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Hyponatremia
Overview
Fluid compartments and solutes
Define hypoNa
Epidemiology
Normal physiology preventing hypoNa
Pathophysiology of hypoNa
Manifestations
Work-up & Differential Diagnosis
Treatment
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Hyponatremia
Fluid Compartments/Solutes
Distribution of water- due to osmotic forces
Na is mainly extracellular, K is intracellular
Serum osmol = 2(Na)+ BUN/2.8 + Gluc/18 Sodium is the primary determinant
Serum osmol tightly regulated (275 290)
Mechanisms for regulation If osmol 1. thirst mechanism, 2. ADH
Effective circulating volume also ADH
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Hyponatremia
Hyponatremia
Definition: Commonly defined as a serum sodium concentration
135 meq/L
Hyponatremia represents a relative excess of water inrelation to sodium.
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Hyponatremia
Hyponatremia
Most often due to retention of free water
2ndary to impaired excretion of free water
Occ. due to Na loss exceeding water loss
i.e. thiazide-induced hypoNa (elderly women)
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Hyponatremia
Hyponatremia
Epidemiology:
Frequency
Hyponatremia is the most common electrolyte
disorder
incidence of approximately 1%
prevalence of approximately 2.5%
surgical ward, approximately 4.4%
30% of patients treated in the intensive care unit
ocw.jhsph.edu
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Hyponatremia
Hyponatremia
Epidemiology Cont.
Mortality/Morbidity
Acute hyponatremia (developing over 48 h or less)
are subject to more severe degrees of cerebraledema
sodium level is less than 105 mEq/L, the mortality is over
50%
Chronic hyponatremia (developing over more than48 h) experience milder degrees of cerebral
edema
Brainstem herniation has not been observed in patients
with chronic hyponatremia
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Hyponatremia
Hyponatremia
Epidemiology Cont.
Age
Infants
fed tap water in an effort to treat symptoms ofgastroenteritis
Elderly patients with diminished sense of thirst,
especially when physical infirmity limits
independent access to food and drink
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Hyponatremia
Hyponatremia
Physiology
Serum sodium concentration
regulation:
stimulation of thirst
secretion of ADH
feedback mechanisms of the renin-
angiotensin-aldosterone system
renal handling of filtered sodiumwww.daviddarling.info
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Hyponatremia
Hyponatremia
PhysiologyCont.
Stimulation of thirst
Osmolality increases
Main driving force
Only requires an increase of 2% - 3%
Blood volume or pressure is reduced
Requires a decrease of 10% - 15%
Thirst center is located in the anteriolateral centerof the hypothalamus
Respond to NaCL and angiotensin II
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Hyponatremia
Hyponatremia
PhysiologyCont.
Secretion of ADH Synthesized by the neuroendocrine cells in the
supraoptic and paraventricular nuclei of thehypothalamus
Triggeres: Osmolality of body fluids
A change of about 1%
Volume and pressure of the vascular system
Increases the permeability of the collecting duct towater and urea
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Hyponatremia
Hyponatremia
PhysiologyCont
renin-angiotensin-aldosterone Renin
Stemuli are perfusion pressure, sympathetic activity, andNaCl delivery to the macula densa
Increase in NaCl delivery to the macula decreases theGFR by decrease in the renin secretion
Aldosterone
Reduces NaCl excretion by stimulating its resorption Ascending loop of Henle
Distal tubule
Collecting duct
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Hyponatremia
Normal Physiology
Excretion of free water requires: 1. generation of free water by reabsorption of
NaCl w/o water in ascending Loop of Henle
2. excretion of this water by maintenance of
impermeability to water in collecting duct (No
ADH)
Remember that ADH leads to retention of water via
pores
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Hyponatremia
Hyponatremia
www.merricks.com/tech_electrolyte_new.htm
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Hyponatremia
Pathophysiology
Simply, hyponatremia is due to inability tomatch water excretion with water ingestion
1. Defect in water excretion
SIADH (inappropriate ADH release)
Hypovolemic state(appropriate ADH release)
Hyperglycemia (draws water into plasma)
Advanced renal failure 2. System overwhelmed (water ingestion)
i.e. primary polydipsia
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Hyponatremia
Clinical Manifestations
most patients with a serum sodium
concentrationexceeding 125 mEq/L are
asymptomatic
Patients with acutely developing
hyponatremia are typically symptomatic at a
level of approximately 120 mEq/L
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Hyponatremia
Clinical Manifestations (cont.)
Most abnormal findings on physical
examination are characteristically neurologic
in origin
Mild Sx: anorexia, nausea, lethargy
Mod Sx: disoriented, agitated, neuro deficit
Sev Sx: seizures, coma, death
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Hyponatremia
Differential Diagnosis/Work-Up
First test to obtain: serum osmolality
Helps exclude two easier to remember
causes of hyponatremia
1. HyperosmolarhypoNa (osmo > 295)
2. Iso-osmolarhypoNa (280-295 osmo)
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Hyponatremia
HyperosmolarhypoNa
Water shifts from the intracellular to theextracellular compartment, with a resultant
dilution of sodium. The TBW and total body
sodium are unchanged.
