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Disorders of water balance

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 sodiumbalance

Water and sodium balance

Total fluid volume and distribution

Body fluid composition

Osmolality of the body fluid

Water balance

Mechanisms of regulation of body fluidand sodium balance

Total fluid volume and distribution

Total body fluid accounts for 60% of bodymass in males.

Total body fluid is mainly distributed inintracellular 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 aselective cell membrane that is onlypermeable to a limited number ofsubstances such as water, oxygen andcarbon dioxide, but not to most of theelectrolytes in the body.

The concentration of ions in theinterstitial fluid and plasma areconsidered to be equal except forprotein.

Osmolality of the body fluid

The total osmolality is almost equal amongplasma, the interstitial and intracellular fluidswith a range from 280-310 mOsm/L, due to afree permeability of cell membrane to water.

Nearly 80% of the osmolality of plasma andthe interstitial fluid is induced by sodium andchloride ions. And approximately half of theintracellular osmolality is caused bypotassium.

Water balance

Water intake

•Ingestion in the form of liquid and water in food:2100ml/day

•Metabolism in the body following the oxidation ofcarbohydrates: 300ml/day

Water output

•Insensible evaporation from respiratory tract andthrough the skin: 700ml/day

•Sweating: 100ml/day

•Feces: small amount

•Urine: 1500ml/day

Mechanisms of regulation of body fluidand electrolyte balance

Sensation of thirst

Antidiuretic hormone (ADH)

Renin-angiotensin-aldosterone system

Atrial natriuretic peptide (ANP)

ADH

Main target sites: distal tubules andcollecting ducts in kidney

Function: to Promote the waterreabsorption and cause increased ECFvolume 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 ofcardiac atrim in response to blood volumeexpansion.

Function: ANP inhibits the reabsorption ofsodium and water by the renal tubules, which inturn increases urinary excretion and helps toreturn blood volume back toward normal.

ANP exerts a negative regulation against ADHin the central nervous system.

Edema

Definition of edema

Edema can be defined as palpableswelling produced by expansion of theinterstitial fluid volume.

Edema is caused by excessive fluid inthe interstitial compartment.

Causes and pathogenesis of edema

Increased capillary filtration pressure

Decreased capillary colloidal osmoticpressure

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 colloidalosmotic pressure

Increased loss of plasma proteins

•protein-losing kidney diseases

•extensive burns

Decreased production of plasmaproteins

•liver disease

•starvation

•malnutrition

Increased capillary permeability

Inflammation

Allergic reaction

Malignancy

Tissue injury and burns

Obstruction to lymph flow

Malignant obstruction of lymphaticstructures

Surgical removal of lymph nodes

Manifestations of edema

Life threatening in some locations,such as brain, larynx, lungs.

Interfering with movement and limitingjoint motion.

Increasing the distance for diffusion ofoxygen, nutrients and wastes at thetissue level.

Treatment of edema

Correcting or controlling the cause , andpreventing tissue injury

Diuretic therapy

Elastic support stockings and sleeves forpatients with lymphatic or venousobstruction

Administering albumin intravenously to raisethe colloidal osmotic pressure when edemais caused by hypoalbuminemia.

Alterations in isotonic fluidvolume

Alterations in isotonic fluid volume

Isotonic fluid volume disordersrepresent an expansion or contractionof the ECF brought about byproportionate changes in both sodiumand water.

Two types:

•Isotonic fluid volume deficit

•Isotonic fluid volume excess

Isotonic fluid volume deficit

Definition:

Isotonic fluid volume deficit resultswhen water and sodium are lost inisotonic 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 toexpress 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 andwounds that remove skin

Third-space losses

intestinal obstruction, edema, ascites

Manifestations of isotonic fluidvolume deficit

Acute weight loss

Compensatory increase in ADH

Decreased extracellular fluid volume

Shock

Treatment of isotonic fluid volumedeficit

Treating the underlying causes

Using isotonic electrolyte solutions forreplacement.

Isotonic fluid volume excess

Definition:

It represents an isotonic expansion ofthe extracellular fluid compartment.Water and sodium are increased inisotonic proportions.

Causes:

•Inadequate sodium and water elimination

•Excessive sodium and water intake

Inadequate sodium and waterelimination

Congestive heart failure

Renal failure

Hyperaldosteronism

Liver failure

Excessive sodium and water intake

Excessive sodium intake

Food, sodium containing medications orfluid

Excessive fluid intake

•ingestion of fluid in excess of output

•administration of fluids or blood at anexcessive rate

Manifestations of isotonic fluidvolume excess

Acute weight gain

Increased interstitial fluid volume

Dependent and generalized edema

Increased vascular volume

Treatment of isotonic fluid volumeexcess

Sodium-restricted diet

Diuretic therapy is commonly used toincrease sodium elimination.

Alterations of sodiumconcentration

Alterations of sodium concentration

•Hyponatremia

•Hypernatremia

Hyponatremia

•Definition

Hyponatremia represents a decrease inplasma sodium concentration below135 mmol/L.

Causes of hyponatremia

Excessive sodium losses andreplacement with sodium-free water

Excessive water intake in relation tooutput

Excessive sodium losses andreplacement with sodium-free water

Exercise- or heat-induced sweating

Gastrointestinal losses

Renal losses (some chronic renaldiseases)

Excessive Water Intake in Relationto Output

Excessive administration of sodium-free solutions

Repeated irrigation of body cavitieswith sodium-free solutions

Irrigation of gastrointestinal tube withdistilled water

Kidney disorders that impair waterelimination

Increased ADH level

Manifestations of hyponatremia

Signs Related to Hypo-osmolality ofExtracellular Fluids and Movement of WaterInto 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 orintravenously

Hypernatremia

•Definition

Hypernatremia implies a plasmasodium 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 therapeuticreasons

Unconsciousness or inability toexpress thirst

Excessive Sodium Intake

Rapid or excessive administration ofsodium-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 andmovement of water out of brain cells

–Headache, agitation and restlessness, seizure and coma