3. Hyponatremia
• Definition:
– Commonly defined as a serum sodium concentration<
135 meq/L
– Hyponatremia represents a relative excess of water in
relation to sodium.
– occur due to:
1)Water retention dt impaired free water excretion
2) Less: Na loss>water loss (thiazide induced
hyponatremia)
4. Hyponatremia
Epidemiology:
Frequency
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Hyponatremia is the most common electrolyte disorder
prevalence of approximately 7%
30% of patients treated in the intensive care unit
50% of NHR had atleast one episode of hyponatremia.
5. Hyponatremia
Epidemiology Cont.
Mortality/Morbidity
Acute hyponatremia (developing over 48 h or less) are subject
to more severe degrees of cerebral edema
sodium level is less than 105 mEq/L, the mortality is over 50%
Chronic hyponatremia (developing over more than 48 h)
experience milder degrees of cerebral edema
Brainstem herniation has not been observed in patients with
chronic hyponatremia
6. Hyponatremia
Physiology
Serum sodium concentration regulation:
stimulation of thirst
secretion of ADH
feedback mechanisms of the renin-
angiotensin-aldosterone system
renal handling of filtered sodium
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7. 1- Stimulation of thirst: Thirst center is located in the
anteriolateral center of the hypothalamus
Osmolality increases
Main driving force
Only requires an increase of 2% - 3%
Blood volume or pressure is reduced
Requires a decrease of 10% - 15%
2- Secretion of ADH
Synthesized by the neuroendocrine cells in the supraoptic and
paraventricular nuclei of the hypothalamus
Triggers:
Osmolality of body fluids
A change of about 1%
Volume and pressure of the vascular system
Increases the permeability of the collecting duct to water and urea
10. Age related changes of water metabolism:
The elderly have a delayed and less intense thirst response than
do younger person
total body water decreases because of an increase in fat and a
decrease in lean body mass (from about 60% of body weight in
healthy young adults to about 45% of body weight in the elderly
The ability to concentrate urine decreases with age in part
because of tubular senescence.
Many elderly persons also have resistance to the renal action of
ADH, ie, a form of acquired partial nephrogenic diabetes
insipidus.
Decreased renal conservation of Na dt:
Nephron loss
Decreased renin and aldosterone
Increased ANP
An age-related decrease in serum sodium concentration of 1
mEq/L/decade occurs after age 40
11. Pathophysiology
hyponatremia occur when some condition impairs
normal free water excretion or Na loss exceed water loss
acute drop in the serum osmolality:
neuronal cell swelling occurs due to the water shift from the
extracellular space to the intracellular space
Swelling of the brain cells elicits 2 responses for
osmoregulation, as follows:
It inhibits ADH secretion and hypothalamic thirst center
immediate cellular adaptation
12. Clinical Manifestations
most patients with a serum sodium concentration
exceeding 125 mEq/L are asymptomatic
Patients with acutely developing hyponatremia are
typically symptomatic at a level of approximately 120
mEq/L
Most abnormal findings on physical examination are
characteristically neurologic in origin
patients may exhibit signs of hypovolemia or
hypervolemia
13. Manifestations
In acute hyponatremia, osmotic forces cause water
movement into brain cells leading to cerebral edema
Mild Sx: anorexia, nausea, lethargy
Mod Sx: disoriented, agitated, neuro deficit
Sev Sx: seizures, coma, death
15. Classification According to Plasma Osmolality:
1. Hypotonic hyponatremia
2.Hypertonic hyponatremia: (Redistributive
hyponatremia)
excess of another effective osmole (glc, mannitol) that draws water
intravenously.
hyperglycemia (1.6/100)
3. Isotonic hyponatremia:
*Pseudohyponatremia ; hyperlipidemia or hyperprotienemia results in
low measured Na⁺ concentration (but osmolality is normal)
it is a rare lab artifact
*Artefactual hyponatremia; taking blood from a drip arm into which a low
sodium fluid is being infused.
26. Labs Osm: 275-290 mosm/kg
Plasma
Urine Osm
Volume Status
Urine Na Concentration
27.
28.
29. Treatment
four issues must be addressed
Asymptomatic 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
30. Treatment Cont
next decide what our desired correction rate should 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
31. IV Fluids
One liter of Lactated Ringer's Solution contains:
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−
32. Na+deficit= Target Na - Current Na e.g. 120-115
Total body Na+ deficit= Na+deficit x total body water
= 5 x 0.6x body wt (50kgs)
= 125meq
Amount of 3% NaClneeded (Na=513meq/L)= 125/513=
240ml
Rate of infusion=0.5meq/hour=10 hours
=24ml/hour
33. SIADH
response to isotonic saline is different in the SIADH
In hypovolemia both the sodium and water are retained
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
34. 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
35. Volume depletion:
Isotonic saline:
raises plasma sodium by 1-2 meq/L for every liter of fluid infused
since saline has higher Na concentration (154 meq/L) than
hyponatremic plasma
volume repletion removes stimulation of ADH
36. CHF, Cirrhosis, Nephrotic syndrome
Patients have increased total body sodium stores.
Treatment consists of sodium and water restriction
and attention to the underlying cause. The vasopressin
receptor antagonists conivaptan (Vaprisol) and
tolvaptan (Samsca) are now approved for use in
hospitalized patients with hypervolemic
hyponatremia, though clinical experience is scant
37. Indications for 3% NaCl
Symptomatic hyponatremia (SZ, coma)
Acute severe hyponatremia (<24h, < 120
mEq/L)
SAH with hyponatremia worsening on 0.9%
NaCl
38. Why don’t we correct the hyponatremia
rapidly??
It results in a severe neurological syndrome due to
local areas of demyelination called “Central
Pontine Myelinosis” or “Osmotic Demyelination
Syndrome”.
Symptoms include dysarthia, dysphagia, spastic
quadriplegia, psuedobulbar palsy, and respiratory
arrest.
Occurs in the pons mostly, but also in the basal
ganglia, internal capsule, and cerebral cortex.