Disorders of water and sodium
balance
Zhao Chenghai
Pathophysiology
Outline
Introduction of water and sodium balance
Edema
Alterations in isotonic fluid volume
• isotonic fluid volume deficit
• isotonic fluid volume excess
Alterations in sodium concentration
• hyponatremia
• hypernatremia
Introduction of water and sodium
balance
Water and sodium balance
Total fluid volume and distribution
Body fluid composition
Osmolality of the body fluid
Water balance
Mechanisms of regulation of body fluid
and sodium balance
Total fluid volume and distribution
 Total body fluid accounts for 60% of body
mass in males.
 Total body fluid is mainly distributed in
intracellular and extracellular compartments
 Intracellular fluid ( ICF) : 40%
 Extracellular fluid (ECF): 20%
 Interstitial fluid: 15%
 Plasma: 5%
Body fluid composition
The ICF is separated from the ECF by a
selective cell membrane that is only
permeable to a limited number of
substances such as water, oxygen and
carbon dioxide, but not to most of the
electrolytes in the body.
The concentration of ions in the
interstitial fluid and plasma are
considered to be equal except for
protein.
Osmolality of the body fluid
 The total osmolality is almost equal among
plasma, the interstitial and intracellular fluids
with a range from 280-310 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.
Water balance
 Water intake
• Ingestion in the form of liquid and water in food:
2100ml/day
• Metabolism in the body following the oxidation of
carbohydrates: 300ml/day
 Water output
• Insensible evaporation from respiratory tract and
through the skin: 700ml/day
• Sweating: 100ml/day
• Feces: small amount
• Urine: 1500ml/day
Mechanisms of regulation of body fluid
and electrolyte balance
Sensation of thirst
Antidiuretic hormone (ADH)
Renin-angiotensin-aldosterone system
Atrial natriuretic peptide (ANP)
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 ↓
Renin-angiotensin-aldosterone system
Arterial pressure ↓
Plasma sodium content↓
Arterial pressure↑
Sympathetic nerve ↑
ECF volume ↑
Glomerulus
(juxtaglomerular cells)
Renal retention of sodium
Increase potassium secretion
renin
Angiotensin I
Angiotensin II
Angiotensin converting enzyme
Adrenal gland
aldosterone
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.
Edema
Definition of edema
Edema can be defined as palpable
swelling produced by expansion of the
interstitial fluid volume.
Edema is caused by excessive fluid in
the interstitial compartment.
Causes and pathogenesis of edema
 Increased capillary filtration pressure
 Decreased capillary colloidal osmotic
pressure
 Increased capillary permeability
 Obstruction to lymph flow
Increased capillary filtration pressure
Increased vascular volume
• heart failure
• kidney disease
• pregnancy
Venous obstruction
• liver disease with portal vein obstruction
• venous thrombosis
Decreased capillary colloidal
osmotic pressure
Increased loss of plasma proteins
• protein-losing kidney diseases
• extensive burns
Decreased production of plasma
proteins
• liver disease
• starvation
• malnutrition
Increased capillary permeability
Inflammation
Allergic reaction
Malignancy
Tissue injury and burns
Obstruction to lymph flow
Malignant obstruction of lymphatic
structures
Surgical removal of lymph nodes
Manifestations of edema
Life threatening in some locations,
such as brain, larynx, lungs.
Interfering with movement and limiting
joint motion.
Increasing the distance for diffusion of
oxygen, nutrients and wastes at the
tissue level.
Treatment of edema
 Correcting or controlling the cause , and
preventing tissue injury
 Diuretic therapy
 Elastic support stockings and sleeves for
patients with lymphatic or venous
obstruction
 Administering albumin intravenously to raise
the colloidal osmotic pressure when edema
is caused by hypoalbuminemia.
Alterations in isotonic fluid
volume
Alterations in isotonic fluid volume
Isotonic fluid volume disorders
represent an expansion or contraction
of the ECF brought about by
proportionate changes in both sodium
and water.
