Colorectal Surgery - Outcomes and Scoring

Dermot Burke

Powerpoint File

There are two reasons for the use of a scoring system in surgical practice. The first is to predict the outcome of the proposed management for an individual. This information could possibly influence decisions about treatment e.g. surgical versus conservative management, and has the potential to influence the prioritisation of resources. None of the available scoring systems have sufficient accuracy to be used in this way.

The second reason is to perform stratification of patients by risk of mortality and so allow sensible and meaningful audit. If an adjustment for patients’ risk can be made, to allow for the case-mix, then a fair comparison can be made between either individual surgeons, or more prudently, between surgical units. Such an approach, as was recommended following the Bristol enquiry1, has already come to pass in the discipline of cardiac surgery. Data on mortality rates in the UK following 2 common cardiac operations (CABG and aortic valve replacement) are now freely available at http://heartsurgery.healthcarecommission.org.uk. It is opportune therefore, to explore whether appropriate scoring systems are available for colorectal surgeons.

Scoring systems have been developed in order to assess the risk of specific complications. The risk of both cardiac (2) and pulmonary (3) complications may be assessed with the use of such specific scoring systems. However a lot more work has taken place to identify the overall risk of complications. The ASA grade is an example of a simple system that is still very widely used. The APACHE (Acute Physiology And Chronic Health Evaluation) score was an early attempt to categorise patients and stratify their risk of mortality. This was modified to become the APACHE II, and again to become the APACHE III score. However these scores were developed using data from both medical and surgical patients who had been admitted to intensive care. Their calculation relies upon data collected from a large number of variables over a 24 hour period. They take no account of operative severity. The use of APACHE scores as risk assessment for surgical patients therefore, meant that it was difficult to gather the data in the first place and that no account was paid to the magnitude of the surgical insult. For these reasons it was thought that a method of assessing surgical risk, which was both simple to calculate and took account of the operative findings, was needed.

The POSSUM (Physiological and Operative Severity Score for the Enumeration of Mortality and Morbidity) score is such a method. POSSUM equations for mortality and morbidity were developed by Copeland et al and described in 1991 (4). These equations were to be used to enable the surgeon to predict the overall mortality and morbidity in patients who had undergone surgery. It is important to note that the prediction applies to the overall group (e.g. a group predicted to have a mortality risk of 0-10%) and does not give an individual patient’s risk. Subsequent analysis of data from Portsmouth suggested that mortality was overpredicted by the original POSSUM equation, particularly in patients at low risk. The Portsmouth group suggested a reworking of the original POSSUM mortality equation using their own data, but using the same variables as in the POSSUM equation. This became known as the P-POSSUM equation (5). This, the P-POSSUM equation, predicts mortality only, not morbidity.

Subsequent application of the POSSUM and P-POSSUM equations to patients with general surgical(6) and gastrointestinal(7) conditions respectively confirm that these equations, when applied to a group of surgical patients, have a good predictive value for morbidity and mortality for the group, not for the individual. These papers exemplify the value of the original work by Copeland, as they compare results between surgical teams, and demonstrate that an observed difference in crude mortality and morbidity rates may disappear when allowance is made for operative risk.

A good overview of the scoring systems available was produced by Jones and de Cossart in 1999 (8). Since then, however, subspecialisation has proceeded rapidly within general surgery. The paper by Tekkis et al in 2004 outlined the development of a POSSUM score for patients with colorectal disease (9). This CR-POSSUM uses fewer (10) variables than the original POSSUM equations and was been shown to work well in prediction of outcome in this study. However, when used to predict outcome following surgery for colorectal cancer in the USA all 3 systems (POSSUM, P-POSSUM, CR-POSSUM) were found to overpredict the risk of mortality (10). In patients with colorectal cancer, the Association of Coloproctology (ACPGBI) has developed its own predictive scoring system, based upon the data obtained within the national audit. This compares well when compared with the CR-POSSUM (11). Within the same audit, ACPGBI have developed a predictive model for risk of mortality in patients with malignant bowel obstruction. Leaving aside malignant disease, retrospective data from the Cleveland clinic have been used to try to predict those patients with an ileal pouch whose pouch will fail (12). This model, however, relies heavily on postoperative variables.

