There are many tricks to interpreting ABG’s, the ROME chart is just one of them. ROME stands for “Respiratory Opposite Metabolic Equal”. What that means is that if your pH is High, which is alkalosis, then you would either see a Low CO2 (opposite) or a High Bicarb (equal). On the other hand if your pH is Low, or acidotic, you will either see a High CO2 (opposite) or a Low Bicarb (equal). Remember that our CO2 indicates Respiratory source and Bicarb indicates a Metabolic source. If the numbers you see are reversed, you are likely looking at compensation. Let’s look at an example.
If the pH is 7.5, the pCO2 is 39 and the Bicarb is 32. Normal pH is 7.35 to 7.45, so this pH is high, or alkalotic (draw an up arrow). Normal pCO2 is 35-45, so this pCO2 is normal (draw a flat line). Finally, normal bicarb is 22-26, so this Bicarb is high (draw an up arrow). So what we see is two up arrows – so the arrows are equal – so it is a Metabolic Alkalosis. Let’s look at another example:
If the pH is 7.3, the PCO2 is 55 and the Bicarb is 26. Normal pH is 7.35 to 7.45, so this pH is low, or acidic (draw a down arrow). Normal pCO2 is 35-45, so this pCO2 is high (draw an up arrow). And normal bicarb is 22-26 so this Bicarb is normal (draw a flat line). What we’re left with is a down arrow and an up arrow – so the arrows are opposite – so it is a Metabolic Alkalosis. Now, I mentioned compensation – what would this look like in the ROME method? Well, let’s use this same problem, but change the Bicarb to 32 (change the number and draw an up arrow next to it). In THIS case, you would see a down arrow on the pH, an up arrow on the pCO2, AND an up arrow on the HCO3. Since you know that metabolic arrows are supposed to be equal, you can see that this is a Respiratory sourced Acidosis with metabolic compensation. And since the pH is still out of range, we know it is only partially compensated.
And that’s the ROME method for interpreting ABGs!