So as a brief review for those not familiar with the technology- the ROTEM has a number of reagents and inhibitors you can run together depending on your clinical situation. The two I run on CPB are the EXTEM, which is tissue-factor activated (i.e. a test of the extrinsic pathway) and the FIBTEM, which is an EXTEM with platelet inhibitors added.
So the first thing you get is the EXTEM clotting time, similar to the r time on the TEG. If this time is prolonged, your "extrinsic" factors are deficient, and you order FFP.
Then you look at the FIBTEM amplitude, which looks at the fibrinogen contribution to the clot. This generally reaches something close to its final amplitude fairly quickly. An amplitude of around 7-8 mm is borderline, and represents a fibrinogen concentration of around 150.
Finally, look at the EXTEM alpha angle and amplitude. Both fibrinogen and platelets play a role here, so if the FIBTEM was normal but the EXTEM amplitude is low, you know you need platelets. If both were low, you'd get platelets and cryo (or fibrinogen concentrate). If FIBTEM was marginal but the EXTEM looks fine, no need to order cryo, the platelet function is robust. You'll know ten minutes into the clot how the clot is shaping up, although it'll continue to form and strengthen over time.
I have not seen a properly-run test mislead, so I think it's quicker than the usual tests and more meaningful. It does, however, involve a human pipetting reagents into specimen cups, so there is a small potential for human screw-up, which we've seen once or twice.
Our machine lives in the anesthesia techs' office which is literally across the hall from one heart room, and 20 feet away from the other. So while we're on pump I just go over there and quickly eyeball it as it runs. It has a built-in printer, and you can print while it runs (the vibration doesn't affect it unlike TEG) so if I really have my hands full I can ask the tech to print off a copy.
We still use traditional ACT for heparin management. We don't fuss with INTEM/HEPTEM usually. I consider the the APTEM (an EXTEM with added aprotinin) a worthless test, because all of our patients get anti fibrinolytics anyway, and if there is lysis, you'll see it on the EXTEM without needing to burn reagent on a confirmatory FIBTEM.
TL;DR version- ROTEM gives you valuable clotting information quickly, even while heparinized, and is like super awesome and stuff.