1. ABG INTERPRETATION
STEP 1: PH determination
-
[H+] [HCO3 ]
Valid ABG = ---------------------- =24
P CO2
Normal 7.35 – 7.45
(H+) = 80 – LAST 2 DIGITS OF Ph (eg:7.23)
STEP 2:
PH
(7.34-7.45)
ACIDOSIS
ALKALOSIS
RESPIRATORY
METABOLOC
CO2
HCO3-
ACUTE
RESPIRATORY
METABOLIC
CHRONIC
Dr Ranjith Kumar/ ABG notes
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2. To determine respiratory acidosis whether is acute or chronic:
ΔH
ΔPCO2
<0.3 Chronic Respiratory acidosis
>0.8 Acute Respiratory acidosis
0.3 – 0.8 Acute on Chronic
ΔH = Normal H+ (40) subtracted by Actual patient H+
ΔPco2 = (Patient PCo2 – 40)
Step 3: Compensation
Metabolic compensation for respiratory disorder
Acidosis
Alkalosis
1
2
ACUTE
Acidosis
Alkalosis
3.5
4
CHRONIC
Co2 we will take as 10 in every step
Respiratory acidosis
Acute
[HCO3-] increases by 1 for each 10-mm Hg increase in PCO2
Chronic
[HCO3-] increases by 3.5 for each 10-mm Hg increase in PCO2
Respiratory alkalosis
Acute
[HCO3-] falls by 2 for each 10-mm Hg decrease in PCO2
Chronic
[HCO -
Dr Ranjith Kumar/ ABG notes
3 ] falls by 4 for each 10-mm Hg decrease in PCO2
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3. Respiratory compensation for metabolic disorder
Metabolic acidosis PCO2 = 1.5 × [HCO3-] + 8 ± 2
Metabolic alkalosis PCO increases by 7 mm Hg for each 10 mEq/L increase in serum HCO 2
3
Met.Acidosis
Normal
Positive
Anion gap
Anion gap
10-12
MUDPILES
Diarrhoea
RTA
urinary tract diversion
Ammoniam chloride intake
posthypocapnic
Mixed disorder
-
Corrected HCO3 = Measured HCO3 + Anion gap - 12
HCO3-
Dr Ranjith Kumar/ ABG notes
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