1.
Nutrition &Metabolism
Fluid, Electrolytes ,and Acid-Base Balance
Fluid –is water containing chemical
compounds(electrolytes +blood cells+other
molecules)
45-80% of the body weight is fluid.
46-52% body wt of female is fluid
52-60% of male body wt is fliud
It varies according to :age,fat and sex
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2.
FLUID AND ELECTROLYTES
•Body fluid is located in two fluid compartments
• the intracellular space (fluid in the cells) and
•the extracellular space (fluid outside the cells).
Intracellular space
Contains two third of total body fluid
2/3(42) = 28 L
Has negative environment
Located primarily in the skeletal muscles
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3.
Fluid and electrolytes…..
Extracellular fluid
• Contains less than one third of the total body fluid
• <1/3(42L) = 11L
• Classified in to:
• Interstitial fluid
• Intravascular (fluid within the blood vessels)
• Trans-cellular
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4.
Fluid and electrolytes…..
Interstitial fluid
• Fluid out of cell and out of vascular
• Contains about 11 to 12 L in an adult
• E.g lymphatic fluid
Intravascular
contains plasma
Approximately 3 L of the average 6 L of blood
volume is made up of plasma.
The remaining 3 L is made up of erythrocytes,
leukocytes, and thrombocytes
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5.
Fluid and electrolytes…..
Trans-cellular fluid
• the smallest division of the ECF compartment
• contains approximately1 L of fluid at any given time
• cerebrospinal, pericardial,
• synovial, intraocular, and
• pleural fluids; sweat; and digestive secretions
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6.
Fluid and electrolytes…..
• Body fluid normally shifts between the two major
compartments – equilibrium
• Third-space fluid shift: Loss of ECF into a space that
does not contribute to equilibrium between the ICF and
the ECF
• An early clue of a third-space fluid shift is a decrease in
urine output despite adequate fluid intake
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7.
Fluid and electrolytes…..
Other signs and symptoms of third spacing that indicate
an intravascular fluid volume deficit include:-
• increased heart rate
• decreased blood pressure
• decreased central venous pressure
• edema
• increased body weight and
• imbalances in fluid intake and output (I&O).
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8.
Fluid and electrolytes…..
• Third-space shifts occur in:
• Ascites(an accumulation of fluid in the abdomen)
• Burns
• Peritonitis (inflammation of the peritoneal
membrane )
• Bowel obstruction, and
• Massive bleeding into a joint or body cavity.
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9.
Electrolytes
• Electrolytes in body fluids are active chemicals.
• Are of two types
• Cations: positive charges, and
E.g. sodium(ECF), potassium(ICF), calcium,
magnesium, and hydrogen ions
• Anions: negative charges
E.g. chloride, bicarbonate, phosphate, sulfate, and
proteinate ions
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10.
REGULATION OF BODY FLUID COMPARTMENTS
Osmosis and Osmolality
• diffusion of water caused by a fluid concentration
gradient is known as osmosis
• The magnitude of this force depends on the number
of particles dissolved in the solutions, not on their
weights
• The number of dissolved particles contained in a unit
of fluid determines the osmolality of a solution
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11.
Regulation of body fluid….
• Tonicity is the ability of all the solutes to cause an
osmotic driving force that promotes water movement
from one compartment to another
• The control of tonicity determines the normal state of
cellular hydration and cell size
• Sodium, mannitol, glucose, and sorbitol are effective
osmoles (capable of affecting water movement).
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12.
Regulation of body fluid….
Three other terms are associated with osmosis
• Osmotic pressure is the amount of hydrostatic pressure
needed to stop the flow of water by osmosis.
• It is primarily determined by the concentration of
solutes
• Oncotic pressure is the osmotic pressure exerted by
proteins(eg, albumin).
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13.
Regulation of body fluid….
• Osmotic diuresis occurs when the urine output
increases due to the excretion of substances such as
glucose, mannitol, or contrast agents in the urine.
• Diffusion is the natural tendency of a substance to
move from an area of higher concentration to one of
lower concentration.
