causes and management of hyponatremia

1. Doha Rasheedy Aly

2. Hyponatremia
 Definition
 Epidemiology
 Physiology
 Pathophysiology
 Types
 Clinical Manifestations
 Diagnosis
 Treatment

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
ocw.jhsph.edu
 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

8. ADH
No ADH:  ADH Present: 

9. Renal Physiology

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

14. Plasma osmolarity:
 Serum Osm: 275-290 mosm/kg
 Calc = 2x[Na] + [glucose]/18 + [ BUN]/2.8 +
[ethanol]/4.6

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.

17. Step-wise Approach
 Serum Osm: 275-290 mosm/kg
 Calc = 2x[Na] + [glucose]/18 + [ BUN]/2.8 + [ethanol]/4.6
 Isotonic: PseudohypoNa
 Hyperproteinemia, Hyperlipidemia
 High/Hyperosmolar
 hyperglycemia (1.6/100), mannitol
 Low/Hypoosmolar

19. Labs Osm
 Plasma
 Hyperosmolar, Isoosmolar, Hypoosmolar
 Urine Osm
 Are you able to excrete the extra H2O?
 < or > 100 mosm/kg

21. Labs Osm
 Plasma
 Urine Osm
 Volume Status
 Effective circulating volume
 XS TBW:TB Na
 TB Na is reflected by ECF volume status

23. Volume Status
 Euvolemic
 H2O Inc & Na Stable
 Hypervolemic
 H2O Inc & Na Inc
 H2O > Na
 Hypovolemic
 H2O Dec & Na Dec
 H2O < Na

24. Volume Status
Hypovolemic
 GI solute loss  Euvolemic
 diarrhea, emesis  SIADH
 Third-spacing  Diuretic use
 ileus, pancreatitis  Glucocorticoid deficiency
 Diuretic use  Hypothyroidism
 Addison disease  Beer Potomania, psychogenic
 Salt-wasting nephritis polydipsia
 Reset osmostat
 Hypervolemic w/dec ECV
 Decompensated CHF
 Advanced liver cirrhosis
 Renal Failure

25.  SIADH:
 downward resetting of the osmostat
 Pulmonary Disease
 Small cell, pneumonia, TB, sarcoidosis
 Cerebral Diseases
 CVA, Temporal arteritis, meningitis, encephalitis
 Medications
 SSRI, Antipsychotics, Opiates, Depakote, Tegratol
 miscellaneous
 pain, nausea, post op.)

26. Labs Osm: 275-290 mosm/kg
 Plasma
 Urine Osm
 Volume Status
 Urine Na Concentration

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.