Neutrophil to Lymphocyte Ratio is a Prognosis Factor for Post-Operative Pneumonia in Aneurysmal Subarachnoid Hemorrhage Patients
Aneurysmal subarachnoid hemorrhage (aSAH) remains a life-threatening condition associated with high morbidity and mortality. One of the significant non-neurologic complications in aSAH patients is post-operative pneumonia (POP), which can occur in up to 13% to 37% of patients after surgical treatment. Despite extensive studies and improvements in critical care, predicting POP remains challenging. This study aimed to assess the feasibility of using the admission neutrophil to lymphocyte ratio (NLR) as a predictor of POP in aSAH patients.
Introduction
aSAH is a severe medical condition often complicated by non-neurologic issues such as POP. The occurrence of POP can significantly worsen patient outcomes both during hospitalization and after discharge. While several risk factors for POP have been identified, including age, severity of aSAH, ventilator use, and congestive heart failure, a reliable clinical predictive model has yet to be established. The severity of aSAH, assessed by the World Federation of Neurosurgical Societies (WFNS) grade, is known to correlate with POP. However, early prediction of POP risk could facilitate optimized care and improve patient outcomes.
The NLR, a marker of systemic inflammation, has been shown to predict clinical prognosis in various conditions, including ischemic and hemorrhagic stroke, stroke-associated pneumonia, and community-acquired pneumonia. However, the relationship between NLR and POP following aSAH has not been thoroughly investigated. This study sought to explore this connection and evaluate the predictive value of NLR for POP in aSAH patients.
Methods
This study was conducted in accordance with the Declaration of Helsinki and approved by the local Ethics Committee of the First Affiliated Hospital of Fujian Medical University. Informed consent was obtained from all patients or their authorized legal representatives.
Study Population
Patients with aSAH admitted to the Department of Neurosurgery of the First Affiliated Hospital of Fujian Medical University between January 2013 and June 2018 were prospectively enrolled. Inclusion criteria included: confirmed SAH due to intracranial aneurysm via computed tomography angiography (CTA) or digital subtraction angiography (DSA), admission blood cell counts data, admission within seven days of symptom onset, and undergoing clipping or coiling of the aneurysm. Exclusion criteria included: age under 18 years, pre-admission pneumonia diagnosis, prior use of steroids or immunosuppressants, history of other neurological diseases, systemic diseases such as autoimmune disease or cancer, and refusal to sign informed consent.
Patient Management
Clinical management followed guidelines from the American Heart Association and American Stroke Association, and critical care management followed guidelines from the Neurocritical Care Society. Pre-operative prophylactic antibiotics were administered according to local antibiotic stewardship committee recommendations.
Clinical Variables
Comprehensive data, including medical history, clinical admission status, imaging, and treatment received, were collected. The severity of aSAH was assessed using the WFNS grade and modified Fisher scale. White blood cell (WBC) differential counts were obtained at admission, and NLR was calculated as the neutrophil count divided by the lymphocyte count. POP was diagnosed based on modified Centers for Disease Control and Prevention criteria within 30 days post-surgery.
Statistical Analysis
Statistical analysis was performed using SPSS 17.0 and R statistical software. Continuous variables were expressed as mean ± standard deviation and analyzed using the t-test. Categorical variables were expressed as counts (percentage) and analyzed using the Pearson chi-square test or Fisher’s exact test. Multivariate Cox regression was used to calculate hazard ratios and 95% confidence intervals (CIs). Kaplan-Meier analysis was used to assess 30-day POP survival rates, and receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive value of NLR.
Results
Patient Characteristics
A total of 711 patients were included, with 219 (30.8%) developing POP. Patients with POP had significantly higher NLR than those without (14.11 ± 8.90 vs. 8.80 ± 5.82, P < 0.001). Multivariate analysis revealed that NLR remained a significant independent predictor of POP after adjusting for age, WFNS grade, endovascular treatment, and ventilator use. The predictive value of NLR increased when combined with WFNS grade (P = 0.011).
NLR and POP
NLR was significantly associated with POP, with higher NLR values correlating with increased POP risk. ROC curve analysis identified an NLR threshold of 10.04 for predicting POP, with a sensitivity of 63.5% and specificity of 70.7%. Patients with NLR >10 had a significantly higher incidence of POP than those with NLR ≤10 (40.00% vs. 24.65%, P < 0.001).
POP Survival Analysis
Kaplan-Meier analysis showed that patients with NLR >10 had significantly worse 30-day POP survival rates than those with NLR ≤10, regardless of WFNS grade. Among good-grade patients (WFNS Grade 10 had a significantly lower survival rate than those with NLR ≤10 (69.32% vs. 85.05%, P 10 had a significantly lower survival rate than those with NLR ≤10 (21.30% vs. 43.59%, P = 0.014).
Discussion
This study demonstrated that NLR is a valuable predictor of POP in aSAH patients. Higher NLR values were associated with increased POP risk, and NLR combined with WFNS grade provided enhanced predictive value. The ease of obtaining NLR from routine blood cell counts makes it a practical tool for early prognosis and risk stratification.
The potential connection between NLR and POP may be explained by several factors. First, aSAH can trigger systemic inflammatory responses, leading to neutrophil activation and lymphocyte apoptosis, increasing susceptibility to infections. Second, NLR may serve as a marker for severe aSAH, which is closely associated with POP. Third, elevated NLR could indicate sub-clinical infections, even in the absence of pre-admission pneumonia.
Limitations
This study has several limitations, including its observational design and potential selection bias. The relatively high POP occurrence rate (30.80%) may be due to the inclusion of both possible and confirmed POP cases. Additionally, the study was based on single-center data, and further research is needed to validate the findings and explore the relationship between NLR changes over time and POP onset.
Conclusion
NLR is a useful predictor of POP in aSAH patients, providing a simple and cost-effective method for identifying high-risk individuals. The combination of NLR and WFNS grade enhances predictive accuracy, aiding in early intervention and improved patient outcomes. Future large-scale studies are needed to confirm these findings and evaluate the effectiveness of NLR-based prediction models in clinical practice.
doi.org/10.1097/CM9.0000000000001304
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