Evaluation of Surgical Audit Systems 'POSSUM and P-POSSUM' in Emergency Digestive Surgery

Masaaki Iwatsuki¹⁾²⁾, Yoshio Haga²⁾, Shigeru Katafuchi²⁾, Satoshi Ikei²⁾ and Hideo Baba¹⁾

Department of Gastroenterological Surgery, Graduate School of Medical Sciences, Kumamoto University¹⁾
Department of Surgery, National Hospital Organization, Kumamoto Medical Center²⁾

Background: We evaluated the accuracy of surgical auditing systems, POSSUM and P-POSSUM, developed in the United Kingdom, in emergency digestive surgery. Patients and Methods: Using POSSUM and P-POSSUM, we calculated expected mortality in 294 patients who underwent emergency digestive surgery from January 2001 to December 2003. In the original literature, the endpoint for POSSUM was defined as 30-day mortality and that for P-POSSUM as the in-hospital mortality. The ratio of observed to expected mortality rates (OE ratio) was defined as a measure of accuracy. Results: Overall morbidity was 20.7%, 30-day mortality 6.5%, and in-hospital mortality 7.1%. POSSUM overpredicted mortality rates at a low-risk band where expected rates were 0 to 49%-observed-rate 2/249, 0.80%, vs. expected rate 33/249, 13.3%: OE ratio 0.061 with 95% confidence intervals (CI) of 0.015-0.25. Expected rates were comparable to observed rates at a high-risk band where expected rates were 50 to 100%-observed-rate 17/45, 37.7% vs. expected rate 23/45, 51.1%; the OE ratio 0.74 with 95% CI of 0.46-1.12. Similarly, P-POSSUM overpredicted mortality rates at a low-risk band where expected rates were 0 to 59%-observed rate 6/267, 2.2% vs. expected rate 24/267, 9.0%: OE ratio 0.23 with 95% CI of 0.094-0.58. In contrast, expected rates were closer to the observed rates at a high-risk band where the expected rates were 60 to 100%-observed rate 15/27, 55.6% vs. expected rate 22/27, 81.5%: OE ratio 0.68 with 95% CI of 0.47-1.00. Conclusion: Current single-center data suggests that both POSSUM and P-POSSUM may overpredict mortality rates in low-risk patients who undergo emergency digestive surgery.

Key words
POSSUM, P-POSSUM, emergency digestive surgery

Reprint requests
Masaaki Iwatsuki Department of Gastroenterological Surgery, Graduate School of Medical Sciences, Kumamoto University
1-1-1 Honjo, Kumamoto, 860-8556 JAPAN

Accepted
September 26, 2007

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