 - Renal replacement therapy ( peritoneal or hemodialysis, hemofiltration) is indicated with significant hypernatremia (Na > 180 -200mEq/l) with concurrent renal failure and / or volume over load.

8 - Ensure correction of ongoing fluid losses; frequent biochemical and clinical assessment is needed.