ACIDBASE BALANCE ABG INTERPRETATION DR NABIL BASHIR RESPIRATORY

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

Henderson–Hasselbalch equation where: p. H: is the negative logarithm of molar concentration of hydrogen ions. p. Ka H 2 CO 3: 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 [H 2 CO 3] 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 CO 2: ACIDIFYING EFFECT LOW CO 2: ALKALINIZING EFFECT HIGH HCO 3: ALKALINIZING EFFECT LOW HCO 3: ACIDIFYING-EFFECT

STEP 1: p. H: NORMAL RANGE: 7. 35 -7. 45 IF p. H >7. 45, ALKALEMIA IF p. H < 7. 35, ACIDEMIA

STEP 2: CO 2 NORMAL RANGE: 35 -45 mm. Hg or (4. 7 -6. 0) ACIDIFYING: CO 2 >45 ALKALINIZING: CO 2< 35

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

PH : LOW, ACIDEMIA CO 2: LOW, ALKALINIZING PH AND CO 2 ARE IN OPPOSITE DIRECTION, SO THE PROBLEM IS METABOLIC ACIDOSIS PH : HIGH, ALKALEMIA CO 2: HIGH, ACIDIFYING PH AND CO 2 ARE IN OPPOSITE DIRECTION, SO THE PROBLEM IS IS METABOLIC ALKALOSIS

Step 3: HCO 3 NORMAL RANGE: 22 -26 MMOL/L HCO 3>26, ALKALINIZING HCO 3<22, ACIDIFYING PH : LOW, ACIDEMIA CO 2: HIGH, ACIDIFYING HCO 3: HIGH, ALKALINIZING HCO 3 IS IN OPPOSITE DIRECTION, ALKALINIZING- TO COMPENSATE. THE PROBLEM IS RESPIRATORY ACIDOSIS WITH PARTIAL COMPENSATION

PH: LOW, ACIDIC CO 2: LOW, ALKALINIZING HCO 3: LOW, ACIDIFYING PH AND HCO 3 GO IN THE SAME DIRECTION, THEN THE PROBLEM IS METABOLIC ACIDOSIS WITH PARTIAL COMPENSATION BY CO 2

PH: HIGH, ALKALINE CO 2: LOW, ALKALINIZING HCO 3: LOW, ACIDIFYING SINCE PH AND CO 2 GO IN THE SAME DIRECTION, SO THE PROBLEM IS RESPIRATORY ALKALOSIS WITH PARTIAL COMPENSATION BECAUSE HCO 3 IS IN THE OPPOSITE DIRECTION

PH; HIGH, ALKALINE CO 2: HIGH, ACIDIFYING HCO 3: 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, CO 2 AND HCO 3, OR 2. THERE IS ACID BASE DISORDER WITH NO COMPENSATION PH: NORMAL CO 2: HIGH, ACIDIFYING HCO 3: 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 CO 2 AND BECOME ACEDEMIC SO HCO 3 WILL RISE AND STAY HIGH FOR COMPENSATION

PH: NORMAL CO 2: LOW, ALKALANIZING HCO 3: LOW, ACIDIFYING COULD BE RESPIRATORY ALKALOSIS OR METABOLIC ACIDOSIS WITH COMPLETE COMPENSATION. DECISION DEPENDS ON CLINICAL CASE