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Introduction
The prevalence of diabetes in patients undergoing cardiac surgery has increased each year during the past four decades (Raza, Sabik, Ainkaran, & Blackstone, 2015 ). Among patients undergoing coronary artery bypass grafting (CABG), about 30% to 50% of patients have a history of diabetes (McAlister, Man, Bistritz, Amad, & Tandon, 2003; Raza et al., 2015; Schmeltz et al., 2007 ), and 60% to 90% of them develop hyperglycemia during the perioperative period (McAlister et al., 2003; Schmeltz et al., 2007; Umpierrez et al., 2015 ). Diabetes has been identified as independent risk factors of morbidity and mortality after cardiac surgery (Carson et al., 2002; Furnary et al., 2003; Thourani et al., 1999 ). Patients with diabetes have worse surgical outcomes when compared to those without diabetes; specifically higher mortality, deep sternal wound infections, renal failure, postoperative strokes, and longer hospital stay (Carson et al., 2002; Furnary et al., 2003; Guvener, Pasaoglu, Demircin, & Oc, 2002; Herlitz et al., 2000; Thourani et al., 1999 ), as well as increased resource utilization and hospitalization costs (Estrada, Young, Nifong, & Chitwood, 2003; Greco et al., 2016; Raza et al., 2015 ).
During the past decade, there has been ongoing debate about the benefits of intensive glycemic control in cardiac surgery patients. Many observational studies have reported that intensive control reduces the number of hospital complications, shorter length of stay, and lower mortality in intensive care unit (ICU) and cardiac surgery patients (Cunningham, Daoud, Baimbridge, Baimbridge, & Abdelnour, 2013; Estrada et al., 2003; Furnary et al., 2003; Gandhi et al., 2007 ). The results of randomized controlled trials; however, have reported controversial results; with some showing a reduction in complications with intensive glucose control (Hruska, Smith, Hendy, Fritz, & McAdams, 2005; Lazar et al., 2004; van den Berghe et al., 2001 ) and others reporting no differences in outcomes (Finfer et al., 2009; Kansagara, Fu, Freeman, Wolf, & Helfand, 2011; Lazar et al., 2011 ). Adding to the controversy, our group and others recently reported heterogeneity in the treatment effect according to diabetes status in cardiac surgery patients, reporting no differences in the rate of perioperative complications among patients with diabetes treated with intensive or conservative regimens, but...