Basic steps to analyse an ABGA slowing progressing towards mastery. Please leave a comment if you like it..

1. Normal (Mixed) Acidemia (pH<7.35)
PaCO2 < 35/N
(Primary Metabolic)
PaCO2 (Expected)
= [(1.5xHCO3)+8]±2
Measured PaCO2 >
Expected PaCO2
(Secondary Resp.
Acidosis
Measured PaCO2 <
Expected PaCO2
(Secondary Resp.
Alkalosis)
Gap- Gap ratio
= (AG-12)/(24-
HCO3)
G-G <1
Hyperchloremic
Met . Acidosis
G-G = 1
High AG Met
Acidosis
G-G < 1
Met Acidosis +
Met. Alkalosis
SSSecondary
Metabolic
Acidosis
Fio2 : PaO2 = 1 : 5
Anion Gap = Na – (Cl + HCO3)
= (2xAlb) +( 0.5xPO4)
High > 12 ; Low < 12
HCO3= N or Near N = Acute
HCO3= abN = Chronic
Acute: ▲pHa= 0.008 x ▲PaCO2
Chronic: ▲pHc= 0.003 x ▲PaCO2
pH
Acidemia (pH<7.35)
PaCO2 > 45
(Primary Respiratory)
Alkalemia (pH>7.45)
PaCO2 < 35
(Primary Respiratory)
= [(0.7 x HCO3)+21]
SSSecondary
Metabolic
Acidosis
SSSecondary
Metabolic
Alkalosis
SSSecondary
Metabolic
Acidosis
RESP. ACIDOSIS RESP. ALKALOSIS
SSSecondary
Metabolic
Alkalosis
Partially
Compensated
Partially
Compensated
pHa pHc pHc pHa
pH = 7.4
Key Points:
1. Every Acid-Base Disorder elicits a compensatory response.
2. Compensatory Response do not correct, but they limit the change in pH
3. Body Never Overcompensates.
4. Renal compensatory response is slow. (2 – 4 days).
Alkalemia (pH>7.45)
PaCO2 > 45/N
Primary Metabolic)
PaCO2 (Expected)
= [(0.7 x HCO3)+21]±2
Meas. PaCO2 > Exp.
PaCO2
(Secondary Resp.
Acidosis)
Meas. PaCO2 < Exp
PaCO2
(Secondary Resp
Alkalosis)
RANGE FOR
CALCULATION
pH 7.35 – 7.45 7.4
pCO2 35 - 45 40
HCO3 21 - 24 24
Base Disorder elicits a compensatory response.
Compensatory Response do not correct, but they limit the change in pH.
days).