Disorders of water and sodium balance

Zhao Chenghai

Pathophysiology

OutlineIntroduction of water and sodium balanceEdemaAlterations 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 distributionBody fluid compositionOsmolality of the body fluidWater balanceMechanisms 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/dayWater 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 thirstAntidiuretic hormone (ADH)Renin-angiotensin-aldosterone systemAtrial 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↓

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

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

InflammationAllergic reactionMalignancyTissue 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 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.

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 swallowInability to obtain fluidsImpaired thirst sensationTherapeutic withholding of fluidsUnconsciousness or inability to

express thirst

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

Manifestations of isotonic fluid volume deficit

Acute weight lossCompensatory increase in ADHDecreased extracellular fluid volume

Shock

Treatment of isotonic fluid volume deficit

Treating the underlying causesUsing 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 failureRenal failureHyperaldosteronism Liver failure

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

Manifestations of isotonic fluid volume excess

Acute weight gain Increased interstitial fluid volumeDependent and generalized edemaIncreased 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 sweatingGastrointestinal lossesRenal losses (some chronic renal

diseases)

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

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

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 LossesDecreased Water IntakeExcessive Sodium Intake

Excessive water losses

Watery diarrheaExcessive sweatingHyperventilation Decrease level of ADH

Decreased Water Intake

Unavailability of waterOral trauma or inability to swallowImpaired thirst sensationWithholding water for therapeutic

reasonsUnconsciousness 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 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

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• Edema • Isotonic fluid volume deficit• Isotonic fluid volume excess• Hyponatremia• hypernatremia