Two types:
• Isotonic fluid volume deficit
• Isotonic fluid volume excess
Isotonic fluid volume deficit
Definition:
Isotonic fluid volume deficit results
when water and sodium are lost in
isotonic proportions
Causes:
• Inadequate fluid intake
• Excessive fluid losses
Inadequate fluid intake
Oral trauma or inability to swallow
Inability to obtain fluids
Impaired thirst sensation
Therapeutic withholding of fluids
Unconsciousness or inability to
express thirst
Excessive fluid losses
Excessive gastrointestinal fluid losses
vomiting, diarrhea, gastrointestinal suction
Excessive renal losses
diuretic therapy, osmotic diuresis, adrenal
insufficiency
Excessive skin losses
fever, exposure to hot environment, burns and
wounds that remove skin
Third-space losses
intestinal obstruction, edema, ascites
Manifestations of isotonic fluid
volume deficit
Acute weight loss
Compensatory increase in ADH
Decreased extracellular fluid volume
Shock
Treatment of isotonic fluid volume
deficit
Treating the underlying causes
Using isotonic electrolyte solutions for
replacement.
Isotonic fluid volume excess
Definition:
It represents an isotonic expansion of
the extracellular fluid compartment.
Water and sodium are increased in
isotonic proportions.
Causes:
• Inadequate sodium and water elimination
• Excessive sodium and water intake
Inadequate sodium and water
elimination
Congestive heart failure
Renal failure
Hyperaldosteronism
Liver failure
Excessive sodium and water intake
Excessive sodium intake
Food, sodium containing medications or
fluid
Excessive fluid intake
• ingestion of fluid in excess of output
• administration of fluids or blood at an
excessive rate
Manifestations of isotonic fluid
volume excess
Acute weight gain
Increased interstitial fluid volume
Dependent and generalized edema
Increased vascular volume
Treatment of isotonic fluid volume
excess
Sodium-restricted diet
Diuretic therapy is commonly used to
increase sodium elimination.
Alterations of sodium
concentration
Alterations of sodium concentration
• Hyponatremia
• Hypernatremia
Hyponatremia
• Definition
Hyponatremia represents a decrease in
plasma sodium concentration below
135 mmol/L.
Causes of hyponatremia
Excessive sodium losses and
replacement with sodium-free water
Excessive water intake in relation to
output
Excessive sodium losses and
replacement with sodium-free water
Exercise- or heat-induced sweating
Gastrointestinal losses
Renal losses (some chronic renal
diseases)
Excessive Water Intake in Relation
to Output
Excessive administration of sodiumfree solutions
Repeated irrigation of body cavities
with sodium-free solutions
Irrigation of gastrointestinal tube with
distilled water
Kidney disorders that impair water
elimination
Increased ADH level
Manifestations of hyponatremia
 Signs Related to Hypo-osmolality of
Extracellular Fluids and Movement of Water
Into Brain Cells and Neuromuscular Tissue
Muscle cramps, Weakness, Headache, Depression,
Personality changes, Lethargy and coma
 Gastrointestinal Manifestations
Anorexia, nausea, vomiting, Abdominal cramps,
diarrhea
Treatment of hyponatremia
water intoxication
 Limit water intake
 Administer diuretics
sodium deficiency
Administer saline solution orally or
intravenously
Hypernatremia
• Definition
Hypernatremia implies a plasma
sodium level above 145 mmol/L.
Causes of hypernatremia
Excessive Water Losses
Decreased Water Intake
Excessive Sodium Intake
Excessive water losses
Watery diarrhea
Excessive sweating
Hyperventilation
Decrease level of ADH
Decreased Water Intake
Unavailability of water
Oral trauma or inability to swallow
Impaired thirst sensation
Withholding water for therapeutic
reasons
Unconsciousness or inability to
express thirst
Excessive Sodium Intake
Rapid or excessive administration of
sodium-containing solutions
Manifestations of hypernatremia
 Thirst and signs of increased ADH levels
Oliguria or anuria
 Intracellular dehydration
– Dry skin and mucous membranes
– tongue rough and fissured
– decreased salivation
 Signs related to hyperosmolality of ECF and
movement of water out of brain cells
–
Headache, agitation and restlessness, seizure and coma
Treatment of hypernatremia
Treating the underlying causes of the
disorder
Fluid replacement therapy to treat the
accompanying dehydration.
Today you learned:
How to regulate the normal water and
sodium balance?
Definition, causes, manifestations and
treatment of the following pathological
conditions
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Edema
Isotonic fluid volume deficit
Isotonic fluid volume excess
Hyponatremia
hypernatremia