hypernatremic disorders

1. Hypernatremic Disorders
Dr M Taimour

2. Hypernatremia
• serum sodium level >145 mEq/L
• hypertonic by definition
• usually due to loss of hypotonic fluid
– occasionally infusion of hypertonic fluid
• due to too little water, too much salt, or a
combination
– typically due to water deficit plus restricted access to
free water
• approximately 1-4% of hospitalized patients
• tends to be at the extremes of age

3. Hypernatremia
• usually occurs in infants or adults
– particularly the elderly
– impaired mental status
• may have an intact thirst mechanism but are
unable to ask for water
– increasing age is also associated with
diminished osmotic stimulation of thirst
• unknown mechanism

4. Hypernatremia
• normal plasma osmolality (Posm )
– 285 to 290 mosmol/kg
• Na is the primary determinant of serum
osmolarity
• number of solute particles in the solution
• mechanisms to return the Posm to normal
– sensed by receptor cells in the hypothalamus
• affect water intake via thirst
– water excretion via ADH
• increases water reabsorption in the
collecting tubules

5. ADH Mechanism of Action

6. Protection Mechanism
• major protection against the development
of hypernatremia
– is increased water intake
– initial rise in the plasma sodium concentration
stimulates thirst
• via the hypothalamic osmoreceptors

8. Protective Mechanism
• cells respond to combat this shrinkage
– by transporting electrolytes across the cell
membrane
– altering rest potentials of electrically active
membranes
• intracellular organic solutes
– generated in an effort to restore cell volume
and avoid structural damage

9. Risk factors for hypernatremia
– Age older than 65 years
– Mental or physical disability
– Hospitalization (intubation, impaired cognitive
function)
– Residence in nursing home
– Inadequate nursing care
– Urine concentrating defect (diabetes
insipidus)
– Solute diuresis (diabetes mellitus)
– Diuretic therapy

10. Assessment
• Two important questions:
– What is the patient's volume status?
– Is the problem acute or chronic?
• Does the patient complain of polyuria or
polydipsia ?
– Central vs Nephrogenic DI
– often crave ice-cold water

12. Clinical Manifestations
• lethargy
• general weakness
• irritability
• weight loss
• diarrhea
• twitching
• seizures
• coma
• orthostatic hypotension
• tachycardia
• oliguria
• prerenal :High BUN-to-
creatinine ratio
• hyperthermia
• poor skin turgor
• nystagmus
• myoclonic jerks

13. Work-up : Sodium levels
– more than 170 mEq/L usually indicates long-
term salt ingestion
– 50-170 mEq/L usually indicates dehydration
– chronicity typically has fewer neurologic
symptoms

14. Lab Work-up : Sodium levels
• order urine osmolality and sodium levels
• glucose level to ensure that osmotic
diuresis has not occurred
• CT or MRI head
• water deprivation test
• ADH stimulation

15. Hypernatremia Work -Up
• Head CT scan or MRI is
suggested in all patients
• Traction on dural bridging
veins and sinuses
• Leads to intracranial
hemorrhage
– most often in the
subdural space

16. Treatment
• Replace free water deficit
– IVF
– TPN / tube feeds
• Rapid correction of extracellular
hypertonicity
– passive movement of water molecules into
the relatively hypertonic intracellular space
– causes cellular swelling, damage and ultimate
death

17. Treatment
• First, estimate TBW (Total Body Water)
– TBW= .60 x IBW x 0.85 if female & 0.85 if
elderly
• IBW for women= 100 lbs for the first 5 feet and
5lbs for each additional inch
• IBW men= 110 lbs for the first 5 feet and 5 lbs for
each additional inch
• Our pt IBW= 120 (5 ft , 4’’)
• TBW= 52.0
– = .60 x 120 x 0.85. 0.85

18. General Treatment
• Next, calculate the free water deficit
• Free water deficit= TBW x (serum Na -
140/140)
• Our Pt’s FWD= 52 x (154-140/140)
– = 52 x 0.1
– = 5.2 L free water deficit

