disorders of water and sodium balance zhao chenghai pathophysiology
TRANSCRIPT
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Disorders of water and sodium balance
Zhao Chenghai
Pathophysiology
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OutlineIntroduction of water and sodium balanceEdemaAlterations in isotonic fluid volume
• isotonic fluid volume deficit• isotonic fluid volume excess
Alterations in sodium concentration• hyponatremia• hypernatremia
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Introduction of water and sodium balance
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Water and sodium balance
Total fluid volume and distributionBody fluid compositionOsmolality of the body fluidWater balanceMechanisms of regulation of body fluid
and sodium balance
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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%
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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.
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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.
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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/dayWater output
• Insensible evaporation from respiratory tract and through the skin: 700ml/day
• Sweating: 100ml/day• Feces: small amount• Urine: 1500ml/day
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Mechanisms of regulation of body fluid and electrolyte balance
Sensation of thirstAntidiuretic hormone (ADH)Renin-angiotensin-aldosterone systemAtrial natriuretic peptide (ANP)
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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 ↓
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Renin-angiotensin-aldosterone system
Arterial pressure ↓
Plasma sodium content↓
Sympathetic nerve ↑
Glomerulus (juxtaglomerular cells)
renin
Angiotensin I Angiotensin II
Angiotensin converting enzyme
aldosterone
Renal retention of sodium
Increase potassium secretion
ECF volume ↑
Arterial pressure↑
Adrenal gland
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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.
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Edema
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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.
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Causes and pathogenesis of edema
Increased capillary filtration pressure Decreased capillary colloidal osmotic
pressure Increased capillary permeability Obstruction to lymph flow
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Increased capillary filtration pressure
Increased vascular volume• heart failure• kidney disease• pregnancy
Venous obstruction • liver disease with portal vein obstruction• venous thrombosis
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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
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Increased capillary permeability
InflammationAllergic reactionMalignancyTissue injury and burns
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Obstruction to lymph flow
Malignant obstruction of lymphatic structures
Surgical removal of lymph nodes
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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.
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Treatment of edema
Correcting or controlling the cause , and preventing tissue injury
Diuretic therapyElastic 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.
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Alterations in isotonic fluid volume
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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
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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
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Inadequate fluid intake
Oral trauma or inability to swallowInability to obtain fluidsImpaired thirst sensationTherapeutic withholding of fluidsUnconsciousness or inability to
express thirst
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Excessive fluid losses
Excessive gastrointestinal fluid losses
vomiting, diarrhea, gastrointestinal suction
Excessive renal lossesdiuretic 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
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Manifestations of isotonic fluid volume deficit
Acute weight lossCompensatory increase in ADHDecreased extracellular fluid volume
Shock
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Treatment of isotonic fluid volume deficit
Treating the underlying causesUsing isotonic electrolyte solutions for
replacement.
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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
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Inadequate sodium and water elimination
Congestive heart failureRenal failureHyperaldosteronism Liver failure
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Excessive sodium and water intake
Excessive sodium intakeFood, sodium containing medications or fluid
Excessive fluid intake• ingestion of fluid in excess of output• administration of fluids or blood at an
excessive rate
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Manifestations of isotonic fluid volume excess
Acute weight gain Increased interstitial fluid volumeDependent and generalized edemaIncreased vascular volume
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Treatment of isotonic fluid volume excess
Sodium-restricted diet Diuretic therapy is commonly used to
increase sodium elimination.
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Alterations of sodium concentration
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Alterations of sodium concentration
• Hyponatremia
• Hypernatremia
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Hyponatremia
• Definition
Hyponatremia represents a decrease in plasma sodium concentration below 135 mmol/L.
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Causes of hyponatremia
Excessive sodium losses and replacement with sodium-free water
Excessive water intake in relation to output
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Excessive sodium losses and replacement with sodium-free water
Exercise- or heat-induced sweatingGastrointestinal lossesRenal losses (some chronic renal
diseases)
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Excessive Water Intake in Relation to Output
Excessive administration of sodium-free 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
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Manifestations of hyponatremia
Signs Related to Hypo-osmolality of Extracellular Fluids and Movement of Water Into Brain Cells and Neuromuscular TissueMuscle cramps, Weakness, Headache, Depression, Personality changes, Lethargy and coma
Gastrointestinal ManifestationsAnorexia, nausea, vomiting, Abdominal cramps, diarrhea
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Treatment of hyponatremia
water intoxication Limit water intake Administer diuretics
sodium deficiency Administer saline solution orally or
intravenously
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Hypernatremia
• Definition
Hypernatremia implies a plasma sodium level above 145 mmol/L.
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Causes of hypernatremia
Excessive Water LossesDecreased Water IntakeExcessive Sodium Intake
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Excessive water losses
Watery diarrheaExcessive sweatingHyperventilation Decrease level of ADH
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Decreased Water Intake
Unavailability of waterOral trauma or inability to swallowImpaired thirst sensationWithholding water for therapeutic
reasonsUnconsciousness or inability to
express thirst
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Excessive Sodium Intake
Rapid or excessive administration of sodium-containing solutions
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Manifestations of hypernatremia
Thirst and signs of increased ADH levelsOliguria 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
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Treatment of hypernatremia
Treating the underlying causes of the disorder
Fluid replacement therapy to treat the accompanying dehydration.
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Today you learned:How to regulate the normal water and
sodium balance?Definition, causes, manifestations and
treatment of the following pathological conditions• Edema • Isotonic fluid volume deficit• Isotonic fluid volume excess• Hyponatremia• hypernatremia