January 14, 2016 - Arterial Blood Gas

Question 1

Arterial Blood Gas Format

Answer 1

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)

Question 2

Acidemia

Answer 2

A decrease in blood pH below 7.36

Implies an acidosis, but acidosis does not always imply acidemia.

Question 3

Acidosis

Answer 3

A process that lowers blood pH.

Question 4

Alkalemia

Answer 4

An increase in blood pH above 7.44

Question 5

Alkalosis

Answer 5

A process that tends to raise blood pH.

Question 6

Respiratory Acidosis

Answer 6

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⁺

Question 7

Respiratory Alkalosis

Answer 7

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+

Question 8

Acute Respiratory Acidosis

Answer 8

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

Question 9

Compensation - Respiratory vs. Metabolic

Answer 9

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.

Question 10

Chronic Respiratory Acidosis

Answer 10

Every increase of 10 to pCO2, the bicarbonate will increase by 3.

(Kidneys retain HCO3)

10:3 ratio

Question 11

Acute Respiratory Alkalosis

Answer 11

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

Question 12

Chronic Respiratory Alkalosis

Answer 12

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

Question 13

Metabolic Acidosis

Answer 13

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.

Question 14

Anion Gap

Answer 14

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

Question 15

Changes in Anion Gap

Answer 15

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.

Question 16

Normal Anion Gap

Answer 16

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

Question 17

Metabolic Acidosis with Normal Anion Gap

Answer 17

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.

Question 18

Metabolic Alkalosis

Answer 18

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

Question 19

Mixed Metabolic Disorders and the Delta Gap

Answer 19

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.