Acid-Base Balance.ppt

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Acid-Base Balance

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Acid-Base Balance
Acids are formed as end-products of protein,
carbohydrate, and fat metabolism.
To maintain the body’s normal pH (7.35-7.45) the
H+ must be neutralized or excreted.
Lungs, kidneys, and bones are major organs
involved in the regulation of acid-base balance.

Acid-Base Balance
Body acids exist in two forms
o Volatile
 H2CO3 (can be eliminated as CO2 gas)
o Nonvolatile
 Sulfuric, phosphoric, and other organic
acids
 Eliminated by the renal tubules with
the regulation of HCO3
–

Acid-Base Balance
Sources of H+ ions
o CO2 diffuses into the bloodstream where the
following reaction occurs:
Regulated by the Lung Regulated by the Kidney
CO2 + H2O 
H2CO3 
 HCO3
–+ H+

Respiratory versus Metabolic
Respiratory
o CO2 is regulated by the lungs
Metabolic
o HCO3 (bicarbonate) is regulated by the kidneys

Acid-Base Imbalances
Normal arterial blood pH
o 7.35 to 7.45
o Obtained by arterial blood gas (ABG)
sampling
Acidosis
o Systemic increase in H+ concentration
Alkalosis
o Systemic decrease in H+ concentration

Arterial Blood Gases
pH is the most important
pH = 7.35 - 7.45 is NORMAL
pH < 7.35 is ACIDOTIC
pH > 7.45 is ALKALOTIC

Normal ABG Acceptable Ranges
ABG Acceptable Range
pH 7.35 – 7.45
PO2 95-100
PCO2 35 – 45
HCO3 22-26
O2 Sat >95%

Acidosis and Alkalosis
Four categories
1. Respiratory acidosis—Elevation of pCO2 as a
result of ventilation depression
2. Respiratory alkalosis—Depression of pCO2 as a
result of hyperventilation
3. Metabolic acidosis—Depression of HCO3
– or an
increase in noncarbonic acids
4. Metabolic alkalosis—Elevation of HCO3
–, usually
as a result of an excessive loss of metabolic acids

pH
CO2
HCO3
35 ------------ 45
7.35 ------------ 7.45
22 ------------ 26

pH
CO2
HCO3
35 ------------ 45
7.35 ---------- 7.45
22 ------------ 26
A
A
A
B
B
B

pH
CO2
HCO3
35 ------------ 45
7.35 ---------- 7.45
22 ------------ 26
A
A
A
B
B
B
Alk, Alk,
Alk!
accccccccidosis

pH
CO2
HCO3
35 ------------ 45
7.35 ---------- 7.45
22 ------------ 26
A
A
A
B
B
B
Rid the base out of your
accccccidosis
Alk alk,
throwing
up acid

Acid Base Imbalances:
Single Disorder
This occurs when ONE component (respiratory or
metabolic) is out of normal range and agrees with the
pH and the other component remains within normal
limits

Acid-Base Analysis
pH 7.24
PaCO2 60
HCO3 22
How would you analyze this?

and the ANSWER is...
pH 7.24
PaCO2 60
HCO3 22
pH of 7.24 is < 7.45 = acidosis
PaCO2 of 60 is > 45 = acidosis (agrees with pH)
HCO3 of 22 is normal
This is a RESPIRATORY ACIDOSIS

Try this one
pH 7.48
PCO2 30
HCO3 26

Here you go...
pH 7.48
PaCO2 30
HCO3 26
pH is 7.48 alkalosis
PaCO2 30 (below 35) = alkalosis (agrees
with pH)
HCO3 of 26 is normal
This is RESPIRATORY ALKALOSIS

Try just one more...
pH 7.25
PaCO2 38
HCO3 14

What did you come up with?
pH 7.25
PaCO2 38
HCO3 14
pH is 7.25 (< 7.45) = acidosis
PaCO2 of 38 = normal
HCO3 is 14 (< 22) = acidosis (agrees with pH)
This is a METABOLIC ACIDOSIS

Acid Base Imbalances:
Double Disorder
This occurs when BOTH components (respiratory and
metabolic) are out of normal range and agree with the pH.

Let’s Look at an Example of a
Double Disorder...
pH 7.09
PaCO2 60
HCO3 14
pH is 7.09 (< 7.45) = acidosis
PaCO2 is 60 (> 45) = acidosis (agrees with pH)
HCO3 is 14 (< 22) = acidosis (agrees with pH)
This is a RESPIRATORY and METABOLIC ACIDOSIS

One for you to try on your own...
pH 7.60
PaCO2 30
HCO3 32
What is
this?

What did you come up with?
pH 7.60
PaCO2 30
HCO3 32
pH is 7.60 (above 7.45) = alkalosis
PaCO2 is 30 (below 35) = alkalosis (agrees with pH)
HCO3 is 32 (above 26) = alkalosis (agrees with pH)
This is a RESPIRATORY and METABOLIC ALKALOSIS

Sometimes we compensate
The body compensates to make pH as normal as possible
Respiratory mechanisms can compensate for metabolic
changes
Renal mechanisms compensate for respiratory induced pH
changes, but this takes longer to achieve

Compensation example
pH= 7.48
CO2= 31
HCO3= 23
pH is alkalotic
CO2 is alkalotic
HCO3 is closer to acidic

pH= 7.48
CO2= 31
HCO3= 23
 pH is alkalotic
 CO2 is alkalotic
 HCO3 is closer to acidic
Respiratory Alkalosis, partially compensated

pH= 7.33
CO2= 35
HCO2= 22
pH is acidotic
CO2 is closer to alkalotic
HCO3 is closer to acidotic

pH= 7.33
CO2= 35
HCO2= 22
 pH is acidotic
 CO2 is closer to alkalotic
 HCO3 is closer to acidotic
Metabolic acidosis, partially compensated

Acid-Base Balance.ppt

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