Normal Blood Gases Values Acidemia and Alkalemia

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What You Must Look at to Interpret ABGs
Look at Your pH
•    Is it normal?
•    Is it high ?
•    Is it low?Examples

•    pH = 7.36
•    pH = 7.23
•    pH = 7.47
•    A high pH indicates alkalosis
•    A low pH indicates acidosis

Look at Your PaCO2
•    Is it normal ?
•    Is it high ?
•    Is it low ?
•    This is the respiratory component
•    An abnormality in the PaCO2 will indicate a respiratory problem
–    Hyperventilating? (Decreased PaCO2)
–    Hypoventilating?  (Increased PaCO2)
–    Normal ventilation

Examples
•    PaCO2 = 40 mm Hg
•    PaCO2 = 23 mm Hg
•    PaCO2 = 48 mm Hg
•    A high PaCO2 indicates acidity
•    A low PaCO2 indicates alkalosis

PaCO2
•    Lungs will increase or decrease ventilation to remove the appropriate amount of CO2
•    Lung compensation begins quickly
Now Look at Your HCO3
•    Is it normal ?
•    Is it high ?
•    Is it low ?
•    This is the metabolic component
•    An abnormality in the HCO3 indicates a metabolic problem

Examples
•    HCO3 = 25 mEq/l
•    HCO3 = 19 mEq/l
•    HCO3 = 32 mEq/l
•    A low HCO3 indicates acidity
•    A high HCO3 indicates alkalosis
HCO3
•    The kidneys excrete Hydrogen (acid) & retain bicarbonate (base) to help maintain pH
•    Renal compensation is slow
Let’s Look at the 4 Situations that Can Occur
Acidosis
Develops when:
•    Excess accumulation of acid
•    Decreased amount of alkali
•    Can be respiratory or metabolic

Metabolic Acidosis
ABG:
Low pH (below 7.35)
Decreased HCO3 (below 22)
PaCo2 will be normal
Remember both the pH & HCO3 will be low
•    Caused by too much acid in the body or loss of bicarbonate
•    Diarrhea (loss of HCO3)
•    Diabetic ketoacidosis
•    Renal failure

Respiratory Acidosis
•    ABG:
•    Low pH  (below 7.35)
•    Increased PaCO2   (above 45)
•    HCO3 will be normal
•    Remember the pH will be low & PaCO2 will be elevated.
•    Caused by acid buildup due to lungs not eliminating CO2
•    Anything that decreased respirations can cause respiratory acidosis
•    Chronic respiratory disease
•    CNS depression

Alkalosis
Develops when:
•    Excess accumulation of bicarbonate
•    Loss of acid

Metabolic Alkalosis
ABG:
•    Increase in pH   (greater than 7.45)
•     Increased HCO3  (greater than 26)
•    PaCO2 will be normal
•    Remember both the pH & the HCO3 will be elevated
•    Loss of acid or increase in HCO3
•    Vomiting or NG drainage (loss of Hydrogen)
•    Excessive use of antacids

Respiratory Alkalosis
ABG:
•    Increase in pH    (greater than 7.45)
•    Decrease in PaCO2  (less than 35)
•    HCO3 will be normal
•    Remember the pH will be high & PaCO2 will be low.
•    Caused by too much CO2 being excreted by the lungs
•    Hyperventilation

Problems
•    pH of 7.33
•    PaCO2 of 40 mmHg
•    HCO3 of 20 mEq/L
•    What does this indicate
•    Break it down
•    pH = acidosis
•    PaCO2 = normal
•    HCO3 = acidosis
•    An abnormal HCO3 indicates a “Metabolic Acidosis”
Problem
•    pH of 7.59
•    PaCO2 of 29 mm Hg
•    HCO3 of 24mEq/L
•    What does this indicate
•    Break it down
•    pH = alkalosis
•    PaCO2 = alkalosis
•    HCO3 = normal
•    An abnormal PaCO2 indicates “Respiratory Alkalosis”

Problem
•    pH of 7.25
•    PaCO2 of 61 mmHg
•    HCO3 of 26 mEq/L
•    What does this indicate
•    Break it down
•    pH = acidosis
•    PaCO2 = acidosis
•    HCO3 = normal
•    An abnormal PaCO2 indicates “Respiratory Acidosis”
Problem
•    pH of 7.51
•    PaCO2 of 44mmHg
•    HCO3 of 56
•    What does this indicate
•    Break it down
•    pH = alkalosis
•    PaCO2 = normal
•    HCO3 = alkalosis
•    An abnormal HCO3 indicates “Metabolic Alkalosis”
Compensation
•    Occurs as the body begins to correct the acid base imbalance
•    pH will be normal or near normal if total compensation
•    pH will be abnormal if partial compensation
•    Both the PaCo2 & HCO3 will be abnormal
•    Respiratory imbalances are compensated for by the renal system
•    Metabolic imbalances are compensated for by the respiratory system

Example
•    pH of 7.27
•    PaCO2 of 27 mm Hg
•    HCO3 of 10 mEq/l
•    Note that both the PaCO2 & the HCO3 are low

Let’s Break it Down
•    Low pH = acidosis
•    Low PaCO2 = alkalosis
•    Low HCO3 = acidosis
•    HCO3 corresponds with the pH
•    This is a metabolic problem
•    Metabolic acidosis with partial compensation

Problems
•    pH of 7.52
•    PaCO2 of 47 mmHg
•    HCO3 of 36 mEq/L
•    What does this indicate
•    Break it down
•    pH = alkalosis
•    PaCO2 = acidosis
•    HCO3 = alkalosis
•    Which 2 go together
•    Metabolic Alkalosis with Partial Compensation
Problems
•    pH of 7.45
•    PaCO2 of 50 mmHg
•    HCO3 of 33 meq/L
•    Break it down
•    pH = normal
•    PaCo2 = acidosis
•    HCO3 = alkalosis
•    Your pH leans toward the alkalosis side
•    ” Fully Compensated Metabolic Alkalosis”

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