Laparoscopic liver resection (LLR) involves a difficult learning curve, for which multiple difficulty scores have been proposed to assist with safe adaptation. The IWATE Criteria is a 4-level difficulty score shown to correlate with conversion to open surgery, estimated blood loss (EBL), and operative time in Japanese and French cohorts. We set out to validate the IWATE Criteria in a North American cohort, describe the evolution of our LLR program, and analyze the IWATE Criteria's ability to predict conversion to open surgery. Methods Patients that underwent LLR between January 2006 and December 2019 were selected from a prospectively maintained database. Difficulty outcomes, including conversion to open surgery, EBL, operative time, and post-operative complications were analyzed according to IWATE difficulty level, both overall and between chronological eras. The IWATE Criteria's ability to predict conversion to open surgery was assessed with a receiver operating characteristic (ROC) analysis. Results
A total of 426 patients met inclusion criteria. Operative time, EBL, and conversion to open surgery increased in concordance with low to advanced IWATE difficulty. ROC analysis for conversion to open surgery demonstrated an overall area under the curve (AUC) of 0.694. Predictive performance was superior during the first two eras, with AUCs of 0.771 and 0.775; predictive value decreased as the LLR program gained experience, with AUCs of 0.708 and 0.551 for eras three and four. Conclusions This study validated the IWATE Criteria in a North American population distinct from previous Japanese and French cohorts, based on its correlation with operative time, EBL, and conversion to open surgery. The IWATE Criteria may be of utility for identification of LLR cases appropriate for surgeon experience, as well as determination of laparoscopic feasibility. Interval difficulty score recalibration may be warranted as surgeon perception of difficulty evolves.