RT-01 · Analysis & Monitoring

Arterial Blood Gas Interpretation

A repeatable four-step read of any ABG — acid-base status, compensation, oxygenation, and the clinical story that produced it.

~24 min read6 concept sections·8 questions with rationale

What you'll be able to do

  • Classify a gas as acidemic or alkalemic and identify the primary disorder
  • Distinguish uncompensated, partially compensated, and fully compensated states
  • Separate oxygenation failure from ventilation failure
  • Recognize when the numbers do not match the patient in front of you
Concept breakdown
01

Step 1 — Read the pH first, never the CO2

The pH tells you which direction the body has actually landed, and it is the only value that defines the primary disorder when two abnormalities coexist.

  • Normal pH 7.35–7.45. Below 7.35 is acidemia; above 7.45 is alkalemia.
  • If the pH is abnormal, look at ROME (Respiratory Opposite, Metabolic Equal).
  • Metabolic disorders move in the same direction as the pH derangement (e.g., low pH and low HCO3).
  • Respiratory disorders move in the opposite direction of the pH derangement (e.g., low pH and high PaCO2).
  • A normal pH with abnormal PaCO2 and HCO3 means full compensation or a mixed disorder — it never means a normal patient.
At the bedside

A pH of 7.38 with a PaCO2 of 68 is a chronically compensated retainer, not a normal gas. Treat the trend, not the single number.

Practice quiz

Check yourself before you read the rationale.

Question 1 of 1

A 58-year-old with severe COPD, baseline PaCO2 in the 50s, arrives drowsy. Gas on room air: pH 7.25, PaCO2 78, HCO3 33, PaO2 51. Which description — and implication — is correct?

Practice questions

Answer first, then read why the distractors fail.

Question 1

A 58-year-old with severe COPD, baseline PaCO2 in the 50s, arrives drowsy. Gas on room air: pH 7.25, PaCO2 78, HCO3 33, PaO2 51. Which description — and implication — is correct?

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5 more concept sections, 7 more questions, and the exam-day playbook for this module.

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