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Page 39 from: Mudpiles Quick Medical Reference
First 3 steps of 7 in the Acid Base Evaluation; complements of Mudpiles
See additional sample pages or PURCHASE at:
http://www.mudpiles.com/reference.html
ABG/Acid-Base Interpretation
ABGs usually HAVE to be on ice when delivered to most labs.
Step 1: Determine Acid- or Alkylemia
Normals: pH = 7.40 ± 0.04; acidemic (pH <7.38) or alkalemic (pH> 7.42); pCO2 = 40; HCO3- = 24±4
pCO2 ↑ 10 mmHg causes pH ↓ 0.08
pH ↑ 0.15 causes Base (HCO3-) ↓ 10 mEq
Step 2: Respiratory, Metabolic or Mixed
[H+] = (24 * pCO2) / [HCO3-]
[H+] = 80-decimal part of pH
(so if pH = 7.30, [H+] = (80-30) = 50)
Acidemic=respiratory if the PaCO2 is >45; metabolic if the HCO3 is <22; Alkalemic=respiratory if the PaCO2 is <35; metabolic if the HCO3 is >26
Determine A-a gradient = (FiO2 x 713) (PaCO2/0.8) PaO2
Nml = age/4 + 4
Step 3: Compensation
A: Respiratory Alkalosis:
Acute change in PaCO2 by 10 mmHg will change the pH by 0.08
Acute causes: Anxiety, hypoxia, lung dz., meds= (ASA, Catecholes,
PG), pregnancy, sepsis, ventilation.
Acute respiratory acidosis  pH ↓ = [0.08 x (PaCO2 -40)]/10
Winters formula: expected change in PaCO2 = [1.5 x serum HCO3-] +8 +/- 2; if measured PaCO2 is > expected by Winters formula then there is a respiratory acidosis.
Chronic causes: COPD
Chronic changes in PaCO2 by 10 mmHg will change the pH by 0.10; Chronic= pCO2 ↓ of 10 causes 1 to 3.5 ↓ HCO3
B: Respiratory Acidosis:
Expected HCO3- compensation:
Acute: pCO2 ↑ of 10 causes 0-1 ↑ HCO3 (max 35)
Chronic: pCO2 ↑ of 10 causes 1-3.5 ↑ HCO3 (max 50)
Acute causes: CNS depression, airway obstruction, pneumonia or edema, PE
C: Metabolic Alkalosis:
Expected pCO2 compensation:
pCO2 = (HCO3 x 0.9) + 15 ± 2
Causes: Low Urine Chloride from suction, vomiting, diuretics, hypercapnia
Nml or High UChl from Cushing`s, Conn`s, steroids, licorice, diuretics, re-feeding
D: Metabolic Acidosis:
NonAG (↓ HCO3 but ↑ Cl) = from diarrhea or RTA
AG (↓ HCO3 but ↑ unmeasured cation) from: Methanol, Uremia, Lactic acidosis, Ethylene glycol, Paraldehyde, Aspirin, Ketoacidosis.
Expected pCO2 compensation = (HCO3 x 1.5) + 8 ± 2
First 3 steps of 7 in the Acid Base Evaluation; complements of Mudpiles
See additional sample pages or PURCHASE at:
http://www.mudpiles.com/reference.html
ABG/Acid-Base Interpretation
ABGs usually HAVE to be on ice when delivered to most labs.
Step 1: Determine Acid- or Alkylemia
Normals: pH = 7.40 ± 0.04; acidemic (pH <7.38) or alkalemic (pH> 7.42); pCO2 = 40; HCO3- = 24±4
pCO2 ↑ 10 mmHg causes pH ↓ 0.08
pH ↑ 0.15 causes Base (HCO3-) ↓ 10 mEq
Step 2: Respiratory, Metabolic or Mixed
[H+] = (24 * pCO2) / [HCO3-]
[H+] = 80-decimal part of pH
(so if pH = 7.30, [H+] = (80-30) = 50)
Acidemic=respiratory if the PaCO2 is >45; metabolic if the HCO3 is <22; Alkalemic=respiratory if the PaCO2 is <35; metabolic if the HCO3 is >26
Determine A-a gradient = (FiO2 x 713) (PaCO2/0.8) PaO2
Nml = age/4 + 4
Step 3: Compensation
A: Respiratory Alkalosis:
Acute change in PaCO2 by 10 mmHg will change the pH by 0.08
Acute causes: Anxiety, hypoxia, lung dz., meds= (ASA, Catecholes,
PG), pregnancy, sepsis, ventilation.
Acute respiratory acidosis  pH ↓ = [0.08 x (PaCO2 -40)]/10
Winters formula: expected change in PaCO2 = [1.5 x serum HCO3-] +8 +/- 2; if measured PaCO2 is > expected by Winters formula then there is a respiratory acidosis.
Chronic causes: COPD
Chronic changes in PaCO2 by 10 mmHg will change the pH by 0.10; Chronic= pCO2 ↓ of 10 causes 1 to 3.5 ↓ HCO3
B: Respiratory Acidosis:
Expected HCO3- compensation:
Acute: pCO2 ↑ of 10 causes 0-1 ↑ HCO3 (max 35)
Chronic: pCO2 ↑ of 10 causes 1-3.5 ↑ HCO3 (max 50)
Acute causes: CNS depression, airway obstruction, pneumonia or edema, PE
C: Metabolic Alkalosis:
Expected pCO2 compensation:
pCO2 = (HCO3 x 0.9) + 15 ± 2
Causes: Low Urine Chloride from suction, vomiting, diuretics, hypercapnia
Nml or High UChl from Cushing`s, Conn`s, steroids, licorice, diuretics, re-feeding
D: Metabolic Acidosis:
NonAG (↓ HCO3 but ↑ Cl) = from diarrhea or RTA
AG (↓ HCO3 but ↑ unmeasured cation) from: Methanol, Uremia, Lactic acidosis, Ethylene glycol, Paraldehyde, Aspirin, Ketoacidosis.
Expected pCO2 compensation = (HCO3 x 1.5) + 8 ± 2
