1. Acid base principles and disorders
Biochemistry
Nabil Bashir
4/2016

2. Acid base equilibrium
CO2 + H2O ↔ HCO3- + H+ ↑ determines pH

3. maintained by kidneys ↓ CO2 + H2O ↔ HCO3- + H+ ↑ ↑ maintained by lungs determines pH

4. low value→high H+(Low PH) ↓ CO2 + H2O ↔ HCO3- + H+ ↑
Acid base equilibrium
low value→high H+(Low PH)
high value → low H+(high pH) ↓
CO2 + H2O ↔ HCO H+ ↑
low value→low H+(high PH)
high value→high H+(low PH)

5. Henderson-Hasselbalch Equation

6. Acid base equilibrium
Normal HCO3=22-26 mEq/L <24> in venous blood
Normal pCO2= mmHg <40> arterial blood
Normal pH= arterial blood

7. Acidosis symptoms
Hyperventilation
Depression of myocardial contractility
Cerebral vasodilation; increased cerebral blood flow.
CO2 + H2O ↔ HCO H+

8. CNS depression( very high CO2 levels)
Hyperkalemia; high H+ shifts into cells in exchange for K+
Shift in oxygen hemoglobin dissociation curve; Bohr effect;
low pH leads to hemoglobin releasing oxygen

9. Alkalosis symptoms
Inhibition of respiratory drive: retain CO2
Depression of myocardial contractility
Cerebral vasoconstriction; decrease in cerebral blood flow
Hypokalemia
Shift in hemoglobin dissociation curve

10. Acid- base problems
Check the pH
pH< 7.35 = acidosis
pH > 7.45 –alkalosis
2. Check the HCO3 and pCO2
HCO3 from veinpuncture, normal 22-28
pCO2 from ABG; normal 35-45

11. 3. Determine acid-base disorder
Acidosis+ low HCO3= metabolic acidosis
Acidosis+ high pCO2= respiratory acidosis
Alkalosis+high HCO3= metabolic alkalosis
Alkalosis+ low CO2= respiratory alkalosis
CO2 + H2O ↔ HCO H+

12. Step 1: what is acid base disorder?
Metabolic acidosis, resp alkalosis,etc….
Step 2;
Is there a second disorder?
Is the compensation appropriate?

13. Compensatory changes Low HCO3=metabolic acidosis
Compensation= lowering CO2
High HCO3= metabolic alkalosis
Compensation= retain CO2
High CO2= resp acidosis
Compensation= increasing HCO3
Low CO2= respiratory alkalosis
compensation-= lowering HCO3
CO2 + H2O ↔ HCO H+

14. Cause vs compensation
Most acid-base disorders; abnormal HCO3 and abnormal Pco2
One is causing disorder
Other is compensatory change
Example 1:
pH=7.30 (acidosis)
HCO3 =low
pCO2= = low
Metabolic acidosis with respiratory compensation
CO2 + H2O ↔ HCO3- + H+

15. Example 2: pH=7.30 (acidosis) HCO3 =high pCO2= = high respiratory acidosis with compensation Metabolic CO2 + H2O ↔ HCO3- + H+

16. Respiratory compensation
Hyper or hypoventilation
Changes pCO2 to compensate for metabolic disorders

17. Respiratory compensation
Hyperventilation:
Blows off CO2
Plasma CO2 levels fall
Less H+ in blood
pH rises CO2+H2O ↔HCO3+H+
Hypoventilation:
Retains CO2
Plasma CO2 level rises
More H+ in blood
pH falls

18. Renal compensation Acidosis: Excess H+ filtered/secreted into nephron
more Bicarb reabsorbed
Urinary buffers excreted:
-HPO4 -2 EXCRETED
-NH3 excreted
-these bind H+(buffers)
-prevent severe drops in pH
Alkalosis:
-reverse of acidosis

19. Mixed disorders Two disorders at same time
-metabolic acidosis and respiratory alkalosis/acidosis
-metabolic acidosis and metabolic alkalosis
-two metabolic acidosis
-occurs in many pathological states
-i.e. vomiting and diarrhea
To uncover, determine expected response:
-expected HCO3 for respiratory disorder
-expected CO2 for metabolic disorder
-use renal formulas to determine expected response
If actual≠ expected →2nd disorder present

20. Mixed disorders If actual ≠ expected, determine abnormality
i.e. if CO2 higher than expectedsecondary resp disorder
i.e. HCO3 lower than expectedsecondary metab disorder
Usual rules then apply for determining secondary disorders:
High CO2 = acidosis
Low CO2= alkalosis
Low HCO3= acidosis
High HCO3= alkalosis

21. Compensation formulas
Winters formula
Metabolic alkalosis formula
Acute/chronic respiratory formula

22. Metabolic acidosis compensation
Compensation respiratory alkalosis (lowering CO2)
Hyper venttilation
Winters formula: tells you expected increase in CO2
If actual CO2 ≠expected, mixed disorder
pCO2= 1.5 (HCO3)+ 8 +/-2
EXAMPLE:
pH=7.2
HCO3=9mEq/L
pCO2= 22mmhg
Expected CO2= 1.5(9)+8=22 +/-2 (20-24)
No secondary disorder

23. Example 2: Ph= 7. 28 HCO3=12MEq/L pCO2= 40 mmhg Expected pCO2 =1
Example 2: Ph= 7.28 HCO3=12MEq/L pCO2= 40 mmhg Expected pCO2 =1.5(12) +8= 26 +/-2 =28-30 pCO2 > expected Concomitant respiratory acidosis

24. Metabolic alkalosis compensation
Compensatory respiratory acidosis (to raise pCO2)
Hypoventilation
Rise pCO mmHg per 1.0 meq/L rise HCO3
If actual Pco2 ≠ expected, mixed disorder
ΔpCO2 = 0.7 * ( Δ HCO3)
Example:
pH=7.5
HCO3=34
pCO2=47
ΔHCO3=34-24=10
Expected ΔpCO2=0.7(10)=7
ActualΔpCO2=47-40=7
No secondary disorder

25. Respiratory acidosis compensation
Acute compensation:
-minutes
-intracellular buffers raise HCO3
-hemoglobin and other proteins
-small rise in pH
Chronic compensation
-days
-renal generation of large HCO3
-large increase in pH( but not back to normal)

26. Respiratory acidosis compensation
Acute compensation:
-1 meq/l rise HCO3 for every 10 mmHg increase pCO2 -ΔHCO3=ΔpCO2/10
Chronic compensation:
-3.5 meq/l rise HCO3 for every 10 mmHg increase pCO2
-ΔHCO3= 3.5*ΔpCO2/10
Example:
pH=7.15
pCO2 =80
Acute ΔHCO3=40/10=4
HCO3=28(24+4); pH7.17 (H-H)
Chronic ΔHCO3=3.5*40/10=14
HCO3=38; pH=7.3

27. Respiratory alkalosis compensation
Acute compensation
-2 meq/l fall HCO3 for every 10 mmHg drop pCO2
-ΔHCO3=2*ΔpCO2/10
Chronic compensation
-4meq decrease in HCO3 for every 10 decrease in Pco2
-ΔHCO3=4* ΔpCO2/10
Example:
pH=7.65
pCO2=20
Acute ΔHCO3=2*20/10=4
HCO3=20, pH=7.63
Chronic ΔHCO3 =4*20/10=8
HCO3=16; pH=7.53

28. Compensation timeframe
Respiratory compensation to metabolic disorders:
-rapid
-change in respiratory rate
=minutes
Metabolic compensation to respiratory disorders:
-acute, mild compensation in minutes from cells
-chronic, significant compensation in days from kidneys