January 14, 2016 - Arterial Blood Gas Flashcards
Arterial Blood Gas Format
pH / pCO2 / pO2 / HCO3
Normal values are…
pH 7.40 - (7.36 - 7.44)
pCO2 - 40 (37-42)
pO2 - (80-100)
HCO3 - 24 (22-26)
Acidemia
A decrease in blood pH below 7.36
Implies an acidosis, but acidosis does not always imply acidemia.
Acidosis
A process that lowers blood pH.
Alkalemia
An increase in blood pH above 7.44
Alkalosis
A process that tends to raise blood pH.
Respiratory Acidosis
A medical emergency in which decreased ventilation (hypoventilation) increases the concentration of CO2 in the blood and decreases the blood’s pH (acidosis).
Carbon dioxide is produced continuously as the body’s cells respire, and this CO2 will accumulate rapidly if the lungs do not adequately expel it through alveolar ventilation.
CO2 + H2O <—> HCO3- + H+
Respiratory Alkalosis
Is a medical condition in which increased respiration elevates the blood pH above the normal range of 7.44. There are two types of respiratory alkalosis; chronic and acute.
CO2 + H2O <—> HCO3- + H+
Acute Respiratory Acidosis
A medical emergency in which decreased ventilation increases the concentration of carbon dioxide in the blood and decreases the blood’s pH.
In acute respiratory acidosis, the PaCO2 is elevated above the upper limit with an accompanying acidemia.
This is a 10:1 ratio of CO2 to HCO3
Compensation - Respiratory vs. Metabolic
For respiratory disorders, the kidneys compensate by adjusting the HCO3 in 3-5 days.
For metabolic disorders, the lungs compensate by adjusting the pCO2 immediately.
Chronic Respiratory Acidosis
Every increase of 10 to pCO2, the bicarbonate will increase by 3.
(Kidneys retain HCO3)
10:3 ratio
Acute Respiratory Alkalosis
A medical condition in which increased respiration elevates the blood pH beyond the normal range of 7.44 with a concurrent reduction in arterial levels of CO2.
This occurs rapidly.
For every drop of 10 to the pCO2 concentration, there is a drop of 2 to the HCO3
10:2 ratio
Chronic Respiratory Alkalosis
A medical condition in which increased respiration elevates the blood pH beyond the normal range of 7.44 with a concurrent reduction in arterial levels of CO2.
For every drop of 10 to the pCO2 concentration, there is a drop of 4 to the HCO3
10:4 ratio
Metabolic Acidosis
Is a condition that occurs when the body produces excessive quantities of acid, or when the kidneys are not removing enough acid from the body.
Can occur in two ways; producing too much acid, or bicarb loss.
Anion Gap
A shorthand method of quickly determining if there was an abnormal acid. It is the ‘footprint’ left by the addition of an abnormal acid.
Cations = Anions
Use commonly measured electrolytes…
Anion Gap = Na - (HCO3 + Cl)
Anion Gap = 12 is NORMAL
Changes in Anion Gap
Assuming our normal anion gap is 12, then an increase in anion gap (such as 13) will mean that we have one extra unmeasured anion which represents one metabolic acid.
Normal Anion Gap
Normally, the Anion Gap = 12
Normal range is 9-12
For example, if Na = 140, Cl = 104, and HCO3 = 24
AG = 140 - (104 + 24)
AG = 12
Metabolic Acidosis with Normal Anion Gap
Also known as bicarb loss metabolic acidosis.
Loss of HCO3 by GI tract or kidneys.
Net effect is that for every decrease in HCO3, there is an increase of Cl in a 1:1 ratio. Because of this, the ANION GAP REMAINS NORMAL.
How do we know that there is a metabolic acidosis? The low HCO3.
Metabolic Alkalosis
Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range (7.36-7.44). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations.
The loss of H+ and the inability of the kidenys to excrete excess HCO3. Can be due to vomiting or diuretics.
Your body compensates by retaining CO2. For every increase of HCO3 by 10, pCO2 increases by 7.
10:7 ratio
Mixed Metabolic Disorders and the Delta Gap
The delta gap is (AG-12) vs. (24-HCO3)
If the AG is up by say… 8, you would expect that 8 HCO3 would have been used up and you would have an HCO3 value of 16. If it was lower than 16… say 10… this indicates that you also have Anion Gap Acidosis.
