water and electrolyte

Fluid & Electrolyte Balance

Dr . N. Sivaranjani ,MD biochem

Asst prof.

60% of body consists of fluid

Intracellular space

Extracellular space

Distribution of water in different body water compartments depends on the solute

content of each

compartment

Osmolality of the intra andextra-cellular fluid is the same, but there is marked difference in the solute content.Dr. N. Sivaranjani 3

Distribution of Body Water

Intravascular

Interstitial

IntracellularICF

ECF Na+

K+

Cl-

Essential for normal cell function

Provides medium for metabolic processes

spaces between cells

plasma-arteries, veins, capillaries

Cerebrospinal fluid, Pleural spaces, Synovial spacesPeritoneal fluid spaces

Transcellular1 L

Dr. N. Sivaranjani 4

Fluid composition varies with body fat, age and gender

75% water

ECF=45%,ICF=30%65% water,

ECF= 25%, ICF = 40%

Adult female

50% water, ECF=10-15%, ICF=40%

fat cells contain little water and lean tissue is rich in water, the more obese the person, the smaller the percentage of total body water. Dr. N. Sivaranjani 5

Human life is suspended in a saline solution having a salt concentration of 0.9%

Body fluids must remain fairly constant with regard to amount of H2O & specific electrolytes

Primary component of body fluid: WaterWomen lower % body water than menTotal body water decreases with age

Dr. N. Sivaranjani

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How importance is water Water provides a medium for transporting nutrients to cells and

wastes from cells and for transporting substances such as hormones, enzymes, blood platelets, and red and white blood cells

Water facilitates cellular metabolism and proper cellular chemical functioning

Water acts as a solvent for electrolytes and nonelectrolytes

Helps maintain normal body temperature

Facilitates digestion and promotes elimination

Acts as a tissue lubricant

Component in all body cavities [parietal, pleural… fluids]

Water is the principal body fluid which is essential for life.


Intake and output of water

Factors that Dictate Body Water Requirement

1) Amount needed to give the proper osmotic concentration2) Amount needed to replace water lost excretion

Normal Routes of water gain and loss

INTAKE OUTPUTml/day ml/day

Exogenous :-

Fluid intake 1,500

Food 700

Endogenous :-

Metabolism 300

TOTAL 2,500

Insensible loss (skin + lung) 850

Feces 150

Urine (kidney) 1,500

TOTAL 2,500

Regulation of Body Fluid Compartments

Diffusion

Molecules → from an area of ↑ concentration to an area of ↓concentration

Osmosis

is the movement of water through a semipermeable membrane to a higher concentration of solutes.

Active Transport

is movement of substance across permeable membrane and gradient; requires energy and pump.

Filtration

H2O & dissolved substances → from an area of high hydrostatic pressure to an area of low hydrostatic pressure


Diffusion

High Solute Concentration Low Solute Concentration

Fluid

Solutes


Osmosis

Fluid

High Solution

Concentration,

Low Fluid

Concentration

Low Solute

Concentration,

High Fluid

Concentration

Controls body fluid movement between ICF & ECF


Dr. N. Sivaranjani

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Osmotic Pressure

The amount of hydrostatic pressure required to stop the flow of water by osmosis

Osmolality

reflects the concentration of fluid that affects the movement of water between fluid compartments by osmosis


Osmolality : Number of osmotically active particles present per kilogram of water.

Osmolarity: Number of osmotically active particles present per litre of water.

Electrolytes: Electrolytes are substances whose molecules dissociate into ions when placed in solution

Ions : An ion is an atom or group of atoms with an electrical charge.


Normal plasma Osmolality = 285-292 mOsm/kg

Plasma osmolality can be measured directly using the osmometer

or indirectly as the concentration of effective osmoles

Osmolality =2(Na+) + 2(K+) + Urea + Glucose, mmol/L.

Plasma osmolality (mmol/kg) = 2x Plasma Na+(mmol/l)

Estimated by doubling serum Na concentration

Clinical uses :- diagnosis of disorders of water and electrolyte

balance and NKHC

Osmolality increases – Hyperglycemia, DKA, NKHC, Hypernatremia with water loss (DI)

Decreased – Hyponatremia – water and Na gain (CCF), SIADH. Dr. N. Sivaranjani 17

The difference in measured osmolality and calculated osmolality called Osmolar Gap. (normal - numerically similar)

Increase in osmotically active substances – Ethanol, Mannitol, neutral and cationic amino acids.

Fractional water content of plasma is reduced –hyperlipidemia or hyperproteinemia .


