Validation of index-based IWATE criteria as an improved difficulty scoring system for laparoscopic liver resection

The original difficulty scoring system was revised after discussion at the 2nd International Consensus Conference on Laparoscopic Liver Resection held in Morioka (Iwate Prefecture) in Japan and renamed the IWATE criteria (a 4-level classification system involving 6 preoperative factors). We used Japanese and French cohorts to validate the IWATE criteria by evaluating their association with the procedure-based difficulty classification proposed by the Institut Mutualiste Montsouris.Patients who had undergone laparoscopic liver resection at multiple Japanese multi-institutions or the Institut Mutualiste Montsouris were assigned to the multiple Japanese multi-institution (n = 1,867) or Institut Mutualiste Montsouris cohort (n = 433). We analyzed clinical characteristics and outcomes according to the 4-level IWATE criteria difficulties (low, intermediate, advanced, and expert) and evaluated their association with 11 laparoscopic liver resection procedures in the Institut Mutualiste Montsouris classification (low, intermediate, and high levels).We found significant differences in age, surgical indications, and the 4-level IWATE criteria difficulties between the cohorts (all, P.001). Operation time and blood loss were significantly different among the 4-level difficulties in both cohorts (all, P.001). The rates of conversion, postoperative complications, liver failure, and in-hospital deaths also increased significantly with increasing difficulty (all, P.001). The IWATE criteria classified the three low-level Institut Mutualiste Montsouris procedures in the low-to-intermediate levels, the two intermediate-level procedures in the intermediate-to-advanced levels, and the six high-level procedures in the advanced-to-expert levels.We observed associations between the IWATE criteria and intraoperative and postoperative outcomes in the Japanese multi-institution and Institut Mutualiste Montsouris cohorts and thus validated the IWATE system.