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The Ultimate Acid-Base Imbalance Study Guide for
NCLEX & Med-Surg
From Confusion to Clarity: A Simplified, Visual Approach
Level: Undergraduate (Nursing), NCLEX Prep
Subject: Medical-Surgical Nursing, Pathophysiology
How to Use This Guide
This guide is structured to move from foundational concepts to complex
clinical application. We will progress from understanding the basic labs
to analyzing complex, mixed acid-base disorders.
1. Master the Basics: The "Rule of the B's" and normal values.
2. Understand the Compensatory Mechanisms: How the lungs and
kidneys work as a team.
3. Memorize the Uncompensated Chart: The core of each disorder.
4. Learn to Interpret ABGs: The Tic-Tac-Toe and ROME methods.
5. Apply to Med-Surg: Connecting the disorder to the disease and
nursing interventions.
Section 1: The Foundation - What You MUST Know
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1.1 The "Big Three" Lab Values
You cannot interpret an ABG without these values memorized.
Normal
Lab Value Critical Thinking Point
Range
7.35 -
pH Below 7.35 = Acidosis; Above 7.45 = Alkalosis.
7.45
35 - 45 Respiratory Component. High PaCO2 (>45) = Acid
PaCO2
mmHg Low PaCO2 (<35) = Alkaline.
HCO3- 22 - 26 Metabolic (Renal) Component. High HCO3 (>26) =
(Bicarb) mEq/L Alkaline. Low HCO3 (<22) = Acidic.
80 - 100
PaO2 Indicates oxygenation status, not acid-base.
mmHg
Base A positive value indicates a base excess (metabolic
Excess -2 to +2 alkalosis). A negative value indicates a base deficit
(BE) (metabolic acidosis).
1.2 The "Rule of the B's"
A simple way to remember the relationship between pH and PaCO2:
• Below normal pH (Acidosis) = Below normal PaCO2? No! Below
normal pH means the patient is Acidic. If the cause
is Respiratory, the PaCO2 will be the Opposite.
• Better yet, use the ROME method (see Section 4).
The Ultimate Acid-Base Imbalance Study Guide for
NCLEX & Med-Surg
From Confusion to Clarity: A Simplified, Visual Approach
Level: Undergraduate (Nursing), NCLEX Prep
Subject: Medical-Surgical Nursing, Pathophysiology
How to Use This Guide
This guide is structured to move from foundational concepts to complex
clinical application. We will progress from understanding the basic labs
to analyzing complex, mixed acid-base disorders.
1. Master the Basics: The "Rule of the B's" and normal values.
2. Understand the Compensatory Mechanisms: How the lungs and
kidneys work as a team.
3. Memorize the Uncompensated Chart: The core of each disorder.
4. Learn to Interpret ABGs: The Tic-Tac-Toe and ROME methods.
5. Apply to Med-Surg: Connecting the disorder to the disease and
nursing interventions.
Section 1: The Foundation - What You MUST Know
, 2|Page
1.1 The "Big Three" Lab Values
You cannot interpret an ABG without these values memorized.
Normal
Lab Value Critical Thinking Point
Range
7.35 -
pH Below 7.35 = Acidosis; Above 7.45 = Alkalosis.
7.45
35 - 45 Respiratory Component. High PaCO2 (>45) = Acid
PaCO2
mmHg Low PaCO2 (<35) = Alkaline.
HCO3- 22 - 26 Metabolic (Renal) Component. High HCO3 (>26) =
(Bicarb) mEq/L Alkaline. Low HCO3 (<22) = Acidic.
80 - 100
PaO2 Indicates oxygenation status, not acid-base.
mmHg
Base A positive value indicates a base excess (metabolic
Excess -2 to +2 alkalosis). A negative value indicates a base deficit
(BE) (metabolic acidosis).
1.2 The "Rule of the B's"
A simple way to remember the relationship between pH and PaCO2:
• Below normal pH (Acidosis) = Below normal PaCO2? No! Below
normal pH means the patient is Acidic. If the cause
is Respiratory, the PaCO2 will be the Opposite.
• Better yet, use the ROME method (see Section 4).
