• J S Nagabhushan, S Srinath, F Weir, W J Angerson, B A Sugden, and C G Morran.
• Department of Surgery, Crosshouse Hospital, Kilmarnock, UK. nags1970@aol.com
• Postgrad Med J. 2007 May 1;83(979):355-8.

BackgroundP-POSSUM (Physiological and Operative Severity Score for the enumeration of Mortality and morbidity) predicts mortality and morbidity in general surgical patients providing an adjunct to surgical audit. O-POSSUM was designed specifically to predict mortality and morbidity in patients undergoing oesophagogastric surgery.AimTo compare P-POSSUM and O-POSSUM in predicting surgical mortality in patients undergoing elective oesophagogastric cancer resections.MethodsElective oesophagogastric cancer resections in a district general hospital from 1990 to 2002 were scored by P-POSSUM and O-POSSUM methods. Observed mortality rates were compared to predicted mortality rates in six risk groups for each model using the Hosmer-Lemeshow goodness-of-fit test. The power to discriminate between patients who died and those who survived was assessed using the area under the receiver-operator characteristic (ROC) curve.Results313 patients underwent oesophagogastric resections. 32 died within 30 days (10.2%). P-POSSUM predicted 36 deaths (chi2 = 15.19, df = 6, p = 0.019, Hosmer-Lemeshow goodness-of-fit test), giving a standardised mortality ratio (SMR) of 0.89. O-POSSUM predicted 49 deaths (chi2 = 16.51, df = 6, p = 0.011), giving an SMR of 0.65. The area under the ROC curve was 0.68 (95% confidence interval 0.59 to 0.76) for P-POSSUM and 0.61 (95% confidence interval 0.50 to 0.72) for O-POSSUM.ConclusionNeither model accurately predicted the risk of postoperative death. P-POSSUM provided a better fit to observed results than O-POSSUM, which overpredicted total mortality. P-POSSUM also had superior discriminatory power.

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