9315628 Fluids and Electrolytes

7/28/2019 9315628 Fluids and Electrolytes

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Review: Plasma MembraneReview: Plasma Membrane

Phospholipid bilayerPhospholipid bilayer

Freely permeable toFreely permeable to non-polarnon-

polarmolecules (COmolecules (CO22, O, O22, steroids), steroids)

Impermeable to largeImpermeable to largepolar and

polar andchargedchar

ged molecules (ions,molecules (ions,proteins, glucose)proteins, glucose)

Generally permeable to water (though someGenerally permeable to water (though somecells require aquaporins)cells require aquaporins)


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60%Adult

64%12-24 months

70-80%Newborn infant

90%Premature infant

Approx water

content in body

Age group


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60%fluids

55%fluids

Total Body MassTotal Body Mass

female male

45%solids

40%solids

2/3Intra-

cellularfluid(ICF)

1/3(ECF)

80%

20%

Interstitialfluid

Plasma

Some fluid is lost from blood in theSome fluid is lost from blood in theinterstitial tissues, and returned by theinterstitial tissues, and returned by the

lymphatic system

lymphatic system

(also lymph and othermiscellaneous fluids)


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5

2/3 (65%) of TBW is intracellular (ICF)

1/3 extracellular water

25 % interstitial fluid (ISF)

5- 8 % in plasma (IVF intravascular fluid)

1- 2 % in transcellular fluids CSF, intraocular

fluids, serous membranes, and in GI, respiratory and

urinary tracts (third space)


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Function of ICF & ECF: ICF: is vital to normal cell function, its contain

solutes such as oxygen, electrolytes and glucose.

It provides a medium to metabolic process.

ECF: it is the transport system that carries

nutrients and waste product from the cell.


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The proportion of water decreases with aging because fat, age

and sex effect of total body water.

Infants have a greater proportion of extracellular fluid

than older children and adults.

Because extracellular fluid is more easily lost from

the body than intracellular fluid, infants are more at

risk of developing dehydration than older children and

adults (infants also have a larger surface area to body

mass ratio).


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NaNa++

ClCl--

HCOHCO33--

KK++

MgMg2+2+

POPO443-3-

++ ++ ++ ++-- -- -- --


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9

Electrolytes charged particles

Cations positively charged ions

Na+, K+ , Ca++, H+

Anions negatively charged ions

Cl-, HCO3- , PO4

3-

Non-electrolytes - Uncharged

Proteins, urea, glucose, O2, CO2


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ICF (mEq/L) ECF (mEq/L)

Sodium 20 135-145

Potassium 150 3-5

Chloride --- 98-110Bicarbonate 10 20-25

Phosphate 110-115 5

Protein 75 10


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oOsmolarity = solute/(solute+solvent)Osmolarity = solute/(solute+solvent)

o Osmolality = solute/solvent (Osmolality = solute/solvent (275-295 mOsm/L))

o Tonicity = effective osmolalityTonicity = effective osmolality

o Plasma osmolility = 2 x (Na) + (Glucose/18) +Plasma osmolility = 2 x (Na) + (Glucose/18) +

(Urea/2.8)(Urea/2.8)

o Plasma tonicity = 2 x (Na) + (Glucose/18)Plasma tonicity = 2 x (Na) + (Glucose/18)


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MW (Molecular Weight) = sum of the weights of

atoms in a molecule

mEq (milliequivalents) = MW (in mg)/ valence

mOsm (milliosmoles) = number of particles in a

solution


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Tonicity

Isotonic

Hypertonic

Hypotonic


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14


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Cell in a

hypotonic

solution


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16

Cell in a

hypertonicsolution


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MOVEMENT OF BODY FLUIDSMOVEMENT OF BODY FLUIDS

Diffusion

Osmosis

FiltrationActive transport


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1. Osmosis:

Is the movement of water across cell

membranes, from the less concentrated solution

to more concentrated solution. In other word

water move toward higher concentration.


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Solutes are substance dissolved in liquid.

Crystalloid: salts that dissolved readily in to true solution.