19. Avoiding Complications: Cerebral Edema
• Acute hypernatremia
– occurring in a period of less than 48 hours
– can be corrected rapidly (1-2 mmol/L/h)
• Chronic hypernatremia
– rate not to exceed 0.5 mmol/L/h or a total of
10 mmol/d
– Change in conc of Na per 1L of infusate =
conc of Na in serum- conc of Na in infusate /
TBW + 1

20. Common Na Contents
5% dextrose in water
(D5W)
0 mEq Na
0.2% sodium chloride in
5% dextrose in water
(D5 1/4 NS)
34 mmol/L
0.9 NS 154 mmol/L
0.45NS 77 mmol/L
Lactated Ringer’s 130 mmol/L

21. Hypervolemic Hypernatremia
• Hypertonic saline
• Sodium bicarbonate administration
• Accidental salt ingestion
• Mineralocorticoid excess (Cushing’s syndrome)
– ectopic ACTH
• small cell lung ca, carcinoid, pheo, MTC (MEN II)
– pituitary adenoma
– pituitary hyperplasia
– adrenal tumor
– Dx: Dexamethasone suppression test

22. Hypervolemic Hypernatremia
• Treatment
– D5 W plus loop diuretic such as Lasix
– may require dialysis for correction

23. Hypovolemia Hypernatremia
• water deficit >sodium deficit
– Extrarenal losses
• diarrhea, vomiting, fistulas, significant burns
• Urine Na less than 20 and U Osm >600
– Renal losses
• urine Na >20 with U Osm 300-600
• osmotic diuretics, diuretics, postobstructive
diuresis, intrinsic renal disease
• DM / DKA
– increased solute clearance per nephron, increasing free
water loss

24. Euvolemic Hypernatremia
• Diabetes Insipidus
– Typically mild hypernatremia with severe
polyuria
– Central DI = ADH deficiency
• Sx, hemorrhage, infxn, ca/tumor, trauma,
anorexics, hypoxia, granulomatous dz (Wegener’s,
sarcoidosis, TB), Sheehan’s
• U Osm less than 300
• Tx is DDAVP

25. Diabetes Insipidus: Euvolemic
Hypernatremia
Nephrogenic DI = ADH
resistance
• Congenital
• Meds – Lithium, ampho B,
demeclocycline,foscarnet
• Obstructive uropathy
• Hypercalcemia, severe
hypokalemia
• Chronic tubulointerstitial
diseases - Analgesic abuse
nephropathy, polycystic
kidney disease, medullary
cystic disease
• Pregnancy
• Sarcoidosis
• Sjogren’s synd
• Sickle Cell Anemia
– U osm 300-600
– Tx: salt restriction plus
thiazide
– Tx underlying cause

26. Euvolemic Hypernatremia
• Seizures where osmoles are generated
that cause water shifts
– transient increase in Na
• Increased insensible losses
(hyperventilation)

27. Hypovolemia Hypernatremia
• Combo of volume deficit plus
hypernatremia
– intravascular volume should be restored with
isotonic sodium chloride (.9 NS) before free
water administration

29. Summary
• Dehydration is NOT synonomous with
hypovolemia
• Hypernatremia due to water loss is called
dehydration.
• Hypovolemia is where both salt and water are
lost.
• Two important questions:
– What is the patient's volume status?
– Is the problem acute or chronic?
• Does the patient complain of polyuria or
polydipsia ?

30. Summary
• Divide causes of hypernatremia into hyper,
hypo, and euvolemic.
• Estimate TBW (Total Body Water)
– TBW= .60 x IBW x 0.85 if female & 0.85 if elderly
• Free water deficit= TBW x (serum Na -140/140)
• Check electrolytes frequently not to replace Na
more than 0.5 mmol/L/h or a total of 10 mmol/d
• Avoid cerebral edema

31. References
• Harrison’s Internal
Medicine
• E-medicine
• http://www.mdcalc.co
m/bicarbdeficit.php