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Oxygen Measurements on the ABG

In this course, we explain the nature and correct interpretation of the three key measurements of arterial oxygenation reported on the arterial blood gas (ABG). We explain the use and limitations in clinical practice of the SpO₂ measured by pulse oximetry.

1.5 x AMA PRA Category 1 Credits™
Available on the Pro Plan



In this course, we explain the meaning of the term ‘partial pressure of a gas’. We illustrate the relationship between the three key measurements of arterial oxygenation reported on the arterial blood gas (ABG); the partial pressure of oxygen in the arterial blood (PaO2), the  percentage saturation of haemoglobin in the arterial blood (the SaO2) and the total oxygen content of the arterial blood (the CaO2). We explain the scientific basis of co-oximetry and  pulse oximetry. We illustrate the clinically important differences between these two techniques and, in particular, the uses and limitations of  the SpO2 measured by pulse oximetry in clinical practice.


Planner and Author: Dr John Seery MB PhD

  • Consultant Physician at St. Vincent's University Hospital, Dublin, Ireland
  • Lecturer at the School of Medicine and Medical Science, University College Dublin, Ireland
  • Studied medicine at the University of Cambridge, United Kingdom
  • A Natural Sciences graduate of Trinity College Dublin, Ireland
  • PhD in Cell Biology from University College London, United Kingdom

Planner: Dr Karen Strahan PhD (University of Cambridge), Head of Editorial
Planner: Tommy O'Sullivan, CME Manager

Estimated Time to Complete

1.5 hours

Target Audience

  • Physicians
  • Nurses
  • Nurse Practitioners
  • Physician Assistants
  • Paramedics

Learning Objectives

Upon successful completion of this activity, you will be able to:

  • Explain the meaning of the term ‘partial pressure of a gas’
  • Explain the relationship between the PaO2, the SaO2 and the CaO2 measured by the blood gas analyser and the SpO2 measured by pulse oximetry
  • Explain the physical principles underlying pulse oximetry
  • Avoid error in the interpretation of the SpO2 during patient assessment and management
  • Utilize the measurements made by the co-oximeter on the ABG analyser to diagnose forms of poisoning
  • Utilize appropriate terminology when communicating with colleagues concerning arterial oxygen levels

Course Content

  • Introduction
  • Partial Pressure of a Gas
  • Partial Pressure of a Gas in Air & Blood
  • The ABG Analyser and the Co-oximeter
  • Oxygen Measurements on the ABG
  • Pulse Oximetry - Part 1
  • Pulse Oximetry - Part 2
  • Pulse Oximetry - Part 3
  • Case Examples
  • Quiz

Release date


Expiration date


Instructions for Participation

Participants must complete the online activity during the valid period as noted above.
Follow these steps:

  1. View videos in sequence
  2. Complete quiz
  3. Complete the activity evaluation form to provide feedback for continuing education purposes and for the development of future activities
  4. Download the Certificate of Completion

Relevant Financial Disclosures

Acadoodle adheres to the ACCME's Standards for Integrity and Independence in Accredited Continuing Education. Any individuals in a position to control the content of a CE activity, including faculty, planners, reviewers or others are required to disclose all relevant financial relationships with ineligible entities (commercial interests). All relevant conflicts of interest have been mitigated prior to the commencement of the activity.

Planners and faculty for this activity have no relevant financial relationships with commercial interests to disclose.


Ortega R et al. Pulse Oximetry. N Engl J Med. 2011;364:e33.

Additional Reading

Tremper KK. Pulse Oximetry. Chest.1989;95(4):713-5.

Elliot M et al. Do clinicians know how to use pulse oximetry? A literature review and clinical implications. Aus Crit Care. 2006;19(4):139-44.

DeMeulenaere S. Pulse Oximetry: Uses and Limitations.312-7. 2007;3(5):312-7.


ACCME Accreditation Statement

Acadoodle, Ltd is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

Credit Designation Statement

AMA Physician’s Recognition Award

Acadoodle, Ltd designates this enduring material activity for a maximum of 1.5 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

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