Development and Validation of a Nigeria-Specific Surgical Risk Scoring System for Emergency Abdominal Surgery

Existing surgical risk scoring systems such as POSSUM and P-POSSUM were developed in high-income country populations and have demonstrated poor calibration when applied to Nigerian surgical patients due to differences in comorbidity profiles, physiological presentation, and resource availability. This dissertation develops and validates a Nigeria-specific surgical risk scoring system (NSRSS) for emergency abdominal surgery. A derivation cohort of 1,200 emergency abdominal surgical patients from six teaching hospitals across all geopolitical zones was assembled between 2018 and 2022. Using binary logistic regression with bootstrap internal validation, 12 independent clinical and laboratory predictors of 30-day mortality were identified and weighted into the NSRSS. The model was externally validated in a prospective cohort of 400 patients from three independent hospitals in 2022 to 2023. The NSRSS demonstrated strong discrimination (AUC 0.87) and excellent calibration (Hosmer-Lemeshow p=0.41) in the external validation cohort. POSSUM predicted mortality within an acceptable range in only 58% of patients. Key predictors unique to the Nigerian context included delayed presentation exceeding 48 hours, haemoglobin below 7 g/dL, and absence of intensive care support. The NSRSS is offered as a free-to-use clinical tool and recommends mandatory prospective validation by the Society of Surgeons of Nigeria. Keywords: surgical risk scoring, emergency laparotomy, mortality prediction, Nigeria, POSSUM