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P-POSSUM

Portsmouth Physiological and Operative Severity Score for Enumeration of Mortality

P-POSSUM uses the same 18 inputs as POSSUM but applies an improved mortality equation that corrects POSSUM's overestimation at low risk levels. The gold standard for surgical mortality prediction.

Surgical RiskMortality PredictionPerioperative
P-POSSUM Calculator
P-POSSUM uses the same inputs as POSSUM but applies the Portsmouth mortality equation, which is more accurate — particularly at low risk levels where POSSUM overestimates mortality.
Physiological Score (12 factors)
Operative Score (6 factors)
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P-POSSUM Predicted Mortality

P-POSSUM Mortality Equation

ln(R / 1−R) = −9.065 + (0.1692 × PS) + (0.1550 × OS)

Mortality % = e^logit / (1 + e^logit) × 100

PS = Physiological Score (range 12–88)
OS = Operative Score (range 6–48)

Compare with POSSUM mortality equation: ln(R/1−R) = −7.04 + (0.13 × PS) + (0.16 × OS). P-POSSUM has a more negative intercept (−9.065 vs −7.04), yielding lower mortality estimates at low PS/OS values — matching observed outcomes better.

P-POSSUM vs POSSUM: Key Differences

FeaturePOSSUMP-POSSUM
Morbidity predictionYes (widely used)Not calculated
Mortality predictionYes (overestimates at low risk)Yes (more accurate)
Derivation cohortMixed general surgicalPortsmouth, UK general surgical
Recommended useMorbidity prediction; auditMortality prediction; consent
Year19911998

Interpretation

P-POSSUM MortalityRiskRecommended Action
< 5%LowStandard consent and perioperative care
5–10%IntermediateExplicit mortality discussion, HDU access
10–25%HighSenior anaesthetic review, ICU bed booking, goals discussion
> 25%Very HighMDT review; consider non-operative alternatives; family meeting

Clinical Application

  • Preferred over POSSUM for mortality prediction, especially in elective and low-risk surgery where POSSUM significantly overestimates risk.
  • Consent tool: Quote P-POSSUM mortality when obtaining consent for major general surgical procedures. Always present as a population estimate, not a guarantee.
  • POSSUM morbidity: Continue to use the POSSUM morbidity equation alongside P-POSSUM — P-POSSUM only calculates mortality.
  • Subspecialty notes: For colorectal surgery, CR-POSSUM may be more appropriate. For oesophageal surgery, O-POSSUM. These have been derived in more homogeneous populations.
  • Audit: Observed-to-expected (O:E) ratios using P-POSSUM are used by HQIP and NHS to benchmark surgical performance.

References

  1. Prytherch DR, et al. POSSUM and Portsmouth POSSUM for predicting mortality. Br J Surg. 1998;85(9):1217–1220.
  2. Copeland GP, Jones D, Walters M. POSSUM: a scoring system for surgical audit. Br J Surg. 1991;78(3):355–360.
  3. Tekkis PP, et al. Evaluation of POSSUM and P-POSSUM scoring systems in colorectal surgery. Br J Surg. 2003;90(3):340–345.

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