Abstract
<title>Abstract</title> <p> <bold>Objective</bold> To assess preoperative NLR as a predictor of PONV after lumbar spine surgery; validate NLR ≥ 2.0 as an inflammatory threshold for PONV risk; and characterize the NLR–PONV dose–response relationship. <bold>Methods</bold> We analyzed 220 patients who underwent lumbar spine surgery. Using a prespecified NLR cutoff of 2.0—based on prior non-spine surgical evidence—we divided them into low-NLR (< 2.0, n = 110) and high-NLR (≥ 2.0, n = 110) groups without matching or balancing. Restricted cubic spline regression (3 knots at 10th, 50th, 90th percentiles) assessed nonlinearity. Multivariable logistic regression adjusted for age, sex, blood loss, and surgery duration. Internal validation used 1,000 bootstrap resamples. Primary outcome: PONV within 24 hours postoperatively. <bold>Results</bold> Overall PONV incidence was 33.6% (74/220). High-NLR patients had higher PONV rates than low-NLR patients (47.3% vs. 20.0%; P < 0.001). After adjustment, NLR ≥ 2.0 remained strongly associated with PONV (OR = 5.85; 95% CI: 2.79–12.26; P < 0.001). RCS revealed a J-shaped association (P for nonlinearity = 0.004), with inflection near NLR = 2.0. The finding held in bootstrap validation. Postoperative NLR showed an S-shaped pattern, but causality is uncertain due to timing ambiguity. Preoperative CRP, ESR, and PCT showed no significant association with PONV after adjustment. <bold>Conclusion</bold> Preoperative NLR ≥ 2.0 independently predicts PONV after lumbar spine surgery in a J-shaped pattern—supporting its role as a biologically plausible inflammatory threshold. Prospective validation in larger cohorts is needed before clinical use. The study was prospectively registered with the National Library of Medicine (NCT06127966; registration date: October 29, 2023) </p>