We have now discussed the basics of ABG interpretations. It is best to try to practice as much as you can. It will become second nature the more you do it. The best way to approach ABG interpretation is to understand the “why” and not just memorize the patterns. In the next chapter, we will take these skills and start to make changes on ventilation settings, so make sure you understand the relationships between CO2, HCO3 and pH.

A final word of caution with ABG interpretations

Sometimes when looking at ABGs is easy to miss a “normal” gas. Clinicians can get so caught up with diagnosing a problem, that they may miss a normal reading. If all values are within normal limits, that ABG is normal and no other interpretation is needed. Normal means the body is perfectly balanced with no extra acid or base anywhere. All values are normal—there is a perfectly matched game of Tug O’ War with the pH/rope in the normal position and with normal team numbers on both sides.


ABG interpretation is an essential part of effective ventilation, as the information you learn will inform initial settings (when possible) and adjustments. In this chapter, you learned about the theory behind arterial blood gases: the acid-base “Tug O’ War” in the body. Then, you learned what an ABG is, and the values that it produces: pH, pCO2, pO2, HCO3. Finally, you learned how to answer the four main questions that underly the ABG interpretation:

  • Uncompensated, partially compensated or fully compensated?
  • Respiratory or metabolic?
  • Acidosis or alkalosis?
  • Hypoxemic, hyperoxic, or normal?

What’s next?

In Chapter 9, the final chapter of this book, you will learn what to do with your ABG interpretation in the context of choosing and adjusting ventilator settings.


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