• It occurs through the random movement of ions and
molecules
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14.
Regulation of body fluid….
E.g. of diffusion
• Exchange of oxygen and carbon dioxide between the
pulmonary capillaries and alveoli and
• The tendency of sodium to move from the ECF to
ICF
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15.
Regulation of body fluid….
Filtration
• Hydrostatic pressure in the capillaries tends to filter fluid out
of the vascular compartment into the interstitial fluid.
• Movement of water and solutes occurs from an area of high
hydrostatic pressure to an area of low hydrostatic pressure.
• Filtration allows the kidneys to filter 180 L of plasma per
day
• E.g. the passage of water and electrolytes from the arterial
capillary bed to the interstitial fluid
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16.
ROUTES OF GAINS AND LOSSES
Kidneys
• The usual daily urine volume in the adult is 1 to 2 L.
• A general rule is that the output is approximately 1 mL
of urine per kilogram of body weight per hour (1
mL/kg/h) in all age groups.
Skin
• Sensible perspiration refers to visible water and
electrolyte loss through the skin (sweating)
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17.
Routes…
• The chief solutes in sweat are sodium, chloride, and
potassium.
• Actual sweat losses can vary from 0 to1,000 mL or more
every hour, depending on the environmental temperature.
• Continuous water loss by evaporation (approximately600
mL/day) occurs through the skin as insensible
perspiration, a nonvisible form of water loss
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18.
Routes…
Lungs
• The lungs normally eliminate water vapor at a rate of
approximately 400 mL every day.
• The loss is much greater with increased respiratory
rate or depth, or in a dry climate.
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19.
Routes…
GI Tract
• The usual loss through the GI tract is only 100 to 200
mL daily
• approximately 8 L of fluid circulates through the GI
system every 24 hours (called the GI circulation).
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20.
Average Daily Intake and Output in an Adult
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21.
LAB. TESTS FOR EVALUATING F LUID STATUS
Osmolality
 reflects the concentration of fluid that affects the
movement of water between fluid compartments by
osmosis.
 measures the solute concentration per kilogram in blood
and urine.
 It is also a measure of a solution’s ability to create
osmotic pressure and affect the movement of water
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22.
Lab. Tests…
• Serum osmolality primarily reflects the concentration of
sodium.
• Urine osmolality is determined by urea, creatinine, and uric
acid
• When measured with serum osmolality, urine osmolality is
the most reliable indicator of urine concentration.
• Osmolality is reported as milliosmoles per kilogram of
water (mOsm/kg).
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23.
Lab. Tests…
• Normal serum osmolality is 280 to 300mOsm/kg
• normal urine osmolality is 250 to 900mOsm/kg.
Osmolarity, describes the concentration of solutions
measured in milliosmoles per liter (mOsm/L).
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24.
Lab. Tests…
Factors increasing osmolality
• Serum osmolality
• Free water loss
• Diabètes insipides
• Sodium overload
• Hyperglycemia(elevated blood glucose level)
• Uremia (blood poisenening)
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25.
Lab. Tests…
Factors increasing osmolality
• Urine osmolality
• Fluid volume deficit
• SIADH(Syndrome of inappropriate antidiuretic
hormone)
• HF
• Acidosis
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26.
Lab. Tests…
Factors decreasing osmolality
• Serum osmolality
• SIADH
• Renal failure
• Diuretic use
• Adrenal insufficiency
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27.
Lab. Tests…
Factors decreasing osmolality
• Urine osmolality
• Fluid volume excess
• Diabetes insipidus
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28.
Lab. Tests…
Urine specific gravity
measures the kidneys’ ability to excrete or conserve
water.
Compared to the weight of distilled water, which has a
specific gravity of 1.000.
The normal range of specific gravity is 1.010 to 1.025.
varies inversely with urine volume; normally, the larger
the volume of urine, the lower the specific gravity
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29.
Lab. Tests…
• Specific gravity(relative density) is a less reliable
indicator of concentration than urine osmolality
• increased glucose or protein in urine can cause a
falsely high specific gravity.
