fluids acid base

8/3/2019 Fluids Acid Base

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General Principles ofPathophysiology

The Cellular Environment

Fluids & ElectrolytesAcid-base Balance & Maintenance


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Topics

Describe the distribution of water in thebody

Discuss common physiologic electrolytes Review mechanisms of transport

osmosis, diffusion, etc

Discuss hemostasis & blood types

Discuss concepts of acid-base maintenance


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Distribution of Water

Total Body Weight/ Total Body Water

Intracellular - ICF (45%/75%)

Extracellular - ECF (15%/25%)

Intravascular (4.5%/7.5%)

Interstitial (10.5%/17.5%)


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Intra-

cellular

45%

31.5 kg

Interstitial

10.5 %

7.35 kg

Intra-

vascular

4.5%

3.15 kg

Total Body Weight

Fluid Distribution

Extracellular

CellMembrane

Ca

pillaryMembrane


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Fluid Distribution

Intra-

cellular

75%

31.5 L

Interstitial

17.5 %

7.35 L

Intra-

vascular

7.5%

3.15 L

Total Body Water

Extracellular

C

ellMembrane

Cap

illaryMembrane


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Total Body Weight

45.0%

4.5%

10.5%

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Intracellular Intravascular Interstitial


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Total Body Water

75.0%

7.5%

17.5%

0%

10%

20%

30%

40%

50%

60%

70%

80%

Intracellular Intravascular Interstitial


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Edema

Fluid accumulation in the interstitialcompartment

Causes:

Lymphatic leakage

Excessive hydrostatic pressure

Inadequate osmotic pressure


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Fluid Intake

Water from

beverages:

1600 ml (64%)

Water from

food:

700 ml

(28%)

Water from

metabolism:

200 ml (8%)


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Fluid Output

Water from

skin:

550 ml

(25%)

Water from

feces:

150 ml (5%)

Water from

lungs:

300 ml (11%)

Water from

urine:

1500 ml

(59%)


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Osmosis versus Diffusion

Osmosis is the netmovement of water

from an area of LOWsolute concentration toan area of HIGHERsolute concentration

across a semi-permeable membrane.

diffusion of water

in terms of [water]

Diffusion is the netmovement of solutes

from an area of HIGHsolute concentration toan area of LOWERsolute concentration.


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Silly definition stuff

Osmolarity =osmoles/L of solution

Osmolality =osmoles/kg of solution

Where an osmole is 1 mole (6.02 x 1023 particles)

The bottom line?

Use them synonymously!


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Tonicity

Isotonic

Hypertonic

Hypotonic


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Isotonic Solutions

Same solute concentration as RBC

If injected into vein: no net movement of

fluid

Example: 0.9% sodium chloride solution

aka Normal Saline


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Hypertonic Solutions

Higher solute concentration than RBC

If injected into vein:

Fluid moves INTO veins


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Hypotonic Solutions

Lower solute concentration than RBC

If injected into vein:

Fluid moves OUT of veins


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Affects of Hypotonic Solution on

Cell

CellSwellingCell

Swollen

CellRuptured

Cell

The [solute] outsidethe cell is lower than

inside. Water moves from low

[solute] to high[solute].

The cell swells andeventually bursts!


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Affects of Hypertonic Solution on

Cell

Cell

The [solute] outsidethe cell is higher than

inside. Water moves from low

[solute] to high[solute].

The cell shrinks!

Shrinking

Cell

Shrunken

Cell


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Infusion ofhypertonicsolution into veins

No fluidmovement

Fluidmovementinto veins

Fluidmovementout of veins

Infusion ofisotonic solution

into veins

Infusion ofhypotonic solutioninto veins


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Ion Distribution

0

50

100

150

50

100

150

mEq/L

Na+

K+

Cl-

PO4-

Protein-

Cations Anions

Extracellular

Intracellular


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Example of Role of Electrolytes

Nervous System

Propagation of Action Potential

Cardiovascular System

Cardiac conduction & contraction


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Cardiac Conduction / Contraction


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Composition of Blood

8% of total body weight

Plasma: 55%

Water: 90%

Solutes: 10%

Formed elements: 45%

Platelets

Erythrocytes


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Hematrocrit

% of RBC in blood

Normal:

37% - 47% (Female)

40% - 54% (Male)


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Blood Components

Plasma: liquid portion of blood

Contains Proteins

Albumin (60%) contribute to osmotic pressure

Globulin (36%): lipid transport and antibodies

Fibrinogen (4%): blood clotting


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Blood Components

Formed Elements

Erythrocytes

Leukocytes

Thrombocytes


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Erythrocytes

biconcave disc

7-8 mcm diameter

Packed with hemoglobin

4.5 - 6 million RBC/mm3 (males)

Anucleate

120 day life span

2 million replaced per second!


