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Learning ABG as easy as ABC

Arterial Blood Gases

ABG for short, is a topic most of the nurses find difficult to fully understand.

Arterial Blood Gas analysis is an excellent way to know how good (or bad) one’s oxygenation status is.

However, ABG’s results can only recognize the status at the time being. To put into example, the arterial blood you have drawn 30 minutes ago is not suitable to identify one’s oxygenation at this very moment. That’s why physician’s order Arterial Blood Gas analysis every now and then.

So where do arterial blood is drawn from? Well, arteries, of course.

But how do you know it is an artery? Nurses, you have to look for that good, lovely bounding pulse.

Here’s an image guide of ABG sites, having the Radial Artery as the most common site for arterial blood gas withdrawal.

It is noteworthy to note that patients on blood thinners are contraindicated with the procedure. Also, the use of tourniquet is not necessary – we don’t want that additional pressure for extra blood squirt, do we?

Prior to taking an arterial blood gas sample, we should first perform the Allen’s Test.

This is done to ensure good blood circulation at the site, and that the radial or ulnar arteries are suitable for blood withdrawal. Once arterial patency is established, you may proceed with the arterial blood withdrawal.

Interpreting Arterial Blood Gas Values

The ABG interpretation confuse many nurses most of the time. But, here’s the easy way:

We actually have 2 ways to interpret the Arterial Blood Gases. First is through the laboratory values, and second is through Clinical Diagnosis.


  1. There are only two (2) laboratory values you should focus on:

pH level
7.35 – 7.45

HC03 level
22 – 26

Yes, you should only focus on the pH level and the Bicarbonate level.

pH below 7.35 = Acidosis, and pH above 7.45 is Alkalosis


2. The next step is to use the R.O.M.E. Method

Respiratory is Opposite (in values)



Metabolic is Equal (in values)


pH of 7.30, HC03 of 31
Respiratory Acidosis

pH of 7.48, HC03 of 30
Metabolic Alkalosis

pH of 7.25, HC03 of 20
Metabolic Acidosis

pH of 7.47, HC03 of 17
Respiratory Alkalosis

pH of 7.34, HC03 of 28
Respiratory Acidosis


First, you have to ask yourself:

Is it a respiratory problem?

If YES —

Respiratory Alkalosis
Conditions with rapid breathing

Respiratory Acidosis
Conditions with too slow breathing

If NOT —

then, it is a Metabolic condition

Metabolic Alkalosis
Conditions with vomiting or suctioning

Metabolic Acidosis
Conditions that are anything else



Dog bite
Metabolic Acidosis

Depressed respiration from drug overdose
Respiratory Acidosis

Patient hiked for 2 hours in the mountain
Respiratory Alkalosis

Pancreatitis with continuous suctioning
Metabolic alkalosis

Blood glucose level of 29
Metabolic Acidosis

Patient is in coma
Respiratory Acidosis


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  • ReMar NCLEX Review – ABG Interpretation

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