Relationship Between Preoperative Neutrophil-to-Lymphocyte Ratio and Patient-Controlled Analgesia Consumption Following Cardiac Surgery: A Retrospective Study

Background The neutrophil-to-lymphocyte ratio (NLR), an inflammatory marker, is known to predict postoperative complications. However, its predictive value for postoperative inflammatory status and postoperative pain (POP) following cardiac surgery remains unclear. This study aimed to determine whether elevated preoperative NLR is associated with increased postoperative analgesic consumption. Methods We retrospectively analyzed patients aged over 18 years who underwent cardiac surgery and received intravenous patient-controlled analgesia (IVPCA) for POP between April 2017 and March 2019. The IVPCA solution contained fentanyl (5 μg/mL), lidocaine (8 mg/mL), ketamine (0.8 mg/mL), and droperidol (50 μg/mL). The primary outcome was the correlation between preoperative NLR and postoperative IVPCA consumption. Patients were categorized into high (> median) and low (< median) preoperative NLR groups. To adjust for baseline differences, propensity score matching was applied. Post-matching, we compared perioperative variables and reassessed the association between preoperative NLR and IVPCA usage. Results A total of 131 patients were included. The median preoperative NLR was 2.29 (IQR: 1.58-3.39). Across all patients, preoperative NLR was not correlated with postoperative IVPCA consumption (ρ = -0.08, P = 0.34). After excluding the patient with the median NLR, 76 patients (38 in each group) remained for analysis post-matching. IVPCA consumption was comparable between the high and low NLR groups (108.6 (77.6-164.0) mL vs. 97.1 (83.1-148.0) mL, P = 0.97). However, patients with higher preoperative NLR had significantly elevated NLR on postoperative days 2 and 3 compared to those with lower preoperative NLR (11.0 (7.8-16.4) vs. 7.4 (6.2-10.8), P = 0.02; and 11.3 (7.5-17.3) vs. 6.6 (3.3-4.6), P = 0.008, respectively). Despite this, preoperative NLR was not associated with any clinical outcomes. Conclusions Preoperative NLR was not predictive of IVPCA consumption or clinical outcomes following cardiac surgery.