POSSUM Score

Physiological and Operative Severity Score for Enumeration of Mortality and Morbidity

POSSUM uses 12 physiological and 6 operative factors to predict 30-day morbidity and mortality in general surgical patients. Widely validated across surgical specialties. Use worst pre-operative values for physiological score.

Surgical RiskPerioperativeMortality Prediction

POSSUM Calculator

Physiological Score (12 factors)

Age

Cardiac history

Respiratory history

ECG

Systolic BP (mmHg)

Heart Rate (bpm)

Haemoglobin (g/dL)

WBC (× 10⁹/L)

Urea (mmol/L)

Sodium (mmol/L)

Potassium (mmol/L)

Glasgow Coma Scale

Operative Score (6 factors)

Operative severity

Number of procedures

Intraoperative blood loss (mL)

Peritoneal contamination

Malignancy

Urgency of surgery

—

Morbidity %

—

Mortality %

POSSUM Equations

Morbidity:
ln(R / 1−R) = −5.91 + (0.16 × PS) + (0.19 × OS)

Mortality:
ln(R / 1−R) = −7.04 + (0.13 × PS) + (0.16 × OS)

Where R = predicted probability. Solve: R = e^logit / (1 + e^logit)

PS (Physiological Score) ranges 12–88. OS (Operative Score) ranges 6–48. Total POSSUM = PS + OS.

Interpretation

Predicted Mortality	Risk Level	Action
< 5%	Low	Routine surgical care
5–10%	Intermediate	Enhanced recovery, HDU consideration
> 10%	High	ICU planning, consent discussion, anaesthetic review

POSSUM tends to overestimate mortality at low risk levels. P-POSSUM (Portsmouth modification) corrects this — use P-POSSUM for mortality prediction in low-risk patients.

Clinical Application

Timing: Calculate using worst pre-operative values for PS; OS is completed after surgery for retrospective audit, or estimated pre-operatively for consent.
Audit tool: POSSUM is the gold standard for surgical audit — compare observed vs. predicted morbidity/mortality (O:E ratio) across surgeons/units.
Consent: Predicted morbidity % can be shared with patients as part of informed consent; quote as a range rather than a point estimate.
Subspecialty variants: CR-POSSUM (colorectal), O-POSSUM (oesophageal), and Vascular POSSUM exist for more accurate specialty-specific prediction.
P-POSSUM: Use Portsmouth POSSUM for mortality prediction — it corrects POSSUM's overestimation at low risk. POSSUM morbidity prediction remains valid and widely used.

References

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

POSSUM Score

POSSUM Equations

Interpretation

Clinical Application

References

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