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30.
Lab. Tests…
Blood urea nitrogen (BUN)
• made up of urea, an end product of metabolism of
protein by the liver
• The normal BUN is 10 to 20 mg/dL (3.5–7 mmol/L)
• The BUN level varies with urine output
Factors that increase BUN include:
• decreased renal function, GI bleeding, dehydration,
increased protein intake, fever, and sepsis
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31.
Lab. Tests…
• Factors that decrease BUN include:
• end-stage liver disease
• a low-protein diet
• starvation, and
• any condition that results in expanded fluid
volume(e.g, pregnancy).
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32.
Lab. Tests…
Creatinine
• The end product of muscle metabolism.
• It is a better indicator of renal function than BUN
because it does not vary with protein intake and
metabolic state.
• The normal serum creatinine is approximately 0.7 to 1.5
mg/dL; however, its concentration depends on lean body
mass and varies from person to person
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33.
Lab. Tests…
• Serum creatinine levels increase when renal function
decreases
Hematocrit
• measures the volume percentage of red blood
cells(erythrocytes) in whole blood
• normally ranges from 44% to52% for males and 39% to
47% for females.
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34.
Lab. Tests…
• Conditions that increase the hematocrit value are
• dehydration and
• Polycythemia(increase in the red blood cell
• concentration in the blood)
• Those that decrease hematocrit are:
• over hydration and
• anemia
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35.
Lab. Tests…
• Urine sodium values change with sodium intake and the
status of fluid volume
• Normal urine sodium levels range from 50 to 220
mEq/24 h(50–220 mmol/24 h).
• Urine sodium levels are used to assess volume status
and are useful in the diagnosis of hyponatremia(sodium
depletion) and acute renal failure
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36.
HOMEOSTATIC MECHANISMS
• Organs involved in homeostasis include:
• Kidneys
• Lungs
• Heart
• Adrenal glands
• Parathyroid glands, and
• Pituitary gland.
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37.
Kidneys functions
• kidneys normally filter 170 L of plasma everyday in the
adult, while excreting only 1.5 L of urine
Major functions of the kidneys in maintaining normal fluid
balance include the following:
• Regulation of ECF volume and osmolality by selective
retention and excretion of body fluids
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38.
Kidneys…
• Regulation of electrolyte levels in the ECF by selective
retention of needed substances and excretion of
unneeded substances
• Regulation of pH of the ECF by retention of hydrogen
ions
• Excretion of metabolic wastes and toxic substances
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39.
Pituitary Functions
• The hypothalamus manufactures ADH
• ADH is sometimes called the water-conserving
hormone because it causes the body to retain water.
• Functions of ADH include maintaining the osmotic
pressure of the cells by controlling the retention or
excretion of water by the kidneys and by regulating
blood volume
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40.
Adrenal Functions
Aldosterone
• has a profound effect on fluid balance.
• Increased secretion of aldosterone causes sodium
retention (and thus water retention) and potassium loss.
• Conversely, decreased secretion of aldosterone causes
sodium and water loss and potassium retention
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41.
Adrenal Functions…
Cortisol
• has only a fraction of the mineralocorticoid potency
of aldosterone.
• When secreted in large quantities, however, it can
also produce sodium and fluid retention and
potassium deficit.
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42.
Baroreceptors
 are small nerve receptors that detect changes in pressure
within blood vessels and transmit this information to
the central nervous system.
 responsible for monitoring the circulating volume, and
 they regulate sympathetic and parasympathetic neural
activity as well as endocrine activities
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43.
Baroreceptors…
• They are categorized as:
Low-pressure: located in the cardiac atria, particularly the
left atrium
High-pressure: nerve endings in the aortic arch and in the
cardiac sinus
• Also located in the afferent arteriole of the
juxtaglomerular apparatus of the nephron
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44.
Renin–Angiotensin–Aldosterone System
• Rennin is released by the juxtaglomerular cells of the
kidneys in response to decreased renal perfusion.
