Hypernatremia and Fluid Resuscitation

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Hypernatremia and Fluid Resuscitation

• Staci Smith, DO

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Hypernatremia

• serum sodium level gt145 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

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Mortality Eye Opener

• mortality rate across all age groups is
  approximately 45.
• mortality rate in the geriatric age group is as
  high as 79

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Hypernatremia

• sodium levels are tightly controlled
• by regulation of urine concentration
• production and regulation of the thirst response
• normally water intake and losses are matched
• to maintain salt homeostasis, the kidneys adjust
  urine concentration to match salt intake and loss
• kidneys' normal response
• is excretion of a minimal amount of maximally
  concentrated urine

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Hypernatremia

• normal plasma osmolality (Posm )
• 275 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

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ADH
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ADH Mechanism of Action
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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

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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

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Hypernatremia

• cells become dehydrated
• sodium acts to extract water from the cells
• primarily an extracellular ion
• is actively pumped out of most cells
• dehydrated cells shrink from water extraction
• effects seen principally in the CNS

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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

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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

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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

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Clinical Manifestations

• lethargy
• general weakness
• irritability
• weight loss
• diarrhea
• twitching
• seizures
• coma

• orthostatic hypotension
• tachycardia
• oliguria
• prerenal High BUN-to-creatinine ratio
• dry axillae/ dry MMM
• hyperthermia
• poor skin turgor
• nystagmus
• myoclonic jerks

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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

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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

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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

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Intracranial Hemorrhage
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Intracranial Hemorrhage
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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

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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

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General Treatment

• Next, calculate the free water deficit
• Free water deficit TBW x (serum Na -140/140)
• Our Pts FWD 52 x (154-140/140)
• 52 x 0.1
• 5.2 L free water deficit

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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

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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 Ringers 130 mmol/L
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Hypervolemic Hypernatremia

• Hypertonic saline
• Sodium bicarbonate administration
• Accidental salt ingestion
• Mineralocorticoid excess (Cushings syndrome)
• ectopic ACTH
• small cell lung ca, carcinoid, pheo, MTC (MEN II)
• pituitary adenoma
• pituitary hyperplasia
• adrenal tumor
• Dx Dexamethasone suppression test

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Hypervolemic Hypernatremia

• Treatment
• D5 W plus loop diuretic such as Lasix
• may require dialysis for correction

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Hypovolemia Hypernatremia

• water deficit gtsodium deficit
• Extrarenal losses
• diarrhea, vomiting, fistulas, significant burns
• Urine Na less than 20 and U Osm gt600
• Renal losses
• urine Na gt20 with U Osm 300-600
• osmotic diuretics, diuretics, postobstructive
  diuresis, intrinsic renal disease
• DM / DKA
• increased solute clearance per nephron,
  increasing free water loss

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Euvolemic Hypernatremia

• Diabetes Insipidus
• Typically mild hypernatremia with severe
  polyuria
• Central DI ADH deficiency
• Sx, hemorrhage, infxn, ca/tumor, trauma,
  anorexics, hypoxia, granulomatous dz (Wegeners,
  sarcoidosis, TB), Sheehans
• U Osm less than 300
• Tx is DDAVP

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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
• Sjogrens synd
• Sickle Cell Anemia

• U osm 300-600
• Tx salt restriction plus thiazide
• Tx underlying cause

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Euvolemic Hypernatremia

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

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Hypovolemia Hypernatremia

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

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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 ?

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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

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References

• Harrisons Internal Medicine
• E-medicine
• http//www.mdcalc.com/bicarbdeficit.php