Hypoglycemic exposure and glycemic variability are associated with surgical site infection after cardiac surgery

Perioperative hyperglycemia is a recognized risk factor for surgical site infection (SSI) after cardiac surgery. However, the independent contribution of hypoglycemic exposure and glycemic variability remains incompletely defined. We evaluated whether perioperative dynamic glycemic metrics are associated with SSI risk after cardiac surgery independently of chronic glycemic control. We conducted a historical cohort study at a high-volume tertiary referral center. Among 4,425 consecutive adult patients undergoing open cardiac surgery between 2014 and 2022, 462 patients with diabetes or perioperative hyperglycemia and high-density glucose monitoring (≥ 4 measurements/day) were included. Time below range (TBR), time in range (TIR), time above range (TAR), and coefficient of variation (CV) were calculated. The primary outcome was SSI within 90 days, defined using Centers for Disease Control and Prevention (CDC) criteria. Associations were evaluated using logistic regression adjusted for age and sex, with sensitivity analyses including HbA1c and clinical covariates. SSI occurred in 32 patients (6.9%). Patients with SSI had higher CV ( p = 0.0094), higher TBR ( p < 0.0001), higher TAR ( p = 0.0419), lower TIR ( p = 0.0112), and higher HbA1c ( p = 0.0055). In adjusted analyses, CV (OR 1.47 per 5% increase, p = 0.0005) and TBR (OR 1.69 per 1% increase, p < 0.0001) were independently associated with SSI, and any hypoglycemia (TBR > 0) was also associated with higher SSI risk. Higher TIR was associated with lower SSI risk (OR 0.75 per 10% increase, p = 0.0013). After adjustment for HbA1c, TBR and CV remained independently associated with SSI. Perioperative hypoglycemic exposure and greater glycemic variability were strongly and independently associated with SSI after cardiac surgery. These findings support greater attention to glycemic stability and hypoglycemia avoidance, beyond average glycemic control, in perioperative glucose management.