1. ACID-BASE BALANCE ABG INTERPRETATION
DR. NABIL BASHIR
RESPIRATORY SYSTEM/BIOCHEMISTRY

2. Henderson–Hasselbalch equation
where: pH: is the negative logarithm of molar concentration of hydrogen ions. pKa H2CO3: is the logarithm of the acid dissociation constant of carbonic acid. It is equal to 6.1. [HCO−3] is the molar concentration of bicarbonate in the blood plasma [H2CO3] is the molar concentration of carbonic acid .

3. However, since the carbonic acid concentration is directly proportional to the partial pressure of carbon dioxide the equation can be rewritten as follows

4. DEFINITIONS LOW PH: ACIDEMIA HIGH PH: ALKALEMIA
HIGH CO2: ACIDIFYING EFFECT
LOW CO2: ALKALINIZING EFFECT
HIGH HCO3: ALKALINIZING EFFECT
LOW HCO3: ACIDIFYING-EFFECT

5. STEP 1: pH
pH: NORMAL RANGE: IF pH >7.45, ALKALEMIA IF pH < 7.35, ACIDEMIA

6. STEP 2: CO2
NORMAL RANGE: mmHg or ( ) ACIDIFYING: CO2 >45 ALKALINIZING: CO2< 35

7. INTERPRETATION
COMBINE STEP 1 AND 2 STEP1: PH LOW: ACIDEMIA STEP2: CO2 HIGH: ACIDIFYING BOTH IN THE SAME DIRECTION, SO THE PROBLEM IS RESPIRATORY ACIDOSIS STEP 1: PH HIGH: ALKALEMIA STEP 2: CO2 LOW: ALKALINIZING THE PROBLEM IS RESPIRATORY ALKALOSIS

8. PH : LOW, ACIDEMIA CO2: LOW, ALKALINIZING PH AND CO2 ARE IN OPPOSITE DIRECTION, SO THE PROBLEM IS METABOLIC ACIDOSIS PH : HIGH, ALKALEMIA CO2: HIGH, ACIDIFYING PH AND CO2 ARE IN OPPOSITE DIRECTION, SO THE PROBLEM IS IS METABOLIC ALKALOSIS

9. Step 3: HCO3
NORMAL RANGE: MMOL/L HCO3>26, ALKALINIZING HCO3<22, ACIDIFYING PH :LOW, ACIDEMIA CO2: HIGH, ACIDIFYING HCO3: HIGH, ALKALINIZING HCO3 IS IN OPPOSITE DIRECTION, ALKALINIZING- TO COMPENSATE . THE PROBLEM IS RESPIRATORY ACIDOSIS WITH PARTIAL COMPENSATION

10. PH: LOW, ACIDIC CO2: LOW, ALKALINIZING HCO3: LOW, ACIDIFYING PH AND HCO3 GO IN THE SAME DIRECTION, THEN THE PROBLEM IS METABOLIC ACIDOSIS WITH PARTIAL COMPENSATION BY CO2

11. PH: HIGH, ALKALINE CO2: LOW, ALKALINIZING HCO3: LOW, ACIDIFYING SINCE PH AND CO2 GO IN THE SAME DIRECTION, SO THE PROBLEM IS RESPIRATORY ALKALOSIS WITH PARTIAL COMPENSATION BECAUSE HCO3 IS IN THE OPPOSITE DIRECTION

12. PH; HIGH, ALKALINE CO2: HIGH, ACIDIFYING HCO3: HIGH, ALKALINIZING PROBLEM: METABOLIC ALKALOSIS WITH PARTIAL COMPENSATION

13. NORMAL PH?
WHAT HAPPENS WHEN THE PH IS NORMAL? 1. THE PATIENT DOES NOT HAVE AND ACID BASE PROBLEM WITH NORMAL PH, CO2 AND HCO3, OR 2. THERE IS ACID BASE DISORDER WITH NO COMPENSATION PH: NORMAL CO2: HIGH, ACIDIFYING HCO3: HIGH, ALKALINIZING FULLY COMPENSATED RESPIRATORY ACIDOSIS OR FULLY COMPENSATED METABOLIC ALKALOSIS. YOU HAVE TO RELATE THIS PICTURE TO THE CLINICAL CASE, IT IS MORE PROBABLY TO BE RESPIRATORY ACIDOSIS BCZ THE COPD PATIENTS RETAIN CO2 AND BECOME ACEDEMIC SO HCO3 WILL RISE AND STAY HIGH FOR COMPENSATION

14. PH: NORMAL CO2: LOW, ALKALANIZING HCO3: LOW, ACIDIFYING COULD BE RESPIRATORY ALKALOSIS OR METABOLIC ACIDOSIS WITH COMPLETE COMPENSATION. DECISION DEPENDS ON CLINICAL CASE

15. EXAMPLES
PH: 7.3 ( ) CO2: 9 ( ) HCO3: 30 (22-26) RESPIRATORY ACIDOSIS WITH PARTIAL COMPENSATION

16. PH: 7.5, ALKALINE CO2: 2.7 ( ), ALKALINIZING HCO3: 20 (22-26), ACIDIFYING RESPIRATORY ALKALOSIS WITH PARTIAL COMPENSATION

17. PH: 7.3, ACIDEMIA CO2: 3.0, LOW, ALKALINIZING HCO3: 18, LOW, ACIDIFYING METABOLIC ACIDOSIS WITH PARTIAL COMPENSATION

18. PH: 7.37, NORMAL CO2: 8, ACIDIFYING HCO3: 33, ALKALINIZING DIAGNOSIS?

19. PH: 7.2, ACIDEMIA CO2: 9, ACIDIFYING HCO3:26 RESPIRATORY ACIDOSIS WITHOUT COMPENSATION

20. PH: 7.50, ALKALEMIA CO2: 2.2, ALKALINIZING HCO3: 24, NORMAL DIAGNOSIS: RESPIRATORY ALKALOSIS WITH NO COMPENSATION

21. PH: 7.10, ACIDEMIA CO2: 4.8, NORMAL HCO3: 9, LOW, ACIDIFYING DIAGNOSIS: METABOLIC ACIDOSIS WITHOUT COMPENSATION

22. PH: 7.51, ALKALEMIA CO2: 3.3, ALKALINIZING HCO3: 23, NORMAL DIAGNOSIS: RESPIRATORY ALKALOSIS WITH NO COMPENSATION

23. PH: 7.11, ACIDENIA CO2: 4.9, NORMAL HCO3: 8, LOW ACIDIFYING DIAGNOSIS: METABOLIC ACIDOSIS WITHOUT COMPENSATION

24. PH: 7.30, ACIDEMIA CO2: 3, ALKALINIZING HCO3: 15, ACIDIFYING DIAGNOSIS: METABOLIC ACIDOSIS WITH PARTIAL COMPENSATION

25. PH: 7.27, ACIDEMIA CO2: 2.5, ALKALINIZING HCO3: 7, ACIDIFYING DIAGNOSIS: METABOLIC ACIDOSIS WITH PARTIAL COMPENSATION

26. PH: 7.50, ALKALEMIA CO2: 7.5, ACIDIFYING HCO3: 33, ALKALIZING DIAGNOSIS: METABOLIC ALKALOSIS WITH PARTIAL COMPENSATION

27. PH: 7.20, ACIDEMIA CO2: 7, ACIDIFYING HCO3: 15, ACIDIFYING DIAGNOSIS: MIXED METABOLIC AND RESPIRATORY ACIDOSIS