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Leukocytes

Most work done in tissues

5,000 - 6,000/mm3

Neutrophils (60-70%)

Basophils (Mast Cells) (


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Thrombocytes

Platelets

Cell fragments

250,000 - 500,000/mm3

Form platelet plugs


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Hemostasis

The stoppage of bleeding.

Three methods

Vascular constriction

Platelet plug formation

Coagulation


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Coagulation

Formation of blood clots

Prothrombin activator

Prothrombin Thrombin

Fibrinogen Fibrin

Clot retraction


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Coagulation

Prothrombin

Activator

ProthrombinThrombin

Fibrinogen Fibrin

Clot


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Fibrinolysis

Plasminogen

tissue plasminogen activator (tPA)

Plasmin


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Blood Types

Agglutinogens (Blood Antigens)

Agglutinins (Blood Antibodies)

Agglutination (RBC clumping)

ABO

Rh Antigens


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Type A Blood


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Type B Blood


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Type AB Blood


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Type O Blood


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Rh Antigens


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Bottom line of Acid-Base

Regulation of [H+]

normally about 1/3.5 million that of [Na+]

0.00004 mEq/L (4 x 10-8 Eq/L)

Dependent upon

Kidneys

Chemical Buffers

Precise regulation necessary for peakenzyme activity


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pH Effects on Enzyme Activity

pH

EnzymeActivity

activity

Peak Activity

activity


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Acid Base

Acids release H+

example: HCl -> H+ + Cl-

Bases absorb H+

example: HCO3- + H+ -> H2CO3


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pH is logarithmic

pH = log 1/[H+]

= - log [H+]

= - log 0.00000004 Eq/L

pH = 7.4

Think of pH as power of [H+]


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pH is Logarithmic

pH is inversely

related to [H+]

Small pH meanlarge [H+]

as

[H+]

pH

as

[H+]

pH

&

pH 7.4 = 0.00000004

pH 7.1 = 0.00000008

(it doubled!)


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Buffers Resist pH Changes

Weak acid & conjugate base pair

H2CO3 HCO3- + H+

Conjugate Acid conjugate base + acid


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Henderson-Hasselbalch Equation

pH = pKa + log [base]/[acid]

Ex:

= 6.1 + log 20/1 = 6.1 + 1.3

= 7.4

Key ratio is base: acid HCO3- : CO2 (standing in for H2CO3)


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pH Scale

0 : Hydrochloric Acid

1: Gastric Acid

2: Lemon Juice 3: Vinegar, Beer

4: Tomatoes

5: Black Coffee 6: Urine

6.5: Saliva

7: Blood

8: Sea Water

9: Baking Soda 10: Great Salt Lake

11: Ammonia

12: Bicarbonate 13: Oven Cleaner

14: NaOH


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Acid Base Compensation

Buffer System

Respiratory System

Renal System


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Buffer System

Immediate

CO2 + H20 H2CO3 H+ + HCO3

-

Equilibrium: 20 HCO3- to 1 CO2 (H2CO3)

Excessive CO2 acidosis

Excessive HCO3

- alkalosis

Simplified:

CO2 H+


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Question...

Is the average pH of the blood lower in:

a) arteries

b) veinsVeins!

Why?

Because veins pick up thebyproducts of cellular metabolism,

including

CO2!


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Respiratory System

Minutes

CO2 H+

Respiration : CO2: H+

Respiration : CO2: H+


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Renal System

Hours to days

Recovery of Bicarbonate

Excretion of H+

Excretion of ammonium


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Disorders

Respiratory Acidosis

Respiratory Alkalosis

Metabolic Acidosis

Metabolic Alkalosis


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Simplified:

CO2 H+


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Simplified:

CO2 H+


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Metabolic Acidosis

H+ + HCO3 H2CO3 H20 + CO2

Simplified:

Producing too much H+


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Metabolic Alkalosis

H+ + HCO3 H2CO3 H20 + CO2

Simplified:

Too much HCO3


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Normal Values

pH: 7.35 - 7.45

PCO2: 35 - 45


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Abnormal Values

pH PCO2



Metabolic Acidosis Normal

if compensatingMetabolic Alkalosis Normal

if compensating


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All Roads Lead to Rome!

Respiratory Opposes

Metabolic Equals(or doesnt oppose)


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Example:

pH = 7.25

PCO2 = 60

RespiratoryAcidosis!


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Example:

pH = 7.50

PCO2 = 35

MetabolicAlkalosis!


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Example:

pH = 7.60

PCO2 = 20

RespiratoryAlkalosis!


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Example:

pH = 7.28

PCO2 = 38

MetabolicAcidosis!


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Resources

A Continuing Education article on Acid-Base disturbances is available on our web

site at: http://www.templejc.edu/ems/resource.htm

A great online tutorial at:

http://www.tmc.tulane.edu/departments/anesthesiology/acid/acid.html
http://www.templejc.edu/ems/resource.htmhttp://www.templejc.edu/ems/resource.htm

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