1. Arterial blood gas
Dr. Basu MD

2. (Acid) The Respiratory System
↑ ventilation: "blow off" CO2 (acid) →↓ CO2 (acid) → Alkalosis.
↓ ventilation → retain CO2 (acid) → ↑ CO2 (acid) → Acidosis.

3. (Base) The Renal System
Acidosis: ↑ H+ and low HCO3 (base)
Compensation:
Kidney: excreting H+ and retaining HCO3 (base).
Lung: increasing ventilation to blow off CO2 (acid) and decrease the Acidosis.

4. (Base) The Renal System
Alkalosis: ↓ H+ and excess HCO3 (base).
Compensation:
Kidney: excrete HCO3 and retain H+
Lung: hypoventilation to retain CO2 (acid) to decrease the Alkalosis.

5. Normal value
pH ,
pCO2 of mmHg
HCO mmol/L

6. How to reads the data First, look at pH. (Normal = 7.35-7.45)
pH is < 7.35; = ACIDOSIS. pH is > 7.45 = ALKALOSIS.

7. look at pH again If -- 7.35-7.45 (normal): COMPENSATED.
If : pH is <7.35 or >7.45 : UNCOMPENSATED.

8. Metabolic or respiratory
CO2 is <35 or >45= RESPIRATORY.
HCO3 is <22 or >26 = METABOLIC.

9. ? pH = 7.55 , CO2 = 40, HCO3 = 30 pH = 7.35, CO2 = 45, HCO3 = 20
If it is (normal): COMPENSATED.
If the pH is <7.35 or >7.45 : UNCOMPENSATED.
CO2 is <35 or >45= RESPIRATORY.
HCO3 is <22 or >26 = METABOLIC

10. pH = 7.44 PaCO2 = 47 HCO3 = 28 pH = 7.35 PaCO2 = 31 HCO3 = 18.1
CO2 is <35 or >45= RESPIRATORY.
HCO3 is <22 or >26 = METABOLIC
pH = 7.50 PaCO2 = 45 HCO3 = 33
Uncomp.
Met. Alk.
pH = 7.44 PaCO2 = 47 HCO3 = 28
Com Met alka.
pH = 7.20 PaCO2 = 36 HCO3 = 14
Met acidosis
pH = 7.35 PaCO2 = 31 HCO3 = 18.1
Com. Met acidosis

11. pH = 7.43 PaCO2 = 32 HCO3 = 21 pH = 7.42 PaCO2 = 32 HCO3 = 20
Uncomp
Resp. alka
pH = 7.43 PaCO2 = 32 HCO3 = 21
pH = 7.42 PaCO2 = 32 HCO3 = 20
Com Resp alka
pH = 7.23 PaCO2 = 59 HCO3 = 22
Resp acidosis
pH = 7.36 PaCO2 = 56 HCO3 = 31.4
pH = 7.38 PaCO2 = 70 HCO3 = 42
Com Resp acidicosis
CO2 is <35 or >45= RESPIRATORY.
HCO3 is <22 or >26 = METABOLIC

12. Respiratory Acidosis ↑ pCO2 . Compensation: ↑ HCO3 Cause:
Chronic obstructive pulmonary disease (COPD)
Electrolyte deficiencies (K+, P04 - )

13. Initial value / after Compensation
Without Compensation
pH (<7.35)
PaCO2 (>47 mm Hg)
HCO mmol/L
WithCompensation
pH ( ~ 7.35)
PaCO2 (>47 mm Hg)
HCO3: 32mmol/L ( acute)
HCO3: 44mmol/L ( chronic)

14. Respiratory alkalosis
arterial pCO2 falls
Compensation: ↓ bicarbonate slightly.
Hyperventilation
Pneumonia
Shock/decreased cardiac output

15. Respiratory alkalosis
pH (> 7.45)
PaCO2 ( 20 mm Hg)
HCO3 28 mmol/L
pH ( ~ 7.35)
PaCO2 ( 20 mm Hg)
HCO3 18 mmol/L

16. Metabolic acidosis ↑ in fixed acids in the blood.
Compensation: hyperventilation > ↓ pCO2
Cause:
Diarrhea
Alcoholism (ethanol)
Ketoacidosis

17. Metabolic acidosis: ketoacidosis
Glucose > 250
pH: 7.00 to 7.24
HCO3: 10 to < 15
PaCO2 ( 25 mm Hg)
Anion gap: >11
Increased electrolytes

18. Metabolic alkalosis Plasma bicarbonate increases
Compensation: hypoventilation > CO2 retention.
Cause:
Gastric fluid loss Vomiting

19. Metabolic alkalosis pH 7.58 pCO2 21 mmHg HCO3 40 mmol/l > 26
pO2  154 mmHg
pH ~ 7.50
pCO2 : ~ 60 mmHg
HCO3  40 mmol/l
pO2  154 mmHg

20. Thank you