Preoperative predictors of conversion as indicators of local inflammation in acute cholecystitis: strategies for future studies to develop quantitative predictors

Background: Observational studies have identified risk factors for conversion from laparoscopic to open cholecystectomy in acute cholecystitis. The aim of this study is to evaluate the reliability of these predictors and to identify sources of heterogeneity in the studies. Methods: OVID was searched for papers published from 1995 to 2016. Studies with more than 100 patients were included. Risk factors for conversion were abstracted and categorized by statistical significance. Results: Eleven studies were evaluated. Inflammation with difficulty in anatomic identification was the most common reason of conversion. Because of heterogeneity among studies a quantitative approach was not possible. Therefore, qualitative analysis using a heat map was performed along with investigation into sources of heterogeneity with the aim of creating a framework for future quantitative studies. Age, maleness, and white blood cell count were most commonly identified predictors of conversion. Sources of heterogeneity were criteria for diagnosis of acute cholecystitis, selection of patients for laparoscopic cholecystectomy, selection of variables and variations in their thresholds. Conclusions: In acute cholecystitis, inflammation is the most common reason for conversion. Age, maleness and white blood cell count are common predictors of conversion. Large scale prospective studies with minimal heterogeneity are needed to establish validity of these and other predictors.