In summary, therefore, there are a number of scoring systems that are applicable to patients with colorectal disease and all are now widely available. The development of systems specific to colorectal surgery is a recent innovation that needs to be widely tested. In the current political climate, when outcomes between surgeons are under scrutiny, it would be prudent for surgeons who perform colorectal surgery to make use of one scoring system to allow for their own particular case-mix.

Practicalities
Where to calculate prediction scores
The following scores may be calculated directly at http://www.riskprediction.org.uk:
P-POSSUM, CR-POSSUM,
ACGBI model for mortality prediction in malignant bowel obstruction
Cleveland Clinic Ileal Pouch Failure Model for prediction of ileal pouch failure

Where to download POSSUM software
Download ACCESS 97 database from www.edu.rcsed.ac.uk/lectures/lt1.htm
Download e-POSSUM for use on Palm PDA and Pocket PC at www.gaspalm.co.uk/

References
1 Spiegelhalter DJ, Aylin P, Best NG, Evans SJW, Murray GD. Commissioned analysis of surgical performance by using routine data: lessons from Bristol inquiry. J R Statist Soc (Ser A) 2002;165:1-31

2 Goldman L, Caldera DL, Nussbaum SR, Southwick FS, Krogstad D, Murray B et al.
Multifactorial index of cardiac risk in noncardiac surgical procedures. N Engl J
Med 1977; 297: 845-50

3 Lawrence VA, Dhanda R, Hilsenbeck SG, Page CP. Risk of pulmonary complications
after elective abdominal surgery. Chest 1996; 110: 744-50

4 Copeland GP, Jones D, Walters M. POSSUM: a scoring system for surgical audit. Br J Surg. 1991; 78: 355-360

5 Prytherch DR, Whiteley MS, Higgins B, Weaver PC, Prout WG, Powell SJ. POSSUM and Portsmouth POSSUM for predicting mortality. Physiological and Operative Severity Score for the enUmeration of mortality and morbidity. Br J Surg. 1998; 85: 1217-1220.

6 Sagar PM, Hartley MN, Mancey-Jones B, Sedman PC, May J, Macfie J. Comparative audit of colorectal resection with the POSSUM scoring system. Br J Surg. 1994; 81: 1492-1494

7 Tekkis PP, Kessaris N, Kocher HM, Poloniecki JD, Lyttle J, Windosr ACJ. Evaluation of POSSUM and P-POSSUM scoring systems in patients undergoing gastrointestinal surgery. Br J Surg. 2003; 90: 640-345

8 Jones HJ, de Cossart L. Risk scoring in surgical patients. Br J Surg 1999; 86: 149–57.

9 Tekkis PP, Prytherch DR. Kocher HM. Senapati A, Poloniecki JD, Stamatakis JD, Windsor ACJ. Development of a dedicated risk-adjustment scoring system for colorectal surgery (colorectal POSSUM). Br J Surg 2004: 91; 1174-1182.

10 AJ Senagore, A Warmuth, CP Delaney, PP Tekkis, VW Fazio. POSSUM, p-POSSUM, and the CR-POSSUM: implementation issues in a US healthcare for prediction of outcome for colorectal cancer resection. Diseases of the Colon and Rectum 2004; 47(9);1435-41.

11 Al-Homoud S, Purkayastha S, Aziz O, Smith JJ, Thompson MD, Darzi AW, Stamatakis JD, Tekkis PP Evaluating operative risk in colorectal cancer surgery: ASA and POSSUM-based predictive models Surg Oncol 2004: 13; 83–92.

12 Fazio W, Tekkis PP, Remzi F, Lavery IC, Manilich E, Connor J, Preen M, Delaney CP.. Quantification of risk for pouch failure following ileal pouch anal anastomosis surgery. Ann Surg 2003; 238: 605-17.