Elevated neutrophil-to-lymphocyte ratio as a prognostic marker in postoperative cardiac surgery patients: a retrospective cohort study

Introduction: Cardiovascular diseases are the leading cause of death globally, with a significant burden in low-and middle-income countries.Cardiac surgery poses risk stratification challenges, particularly in specialized cardiovascular intensive care units (ICUs).Traditional severity scores often fail to account for postoperative factors, such as inflammation, which can influence outcomes.The neutrophil-to-lymphocyte ratio (NLR) is a low-cost, easily obtainable marker of systemic inflammation that has shown potential as a prognostic tool in various ICU settings, but its utility in post-cardiac surgery patients remains insufficiently studied.Objective: To evaluate the prognostic value of the NLR ratio in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) admitted to a cardiovascular intensive care unit.Methods: This observational, retrospective study included 545 patients who underwent cardiac surgery with cardiopulmonary bypass (CPB) at Instituto Nacional de Cardiología.The NLR was calculated using neutrophil and lymphocyte counts at ICU admission, with a cutoff of NLR > 4 defining the "high NLR" group.We assessed demographic, clinical, and surgical characteristics, and examined associations between abnormal NLRs and postoperative complications, including length of hospital stay, acute kidney injury (AKI), and mortality.Results: Within the cohort, 136 patients had an elevated NLR.Those with a high NLR had a significantly longer hospital stay (median of 13 vs. 10 days; p = 0.03).Although no differences in mortality or major complications were observed, trends indicated that an elevated NLR was associated with higher rates of AKI and blood transfusions.Conclusions: Elevated postoperative NLR in cardiac surgery patients is associated with longer hospital stays and may serve as a cost-effective tool for risk stratification.Further prospective studies are needed to clarify its predictive role and underlying mechanisms in this population.