BackgroundMinimally invasive approaches to liver resection (MILR) are associated with favorable outcomes. The aim of this study was to determine the implications of conversion to an open procedure on perioperative outcomes.MethodsPatients who underwent MILR at 10 North American institutions were identified from the Americas Minimally Invasive Liver Resection (AMILES) database. Outcomes of patients who required conversion were compared to those who did not. Additionally, outcomes after conversion due to unfavorable findings (poor visualization/access, lack of progress, disease extent) versus intraoperative events (bleeding, injury, cardiopulmonary instability) were compared.ResultsOf 1675 patients who underwent MILR, 102 (6.1%) required conversion. Conversion rate ranged from 4.4% for left lateral sectionectomy to 10% for right hepatectomy. The primary reason for conversion was unfavorable findings in 67 patients (66%) and intraoperative adverse events in 35 patients (34%). By multivariable analysis, major resection, cirrhosis, prior liver surgery, and tumor proximity to major vessels were identified as risk factors for conversion (p < 0.05). Patients who required conversion had higher blood loss, transfusion requirements, operative time, and length of stay, (p < 0.05). They also had higher major complication rates (23% vs. 5.2%, p < 0.001) and 30-day mortality (8.8% vs. 1.3%, p < 0.001). When compared to those who required conversion due to unfavorable findings, patients who required conversion due to intraoperative adverse events had significantly higher major complication rates (43% vs. 14%, p = 0.012) and 30-day mortality (20% vs. 3.0%, p = 0.007).ConclusionsConversion from MILR to open surgery is associated with increased perioperative morbidity and mortality. Conversion due to intraoperative adverse events is rare but associated with significantly higher complication and mortality rates, while conversion due to unfavorable findings is associated with similar outcomes as planned open resection. High-risk patients may benefit from early conversion in a controlled fashion if difficulties are encountered or anticipated.