Dynamics of Body Fluids Movement.ppt

8/14/2019 Dynamics of Body Fluids Movement.ppt

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Dynamics of Body FluidsMovement

Endang Melati Maas

Department of Anesthesiologist and Reanimation

Faculty of Medicine Sriwijaya University

Dr. Muhammad Hoesin General Hospital


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Introduction

Fluid management, is a key factor for the

survival of patients who have severe, acute

hypovolemia.

Volume replacement and restoration of

capillary perfusion are essential for reversal

of the ischemic changes that can lead tomultiple organ failure and death.


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Anemia may tolerated better than hypo-volemia. EBM Not enough data to choose what type of

fluids should be given.

understanding ofphysiology, pathophysiology of

body fluids and pharmacology of available intravenous fluid

is very important.


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Fluids Physiology


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Fluids physiology (cont) Total body water: (60% TBW)

Intracellular Fluid / ICF (40%)

Extracellular Fluid / ECF (20%)

Plasma (5%)

Interstitial Fluid / ISF (15%).


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Interstitial15% TBW

Formulae for Blood Volume

Blood Volume = Plasma volume x (100/100-Hct)

Blood Volume = Red cell vol x (100/Hct)

(where Hct = Haematocrit)

Intracellular40% TBW

Plasma5% TBW

Blood cell

Fig. Body fluids compartment

endothel

Capillary

membrane


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Intracellular Fluid

ICF >< ECF cell membrane that is highly

permeable to water but not to most electrolytes.

volume is maintained by the membranesodium-potassium pump.

there are significant differences in theelectrolytic composition of intracellular and

extracellular fluid.


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Extracellular Fluid

IVF >< ISF by capillary membrane.

Highly permeable to almost all solutes in theextracellular fluid except the proteins.

The ionic composition of plasma and interstitial fluid

are similar but the plasma contains a higherconcentration of protein.


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Definition

Molarity: is the number of moles of solute per litre of solution.

Molecular weight of the substance expressed in grams. The MWof NaCl is about 58 so 58g of NaCl = 1 mole. If water added to a

volume of 1l then the result will be a 1 molar solution (1 Mol/l).

Molality: is the number of moles of solute perkgof solvent.

Osmole the weight in grams of a substance producing an osmotic

pressure of 22.4 atm. when dissolved in 1.0 litre of solution.


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Definition (cont)

Osmolarity:

a measure of the osmotic pressure exerted by a

solution across a semi-permeable membrane.

is the number of osmoles of solute per litre of solution.

Osmolality:

is the number of osmoles of solute per kilogram ofsolvent.


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1 M Glucose

+

1 M Sucrose

water 1 L

1 M NaCl

1 M Glucose

1 M Sucrose

osmolarity 2 osm/l

1 M Cl-

1 M Na+

osmolarity 2 osm/l


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Definition (cont)

Colloids:

the large molecular weight (nominally MW >30,000) particles present in a solution.

In normal plasma, the plasma proteins are the

major colloids present.


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Colloids

contain large, oncotically active molecules.

natural products (eg, albumin, FFP)

Semisynthetic (gelatine, starches or dextrans).

more impermeable to intact capillary membranesthan crystalloids.

smaller volumes of colloids than crystalloids are

required for fluid resuscitation.


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Movement of Body Fluid

Diffusion

Particles move from an area of high concentration to an area

of low concentration until concentrations are equalized.

Simple diffusion Substance small enough to pass through the protein pores ( ie

urea, 02, carbon dioxide).

Facilitated diffusion

Substance moves by means of a carrier substance

Large lipid-insoluble substance such as glucose must diffuseinto the cell via a carrier substance.


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Movement of Body Fluid (cont)

Active Transport

Substances move across cell membrane from lessconcentrated solution to more concentrated one.

Differs from diffusion and osmosis in that metabolicenergy is used.

Depends on availability of carrier substances -usually enzyme.

Many important solutes are transported activelyacross cell membranes, including Na, K, H, glucose,and amino acids.


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Starl ing's Forces

this equation predicts the net flux of fluids across amembrane,

Jv = Kf.[(Pc-Pi) - s(pc-pi)]

where,

Jv = net water flux

Kf = the filtration coefficient

Pci = hydrostatic pressures

pci = oncotic pressures

s= Staverman reflection coefficient

the Staverman ref lection coeff icient is a measure of capillarypermeability to protein,s= 1completely impermeable.


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Starlings Hypothesis (1896) (cont)

fluid movement due to

filtration across the wall of a

capillary is dependent on

the balance between the

hydrostatic pressuregradient and the oncotic

pressure gradient across

the capillary.

