Fundamentals of 3-Step ABG Interpretation – Simplified Arterial Blood Gas Analysis Guide 2025/2026

3 Step ABG Interpretation
Mike’s Marching Band Suit Method


Marching band suit method

A B
pH 7.35 7.45 TEST TIP

Write this chart out 5 - 10 times every day the week
B A
PaCO₂
35 45

A B of your ABG exam.
HCO₃
22 26




Side Note: Many students & instructors use the ROME or Tic-Tac-Toe method, but that can get very confusing when interpreting
partial vs. full compensation. Use the marching band suit method to make it simple & get all your ABG questions
correct!


Set Up the Chart

Phase 1 - set up the chart
pH is on 1st!
Step 1 Think pH is primary since it comes first.
pH CO2 comes 2nd.
Step 2 Look at the 2 in CO2, it comes 2nd.
PaCO₂ Lungs on top

HCO3 comes 3rd.
HCO₃ Step 3 Look at the 3 in HCO2, it comes 3nd.
Kidneys on bottom



Phase 2 - key numbers to memorize

A B
pH 7.35 7.45

B A
Top line 7.35 - 7.45
PaCO₂ Middle 35 - 45 (7 goes to heaven)
35 45
Bottom 22 - 26 (think 2+2+2 = 6)
A B
HCO₃
22 26




Phase 3 - Label it A & B


A cid
A B
pH 7.35 7.45

B A
PaCO₂
35 45



B ase HCO₃
A

22
B

26

, ABG Practice Questions
ABG Practice Question 1 Example “marching band suit”

pH 7.25 , PaCO₂ 55 , HCO₃ 25 A B
pH 7.35 7.45
Draw your marching band suit here:
B A
PaCO₂
35 45

A B
HCO₃
22 26




ABG Practice Question 2
pH 7.57 , PaCO₂ 25 , HCO₃ 22
Draw your marching band suit here:




ABG Practice Question 3
pH 7.21 , PaCO₂ 39 , HCO₃ 19
Draw your marching band suit here:

,Acid Base Imbalances + ABGs
Pathophysiology Course


Pathophysiology pH



Acid base imbalances are the balance of Acid & Base in the body, Acidotic NORMAL pH
NORMAL pH Alkalotic
kind of like a tug of war the body loves to keep pH in balance. 7.35
7.35 pHpH 7.45
7.45pHpH


- Normal pH: 7.35 - 7.45
- Acidosis: Less than 7.35 pH
- Alkalosis (base): Over 7.45 pH
MEMORY TRICKS
• Full compensation = FULLY Normal pH 7.35 - 7.45 Base = Bicarbonate Carbon diACID
• Partial compensation = pH is not normal
Hydrogen ions = HIGH acid

Controlling Organs
KEY PLAYERS
Lungs control Kidneys control
Carbon Dioxide CO2 Acid Base
Breath in O2 & breath out CO2 Hydrogen H+ ions (acid)
Found in the urine
H⁺
Hypoventilation leads to
HIGHER CO2 Bicarbonate HCO3 (base)
Hyperventilation lead to Found in the intestines
Hydrogen Acid
O
lower CO2


C
C H
O O
O O
Bicarb
Carbon dioxide Acid




Metabolic Acidosis & Alkalosis - Causes MEMORY TRICKS

Metabolic
Over 7.45 pH Under 7.35 pH ALKalosis



Metabolic ALKalosis Metabolic Acidosis
H⁺

H⁺

H⁺
H⁺




Vomiting Diarrhea
NGT suction Renal Failure
Hypokalemia DKA - Diabetic Ketoacidosis
• Low K+ Potassium (below 3.5) Lactic AcidOSIS Vomiting sounds like
• LOW K+ = AlKaLOWsis • Shock (low perfusion) “ALKKK-alosis”
Compensation • Sepsis (severe infection)
• Slow Compensation
• Shallow respirations • Rapid, deep respirations Metabolic
ACIDosis



K
Memory tricks Memory tricks
Base out the Butt DKA - Diabetic Ketoacidosis
Metabolic ACIDosis

< 3.5
Diarrhea: if it comes
LOW K+ out of your a$$idosis
AlKaLOWsis Renal Failure: when the
kidneys fail, acid prevails!

, ABG Compensation Questions
Full or Partial
ABG Question 1
Full or Partial compensation?
pH 7.32 , PaCO₂ 55 , HCO₃ 42
Draw your marching band suit here:




ABG Question 2
Full or Partial compensation?
pH 7.55 , PaCO₂ 49 , HCO₃ 35
Draw your marching band suit here:




ABG Question 3
Full or Partial compensation?
pH 7.37 , PaCO₂ 52 , HCO₃ 32
Draw your marching band suit here:




ABG Question 4
Full or Partial compensation?
pH 7.43 , PaCO₂ 43 , HCO₃ 33
Draw your marching band suit here: