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

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 .

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

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

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

STEP 2: CO2 NORMAL RANGE: 35-45 mmHg or (4.7-6.0) ACIDIFYING: CO2 >45 ALKALINIZING: CO2< 35

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

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

Step 3: HCO3 NORMAL RANGE: 22-26 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

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

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

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

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

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

EXAMPLES PH: 7.3 (7.35-7.45) CO2: 9 (4.7-6.0) HCO3: 30 (22-26) RESPIRATORY ACIDOSIS WITH PARTIAL COMPENSATION

PH: 7.5, ALKALINE CO2: 2.7 (4.7-6.0), ALKALINIZING HCO3: 20 (22-26), ACIDIFYING RESPIRATORY ALKALOSIS WITH PARTIAL COMPENSATION

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

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

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

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

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

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

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

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

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

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

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