abg analysis dawn

8/3/2019 Abg Analysis Dawn

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BY MS.DAWN LOBO

1STYEAR M.SC NSG


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the symbol pH refers to negative logarithm of

concentration.

A pH of 7.0 is neutral ,that is having an equal number

of acids and bases Acidic solution and alkaline solutions

Because pH is a negative log, arise in pH reflects a

drop in H+ Ions and vice versa.

Normal serum pH is 7.35 to 7.45


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3 physiologic systems acts interdependently to

maintain a normal pH. They are

Chemical buffering of excess acid or base by buffersystems in blood plasma and in cells

Excretion of acids by lungs

Excretion of acids or regeneration of bases by kidneys.


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Buffer system consists of weak acids and a salt of a

base.

Organic acids formed during cellular metabolism are

strong acids, thus may cause large alterations in pH The pH of buffered solutions still remain fairly stable,

despite this because buffer system components

combine with these acids or bases and convert them

into weaker forms.

Buffer systems are present within the hemoglobin of

RBC and protein in plasma.

Negatively charged ions such as phosphates are

important intracellular buffers.


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Open buffer systems

When bases are buffered, CO2 consumed by carbonic

acid formation is readily replenished by normal

metabolism. Dissociation constant of a buffer-pKa

Buffer system acts instantly to minimize the impact of

adding strong acids or bases to body fluids.

Acts as body's 1st

line of defense against acid baseimbalance.

BUT THESE BUFFERS DO NOT ACTUALLY

ELIMINATE ACID OR BASE FROM THE BODY.


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Volatile acids are those that can be converted intogases.

Large quantities ofCO2 is exhaled out by the lungs.

CO2 is produced by the cells during metabolism.

CO2 diffuses from body cells into blood.

Hydrolysis reaction

CO2 and H2CO3 are directly related

Mostly this reaction takes place in the RBC in thepresence of carbonic anhydrase enzyme that catalysesthe reaction.

Hydrolysis reaction at tissue level

Reversal of hydrolysis in the lungs


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Acids that cannot be converted into gases areeliminated by urine.

These acids are sulphuric acid, phosphoric acid,ketones and lactic acid

Kidneys regulate pH by secreting H+ into the urine orby regenerating HCO3 for reabsorption into blood

This system works only until tubular pH falls up to 4.5

At lower pH significant amounts of H+ leak into the

blood. Presence of urinary buffers limits fall of urinary pH

and allows tubular fluid to accept large quantities ofH+.


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3 principal buffer systems in renal tubules are:-

I. Bicarbonate buffer

II. Ammonia buffer

III. Phosphate buffer

Effect of other electrolytes on pH

o Potassium

o Sodium and chloride

o calcium


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Hendersons-Hasselbalchs equation

This equation shows that a ratio of 20 parts of base

to 1 part of acid , yields normal pH.

pH is directly proportional to base and indirectlyproportional to the acid component.

ACID- BASE COMPENSATION

ACID-BASE CORRECTION


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RESPIRATORY ALKALOSIS

RESPIRATORY ACIDOSIS

METABOLIC ALKALOSIS

METABOLICACIDOSIS


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STEPS IN ABG ANALYSIS

CHANGES IN VALUES OF COMPONENTS IN

DISORDERS

COMPENSATION SOURCES OF ERROR IN A SAMPLE OF ABG


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