Colloids: substance such as large protein molecules thatdo not dissolved in true solution.

Sodium is the major determinant of serum

osmolality.


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2. Diffusion:

Is the continual intermingling of molecules in liquid,

gases by random movement of the molecules.3. Filtration:

Is the process where by fluid and solutes moved

together across a membrane from one compartment to

another.

4. Active transport:

substance can move across cell membranes

from a less concentrated solution to amoreconcentrated one by active transport.


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Sodium and potassium concentrations in extra- and

intracellular fluids are nearly opposite

This reflects the activity of ATP-dependent sodium-potassium pumps (Na+-K+ ATPase)

Fl id M t AFl id M t A


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Fluid Movement AmongFluid Movement Among

CompartmentsCompartments

Continuous exchange and mixing of fluid amongcompartments - regulated by osmotic and hydrostatic

pressures

Net leakage of fluid from the blood is picked up by lymphatic

vessels and returned to the bloodstream

Exchanges between interstitial and intracellular fluids are

more complex due to the selective permeability of the cell

membranes


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An increase in ECF solute concentration [NaCl] would cause osmotic anvolume changes in the ICF.

Which way would water move, into or out of cells?

ICF is determined by the ECF solute concentration

solutesolute

solute

solute

solutesolute

solute

solute

solutesolute

More Solute = Less WaterLess Solute = More Water

Hypertonic Solution or

Hypotonic Solution?

solute

solute

solute

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O H2O

H2O

H2O

H2O

H2O

H2O

Which way will Water move?


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solutesolute

solute

solute

solutesolute

solute

solute

solutesolute

H2O

H2O

H2O

H2O

H2O

If the oncotic pressure in the interstitium increased, would this promotinhibit the re-entry of fluid in a capillary b

H2O


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Daily water intake must equal water outputDaily water intake must equal water output

Water IntakeWater Intake Water OutputWater Output

Stimulated byStimulated by thirstthirstcenter ofcenter ofhypothalamushypothalamus

OsmoreceptorsOsmoreceptorsdetect an increasedetect an increasein fluid osmolarityin fluid osmolarity

Thirst center inhibited byThirst center inhibited bydistension of stomach walldistension of stomach wall

SensibleSensible loss: urine,loss: urine,feces, noticible sweatfeces, noticible sweat

InsensibleInsensible loss:loss:respiration and non-respiration and non-noticible sweatnoticible sweat

Urine output is the primary regulator oUrine output is the primary regulator owater out (ADH from posterior pituitarywater out (ADH from posterior pituitarygland)gland)


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Water intake:

Ingested fluid (60%) and solid food (30%)

Metabolic water or water of oxidation (10%)

Water output:

Urine (60%) and feces (4%)

Lost via lungs and skin (28%), sweat (8%)

To remain properly hydrated, water intake must equal water output

Fluid Gain and Loss


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Why are you told to drink plenty of fluids when you have a fever?A fever increases water loss (maybe both insensible and sensible)


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The hypothalamic thirst center is stimulated by:A decline in plasma volume of 10%15%

Increases in plasma osmolality of 12%

Baroreceptor input, angiotensin II, etc.

Feedback signals that inhibit the thirst centers include:

Moistening of the mucosa of the mouth and throat

Activation of stomach and intestinal stretch receptors


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Hormonal regulationHormonal regulation


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Hormonal regulationHormonal regulation


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Regulation of ECFRegulation of ECF


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Body fluids are:

Electrically neutral

Osmotically maintained

Specific number of particles per

volume of fluid


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Ion transport

Water movement

Kidney function


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Water loss (output) exceeds water intake and the body isin negative fluid balance

A common sequala to hemorrhage, severe burns,prolonged vomiting or diarrhea, profuse sweating, water

deprivation, and diuretic abuseSigns and symptoms: dry mouth, thirst, dry flushed skin,

and oliguria

Prolonged dehydration may lead to weight loss, fever, andmental confusion

Other consequences include hypovolemic shock and lossof electrolytes


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Accumulation of fluid in the interstitial space, leading

tissue swelling, caused by anything that increases fluidflow out of the bloodstream or hinders its return

