1. Hyponatremia By
James Yost, MD, MS, MBA
Emory Family Medicine

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.

4. 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
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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 Epidemiology Cont. Age Infants
fed tap water in an effort to treat symptoms of gastroenteritis
Infants fed dilute formula in attempt to ration
Elderly patients with diminished sense of thirst, especially when physical infirmity limits independent access to food and drink

7. 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

8. Hyponatremia Physiology Cont. 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 center of the hypothalamus
Respond to NaCL and angiotensin II

9. Hyponatremia Physiology Cont. Secretion of ADH
Synthesized by the neuroendocrine cells in the supraoptic and paraventricular nuclei of the hypothalamus
Triggeres:
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. Hyponatremia Physiology Cont renin-angiotensin-aldosterone Renin
Stemuli are perfusion pressure, sympathetic activity, and NaCl delivery to the macula densa
Increase in NaCl delivery to the macula decreases the GFR by decrease in the renin secretion
Aldosterone
Reduces NaCl excretion by stimulating it’s resorption
Ascending loop of Henle
Distal tubule
Collecting duct

11. Hyponatremia

12. Hyponatremia Physiology Cont.
extracellular-fluid and intracellular-fluid compartments make up 40 percent and 60 percent of total body water
renal handling of water is sufficient to excrete as much as L of free water per day
sodium is the predominant osmole in the extracellular fluid (ECF) compartment and serum

13. Hyponatremia Pathophysiology
hyponatremia can only occur when some condition impairs normal free water excretion
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

14. Hyponatremia Types Hypovolemic hyponatremia Euvolemic hyponatremia
Hypervolemic hyponatremia
Redistributive hyponatremia
Pseudohyponatremia

15. Hypovolemic hyponatremia
develops as sodium and free water are lost and/or replaced by inappropriately hypotonic fluids
Sodium can be lost through renal or non-renal routes

16. Hypovolemic hyponatremia
Nonrenal loss
GI losses
Vomiting, Diarrhea, fistulas, pancreatitis
Excessive sweating
Third spacing of fluids
ascites, peritonitis, pancreatitis, and burns
Cerebral salt-wasting syndrome
traumatic brain injury, aneurysmal subarachnoid hemorrhage, and intracranial surgery
Must distinguish from SIADH

17. Hypovolemic hyponatremia
Renal Loss
Acute or chronic renal insufficiency
Diuretics

18. Euvolemic hyponatremia
Normal sodium stores and a total body excess of free water
Psychogenic polydipsia, often in psychiatric patients
Administration of hypotonic intravenous or irrigation fluids in the immediate postoperative period

19. Euvolemic hyponatremia
administration of hypotonic maintenance intravenous fluids
Infants who may have been given inappropriate amounts of free water
bowel preparation before colonoscopy or colorectal surgery

20. Euvolemic hyponatremia
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

21. Hypervolemic hyponatremia
Total body sodium increases, and TBW increases to a greater extent.
Can be renal or non-renal
acute or chronic renal failure
dysfunctional kidneys are unable to excrete the ingested sodium load
cirrhosis, congestive heart failure, or nephrotic syndrome

22. Redistributive hyponatremia
Water shifts from the intracellular to the extracellular compartment, with a resultant dilution of sodium. The TBW and total body sodium are unchanged.
This condition occurs with hyperglycemia
Administration of mannitol

23. Hyponatremia Pseudohyponatremia
The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged.
hypertriglyceridemia
multiple myeloma

24. Hyponatremia 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

25. Hyponatremia Diagnosis CT head, EKG, CXR if symptomatic
Repeat Na level
Correct for hyperglycemia
Laboratory tests provide important initial information in the differential diagnosis of hyponatremia
Plasma osmolality
Urine osmolality
Urine sodium concentration
Uric acid level
FeNa

26. Hyponatremia Laboratory tests Cont. Plasma osmolality
normally ranges from 275 to 290 mosmol/kg
If >290 mosmol/kg :
Hyperglycemia or administration of mannitol
If 275 – 290 mosmol/kg :
hyperlipidemia or hyperproteinemia
If <275 mosmol/kg :
Eval volume status

27. Hyponatremia Laboratory tests Cont.
Plasma osmolality < 275 mosmol/kg
Increased volume:
CHF, cirrhosis, nephrotic syndrome
Euvolemic
SIADH, hypothyroidism, psychogenic polydipsia, beer potomania, postoperative states
Decreased volume
GI loss, skin, 3rd spacing, diuretics

28. Hyponatremia Laboratory tests Cont. Urine osmolality
Normal value is > 100 mosmol/kg
Normal to high:
Hyperlipidemia, hyperproteinemia, hyperglycemia, SIADH
< 100 mosmol/kg
hypoosmolar hyponatremia
Excessive sweating
Burns
Vomiting
Diarrhea
Urinary loss

29. Hyponatremia Laboratory tests Cont. Urine Sodium Uric Acid Level FeNa
>20 mEq/L
SIADH, diuretics
<20 mEq/L
cirrhosis, nephrosis, congestive heart failure, GI loss, skin, 3rd spacing, psychogenic polydipsya
Uric Acid Level
< 4 mg/dl consider SIADH
FeNa
Help to determine pre-renal from renal causes

30. 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

31. Hyponatremia 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

32. Hyponatremia Symptomatic or Acute
Treatment Cont. - Here comes the Math!!!
estimate SNa change on the basis of the amount of Na in the infusate
ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
ΔSNa is a change in SNa
[Na + K]inf is infusate Na and K concentration in 1 liter of solution
OH MY GOD, what did he just say!!!!!!!!!!!!!!!!!!

33. Hyponatremia 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−

34. Hyponatremia Example: Answer:
a 60 kg women with a plasma sodium of 110 meq/L
Formula:
ΔSNa = {[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 meq/L

35. Hyponatremia Example: Answer:
a 90 kg man with a plasma sodium of 110 meq/L
Formula:
ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
What is the TBW?
How high will 1 liter of 3% saline raise the plasma sodium?
Answer:
TBW is 54 L
Serum sodium will increase by approximately 7.3 meq/L for a total SNa of meq/L

36. Hyponatremia Asymptomatic or Chronic 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

37. 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

38. 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 this patient have?
What additional labs/studies would you want?

39. Hyponatremia Example Cont.: Tx Noncontrast CT Head:
Ouch!!!!!
Example Cont.:
Noncontrast CT Head: Tx
Call Neurology and neurosurgery
Free water restriction
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40. 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?
What additional labs/studies would you want?
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41. 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?
ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
How will her sodium increase after 1 liter of 3% saline?
By 10.8 mEq/L to mEq/L

42. Hyponatremia What other medication will she need?
Lasix and a foley
Her sodium increases to mEq/L over the next 8-10 hours. How will you continue to correct her hyponatremia?
ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
ΔSNa = 154mEq/L – 118.8mEq/L ÷ 38.5L = 0.9 mEq/L
So 2 liters of normal saline over the next 14 hours

43. Hyponatremia
Congrats!!!!!!!! You saved her!
Questions????