Hypernatremic Dehydration

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Hypernatremic Dehydration
Mary Palomaki
November 8, 2010
Definition
• Serum sodium level greater than 145
mEq/L
• Deficit of water
• Causes:
– pure water loss (diabetes insipidus)
– Hypotonic fluid loss (vomit/diarrhea)
– Hypertonic sodium gain (wrong formula
preparation)
Diabetes Insipidus
• Central or Nephrogenic
• Hypernatremia develops when patient
does not have access to free water or is
unable to drink sufficient water
– Immaturity
– Neurologic impairment
– emesis
Adipsia
• Absence of thirst
• Primary adipsia is rare
• Secondary adipsia from damage to
hypothalamus
– Trauma
– Tumor
– Hydrocephalus
– Histiocytosis
Osmotic Diuresis
• Glucose, mannitol, or urea
• Water losses exceed sodium losses
• Polyuric phase of acute tubular necrosis
– Osmotic diuresis from high levels of urea
– Tubular dysfunction causing inability to
concentrate urine
Breastfeeding Hypernatremia
•
•
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Occurs in infants 1-3 weeks old
First born children
Poor mother-infant interaction
Limited human milk production
Sodium content in human milk remains
high
• 40 cases have been described: mean
serum sodium was 181 mEq/L
Clinical Manifestations
• Children in initial phase of hypernatremic
dehydration tend to show fewer physical exam
findings of dehydration than those with isotonic
or hypotonic
– Intracellular water shifts to extracellular space
– Child can then maintain intravascular volume
• Maintain BP and urine output longer
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Skin feels “doughy”
Muscle weakness
High-pitched cry
Insomnia
Lethargy
Hypernatremia and the Brain
• Water shifts from inside brain cells to
extracellular space
• Brain cells decrease in size
• Total brain volume decreases
• Intracerebral blood vessels can tear
– Shearing forces
– Bridging veins can rupture as brain pulled away from
meninges/skull
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Hemorrhage
Seizures
Encephalopathy
Paralysis
Thrombotic Complications
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Stroke
Dural sinus thrombosis
Peripheral thrombosis
Renal vein thrombosis
Idiogenic Osmoles
• If dehydration develops slowly, brain
develops idiogenic osmoles
• These intracellular osmoles help to
preserve intracellular water content
• Slow correction of hypernatremia is crucial
– If extracellular fluid osmolarity is decreased
too rapidly, water shifts intracellularly causing
brain edema
Treatment
• Goal: decrease serum sodium by 12-15
mEq/L/24 hours (0.5-0.6 mEq/L/hr)
• Frequent monitoring of serum sodium to
ensure rate of correction is not too fast
• First priority is restoration of intravascular
volume
Treatment: Emergency Phase
• Restore intravascular volume
– 10-20 mL/kg of isotonic IV fluid (LR or NS)
– LR: 130 mEq/L sodium
– NS: 154 mEq/L sodium
• In severe dehydration (sodium greater than 175
mEq/L):
– Don’t give NS or LR, as these fluids are hypotonic to
patient
– Make IV fluids with sodium concentration 10-15
mEq/L less than serum sodium (so fluid is isotonic to
patient)
Treatment: Rehydration Phase
• Calculate maintenance IV fluids
• Calculate amount of free water to be replaced
over the next 24 hours
• Assume 60-70% body weight is water (higher in
infants vs. older children)
• Free water deficit is:
• (L) = 0.7 x wt (Kg) [1-current sodium/desired
sodium]
• In mild-moderate dehydration free water deficit
will be replaced over 48h
Treatment: Rehydration Phase
• In mild-moderate dehydration (initial serum
sodium < 175 mEq/L),
• IV fluid of choice is:
• D5 1/4 NS
Treatment: Rehydration Phase
• In severe dehydration (initial serum
sodium is >175 mEq/L),
• IV fluid of choice is similar to IV fluids in
emergency phase
• Make IV fluids with sodium content 10-15
mEq/L less than serum sodium
• Mix 3% (513mEq/L) with D5NS
• Frequent monitoring of serum sodium and
adjustment of sodium in fluids
What if….
• Correction occurs too rapidly?
– Brain Edema
– Administer 3% NS to quickly reverse edema
• Patient has hypernatremia secondary to sodium
administration
– The change is usually rapid-no time for idiogenic
osmoles to accumulate
– Can correct rapidly
• Peritoneal dialysis
• Administration D5W (no sodium) and loop diuretics
References
• Androgue HJ, Madias NE. Hypernatremia.
N Engl J Med 2000;342:1493-1499
• Nelson Textbook of Pediatrics. 18th ed.
PP 273-275.
• Schwaderer, A and Schwartz, G. Treating
hypernatremic dehydration. Peds in Rev
2005;26:148-150
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