fluids and electrolytes.pptx

8/10/2019 Fluids and Electrolytes.pptx

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FLUIDS

&

ELECTROLYTES



Intracellular volume 24 L (60%)

Extracellular volume 16 L (40%)

Interstitial volume 11.2 L (28%)

Plasma volume 3.2 L (8%)

Transcellular volume 1.6 L (4%)

Volumes of Body Fluid Compartments



Volumes and Osmolality of Body FluiThe body fluid is an aqueous solution co

electrolytes and nonelectrolytes, and cons

intracellular and extracellular compartment

intracellular compartment is not a single compartm

each cell has its own separate envi

communicating with other cells only via interst

and plasma.

Consequently, difference exists among cells in

tissues in their solute content and concen

Because cell membranes are permeable to water

the ubiquitous presence of aquaporins (water ch

osmot ic equi l ib r ium is maintained so that the osm

all cells is the same and in equilibrium w

extracellular osmolality ( Agre, 2002 ; Nielsen



Plasma Interstitial fluid Plasma water C

(mEq/L) (mmol/L) (mEq/L) (mmol/L) (mEq/L) (mmol/L) (m

Na+ 140 140 145.3 145.3 149.8 149.8 13

K+ 4.5 4.5 4.7 4.7 4.8 4.8 14

Ca2+ 5.0 2.5 2.8 2.8 5.3 5.3 1 ×

Mg2+ 1.7 0.85 1.0 0.5 1.8 0.9 7.0

Cl-

104 104 114.7 114.7 111.4 111.4 3 HCO3

- 24 24 26.5 26.5 25.7 25.7 10

SO42- 1.0 0.5 1.2 0.6 1.1 0.55 –

P 2.1 1.2[*] 2.3 1.3[*] 2.2 1.2[*] 107

Protein 15 1 8 0.5 16 1 40

Organic

anions 5 5[§] 5.6 5.6[§] 5.3 5.3[§] –

Electrolyte Concentrations in Extracellular and Intracel



The calculation is based on the assumption that the pH of

the extracellular fluid is 7.4 and the pK of H2PO4- is 6.8.

The intracellular molal concentration of phosphate is

calculated with the assumption that the pK of organic

phosphates is 6.1 and the intracellular pH 7.0.

The calculation is based on the assumption that eachmmol of protein has on average 15 mEq, but the nature of

cell proteins are not clearly known.

The assumption has been that all the organic anions are

univalent.



• Extracellular Composition

The concentrations of electrolytes in plasma are easily

and their values well known. These concentrations incrabout 7% when expressed in plasma water, because ab

plasma is solids. Thus, plasma sodium is 140 mEq/L bu

concentration in plasma water is about 150 mEq/L. The

concentrations of electrolytes in interstitial fluid are diff

from those in the plasma because of difference in prote

concentrations between plasma and interstitial fluid. Th

differences in electrolyte concentrations between plasm

interstitial fluid can be predicted by the Donnan

equilibrium



• Intracellular Composition

While sodium, chloride, and bicarbonate are the main solu

the extracellular fluid, potassium, magnesium, phosphate,

proteins are the dominant solutes in the cell. The intracelluconcentrations of sodium and chloride cannot be measure

accuracy, and is estimated by subtracting the amount that

extracellular from the total tissue value. Since concentratio

electrolytes in the extracellular fluid are high, a small error

extracellular water volume measurement will cause a large the measurement of intracellular concentration of these ion

concentration of bicarbonate is calculated from ce

and the bicarbonate concentration shown in Table

based on the assumption that average cell pH is 7.



• The electrolyte composition of intracellular flu

identical throughout the tissues. For example, the conc

chloride in muscle is very low, about 3 mEq/L, but it is about 7

erythrocytes. The concentration of potassium in the muscle c140 mEq/L, but in the platelets only about 118 mEq/L. The conc

sodium in the muscle and red blood cell is about 13 mEq/L

leukocytes about 34 mEq/L. The main phosphate in the red bloo

DPG, but in the muscle ATP and creatinine phosphate ar

phosphates. Because the muscle represents the bulk of the bod

it is customary to use the electrolyte concentration of the musrepresentative of the intracellular electrolyte concentration.

substantial part of the anions inside the cell consists of poly

such as phosphate and protein, the total ionic concentration in

mEq/L is higher than that of the extracellular fluid in order

osmotic equilibrium with the extracellular fluid.



•Tonicity

The tonicity of a solution refers to the effect of a partic

solution on the volume of cells. A hypertonic solution ithat shrinks the cells, while a hypotonic solution is one

causes swelling of the cells. An isotonic solution is on

does not induce any volume change in the cells. A solu

0.9% saline (154 mM solution of sodium chloride) is ge

isotonic. When the term tonicity is applied to a fluid in in the urine, it is used almost interchangeably with tota

osmolality. Thus, urine with a high concentration of ure

called hypertonic

( Pradella, 1988 ).

fluids and electrolytes.pptx

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