1. Practice Problems Acid-Base Imbalances interpretation of Results of Arterial Blood Gases (ABG)

2. Getting an arterial blood gas sample

3. Ulnar Artery
Radial Artery

5. Blood Gas Report Acid-Base Information pH (H+ concentration) PCO2
HCO3 -[calculated vs measured]
Oxygenation Information
PO2 [oxygen tension]
SO2 [oxygen saturation]

6. End-Point: A Constant PCO2/[HCO3- ] Ratio
PRIMARY AND SECONDARY ACID-BASE DERANGEMENTS
End-Point: A Constant PCO2/[HCO3- ] Ratio
Acid-Base Disorder Primary Change Compensatory
Respiratory acidosis PCO2 up HCO3 up
Respiratory alkalosis PCO2 down HCO3 down
Metabolic acidosis HCO3 down PCO2 down
Metabolic alkalosis HCO3 up PCO2 up

8. Steps for Interpretation of ABG
Know normal values of pH, H+, (PCO2) & (HCO3-)
Look at the patient's ABG to determine what's abnormal high or low
Correlate the abnormal values of PCO2 and HCO3- to the abnormality of pH
Name the A/B disorder & source of any compensation
Name the cause of the disorder

9. 1- Normal Values for ABG's:
pH range:
H+ : – 44 nmol/L
PCO mmHg
HCO – 24 mmol/L
2- Evaluate the Patient's ABG's:
Is the pH (or H+) normal?
Is it too high or too low?
Is it acidosis or alkalosis?
Is the HCO3- normal?
Will it cause acidosis or alkalosis?
Will it correct acidosis or alkalosis?
Is the PCO2 normal?

10. 3-Correlate the Abnormal Values:
If only one of the two parameters (CO2 or HCO3-) is abnormal,
then its value should be consistent with the pH
(for example, if the CO2 is high. It causes a drop in pH. So, pH should be low).
If both of the parameter are abnormal, then usually
One is CAUSING the problem
Other is trying to COMPENSATE the problem (correct)
For example,
If the PCO2 is high, and is causing the pH imbalance,
then the pH must be low (as CO2 behaves as an acid).
If HCO3- level is also abnormal, then usually it will be high, to
compensate for the low pH (as HCO3- is a base).

11. 4- Name the Acid-Base Disorder:
(and a source of any compensation)
Respiratory acidosis (with or without renal compensation)
Respiratory alkalosis(with or without renal compensation)
Metabolic acidosis (with or without respiratory compensation)
Metabolic alkalosis (with or without respiratory compensation)
5- Suggest a Cause of the disorder:
For example, a possible cause of chronic respiratory acidosis is emphysema.

12. Practice Problem 1 ABG: H+ 78 nmol/L PCO2 55 mmHg HCO3- 24 mmol/L
Normal values for ABG's:
H+ range 36 – 44 nmol/L
PCO mmHg
HCO mmol/L
H+ is too high So, it is a case of acidosis; 
high PCO2 is correlated with low pH as PCO2 is the cause
So, this is respiratory acidosis
Because bicarbonate is normal, there is no compensation

13. Practice Problem 2 ABG: H+ 65 nmol/L PCO2 55 mmHg HCO3- 35 mmol/L
H high = acidosis
PCO2 high = respiratory acidosis
HCO3 high = renal compensation

14. Practice Problem 3 ABG: H+ 50 nmol/L PCO2 35 mmHg HCO3- 11 mmol/L
H high = acidosis
PCO2 normal = no compensation
HCO3 low = metabolic acidosis

15. Practice Problem 4 ABG: H+ 55 nmol/L PCO2 25 mmHg HCO3- 12 mmol/L
H high = acidosis
PCO2 low = respiratory compensation
HCO3 low = metabolic acidosis

16. Practice Problem 5 ABG: H+ 32 nmol/L PCO2 25 mmHg HCO3- 24 mmol/L
H low= alkalosis
PCO2 low = respiratory alkalosis
HCO3 normal = no compensation

17. Practice Problem 6 ABG: H+ 52 nmol/L PCO2 25 mm Hg HCO3- 18 mmol/L
H high = alkalosis
PCO low = respiratory alkalosis
HCO3 low = renal compensation

18. Practice Problem 7 ABG: H+ 32 nmol/L PCO2 40 mmHg HCO3- 33 mmol/L
H low= alkalosis
PCO normal = no compensation
HCO3 high = metabolic alkalosis

19. Practice Problem 8 ABG's: H+ 33 nmol/L PCO2 55 mm Hg HCO3 33 mmol/L
H low = alkalosis
PCO2 high = respiratory compensation
HCO3 high = metabolic alkalosis