Angiotensinogen angiotensin I Ang.II
• Ang.II with its vasoconstrictor properties, increases
arterial perfusion pressure and stimulates thirst
Rennin ACE
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45.
ADH AND THIRST
• ADH and the thirst mechanism have important roles in
maintaining sodium concentration and oral intake of fluids
• Oral intake is controlled by the thirst center located in the
hypothalamus.
• As serum concentration or osmolality increases or blood
volume decreases, neurons in the hypothalamus are
stimulated by intracellular dehydration; thirst then occurs,
and the person increases oral intake of fluids
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46.
Osmoreceptors
• Located on the surface of the hypothalamus
• Sense changes in sodium concentration.
• As osmotic pressure increases, the neurons become
dehydrated and quickly release impulses to the posterior
pituitary, which increases the release of ADH
• ADH travels in the blood to the kidneys, where it alters
permeability to water, causing increased reabsorption of
water and decreased urine output
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47.
Release of Atrial Natriuretic Peptide
• ANP is released by cardiac cells in the atria of the heart
in response to increased atrial pressure.
• Any disorder that results in volume expansion or
increased cardiac filling pressures (eg, high sodium
intake, heart failure, chronic renal failure, atrial
tachycardia, or use of vasoconstrictor agents) will
increase the release of ANP
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48.
Release of Atrial….
• The action of ANP is the direct opposite of the RAA system
and decreases blood pressure and volume
• The ANP measured in plasma is normally 20 to 77 pg/mL.
• This level increases in acute heart failure, paroxysmal atrial
tachycardia, hyperthyroidism, subarachnoid hemorrhage, and
small cell lung cancer.
• The level decreases in chronic heart failure and with the use
of medications such as urea and prazosin
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49.
FLUID VOLUME DEFICIT
• occurs when loss of extracellular fluid volume exceeds
the intake of fluid
• water and electrolytes are lost in the same proportion as
they exist in normal body fluids
• should not be confused with the term dehydration
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50.
Causes of FVD
abnormal fluid losses, such as those resulting from:
vomiting
diarrhea
GI suctioning
sweating, and
decreased intake, as in nausea or
inability to gain access to fluids (Beck, 2000).
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51.
Third-space fluid shifts
 Burn, edema, ascites
Additional risk factors include:
diabetes insipidus
adrenal insufficiency
osmotic diuresis
hemorrhage and coma
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52.
Clinical Manifestations
• acute weight loss
• decreased skin turgor
• oliguria
• concentrated urine
• postural hypotension
• a weak
• rapid heart rate
• flattened neck veins
• increased temperature
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53.
• decreased central venous pressure
• cool, clammy skin related to peripheral
vasoconstriction
• thirst
• anorexia
• nausea
• muscle weakness and
• cramps.
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54.
Diagnostic Findings
• Elevated BUN
• Hematocrit level is greater than normal
• Hypokalemia
• Hypernatremia
• Increased urine specific gravity
• Urine osmolality is greater than 450 mOsm/Kg
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55.
Medical Management
• When the deficit is not severe, the oral route is preferred
• When fluid losses are acute or severe, however, the IV
route is required
• Isotonic electrolyte solutions are frequently used to treat
the hypotensive patient with FVD because they expand
plasma volume
• E.g. lactated Ringer’s or 0.9% sodium chloride
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56.
• As the patient becomes normotensive, a hypotonic
electrolyte solution is often used to provide both
electrolytes and water for renal excretion of metabolic
wastes
• E.g. 0.45%sodium chloride
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57.
• If the patient with severe FVD is not excreting
enough urine and is therefore oliguric, the health
care provider needs to determine whether the
depressed renal function is the result of reduced
renal blood flow secondary to FVD (prerenal
azotemia) or, more seriously, to acute tubular
necrosis from prolonged FVD. The test used in this
situation is referred to as a fluid challenge test.
During a fluid challenge test, volumes of fluid are
administered at specific rates and intervals while the
patient’s hemodynamic response to this treatment is
monitored (ie, vital signs, breath sounds, sensorium,
central venous pressure, urine output).
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