POSSUM, is the Physiologic and Operative Severity Score for the enUmeration of Mortality and morbidity.
Along with the Portsmouth revision (p)-POSSUM, and colorectal (Cr)-POSSUM, these scoring systems have been developed in the United States as audit tools to compare outcomes in surgical and colorectal patients on the basis of operative risk assessment.
Writing from the Department of Colorectal Surgery at the Cleveland Clinic Foundation and the Quality Institute, Cleveland Clinic Health System, both in Cleveland, Ohio, Anthony J. Senagore and colleagues have carried out an evaluation of the applicability of these systems to a cohort of colon cancer patients undergoing surgery in the United States.
The researchers prospectively collected POSSUM factors from 890 consecutive patients undergoing major surgical procedures for colon cancer in 9 United States hospitals over a 2-year period from January 2000 through to December 2001.
The observed over the expected hospital mortality was then compared by means of the POSSUM, p-POSSUM, and Cr-POSSUM scoring systems.
The Cr-POSSUM appeared to be the most promising audit tool for colorectal cancer surgery
The effect of missing data on the utility of this process for outcome assessment was also assessed with 3 methods for data imputation.
Analysis of the data showed that the number of resections per institution ranged from 13 to 437, with the observed mortality rate ranging from 0.8% to 15.4%, with an overall operative mortality of 2.3%.
The POSSUM, p-POSSUM, and Cr-POSSUM predicted mortality was 10.7%, 11.2%, and 4.9%, respectively.
This meant that the POSSUM and p-POSSUM models over-predicted mortality in all institutions, whereas the Cr-POSSUM demonstrated an observed over expected hospital mortality ratio of >1 in 3 institutions.
The calculations were unaffected by the various methods of inserting missing data.
Commenting on the findings, Dr Senagore observed that an apparent over-prediction of mortality for colon cancer resection was evident with all three POSSUM variants.
"This implies that a calibration process is required for use of these variants in the United States health care system," he said, adding that their analysis showed that missing data may be treated as normal values without influencing outcome.
"The Cr-POSSUM appeared to be the most promising audit tool for colorectal cancer surgery", he concluded.
"However, it will require further refinement to provide process control graphs for identification of potential outliers and improvement in the quality of care in the United States".