In a healthy state, the osmotic pressure of ECF, mainly due to Na+ ions, is equal to the osmotic pressure of ICF which is predominantly due to K+ ions

Dr. N. Sivaranjani

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Tonicity - measure of transport of water across the biological system causing change in cell volume.

0.9% Normal SalineDr. N. Sivaranjani

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0.9% Normal Saline

Dr. N. Sivaranjani

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(0.45% NS)< concentration of solutes as plasma

Causes H2O to move into cells & swell (hemolysis)Dr. N. Sivaranjani

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(3% NS)

> concentration of solutes as plasma

Causes H2O to draw out of cell (shrink)

Mannitol –treatment of cerebral edema.

Dr. N. Sivaranjani

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Dr. N. Sivaranjani

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ELECTROLYTES

Substances whose molecules dissociate into ions (charged particles) when placed into waterCations: positively-chargedAnions: negatively-charged

Sodium – major cation of ECF Chloride - major anion of ECF

Potassium – major cation of ICF Phosphate – major anion of ICF


ELECTROLYTE Composition

Electrolyte Conc Plasma (mEq/L) ICF

Sodium, Na+ 142 10 Potassium, K+ 5 150Calcium, Ca++ 5 2Magnesium, Mg++ 3 40

(155)

Chloride, Cl- 103 2Bicarbonate, HCO3

- 27 10Biphosphate, HPO4

- 2 140Sulfate, SO4

-2 1 5Protein 16 40Organic acids 6 5

(155)Dr. N. Sivaranjani 26

Functions of Electrolytes

Promote neuromuscular irritability

Regulate acid and base balance

Regulate distribution of body fluids among body fluid compartments


are regulated together

kidneys play a predominant role

major regulatory factors are the hormones - Aldosterone, ADH and Renin angiotensinAtrial natriuretic peptide

Hypothalamic regulation - Stimulates thirst and ADH release Pituitary regulation - Releases ADH Adrenal cortical regulation – Releases Aldosterone Renal regulation - Primary organs for regulating fluid and electrolyte balance

Selective reabsorption of water and electrolytesRenal tubules are sites of action of ADH and aldosterone

Electrolyte and water balance


Synthesis Action Action on sodiumand water

Aldosterone secreted by the zonaglomerulosaof the adrenal cortex

regulates theNa+ → K+ exchange and Na+ → H+ exchange atthe renal tubules.

Sodium and waterretention

Anti-Diuretic Hormone (ADH)

Under control of hypothalamus, posterior pituitary releases ADH

increase the waterreabsorption by the renal tubules.

Retention ofwater

Renin-Angiotensin System

release of renin by the juxtaglomerular cells

Angiotensin-II BP by vasoconstriction of the arterioles.It also stimulates

aldosterone production

Retention of sodium and water

Atrial natriuretic peptides

stimulation of atrial stretch receptors

Inhibit renin and aldosterone secretion –cause elimination of sodium

Increases urinary excretion of sodium.Dr. N. Sivaranjani 29

DECREASED FLUID VOLUME

Stimulation of thirst

center in hypothalamus

Increase in thirst

↑ intake of water

INCREASES PLASMA OSMOLALITY


Posterior pituitary

gland

Osmoreceptors in

hypothalamus + ↑Osmolarity

↑ADH

Kidney

↑H2O reabsorption

↑vascular volume and

↓osmolarity

Stress, hypoglycaemia,

Anesthetic agents, Heat,

Nicotine, Antineoplastic

agents, Narcotics,

Surgery

ANTIDIURETIC HORMONE REGULATION MECHANISMS

Fluid

volume

Increase permeability of renal

collecting ducts to water by

binding to V2 receptors –

cause insertion of water

channels to luminal

membrane

Juxtaglomerular cells↓Serum Sodium

↓Blood volume

↓Blood Pressure

↓renal blood flow Angiotensin I

Distal renal

tubules

Angiotensin II

Adrenal Cortex↑Sodium reabsorption (H2O

resorbed with sodium)

Angiotensinogen in

plasmaRENIN

Angiotensin-

converting enzyme

ALDOSTERONE

Via vasoconstriction of arterial smooth muscle

ALDOSTERONE-RENIN-ANGIOTENSIN SYSTEM

Increases Blood Pressure

INCREASED BLOOD VOLUME ,

INCRESED BLOOD PRESSURE

ATRIAL NATRIURETIC PEPTIDE RELEASE

Reduces in thirst

Decreased intake of water

STIMULATION OF ATRIAL STRETCH RECEPTORS

Inhibits release of ADH

Diuresis – increase urine output

Inhibits release of

Aldosterone

Decreases Na reabsorption

Natriuresis – Na excretion

Dr. N. Sivaranjani

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Volume Disorders 2° Alteration in Sodium Balance

ECF Expansion

Isotonic Inc N N Water and Na retention – Edema- 2 ̊ Cardiac failure2 ̊ Hyper- aldosteronism due to hypoalbunemia.

