possum

POSSUM and P-POSSUM surgical risk scores in R.

POSSUM (the Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity) is a risk-adjustment system used in surgical audit. It scores twelve physiological variables and six operative variables, then predicts morbidity and mortality from logistic equations. P-POSSUM is the Portsmouth recalibration of the mortality prediction.

Install

# install.packages("remotes")
# remotes::install_github("chrislongros/possum")
install.packages("possum", repos = c('https://chrislongros.r-universe.dev', 'https://cloud.r-project.org'))

Use

library(possum)

ps <- possum_physiology(age = 72, systolic_bp = 105, pulse = 96, gcs = 15,
                        hb = 11.2, wbc = 14, urea = 12, sodium = 133,
                        potassium = 4.6, cardiac = 2, respiratory = 2, ecg = 1)

os <- possum_operative(severity = 4, n_procedures = 1, blood_loss = 400,
                       soiling = 2, malignancy = 4, urgency = 1)

possum(ps, os)     # POSSUM morbidity and mortality
p_possum(ps, os)   # P-POSSUM mortality

The objective variables (blood pressure, labs, blood loss, ...) are scored from their raw values; the graded variables (cardiac, respiratory, ECG, operative severity, soiling, malignancy, urgency) are entered as their POSSUM points. See ?possum_physiology and ?possum_operative for the cut-point tables and units.

Sources

• Copeland GP, Jones D, Walters M (1991). POSSUM: a scoring system for surgical audit. British Journal of Surgery 78:355–360.
• Prytherch DR, Whiteley MS, Higgins B, Weaver PC, Prout WG, Powell SJ (1998). POSSUM and Portsmouth POSSUM for predicting mortality. British Journal of Surgery 85:1217–1220.

Scope

This package is for audit and research. It is not a validated medical device, and its output must not be used as the sole basis for any clinical decision. Confirm the cut-points and coefficients against the original papers before use.

The POSSUM equations were derived in the 1990s and 2000s. Perioperative mortality has fallen since then, so on contemporary populations these models tend to over-predict, and are better suited to case-mix–adjusted audit than to individual risk prediction. Newer tools (for example NELA, SORT and, in vascular surgery, VBHOM) may be preferable for the latter.

License

MIT.