CLINICAL AUDIT

Comparison of P-POSSUM and O-POSSUM in predicting mortality after oesophagogastric resections

J S Nagabhushan¹, S Srinath¹, F Weir¹, W J Angerson², B A Sugden¹, C G Morran¹

¹ Department of Surgery, Crosshouse Hospital, Kilmarnock, UK
² University Department of Surgery, Glasgow Royal Infirmary, Glasgow, UK

Correspondence to:
Correspondence to:
MrJ S Nagabhushan
Department of HPB Surgery, Glasgow Royal Infirmary, 16, Alexandra parade, Glasgow, G31 2ER, UK; nags1970{at}aol.com

Background: P-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.

Aim: To compare P-POSSUM and O-POSSUM in predicting surgical mortality in patients undergoing elective oesophagogastric cancer resections.

Methods: Elective 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.

Results: 313 patients underwent oesophagogastric resections. 32 died within 30 days (10.2%). P-POSSUM predicted 36 deaths (² = 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 (² = 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.

Conclusion: Neither 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.

Abbreviations: AUC, area under the receiver–operator characteristic curve; H–L, Hosmer–Lemeshow; POSSUM, Physiological and Operative Severity Score for the enumeration of Mortality and morbidity; ROC, receiver–operator characteristic; SMR, standardised mortality ratio

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