Hypertonic Inc Dec Inc Na retention due to excess mineralocorticoid –cushing’s syndrome or conn’s syndrome

Hypotonic Inc Inc Dec water retention due to ADH excess or Glomerular dysfuncion

Volume ECF ICF Conditions

Disorder Vol. Vol. Osmolality

ECF Contraction Isotonic Dec N Normal loss of Na & water

common cause – loss of GIT fluid SI obstruction, SI fistulae, paralytic ileus

Hypertonic Dec Dec Increased water depletionDiarrhea – Commonest cause Diabetes insipidus - rare

Hypotonic Dec Inc Decreased sodium depletioninfusion of IV fluids with low Na-dextrosealdosterone deficiency- Addison’s disease

Volume ECF ICF Conditions

Disorder Vol. Vol. Osmolality

• Dehydration • Fluid Overload


Dehydration / water depletion

Pure (tissue) water loss – less common

Depletion of Na and water – more common

and hypovolemia to sodium loss and thus loss of blood volume.


Causes of water depletion :

Decreased intake of water –

• Inadequate water supply

• Mechanical obstruction for drinking

• Impaired response of thirst center – Comatose patient

Increased loss of water –

• Increased renal loss of water – RTA, DI

• Increased loss of water from skin – Burns,

excessive sweating

• Increased loss through lungs – hyperventilation

• Increased loss of gut – vomiting ,diarrhea Dr. N. Sivaranjani 39

Earliest Detectable Signs

low BP

Dry skin and mucous membranes

Sunken eye balls, fontanels

Circulatory Failure (coolness, mottling of extremities)

Loss of skin elasticity

Delayed cap refill

lethargy , confusion and coma Dr. N. Sivaranjani 40

Skin turgor assessment – this assessment can be done on the forearm. Skin that does not flatten immediately after release is called “tenting”, an example of fluid volume deficit.

Dry and cracked lips

Sunken eyes

Thirst and discomfort


Loss of Skin Elasticity due to dehydration


Manifestations of ECF Deficit (Dehydration)

Signs & Symptoms

Weight loss

Blood pressure drop

Delayed capillary refill

Oliguria

Sunken fontanel

Decreased skin turgor

Physiologic Basis

Decreased fluid vol.

Inadequate circ. Blood

Decreased vascular volume

Inadequate kidney circ.

Decreased fluid volume

Decreased interstitial fluid


Degrees of Dehydration

Mild Moderate SevereFluid Vol loss <50ml/kg 50-90ml/kg >100 ml/kg

Skin Color Pale Gray Mottled

Skin Elasticity Decreased Poor Very Poor

M.M. Dry Very Dry Parched

U.O. Decreased Oliguria Marked Oliguria

BP Normal Normal or lowered

Lowered

Pulse Normal or Increased

Increased Rapid, thready


Biochemical finding : plasma sodium – increased urine volume – decreased urine concentrated

Treatment :Aim - Expand ECF volume and improve circulatory and renal function plenty of water Treatment of underlying causes Replacement of fluid deficit –

5% dextrose

Water intoxication / water excess /over hydration

predominant water excess

Decrease in serum Na+

Causes :

Excessive intake of water

Compulsive drinking of water – psychogenic polydypsia

Excessive administration of fluid through parental route

Impaired renal excretion of water

Severe renal failure

SIADH syndrome of inappropriate ADH

Drugs acting as vasopressin agonistDr. N. Sivaranjani 47

SIADH – Plasma hypo-osmolality Normal renal , thyroid, adrenal function Increased urine Na excretion Dilutional hyponatremia Elevated serum ADH

Clinical features Behavioral disturbances Confusion Headache Muscle twitching Convulsion Coma

Biochemical finding :

plasma sodium – decreased

decreased plasma osmolality

urine dilated

Treatment :

Treatment of underlying causes

Fluid restriction

SIADH – vasopressin antagonist

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Edema

the accumulation of fluid within the interstitial space

Causes:

•increased hydrostatic pressure

• venous obstruction, lymphedema, CHF, renal failure

•lowered plasma osmotic pressure (protein loss)

• liver failure, malnutrition, burns

•increased capillary membrane permeability

• Inflammation, sepsis

Dr. N. Sivaranjani

Dr. N. Sivaranjani

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water and electrolyte

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