Post-operative care

Classifying complications – from minor to major

The list of post-operative complications is long. Most common are fever, chest infection, pneumonia, wound infection, bleeding or deep vein thrombosis. As these post-surgical complications can range from minor, self-limiting problems to major life-threatening events, their definition and severity staging can be challenging.

Daryl J Kor
Daryl J Kor

Therefore, new and reliable definitions and classification systems are needed that allow for systematic strategies to identify, prevent and manage post-operative problems.

The work of ISICEM-referent Dr Daryl J Kor, a physician in the Department of Anaesthesiology Department, Division of Critical Care Medicine at Mayo Clinic, Rochester, USA, is dedicated to the prevention of acute lung injury after surgery. His efforts centre on two key aims: Identification of high-risk patient populations with advanced modelling techniques and the identification of intermediate biologic markers that accurately and reliably predict the development of the fully established syndromes. 

To begin defining risks for adverse postoperative events, he believes the first key step is to specifically define what are the complications of interest. To this end he says, ‘The term “postoperative complication” is very generic and non-descript. When attempting to study risk profiles for postoperative complications, it is essential to understand the specific population of interest. Moreover, it is critical to define very clearly the specific complication or complications that one intends to study.’

One more elaborated definition of the term was provided in 2008 by Daniel K. Sokol and James Wilson who described it as ‘‘an undesirable, unintended, and direct result of an operation affecting the patient which would not have occurred had the operation gone as well as could reasonably be hoped.’’ (Sokol DK, Wilson J; World J Surg, Vol. 32, Nr. 6). In the recent past, there have been some efforts to extend the general definition of major vs. minor complications. 

At the Mayo Clinic in Rochester, Dr Kor and his colleagues typically go with what the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) defines for major postoperative events – primarily, because it has the greatest history of previous literature. ACS NSQIP collects data on approximately 130 variables, including preoperative risk factors, intra-operative variables, and 30-day postoperative mortality and morbidity outcomes. ‘In addition to providing specific definitions for a variety of adverse postoperative events, the NSQIP programme also classifies complications into categories of major and minor. Still, these categorisations are somewhat arbitrary and, in order to significantly improve the accurate identification of high-risk cohorts for potential therapeutically strategies, it is of vital importance to classify specific complications in an objective and reproducible manner,’ Dr Kor says. To this end, in the US Center for Medicare & Medicaid Services is working to refine the classification of major versus minor postoperative complications. 

A second method for classifying postoperative complications is based on the extent of therapies required to treat the complication. This system, termed the Clavien-Dindo Complications Classification, is named after its inventors Pierre A Clavien and Daniel Dindo from the Department of Surgery, University Hospital Zurich, Switzerland. Their classification system grades the variety of complications by invasiveness, extent of surgical procedure etc. ‘One of the strengths of this new classification system is that it removes some of the subjectivity
that exists in alternative complication staging systems. In addition, it tends to stage the severity of a postoperative complication in a manner that is most understandable from the patients’ perspective.

Patients may not understand or appreciate the importance of a diagnosis of “anastomotic leak”, but they do understand its importance when they learn that it will require a return to the operating room’, says Dr Kor. ‘It’s only when the definitions and classifications are well-defined that we can meaningfully start to evaluate and model risk for the development of specific post-operative complications’, Dr Kor says, explaining that there are three key domains that need to be considered in the context.

First comes the pre-operative setting: ‘It has been replicated in multiple studies that the baseline health status and the specific surgical procedure the patient is undergoing are very strong predictors of who ultimately will develop a serious postoperative complication.’ The second domain is the intraoperative environment. Events occurring in the OR can either increase or decrease the pre-operative risk profile to develop a major postoperative problem.

While for certain complications it is quite clear that there are specific intra-operative events that encourage risk, e.g. longer surgical procedures, extent of fluid resuscitation, or aggressive transfusion practice, this area is nevertheless lacking data determining what specific role the intra-operative course really plays in determining who will develop postoperative complications or not. The third domain of risk modification is the postoperative period.

‘Fortunately,’ he says, ‘we have identified some interventions in the postoperative period that indeed do reduce the risks for complications. For instance, we know that the early removal of urinary and central venous catheters will reduce the incidence of urinary tract and catheter-related blood stream infections. ‘However, significant knowledge gaps remain and to make further progress, two key steps will be required. First, we must continue to refine our understanding regarding what aspects of a patient’s baseline health status and the care delivery process are associated with risk for complications of interest. Once this has been more precisely defined, we can then start to evaluate specific strategies to mitigate those risks.

As an example, we have come to believe that aggressive transfusion and fluid resuscitation practices are associated with a complication known as acute lung injury. By attempting to modify provider’s transfusion and fluid resuscitation practices, we can hope to mitigate the development of postoperative acute lung injury.’ Thus, Dr Kor’s own clinical research is attempting to better understand the impact of transfusion practice on patient outcomes. One of his goals is to improve the understanding of the risks associated with blood product administration.


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