1. Hyponatremia Definition:
Commonly defined as a serum sodium concentration 135 meq/L
Hyponatremia represents a relative excess of water in relation to sodium.

2. 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

3. 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

4. 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

5. 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

6. Hyponatremia

7. 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

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

9. 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

10. 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

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

12. 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

13. 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

14. Euvolemic hyponatremia
SIADH (0-5 pmol/L) (500 pmol/L)
Triggers:
Severe hypovolemia/ hypotension, nausea/vomiting
Causes:
Pulmonary Disease
Small cell, pneumonia, TB, sarcoidosis
Cerebral Diseases
CVA, Temporal arteritis, meningitis, encephalitis
Medications
Antipsychotics, Opiates, Tegretol

15. 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

16. 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

17. Hyponatremia Pseudohyponatremia
The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged (normal sodium concentration).
hypertriglyceridemia
multiple myeloma

18. Serum osmolality does not changes as lipids and proteins are not dissolved in the plasma fraction.
Assess by osmolal gap.
Normal osmolality with serum Na 110 mmol/L?

19. 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