Metabolic/Respiratory Alkalosis/Acidosis

missamelissy8 · Nov 6, 2015

Have you been taught the "ROME" acronym? Respiratory Opposite, Metabolic Equal.

If the PCO2 value goes in the "O"pposite direction of the pH (for instance pH of 7.3 and a PCO2 of 50 or pH of 7.5 and PCO2 of 30), then it is a "R"espiratory cause.

If pH and HCO3 are changed in the same ("E"qual) direction (pH of 7.3 and HCO3 of 20 or pH of 7.5 and HCO3 of 30), then it is "M"etabolic.

There are really great methods of using boxes and "tic-tac-toe" grids that make it much easier to do for the purpose of testing. However, I haven't used one in a while and am not sure I could remember them well enough to explain here. But if you google, I'm sure you'll find some great resources!

Hope this helps as a starting point, though!

Duttygal86, BSN, RN · Nov 6, 2015

I would also suggest googling "tic tac acidosis/alkalosis" videos.

Summer Days · Nov 6, 2015

Disorders that primarily alter carbon dioxide will affect the respiratory system. Whereas, disorders that primarily alter bicarbonate will affect the metabolic system. Bicarbonate is largely controlled by the renal system. Take into consideration the history and physical of the patient or the medical diagnosis. Understand that the metabolic system (the renal system) will compensate for respiratory alterations and vice versa. I suggest you review the buffer system as it will really help a lot to distinguish between these two and when you do acid base calculations.

mariok · Nov 7, 2015

Thank you.

Also I am having a hard time with when two of the values are high and two of the values are low. For example ph 7.48, paco2 50 mmhg, and hco3 36 mEq/l. I know that it is alkalosis. How do I determine if it is respiratory or metabolic since the paco2 and hco3 are both high?

la_chica_suerte85, BSN, RN · Nov 7, 2015

Thank you.
Also I am having a hard time with when two of the values are high and two of the values are low. For example ph 7.48, paco2 50 mmhg, and hco3 36 mEq/l. I know that it is alkalosis. How do I determine if it is respiratory or metabolic since the paco2 and hco3 are both high?

Ok, just like with what the 1st reply said about ROME, this might help clue you in to what's going on.

https://abg.ninja/abgbuilder

This link has practice ABGs and you can put your own in and find out what they mean. You can kind of work backward and play with values to see what is going on. Take your time with it, practice as many as you can and you will really start to master the concepts, especially as it explains why certain things are the way they are.

To answer your question about these values, you have to consider how the body begins to compensate for an imbalance. The PaCO2 is high but it's not as far out from the normal range (35-45) as the HCO3 (22-26) is. Consider what systems in the body manage PaCO2 and HCO3. The kidneys deal with HCO3 and the lungs deal with PaCO2 (this is a very basic breakdown to just help understand the concept). Kidneys are metabolic, lungs are respiratory.

We know 7.48 is an alkalotic (slightly) pH. It appears that, since the difference for HCO3 is so far out from the normal range, it is likely metabolic alkalosis. Since the PaCO2 is higher than the reference range, this means the respiratory system has attempted to hold on to CO2 to increase acid to compensate for the metabolic alkalosis. So, this is a partially compensated metabolic alkalosis. It is partially compensated because the pH has not returned to normal yet.

Hope that makes a little bit more sense. Use the practice quiz in the link I included and it should help illuminate a lot of the mystery with ABGs.