A Guide to Understanding ABGs

If you’re someone who struggles with ABGs, you’re not alone.

Reading the results of an Arterial Blood Gas (ABG) test takes practice and unfortunately a bit of memorization. And while that takes time, it’s a critical skill for healthcare professionals.

Blood Gases: Why?

Perhaps the best way to get started in understanding ABGs is to revisit the importance of blood gasses in general.

Arterial blood gas labs are crucial in helping us:

1. Determine the respiratory and metabolic status of a patient
2. Decide if a patient is requiring more aggressive oxygen therapy
3. Decide if our treatments are being beneficial to the patient or if other changes need to be made

ABGs are likely the most commonly used blood gas and are frequently used when assessing someone’s respiratory status. They are also an important reflection of overall pulmonary function and can help with acid-base interpretation.

Breaking Down ABG Results

First things first! When interpreting ABG results, you need to understand what’s normal.

Normal findings for an ABG include:

Index	Normal Range
pH	7.35-7.45
pCO2	35-45 mm Hg
HCO3	22-26
PaO2	At least > 60 mmHg

A common challenge I hear about is remembering whether the results for the pH are an acidotic finding or an alkalotic finding.

An acidotic finding is a LOW pH (< 7.35) and an alkalotic finding is a HIGH pH (> 7.45). When the pH of the blood is outside of the normal range, by manipulating acid and base, the body tries to pull the pH back to normal.

pHs levels outside of the normal range, combined with irregular pCO2 and HCO3 levels, indicate one of four abnormalities:

1. Metabolic acidosis
2. Metabolic alkalosis
3. Respiratory acidosis
4. Respiratory alkalosis

Remember that carbon dioxide is a respiratory acid and bicarbonate is a metabolic base. This means that the lungs and the kidneys work together manipulating acid and base to try and pull the pH back to normal.

Remembering what each of these abnormalities mean (and what it can be caused by) can be another area of confusion.

Refer to this table for a quick reminder:


The next natural question is often “Why? Why is the patient experiencing an abnormal ABG?”

Common causes of abnormal ABG findings are a main topic in my comprehensive online class, Demystifying Lab Values from Head to Toe.

Broken into six advanced sessions, this intensive course will provide you with step–by–step instruction on lab tests using a review of systems, then include why these labs are typically ordered, the pathophysiology behind abnormal values, and an understanding of what types of symptoms your patient will experience as the values either deteriorate or improve.

You’ll end the training with the ability to look beyond the numbers to putting the pieces of the puzzle together. This will allow you a better understand what is happening, why it is happening, and when you need to be concerned.

Enroll now and receive over 60% off. 7.9 CE hours are included in the course tuition.