POSSUM models in open abdominal aortic aneurysm surgery

Area of Science:

• Vascular Surgery
• Surgical Outcomes Research
• Health Services Research

Background:

• Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity (POSSUM) and its variants (Portsmouth POSSUM, Vascular POSSUM) are used to predict mortality in surgical patients.
• The applicability of these established scoring systems to patients undergoing open Abdominal Aortic Aneurysm (AAA) repair, encompassing both elective and emergency procedures, requires evaluation.

Purpose of the Study:

• To assess the validity of POSSUM, Portsmouth POSSUM, and Vascular POSSUM in predicting mortality for open AAA repair.
• To develop and test a new local model (Cambridge POSSUM) using logistic regression if existing models prove inadequate.

Main Methods:

• Prospective collection of POSSUM data for 452 patients undergoing elective and emergency open AAA repair over eight years.
• Comparison of observed operative mortality rates with predictions from POSSUM, P-POSSUM, V-POSSUM, and the newly developed Cambridge POSSUM.

Main Results:

• Vascular POSSUM (physiology only) showed a significant lack of fit in predicting mortality.
• All other models, except V-POSSUM, demonstrated a significant lack of fit.
• The locally developed Cambridge POSSUM model successfully described mortality for both elective and ruptured AAAs with good discrimination (c-index=0.880).

Conclusions:

• Standard POSSUM, V-POSSUM, and P-POSSUM may not be reliable for comparing mortality across different populations undergoing elective and emergency open AAA repair.
• The validated Cambridge POSSUM offers a unified and robust model for predicting mortality in both elective and emergency open AAA repair.
• Further validation of the Cambridge POSSUM in diverse geographical settings is recommended.