1. Hyponatremia-Hypernatremia
Dr Rim Braham

2. Total fluid volume and distribution
Total body fluid accounts for 60% of body mass.
Intracellular fluid ( ICF) : 40%
Extracellular fluid (ECF): 20%
Interstitial fluid: 15%
Plasma: 5%

3. Solute Composition of Body Water
Predominant solutes in ECF:
Sodium (Na+)
Chloride (Cl−)
Bicarbonate (HCO3−)
Predominant solutes in ICF:
Potassium (K+)
Protein−
Phosphate−

4. Osmolality
Posm=2×plasma Na+ +
Glucose/18 + BUN/2.8

5. Osmolality Normal ECF osmolality: 280-290mOsm/kgH2O
ECF and ICF are in osmotic equilibrium, at steady state
The total osmolality is almost equal among plasma, the interstitial and intracellular fluids with a range from mOsm/L, due to a free permeability of cell membrane to water.
Nearly 80% of the osmolality of plasma and the interstitial fluid is induced by sodium and chloride ions. And approximately half of the intracellular osmolality is caused by potassium.

6. Mechanisms of regulation of body fluid and electrolyte balance
Sensation of thirst
Antidiuretic hormone (ADH)
Renin-angiotensin-aldosterone system
Atrial natriuretic peptide (ANP)

7. ADH
ADH synthesized in the cell bodies of hypothalamic neurons in the supraoptic nucleus
ADH is stored in the posterior pituitary— forms the most readily released ADH pool

8. ADH Main target sites: distal tubules and collecting ducts in kidney
Function: to Promote the water reabsorption and cause increased ECF volume and decreased urinary output.
Stimulating factors:
Blood pressure↓
Plasma osmolality↑
Blood volume ↓

9. Renin-angiotensin-aldosterone system
Arterial pressure ↓
Plasma sodium content↓
Sympathetic nerve ↑
Arterial pressure↑
ECF volume ↑
Glomerulus (juxtaglomerular cells)
Renal retention of sodium
Increase potassium secretion
renin
Angiotensin I
Angiotensin II
Adrenal gland
aldosterone
Angiotensin converting enzyme

10. ANP
ANP is a hormone produced by specific cells of cardiac atrim in response to blood volume expansion.
Function: ANP inhibits the reabsorption of sodium and water by the renal tubules, which in turn increases urinary excretion and helps to return blood volume back toward normal.
ANP exerts a negative regulation against ADH in the central nervous system.

11. Hyponatremia 
Serum Na <135 mEq/L

12. Hyponatremia 
Serum Na <135 mEq/L

14. Dısorders of water and sodium balance
Hyponatremia (too much water)
Hypernatremia (too little water)
Hypovolemia (too little sodium, the main extracellular solute)
Edema (too much sodium with associated water retention)

15. Hyponatremia is a disorder of water balance

16. Hyponatremia 
almost always due to the oral or intravenous intake of water that cannot be completely excreted
impaired water excretion that is most often due to:
an inability to suppress the release of antidiuretic hormone (ADH)
or to advanced renal failure

17. Diagnosis
Volume status and serum osmolality are essential to determine etiology

22. Differences between SIADH and cerebral salt wasting
Sherlock M, O’Sullivan E, et all. The incidence and pathophysiology of hyponatraemia after subarachnoid haemorrhage. Clinical Endocrinology; 2006, 64: 250–254

23. Symptoms of Hyponatremia
symptoms depends on severity and acuity hyponatremia
the symptoms reflect neurologic dysfunction induced by cerebral edema and possible adaptive responses of brain cels to osmotic swelling
Nausea, malaise, headache, lethargy, seizures, coma, respiratory arrest
the physical examination should help categorize the patient's volume status into hypovolemia, euvolemia, or hypervolemia.

24. Classification of symptoms of hyponatraemia
Clinical practice guideline on diagnosis and treatment of hyponatraemia; Nephrol Dial Transplant (2014) 0: 1–39

25. Complications of hyponatraemia

27. Vasopressin receptor antagonist

28. Management of hyponatremia
Patients who require emergency therapy are typically treated with hypertonic saline (usually as a 100 mL bolus given over 10 to 15 minutes).

29. Management of hyponatremia
In patients who require non-emergency treatment in the hospital setting:
- In patients with asymptomatic acute or subacute hyponatremia, hypertonic saline (either as a 50 mL bolus or slow continuous infusion) unless the hyponatremia is already autocorrecting due to a spontaneous water diuresis.

30. Management of hyponatremia
In patients who require non-emergency treatment in the hospital setting:
- In patients with chronic severe hyponatremia who have mild to moderate symptoms (eg, dizziness, forgetfulness, gait disturbance, nausea, vomiting, confusion, and lethargy), hypertonic saline (typically as a slow infusion at 15 to 30 mL/hour, but a 50 mL bolus can be used).

31. Management of hyponatremia
In patients who require non-emergency treatment in the hospital setting:
- In patients with chronic moderate hyponatremia who have mild to moderate symptoms, no hypertonic saline.

33. In patients with edematous states (such as heart failure and cirrhosis), SIADH, advanced kidney disease, or primary polydipsia, fluid restriction. In general, fluid intake should be less than 800 mL/day.

35. -In patients with heart failure or in patients with SIADH who also have a high urinary cation concentration, loop diuretics may be necessary.
Vasopressin receptor antagonists are another option in such patients.
Patients with SIADH may also be treated with oral sodium chloride tablets.

36. -In patients with true volume depletion, isotonic saline.
With true volume depletion, the administration of saline will usually correct the hypovolemia, thereby removing the stimulus to the release of antidiuretic hormone (ADH) and allowing the excess water to be excreted in the urine.

37. -In patients with diuretic-induced hyponatremia or drug-induced SIADH, discontinuation of the responsible medication may be all that is required.

39. Hypernatremia 
Serum Na>145 mEq/L

42. Symptoms and Sings of Hypernatremia
Dehydrated patient → orthostatic hypotension and oliguria
Rise in plasma Na and osmolality
→water movement out of the brain
→rupture of the cerebral veins
→focal intracerebral and subarachnoidal hemorrages →possible irreversible neurologic damage
Lethargy, weaknees, irritability, twitching, seuzures, coma
Osmotic demyelination (uncommon)

44. Laboratory Findings
Urine osmolality > 400 mosm/kg → renal water-conserving ability is functioning (hypotonic fluid losses from excessive sweating, the respiratory tract, or bowel movements and lactulose)
Urine osmolality < 250 mosm/kg → characteristic of DI
-Central DI: inadequate ADH release
-Nephrogenic DI: renal insensitivity to ADH
(lithium, demeclocycline, relief of urinary obstruction, interstitial nephritis, hypercalcemia, and hypokalemia)

45. Water deficit ≈
body weight X 0.6 X
(plasma Na concentration/
desired plasma Na concentration) - 1