What are the problems with the blood gas?

When you interpret ABG results, you determine whether the pH is balanced and if you have abnormal CO₂, O₂ and HCO₃ levels. The most important thing to remember here is that, as the ultimate goal, you want to leave the body with a normal pH. We cannot cause problems by fixing CO₂ levels when that action will shift the pH further away from normal. Sometimes we need to allow for abnormal CO₂ levels as long as we maintain a correct pH.

Let’s look at an example ABG and identify the problems in the gas, if there are any. Then, we’ll connect these findings to what we can fix with mechanical ventilation:

Patient | 7.31/57/68/24

Remember, the ABG for this patient is expressed as: pH/pCO₂/pO₂/HCO₃. Take a second and interpret this ABG. Remember, you need to comment on:

1. the compensation,
2. whether it is a respiratory or metabolic issue,
3. whether it is acidosis or alkalosis, and
4. the oxygenation status.

If you got the answer uncompensated respiratory acidosis with mild hypoxemia, you are right!

So, what are the problems in this gas?

• The pH is low and the body is in an acidosis state.
• The pCO₂ is too high and causing the acidosis.
• The pO₂ is low and the patient is hypoxic.

The bicarbonate is normal, so there is no problem here.

Remember, with mechanical ventilation, we can change the O₂ and CO₂ directly, and indirectly effect the pH by changing the CO₂ levels. We cannot affect the HCO₃; that change is done by the body over time.

This is a perfect ABG to affect with mechanical ventilation because we can improve the patient’s oxygenation, change how much CO₂ is being exhaled over time and then normalize the pH by that change in CO₂.