SCAI Shock Stages are Predictive of Mortality Risk

Your group sought to understand if the SCAI shock stages can classify mortality risk. Can you tell us about your research?

For this analysis, we reviewed the different papers that have been published since the original Society for Cardiovascular Angiography and Interventions (SCAI) shock proposed classification.1 In the SCAI shock classification, the severity of shock is graded on a five-stage scale from A to E. Stage A is people who don’t actually have shock, but who are at risk because they have acute cardiovascular disease. Patients in stage B have what I would call pre shock, meaning that they have some form of hemodynamic instability, but still have adequate organ perfusion. Under the SCAI shock classification, the definition of shock as a state of hypoperfusion is key, and Stage C is where you start to see the presence of shock, because there is hypoperfusion requiring some form of an intervention. Stage D shows evidence of deterioration, which is a little hard to define, but essentially means that the initial therapies have not worked effectively. Stage E would be the most severe form of shock, where patients have circulatory collapse, what we usually call extremis. The SCAI shock classification is designed to be very flexible, and as a result, each group came up with a different way to define the various SCAI stages within their own datasets. The different analyses we reviewed all used the same types of variables, but the way these variables were combined by researchers in terms of cutoffs was, in some cases, quite different. A few of the studies used physician chart review to assign the SCAI stages, which theoretically should be the gold standard, but most of the studies just used retrospective data and had to come up with some definitions as a result. In general, the data are combinations of vital signs, laboratory data, and the different therapies that were used. A patient with worse vital sign abnormalities, worse laboratory abnormalities, and/or who is requiring more vasopressor or mechanical circulatory support, would therefore be in a higher SCAI shock stage. Even though there were six or seven different definitions used to define the SCAI stages, all definitions showed the same ability to stratify mortality. Reflecting gradations in mortality is strong evidence that the SCAI shock classification is clinically useful, regardless of how the different stages are defined, and this is one of our key findings. Some of the different classification systems provided greater or lesser degrees of separation, but it is hard to know whether it is because the classification systems weren’t as accurate or if it is simply a reflection of the studies’ unique populations. None of the different SCAI shock stage definitions were compared within the same population, so it would be unfair to say that any one definition is better than another based on the data we have thus far. We did find several subgroups that were of interest, because some of these populations were fairly heterogenous. We sought to confirm that what we saw was not just an artifact of how the population is constructed, but a relevant variable. For example, in cardiac care unit patients who had acute coronary syndrome, we saw very substantial gradations in mortality in the same population. In patients that had heart failure, again, we saw mortality gradations, maybe not quite as impressive, but again, overall, quite similar. One of the key ideas put forward in the SCAI shock consensus statement was that patients with cardiac arrest are a unique and special subgroup at higher risk, which has been confirmed by studies looking at those patients specifically. Our study did look at the presence or absence of cardiac arrest; we found that at any level of SCAI shock stage severity, patients with cardiac arrest were more likely to die, which is a common and well-known observation. However, we looked at whether the mortality risk was due to shock or due to something else. We were able to show that cardiac arrest patients have worse outcomes at every level of shock severity, which suggests that there is more going on with these patients than just shock. While we may be able to successfully treat their shock, cardiac arrest patients may still have other problems like brain injury and organ failure that drive their outcomes. It doesn’t necessarily mean we shouldn’t treat these patients aggressively, but it does mean that we should have a clearer understanding of what to expect with their prognosis and understand that their problems include more than just hemodynamics.