Factors that accelerate fluid loss include:Hypertension, increased capillary permeability, incompetent venous

valves, localized blood vessel blockage, congestive heart failure

EdEdema


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EdemaEdema

Decreased fluid return usually reflects an imbalance incolloid osmotic pressures across capillary membranes

Hypoproteinemia low levels of plasma proteins, may result from protein

malnutrition, liver disease, or glomerulonephritis

Fluids are forced out of capillary beds at the arterial ends by blood pressure, b

fail to return at the venous ends and interstitium becomes congested with fluid

Edema - lymphedemaEdema - lymphedema


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y py p

Blocked (or surgically removed) lymph vessels may resu

in the accumulation of plasma proteins in interstitial fluid

Interstitial colloid osmotic pressure increases,

fluid leaves blood and moves into tissue

Interstitial fluid accumulation could result in a

decrease in blood volume, blood pressure, and

impaired circulation

Protein DeficienciesProtein Deficiencies


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Kwashiorkor - a form of malnutrition caused by inadequate prote

intake and consequent reduced albumin in the blood

hypoalbuminemia and reduced plasma oncotic pressure promote

extravasation of fluid from the plasma into the peritoneal cavity


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:Signs of Hypervolemia:Signs of Hypervolemia

Hypertension

Polyuria

Peripheral edema

Wet lung

Jugular vein engorgement

Especially when hypo-

albuminemia


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:Signs of Hypovolemia:Signs of Hypovolemia

Diminished skin turgor Dry oral mucus membrane Oliguria

-


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:Clinical Diagnosis of Hypovolemia:Clinical Diagnosis of Hypovolemia

Thorough history taking: poor intake, GI

bleedingetc BUN : Creatinine > 20 : 1

- BUN: hyperalimentation, glucocorticoidtherapy, UGI bleeding Increased specific gravity Increased hematocrit

Electrolytes imbalance Acid-base disorder

Clinical parameters for evaluation ofClinical parameters for evaluation of


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Clinical parameters for evaluation ofClinical parameters for evaluation of

water balancewater balance

CVPPulsePeripheral VeinsWeight

Thirst Intake and OutputSkinEdema

Lab Values


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Reasons for fluid therapyReasons for fluid therapy

Preserve oxygen delivery to tissuesPreserve oxygen delivery to tissues Correct hypovolaemiaCorrect hypovolaemia

Maintain cardiac outputMaintain cardiac output

Optimise gas exchangeOptimise gas exchange

Replace electrolytes & waterReplace electrolytes & water

Maintain urine outputMaintain urine output

Colloids + RBCs

Crystalloids

Identify what is the goal

Choose fluid which best achieves the goal


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Methods of Estimating Maintenance FluidMethods of Estimating Maintenance Fluid

Methods of estimating basal or maintenance fluidrequirements Basal Surface Area

Need to know height and weight, requires table, does not allow

for deviations from normal activity Basal or Calorie Expenditure Method

Requires a table, involves calculations, permits correction forchanges in activity or injury, drier

Holliday-Segar SystemEasy to remember, does not require table or difficult

calculations, does not allow for deviations from normal activity


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:Crystalloids:Crystalloids

Isotonic crystalloids

- Lactated Ringers, 0.9% NaCl

- only 25% remain intravascularly Hypertonic saline solutions

- 3% NaCl Hypotonic solutions

- D5W, 0.45% NaCl

- less than 10% remain intra-

vascularly, inadequate for fluid

resuscitation


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:Colloid Solutions:Colloid Solutions

Contain high molecular weight

substancesdo not readily migrate across

capillary walls

Preparations

- Albumin: 5%, 25%

- Dextran

- Gelifundol

- Haes-steril 10%

Common parenteral fluid therapyCommon parenteral fluid therapy


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D5WD5W

3101541545006%6%

HetastarchHetastarch

330130-160

2.5

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9315628 Fluids and Electrolytes

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