NB: Starling's equation predicts the net

movement of fluid across the capillary,

it does not predict what happens to ISF

volume


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Starlings Hypothesis (1896) (cont)

Typical values of Starling Forces in Systemic Capillaries (mmHg)

Arteriolar end

of capillary

Venous end of

capillary

Capillary hydrostaticpressure

25 10

Interstitial hydrostatic

pressure-6 -6

Capillary oncoticpressure

25 25

Interstitial oncotic

pressure5 5


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Gibbs-Donnan Equi l ibr ium:

"in the presence of a non-diffusible ion, thediffusible ion species distribute themselves suchthat at equilibrium their concentration ratios areequal.

The sums of positive and negative charges oneach side of the membrane must be equal, and the

products of diffusible ions on each side must alsobe equal.


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Gibbs-Donnan Equilibrium (cont)

Donnan effect dictates that,

[Na+]A.[Cl-]A= [Na

+]B.[Cl-]B[Na

+]A /[Na+]B = [Cl

-]B / [Cl-]A

but to maintain electroneutrality,

[Na+]B= [Cl-]B

Therefore, [Na+]A> [Cl-]A

Side A Side B

Na+ Na+

Cl- Cl-

Prot-


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Fluid Pressures

Osmotic Pressure

Is the pressure required to prevent the movement of

water from a dilute solution to concentrated solution

across a semipermeable membrane.

Colloid Osmotic Pressure (COP)

Osmotic pressure due to colloid activity in the solvent.

= Oncotic pressure.


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Fluid Pressures (cont)

Hydrostatic Pressure:

Pushing force of fluid against walls of the space, ex.Heart pumps blood which exerts pressure on the bloodvessel wall.

= Filtration pressure (sometimes).

Tonicity:

Is the effective osmolality Is equal to the sum of the concentrations of the solutes

which have the capacity to exerts an osmotic forceacross the membrane.


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Fluid Pressures (cont)

Serum osmolarity:

concentration of particles (major particles are

sodium and protein) in the plasma.

normal serum osmolarity275-295 mOsm/L

HypertonicIsotonicHypotonic

275-295mOsm/L

>>


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Chemical regulation of fluidbalance

Antidiuretic hormone (ADH)

hormone synthesized by hypothalamus and secreted byposterior pituitary, which regulates water.

Aldosterone Hormone produced by adrenal gland that conserves

sodium in body by causing kidneys to retain sodium andexcrete potassium in its place.

Glucocorticoids (cortisol)

Produced and released by adrenal gland when bodystressed

Promote renal retention of sodium and water.


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Chemical regulation of fluid balance (cont)

Atrial natriuretic peptide (ANP)

Cardiac hormone found in atria of heart that is released

when atria are stretched by high blood volume or high BP

Causes vasodilatation by direct effect on blood vessels andsuppression of renin-angiotensin system

Decreases aldosterone release by adrenal glands, causingincreased urinary excretion of sodium and water

Decreases ADH release by pituitary gland, causing increased

urinary excretion of water

Increases glomerular filtration rate, increasing rate or urineproduction and water excretion.


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Chemical regulation of fluid balance (cont)

Thirst Mechanism

osmolarity

TBW

Hypothalamic

osmoreceptor

ADH release

+

+

+

-

Thirst

Water

retention


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Volumes of Distribution

The plasma volume expansion effect is directlyrelated to the volume of distribution.

PVE (% of infused volume) =

Plasma Volume

volume of distribution

Ex.:

NaCl 0.9%PVE 20%

Glucose 5%PVE 6.7%


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ECF

ICF ISF Plasma

3 : 1

Ringer acetateRinger lactateNaCl 0.9%

Isotonic


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ICF ISF Plasma

D5W

N4NaCl 0.45%

ICF > ECF

40 : 15 : 5

Hypotonic

+ Hyponatremia

+ hyperglicemia


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Plasma

ICF ISF Plasma

colloids

hyperoncotic


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Properties of colloids

Magnitude and duration of plasma volume

expansion.

The number, MW and the COP determine the

initial degree of volume expansion.

Hemorrheological effects.

Blood viscosity, which is the tendency of fluids

to resist flow, depends largely on hematocrit, red

cell characteristics, and blood protein

concentration.


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Hemostatic effects.All the semisynthetic colloids have specific effects on

hemostasis in addition to simple dilution of clotting

factors.

Interaction with inflammatory cells.

Hydroxyethyl starch and dextran solutions interact

with both endothelial and inflammatory cells.


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Adverse drug reactions.

Both naturally occurring and semisynthetic colloidsare associated with a small but significant incidence ofanaphylactic and anaphylactoid reactions.

Histamine release is a predictable response to gelatin

infusions and appears to be related to theanaphylactoid reactions that occur.


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Conclusion

Movement of body fluids: Diffusion

Osmosis

Active transport

Starlings forces

Gibbs Donnan equilibrium.

The plasma volume expansion effect of IV fluids is

directly related to the volume of distribution.


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Conclusion (cont)

the choice of fluid type in a variety of clinical

situations can now be rationally guided by an

understanding of physiology and pathophysiology of

Body fluids and the physicochemical and biologicalproperties of the various crystalloid and colloid

solutions available.


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Dynamics of Body Fluids Movement.ppt

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