External validation of a pre-operative nomogram predicting peri-operative mortality risk after liver resections for malignancy

Aim: A pre-operative nomogram using a population-based database to predict peri-operative mortality risk after liver resections for malignancy has recently been developed. The aim of the present study was to perform an external validation of the nomogram using data from a high volume institution. Methods: The National Inpatient Sample (NIS) database (2000-2004) was used initially to construct the nomogram. The dataset for external validation was obtained from a high volume centre specializing in hepatobiliary surgery. Validation was performed using calibration plots and concordance index. Results: A total of 794 patients who underwent liver resection from the years 2000-2010 at the external institute were included in the validation set with an observed mortality rate of 1.6%. The mean total points for this sample of patients was 124.9 [standard error (SE) 1.8, range 0-383] which translates to a nomogram predicted mortality rate of 1.5%, similar to the actual observed overall mortality rate. The nomogram concordance index was 0.65 [95% confidence interval (CI) 0.46-0.82] and calibration plots stratified by quartiles revealed good agreement between the predicted and observed mortality rates. Conclusions: The present study provides an external validation of the pre-operative nomogram to predict the risk of peri-operative mortality after liver resection for malignancy.