This condition occurs with hyperglycemia(100mg1.6 Na) or Administration of
mannitol
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Hyponatremia
Iso-osmolarhypoNa (nl serum
osmo)
Pseudohyponatremia (with old
machines) The aqueous phase is diluted by excessive
proteins or lipids. The TBW and total body
sodium are unchanged. hypertriglyceridemia
multiple myeloma
N.B. problem resolved with the new electrolytes
measuring electrodes
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Hyponatremia
DDx / Work-up
Hypo-osmolarhypoNa (most common) Three types (based on volume status)
Hypervolemic (congested states)
CHF, cirrhosis, nephrotic syndrome, ARF / CRI Hypovolemic (appropriate ADH secretion)
renal loss (diuretics, nephropathy, hypoAldosteron)
GI loss (vomiting, diarrhea, NGT)
Skin loss (sweating, burns, cystic fibrosis)
Peritonitis or sepsis
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Hyponatremia
DDX / Work-up
Euvolemic (normal volume state)
SIADH
Pain and nausea can cause non-osmotic ADH
release
Post-op state, especially TURP
Hypocortisolism or hypothyroidism
Psychogenic polydipsia (water intoxication)
Reset osmostat(pregnancy, psych disorders)
In this case, body thinks normal is lower-> no Tx
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Hyponatremia
DDX / Work-Up Next lab value: Urine osmolality
Is free water excretion, or ability to dilute
the urine, intact in the face of hypoNa?
Remember: problem is too much water Normal physiologic response = excrete water
If Uosm < 100, means appropriate
excretion ofdilute urine
Psychogenic polydipsia or reset osmostat
If Uosm > 200, reflected impaired water
excretion (usu due to inability to stop ADH)
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Hyponatremia
DDx / Work-Up
Final lab value: Urine sodium
UNa < 30 implies hypovolemic or reduced
effective circ volume (CHF, nephrotic,
cirrhosis)
Kidneys reabsorb solutes to retain water and
volume
UNa> 30 seen in the euvolemic type SIADH, diuretics
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Hyponatremia
Hyponatremia
Other helpful Laboratory tests:
Uric Acid Level < 4 mg/dl consider SIADH
FeNa
Help to determine pre-renal from renal causes
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Hyponatremia
Hyponatremia
Treatment
four issues must be addressed
Asyptomatic vs. symptomatic
acute (within 48 hours)
chronic (>48 hours)
Volume status
1st
step is to calculate the total body water total body water (TBW) = 0.6 body weight
(0.5 for females)
H t i
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HyponatremiaHyponatremia
Treatment Cont.
next decide what our desired correction rateshould be
Symptomatic
immediate increase in serum Na level by 8 to 10
meq/L in 4 to 6 hours with hypertonic saline is
recommended
acute hyponatremia
more rapid correction may be possible 8 to 10 meq/L in 4 to 8 hours
chronic hyponatremia
slower rates of correction
12 meq/L in 24 hours
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Hyponatremia
Hyponatremia
Symptomatic or Acute
estimate SNa change on the basis of theamount of Na in the infusate
SNa = {[Na + K]inf SNa} (TBW + 1)
SNa is a change in SNa
[Na + K]inf is infusate Na and K concentration in 1 liter ofsolution
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Hyponatremia
Hyponatremia
IV Fluids One liter of Lactated Ringer's Solutioncontains:
130 mEq of sodium ion = 130 mmol/L
109 mEq of chloride ion = 109 mmol/L
28 mEq of lactate = 28 mmol/L
4 mEq of potassium ion = 4 mmol/L
3 mEq of calcium ion = 1.5 mmol/L
One liter of Normal Saline contains:
154 mEq/L of Na+ and Cl
One liter of 3% saline contains:
514 mEq/L of Na+ and Cl
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Hyponatremia
Hyponatremia
Asymptomatic or Chronic
SIADH
sodium handling is intact in SIADH
administered sodium will be excreted in the urine,
while some of the water may be retained
possible worsening the hyponatremia
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Hyponatremia
Hyponatremia
Asypmtomatic or Chronic
SIADH
Water restriction
0.5-1 liter/day
Salt tablets
Demeclocycline
Inhibits the effects of ADH
Onset of action may require up to one week
H t i
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HyponatremiaHyponatremia Example:
a 60 kg women with a plasma sodium of 110meq/L
Formula:
SNa = {[Na + K]inf SNa} (TBW + 1)
What is the TBW?
How high will 1 liter of normal saline raise the
plasma sodium?
Answer:
TBW is 30 L
Serum sodium will increase by approximately
1.4 meq/L for a total SNa of 111.4 meq/L
H i
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Hyponatremia
Hyponatremia
Example: 85 y/o male with weakness and head ache
SNa is 118 mEq/L
Plasma osmolality is 254 mosmol/kg
Urine osmolality is 130 mosmol/kg
Urine sodium >20 mEq/L
Uric acid is 3mg/dl
What type of hyponatremia does thispatient have?
H t i
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Hyponatremia
Hyponatremia Example:
63 y/o female at 75 Kg with N/V/D for 4 days
SNa is 108 mEq/L
She has had one seizure in the ambulance
Plasma osmolality is 251 mosmol/kg Urine osmolality is 47 mosmol/kg
Uric acid is 6mg/dl
What type of hyponatremia does this
patient have?
H t i
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Hyponatremia
How will you Tx her?
Calculate the total body water
0.5 x weight = 37.5 L
What rate of correction do you want?
8 to 10 mEq/L in 6 to 8 hours
What fluid will you use? 3% Saline
How will you calculate the amount of sodium
to give her? SNa = {[Na + K]inf SNa} (TBW + 1)
How will her sodium increase after 1 liter of
3% saline?
By 10.8 mEq/L to 118.8 mEq/L
H t i
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Hyponatremia
Hyponatremia
What other medication will she need?
Lasix and a foley
Her sodium increases to 118.8 mEq/L over
the next 8-10 hours. How will you continue
to correct her hyponatremia?
SNa = {[Na + K]inf SNa} (TBW + 1)
SNa = 154mEq/L 118.8mEq/L 38.5L = 0.9
mEq/L
So 2 liters of normal saline over the next 14
hours
H t i
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Hyponatremia
Hyponatremia
The End
Questions????