Background:
The physiological and operative severity score for the enumeration of mortality and morbidity (possum) and portsmouth possum (p-possum) equations were derived from a heterogeneous general surgical population and have been used successfully as audit tools to provide risk-adjusted operative mortality rates. their applicability to high-risk emergency colorectal operations has not been established.
Methods:
Possum variables were recorded for 1017 patients undergoing major elective (n = 804) or emergency (n = 213) colorectal surgery in ten hospitals. subgroup analysis was performed to investigate the predictive capability of possum and p-possum in emergency and elective surgery and in patients in different age groups.
Results:
The overall operative mortality rate was 7.5 per cent (possum-estimated mortality rate 8.2 per cent; p-possum-estimated mortality rate 7.1 per cent). in-hospital deaths increased exponentially with age. both scoring systems overpredicted mortality in young patients and underpredicted mortality in the elderly (p < 0.001). death was underpredicted by both systems for emergency cases, significantly so at a simulated emergency caseload of 47.9 per cent (p < 0.05).
Conclusion:
There is a lack of calibration of possum and p-possum systems at the extremes of age and high emergency workload. this has important implication in clinical practice, as consultants with a high emergency workload may seem to underperform when these scoring systems are applied. recalibration or remodelling strategies may facilitate the application of possum-based systems in colorectal surgery.