Background

Pulmonary complications after coronary artery bypass surgery continue to be a significant problem, affecting 5–20% of patients, prolonging hospital stays and increasing costs. In this study, we investigated whether simple blood tests that measure inflammation, such as the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII), could help identify patients at risk before surgery.

Methods

The records of 1034 patients who underwent elective coronary artery bypass grafting with heart-lung machine support between 2023 and 2024 were retrospectively reviewed. NLR, PLR, and SII values were calculated from routine blood tests performed the day before surgery. Patients who developed pulmonary complications were defined according to the European Perioperative Clinical Outcome (EPCO) definitions.

Results

114 patients (11%) developed PPC. Preoperative inflammatory markers were significantly higher in patients with complications (NLR: 3.55 ± 1.07 vs. 1.79 ± 0.54, PLR: 156 ± 47 vs. 120 ± 36, SII: 825 ± 248 vs. 548 ± 164; all p < 0.001). ROC analysis demonstrated excellent discrimination for NLR (AUC 0.939), good for SII (AUC 0.818), and fair-to-good for PLR (AUC 0.724). In multivariate analysis, NLR was by far the strongest independent predictor of PPC, together with COPD, diabetes, active smoking, CPB and ACC durations. PLR and SII also reached statistical significance, but with effect sizes very close to unity (adjusted OR 1.02 and 1.01 respectively), indicating that they offered minimal additional discriminatory value once NLR was taken into account.

Conclusions

In this single-center retrospective cohort, preoperative NLR, PLR and SII were associated with PPC, with NLR accounting for most of the predictive signal. Because they are measured at a single preoperative timepoint, these indices reflect baseline inflammatory tone and cannot capture the acute, surgery-induced inflammatory response that drives postoperative pulmonary complications. In view of the single-center retrospective design, the absence of external validation, and the lack of comparison with validated risk scores such as EuroSCORE II or the STS score, these indices are not yet suitable to guide clinical decision-making on their own. Given their simplicity and ready availability, however, they appear to be promising candidate markers that merit further evaluation in prospective, multicenter studies also incorporating specific inflammatory mediators measured dynamically throughout the perioperative period.