The published POSSUM predictor equation overpredicted mortality by a factor of more than two, especially in low-risk patients, and required modification to fit observed mortality rates.
Observational (n=1,485)
Does the published POSSUM surgical scoring system accurately predict mortality in general surgical patients?
The published POSSUM mortality predictor equation significantly overpredicts mortality in general surgical patients, particularly in low-risk patients, and requires local modification for accurate surgical audit.
POSSUM (Physiological and Operative Severity Score for the enUmeration of Morbidity and mortality) has been studied as a possible surgical audit system for a 9-month interval using a sample of 28 per cent of the general surgical workload. Mortality or survival was analysed as an endpoint. In this sample the published POSSUM predictor equation for mortality overpredicted deaths by a factor of more than two. The bulk of the overprediction occurred in the group at lowest risk (predicted mortality 10 per cent or less), in which death was overpredicted by a factor of six. This is the most important group for audit purposes since it contains the majority of surgical patients and is composed of fit patients undergoing minor surgery. The published predictor equation for mortality returns a minimum predicted mortality of 1.08 per cent, clearly far higher than that expected for a fit patient having minor surgery. Logistic regression was done on a set of 1485 surgical episodes to generate a local predictor equation for mortality. This process gave a predictor equation that fitted well with the observed mortality rate and gave a minimum predicted risk of mortality of 0.20 per cent. The previously published POSSUM predictor equation for mortality performed badly when tested using a standard test of goodness of fit for logistic regression and must be modified.
Whiteley et al. (1996) conducted an observational in General surgical patients (n=1,485). POSSUM surgical scoring system vs. Observed mortality was evaluated on Mortality or survival. The published POSSUM predictor equation overpredicted mortality by a factor of more than two, especially in low-risk patients, and required modification to fit observed mortality rates.