Despite recent advancements in patient care, cardiogenic shock (CS) remains a condition with high mortality rates, reaching up to 50%. Given the diverse presentation and variable severity of CS, achieving effective communication regarding disease progression and patient risk poses a considerable challenge when managing this medical condition. Additionally, variations in the severity of this condition have impacted clinical trials aiming to assess advanced therapies such as temporary mechanical circulatory support (tMCS). To address these complexities, the SCAI introduced a CS Classification in 2019, endorsed by several medical societies, unifying staging and risk prediction in cardiovascular patients. Over the following years, numerous retrospective and some prospective studies evaluated this classification across various cardiovascular patient cohorts, leading to refinements announced in the 2022 SCAI Classification update. Although widely applied in cardiology, it had yet to be assessed in cardiac surgery patients.
This study focused on evaluating the utility of the SCAI Shock Classification for postoperative cardiac surgery intensive care unit (ICU) patients, assessing both hospital mortality and associations with postoperative complications and organ dysfunction.
A retrospective analysis encompassed 26,792 ICU admissions after cardiac surgery at Charité German Heart Center (DHZC) in Berlin from 2012 to 2022. Patients were categorized into SCAI Shock stages A through E, based on clinical, physiological, and laboratory data from the first 24 hours post-surgery, using electronic health record data. The impact of late deterioration (defined as increased vasopressors or lactate levels in the following 24 hours) was also explored as an additional risk factor.
The patient proportions across SCAI Shock stages A through E were 24.4%, 18.8%, 8.4%, 35.5%, and 12.9%, respectively, with corresponding crude hospital mortality rates of 0.4%, 0.6%, 3.3%, 4.9%, and 30.2%. Postoperative complications and multi-organ failure prevalence also increased with higher SCAI Shock categorization. Multivariable analysis showed that each advanced SCAI Shock stage was associated with increased hospital mortality (adjusted OR: 1.26-16.59) compared with SCAI Shock stage A, as was late deterioration (adjusted OR: 8.2). The SCAI Shock Classification demonstrated strong diagnostic performance for hospital mortality prediction (AUROC: 0.84), which increased significantly when late deterioration was included in the model (AUROC: 0.90).
In conclusion, the authors argue that the SCAI Shock Classification is an effective tool for mortality risk stratification and evaluating postoperative complications and organ dysfunction in ICU patients after cardiac surgery. Thus, its application could be extended to cardiac surgery as a triage tool in postoperative care and as a selection criterion in clinical research.
COMMENTARY:
Preoperative risk scales, such as EuroSCORE or STS score, are widely used in numerous cardiac interventions worldwide, helping evaluate prognosis and, in many cases, identify patients unsuitable for surgery. However, these preoperative scores are imperfect and carry significant limitations. A critical limitation is that they do not account for intraoperative events or the patient’s postoperative status. These factors can greatly influence clinical evolution and outcomes for many patients.
It is well known that low cardiac output and, to a lesser extent, vasoplegia post-cardiac surgery are associated with increased mortality. For instance, patients experiencing refractory postoperative cardiogenic shock (PCS) that requires tMCS may face in-hospital mortality rates up to 50%. Although numerous studies have evaluated prognosis in such situations, uncertainty persists regarding risk stratification and outcomes across the shock spectrum in cardiac surgery patients.
The SCAI Shock Classification offers a simple way to assess shock severity across a five-stage scale, covering the entire spectrum of patients with or at risk of CS. Hence, the demonstrated utility of this scale in risk stratification for medically induced CS should also apply to patients undergoing cardiac surgery, which this study aimed to confirm.
From my perspective, this study holds considerable significance for several reasons:
- It contributes significantly to understanding the epidemiology and outcomes related to shock post-cardiac surgery.
- It stands out as the most extensive published study to date on the association between the SCAI Shock Classification and mortality in critically ill patients.
- It marks a milestone as the first study to validate this classification in a population of patients undergoing cardiac surgery.
The SCAI Shock Classification demonstrated excellent discrimination and adequate calibration for mortality prediction, as detailed below. More than 56.8% of patients met the SCAI criteria for shock, exhibiting hypoperfusion, defined as SCAI Shock stages C/D/E. As SCAI Shock stage increased, disease severity, multi-organ failure, and the need for rescue therapies also rose. Additionally, patients with more severe shock (SCAI Shock stages D/E) underwent prolonged and complex surgeries, as evidenced by extended extracorporeal circulation times. Expectedly, hospital mortality increased across SCAI Shock stages, with nearly a 75-fold increase in crude mortality from SCAI Shock stage A to stage E. This incremental increase in mortality across SCAI Shock stages remained after adjusting for intergroup differences, including preoperative and intraoperative variables.
On the other hand, it is worth noting that patients without hypoperfusion (SCAI Shock stages A/B) had very low hospital mortality rates of only 0.5%, even though most received vasoactive medications (not directly used to define shock). In these low-risk patients, an early discharge protocol could be justified. Furthermore, patients with mild or moderate shock (SCAI Shock stages C/D) experienced mortality below 5%, which are still relatively low figures.
Patients who experienced late deterioration, defined as increased vasopressor usage or elevated lactate levels after 24 hours, showed additional increases in subsequent mortality. This association between late deterioration and increased mortality aligns with previous observations in cardiac ICU patients, underscoring the importance of dynamic shock assessment over time.
Comparing these results to studies analyzing non-surgical ICU populations, such as the study by Jentzer et al., shows significantly higher shock prevalence and severity per SCAI Classification in cardiac surgery patients. However, paradoxically, in-hospital mortality at each SCAI Shock stage was higher in medical ICU patients with cardiac conditions. Mortality differences were substantial, for example, 40% vs. 4.9% in SCAI Shock stage D and 67% vs. 30.2% in stage E. This highlights a fundamental distinction between medical and surgical critical illness: post-surgical patients are selected as suitable surgical candidates without life-limiting non-cardiac comorbidities, with a correctable condition expected to improve postoperatively.
Additional plausible explanations exist for why PCS appears to have a more favorable prognosis than CS in non-surgical patients. These include the higher prevalence and severity of vasoplegia and hypovolemia in cardiac surgery, leading to mixed shock states often resolving rapidly. Also, post-cardiac surgery patients commonly require inotropic agents, such as epinephrine, and experience lactic acidosis upon ICU admission, which typically resolves quickly with volume resuscitation, resolution of vasoplegia, and abatement of initial myocardial stunning.
Incorporating the SCAI Shock Classification into early postoperative evaluation alongside preoperative scores we commonly use will likely provide more accurate risk stratification for hospital events. One of the most notable contributions of this analysis could be its potential to predict the elevated risk of severe PCS, particularly in SCAI Shock stage E, allowing for better preparation and, hopefully, prevention of subsequent complications.
In general, this study further supports the validity of the SCAI Shock Classification, providing incremental mortality risk stratification for patients undergoing cardiac surgery. SCAI Shock severity assessment demonstrates a robust prognostic framework in both medical ICU and surgical cardiac ICU populations, even with expectedly lower mortality in post-cardiac surgery patients. Therefore, this pioneering study represents a crucial step toward establishing the SCAI Shock Classification as the international standard for assessing and communicating shock severity.
REFERENCE:
Roeschl T, Hinrichs N, Hommel M, Pfahringer B, Balzer F, et al. Systematic Assessment of Shock Severity in Postoperative Cardiac Surgery Patients. J Am Coll Cardiol. 2023 Oct 24;82(17):1691-1706. doi: 10.1016/j.jacc.2023.08.031.
