Systemic inflammatory response index improves the prediction of postoperative pneumonia following meningioma resection
Meningiomas are the most common non-malignant tumors of the central nervous system, affecting thousands of people worldwide each year. While surgery remains the gold-standard treatment, one of the most persistent and dangerous complications—postoperative pneumonia (POP)—still threatens patients, even with advances in surgical techniques and post-op care. For clinicians, identifying reliable predictors of POP is critical: early intervention for high-risk patients can mean the difference between a smooth recovery and a life-threatening infection.
Enter the Systemic Inflammatory Response Index (SIRI), a simple tool that uses routine blood test results to track inflammation. First proposed in 2016 to predict survival in cancer patients, SIRI combines three key immune cell counts: neutrophils (cells that fight bacterial infections), monocytes (cells that clear debris and pathogens), and lymphocytes (cells that target viruses and regulate immunity). The formula is straightforward: SIRI = (neutrophils × monocytes) / lymphocytes.
Until now, SIRI’s value in predicting postoperative infections like POP hadn’t been studied in meningioma patients. A new retrospective study from Chinese researchers—published in the Chinese Medical Journal—sets out to change that.
The Study: Who, How, and What They Measured
Led by Yue Chen, Yuan-Xiang Lin, and Wen-Hua Fang (from the First Affiliated Hospital of Fujian Medical University and partner institutions), the team analyzed data from 282 patients who underwent meningioma surgery at three hospitals between 2008 and 2019. To ensure accuracy, they excluded patients with prior infections, long-term steroid use, radiotherapy/chemotherapy, or previous craniotomies. All participants provided informed consent, and the study was approved by the ethics committees of participating hospitals (No. MRCTA, ECFAH of FMU [2020]005).
The team focused on one key outcome: POP within 30 days of surgery, diagnosed using criteria from the U.S. Centers for Disease Control and Prevention (CDC) and its National Healthcare Safety Network (NHSN). They used R statistical software to build a logistic regression model—testing how well SIRI (and other common markers like white blood cells [WBC] and neutrophil-lymphocyte ratio [NLR]) predicted POP. They also used the Kaplan-Meier method to track how many patients developed POP over time.
The Results: SIRI Shines for Non-Elderly Patients
The study’s biggest findings?
- A Clear Cutoff for Risk: The optimal SIRI score to predict POP was 1.85 (×10⁹ cells/L). Patients with SIRI ≥1.85 had a 20% risk of POP, compared to just 3.4% for those with SIRI below 1.85. A power analysis confirmed the results were statistically robust (>99% chance of detecting a true effect).
- Age Matters: SIRI’s predictive power was only significant for non-elderly patients (under 60 years old). For this group, SIRI outperformed two common inflammation markers:
- Area Under the Curve (AUC): A measure of how well a test distinguishes between patients with/without a condition. SIRI had an AUC of 0.874 (excellent), vs. 0.794 for WBC and 0.767 for NLR.
- Negative Predictive Value (NPV): For non-elderly patients with low SIRI, the NPV was over 99%—meaning almost no one in this group developed POP.
In contrast, SIRI didn’t help predict POP in elderly patients (60+). The team suspects this is because older adults often have immune dysfunction, making POP risk more complex and harder to capture with a single marker.
Why SIRI Works—and What It Means for Patients
SIRI’s strength lies in its focus on bacterial inflammation—the main cause of POP. Neutrophils and monocytes spike when the body fights bacteria, while lymphocytes rise in viral infections. By combining these three counts, SIRI reflects underlying inflammation before symptoms like cough or fever appear—exactly what clinicians need to intervene early.
For non-elderly patients, the implications are huge:
- Less Monitoring for Low-Risk Patients: With an NPV over 99%, clinicians can safely reduce monitoring for patients with low SIRI, freeing up resources for those at higher risk.
- Early Intervention for High-Risk Patients: Patients with SIRI ≥1.85 can get preemptive care (like chest physiotherapy or antibiotic prophylaxis) to prevent POP.
Limitations to Keep in Mind
No study is perfect. The team noted several caveats:
- Observational Design: Since the study looked back at existing data, it can’t prove that SIRI causes better outcomes—only that it’s linked to POP risk.
- Confounders: Factors like steroid use or undiagnosed infections could have skewed results.
- Bacterial Bias: SIRI is better at predicting bacterial infections (like most POP cases) but may miss viral ones.
- Small Sample of Centers: The study included only three hospitals, so results may not apply to all populations.
The Bottom Line
For clinicians treating non-elderly meningioma patients, SIRI is a simple, reliable tool to predict POP—better than WBC or NLR. Its high negative predictive value means fewer unnecessary tests for low-risk patients, while its ability to flag high-risk patients enables life-saving early intervention.
As the team writes: “SIRI may be a simple way for clinicians to predict a patient’s risk of POP.” For patients and providers alike, that’s a win.
Chen Y, Lin YX, Pang Y, Zhang JH, Gu JJ, Zhang GQ, Yu LH, Lin Zy, Kang DZ, Ding CY, Fang WH. Systemic inflammatory response index improves the prediction of postoperative pneumonia following meningioma resection. Chin Med J 2021;134:728–730. doi:10.1097/CM9.0000000000001298
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