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In this lesson we’re going to talk about the first trick method to interpreting arterial blood gases. It is called the ROME method.
ROME stands for Respiratory Opposite, Metabolic Equal. This has to do with the direction of the values compared to the pH. Remember that Respiratory is represented by CO2 and Metabolic is represented by bicarb or HCO3. Some people have also referred to this as the arrow method.
So we have two options for an abnormal pH, it can either be high (alkalosis) or low (acidosis). For each of these conditions, you could have a respiratory or metabolic source. So, respiratory alkalosis, metabolic alkalosis, respiratory acidosis, and metabolic acidosis. When we talk about opposite and equal, we’re looking at these arrows. Respiratory is opposite, Metabolic is equal. So if the pH is high, then if it’s respiratory, the level will be low (opposite). And remember CO2 is that level. If the pH is high and it’s a metabolic source, or a bicarb issue, the bicarb will be high (equal). Do you see the opposite and equal arrows? So, for a low pH – respiratory opposite means the CO2 would be high. Metabolic equal means the bicarb would also be low, just like the pH. So you can see why some people call it the arrow method. Respiratory has opposite arrows, metabolic has equal arrows. The best way to see this is to put it into practice so let’s do some examples.
Remember we always use our 3 steps. Step 1 is to evaluate each one – in this case, we’ll just use arrows – is it high or low. pH 7.52 is high. PaCO2 is low, bicarb of 22 is normal. We see opposite arrows – respiratory is opposite, so this is a respiratory issue. Since the pH is high, we know it’s a respiratory alkalosis. Step 3 is compensation – but since the bicarb is normal, we know there’s no compensation happening, so we’d call it uncompensated. Done. Next.
Step 1 – pH 7.29 is low, CO2 of 37 is normal, bicarb of 16 is low. We see equal arrows, we know it’s a metabolic issue. With a low pH, it’s metabolic acidosis. Step 3 – the CO2 is normal, so there is NO compensation. Let’s do another.
Step 1 – pH 7.32 is low, CO2 55 is high, bicarb 29 is high. So, now we have to think critically. The respiratory level is showing opposite arrows – is that what we expect? Yes! The metabolic level is also showing opposite arrows – but we know for metabolic to be the source, it should be equal. So we can safely say that our source is respiratory – so this is a respiratory acidosis. So what’s going on here? Well – step 3. Are the CO2 and bicarb BOTH abnormal? Are they representing opposite conditions? Yes! This bicarb is high because it’s trying to fix the problem, right? So we know there’s some compensation going on. Since the pH is still abnormal, we’d call it partially compensated respiratory acidosis. This is where the arrow trick comes in – in this method – if your CO2 and bicarb have arrows going the SAME way – there is compensation. So, let’s look at one more.
Step 1 – pH 7.44 is normal. PaCO2 52 is high. Bicarb 35 is high. Step 2 – what’s our source – well our pH is normal, but we know there’s a problem, right? So is the pH on the high or low side of normal? It’s on the high side. Now, go back to ROME – respiratory opposite? Nope. Metabolic equal – yep! So this was a metabolic alkalosis because of that higher pH. When we shift to step 3, again we see that both of these arrows are going the same way so we know there has been some compensation – and since our pH is normal, we would call it a fully compensated metabolic alkalosis.
So, that’s the ROME method. I know this method works really well for a lot of people. We even provided a cheatsheet for you with that ROME chart on it that you can use as a resource. Again, make sure you do the practice problems found in this lesson using the ROME or arrow method. Then, move on to the next trick method to see which one is going to work best for you. Now, go out and be your best selves today. And, as always, happy nursing!!