This document discusses blood gas analysis and acid-base disorders. It provides details on parameters measured in blood gas analysis like PaO2, PaCO2, HCO3-, and how they are used to evaluate respiratory failure and classify acid-base imbalances. Respiratory failure is classified as type I or II based on PaO2 and PaCO2 levels. Various acid-base disorders like respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis are defined based on changes in pH, PaCO2, and HCO3-. Mixed acid-base disorders involving combinations of respiratory and metabolic components are also described.

1. Blood gas analysis and
acid-basic disorder
Department of internal medicine
Chen Yu

2. Blood Gas Analysis
 Arterial blood
 Sea level (101.3kPa, 760mmHg)
 Quiet
 Anti-coagulate blood
 Inspire air (Whether O2 supply)

3. Clinical Significance
 To evaluate respiratory failure
type Ⅰ or type Ⅱ
 To evaluate acid-basic disorder

4. How to evaluate respiratory failure?
PaO2:
Arterial blood oxygenic partial pressure.
Normal: 95-100mmHg (12.6-13.3kPa)
Estimate formula of age:
PaO2=100mmHg-(age×0.33) ±5mmHg

5. Hypoxia
 Mild: 80-60mmHg
 Mediate: 60-40mmHg
 Severe: <40mmHg

6. Respiratory Failure
PaO2<60mmHg respiratory failure
Notice: sea level, quiet, inspire air
rule off other causes ( heart
disease)

7. Classification of Respiratory Failure
PaCO2: The carbon dioxide partial pressure
of arterial blood
Normal: 35-45mmHg (4.7-6.0kPa)
mean: 40mmHg

8. Classification of Respiratory Failure
Type Ⅰ TypeⅡ
PaO2 (mmHg) <60 <60
PaCO2 (mmHg) ≤50 >50

9. Other Parameters
SaO2: Saturation of arterial blood oxygen
Normal: 0.95-0.98
Significance: a parameter to evaluate
hypoxia, but not sensitive
ODC ( Dissociation curve of oxygenated
hemoglobin): “S” shape

10. SaO2%
PO2
Oxygen dissociation curve

11. PH 2,3DPG temperature CO2
ODC to right deviation
Oxygenated hemoglobin release oxygen
to tissue, prevent hypoxia of the tissue.
But absorbed oxygen of hemoglobin is
decreased from the alveoli.
Bohr effect: movement of ODC place is
induced by PH.

12. PA-aO2: Difference of alveoli-arterial blood
oxygenic partial pressure.
Normal: 15-20mmHg (<30mmHg in the old)
Significance: a sensitive parameter in gas
exchange

13. PvO2: Oxygenic partial pressure of mixed
venous blood.
Normal: 35-45mmHg
mean: 40mmHg
Significance: Pa-vO2 is to reflect the tissue
absorbing oxygen.

14. CaO2: The content of the oxygen of the
arterial blood.
Normal: 19-21mmol/L
Significance: a comprehensive parameter
to evaluate arterial oxygen.

15. Parameters in acid-basic disorder evaluation
PH: negative logarithm of Hydrogen
ion concentration.
Normal: 7.35-7.45
mean: 7.4
〔 HCO3- 〕
PH=Pka+log
0.03PaCO2
20
＝
1
6.1+log

16. HCO3- (bicarbonate):
SB (standard bicarbonate)
AB (actual bicarbonate)
SB: the contents of HCO3- of serum of arterial
blood in 38℃ , PaCO2 40mmHg, SaO2 100%.
Normal: 22-27mmol/L
mean: 24mmol/L
AB: The contents of HCO3- in actual condition.
In normal person: AB=SB

17.  AB and SB are parameters to reflect
metabolism, regulated by kidney.
 Difference of AB-SB can reflect the
respiratory affection on serum HCO3- .
Respiratory acidosis: AB>SB
Respiratory alkalosis: AB<SB
Metabolic acidosis: AB ＝ SB<Normal
Metabolic alkalosis: AB=SB>Normal

18. Buffer bases （ BB) ：
is the total of buffer negative ion of
blood.
BB: HCO3-
hemoglobin
plasma proteins
HPO42- (phosphate)
Normal: 45-55mmol/L
mean: 50mmol/L
Significance: Metabolic acidosis: BB
Metabolic alkalosis: BB

19. Bases excess （ BE):
the acid or bases used to regulate blood
PH 7.4 . ( in 38℃ ， PaCO2 40mmHg,
SaO2 100%)
Normal: 0±2.3 mmol/L
Significance:
add acid: BE(+), BB
add base: BE(-), BB

20. Total plasma CO2 (T-CO2) ：
total content of the CO2 .
Normal: HCO3- >95%

21. Anion gap (AG):
the difference of undetermined anion
and undetermined cation in serum.
AG=Na+ － (Cl-+ HCO3- )
Normal: 8-16mmol/L
Significance:
AG acidosis: ketoacidosis, kidney failure
AG normal acidosis: Cl , diarrhea, fixed
acid decrease
to evaluate mix acid-basic disorder

22. Regulation of Acid-basic Balance
 Chemical buffer
 Dielectric changes of incells and excells
H+---K+, HCO3- ---Cl-
 Physiology regulation of the lung and
kidney

23. Classification of Acid-basic Disorder
 Complementary: PH is normal
 Dis-complementary: PH is abnormal.
 PH,PaCO2, HCO3- are three important
parameters in acid-basic disorder
evaluation.

24. Classification of Acid-basic Disorder
PH PaCO2 HCO3-
Resp. acidosis
Resp. alkalosis
Meta. acidosis
Meta. alkalosis

25. Classification of Acid-basic Disorder
 Mixed acid-basic disorder
 Complementary formula
example:
original disorder: chronic respiratory
acidosis
⊿ HCO3- =⊿ PaCO2 ×0.35±5.58
complementary limit: 45mmol/L

26. Classification of Acid-basic Disorder
 Respiratory acidosis with metabolic acidosis
 Respiratory acidosis with metabolic alkalosis
 Respiratory alkalosis with metabolic acidosis
 Respiratory alkalosis with metabolic
alkalosis

27. Respiratory acidosis with
metabolic acidosis
PaCO2:
HCO3- : , normal, (slight)
AB, SB, BB: , normal, (slight)
PH:
BE: negative value

28. Respiratory acidosis with
metabolic alkalosis
PaCO2:
AB:
PH: , N,

29. Mixed by three types of disorder
 Respiratory
acidosis + metabolic acidosis
+metabolic alkalosis
 Respiratory
alkalosis + metabolic acidosis
+metabolic alkalosis