The systemic immune-inflammation index is associated with early postoperative morbidity and mortality following cardiac surgery

Abstract Background The pathogenesis of cardiovascular diseases (CVD) is sustained by persistent low-grade systemic inflammation. Lipid deposition, atherosclerotic plaque formation, toll-like receptor activation, leukocyte infiltration and secretion of pro-inflammatory mediators collectively promote chronic low-grade inflammation which drives CVD-progression. Despite the well-described inflammatory processes in CVD, its perioperative clinical significance in cardiac surgery is ill-defined. Aim To evaluate the association between the preoperative chronic inflammation and postoperative outcome. We hypothesized that an elevated systemic inflammation predisposes patients to adverse postoperative outcome. Methods A retrospective analysis of 1251 consecutive adults undergoing cardiac surgery between July 2018 and Dec 2019. We used the systemic-immune-inflammation index (SII) as a marker for chronic inflammation and was calculated as follows: “platelet counts x (Neutrophil/Lymphocyte ratio)”. A Receiver Operating Characteristic (ROC) curve was generated by plotting the SII values for in-hospital mortality cases vs successfully discharged patients, the Wilcoxon estimate of area under ROC curve = 0.67; an optimum cut-off point of 647 (sensitivity = 0.72, specificity = 0.59) was chosen to classify patients with an elevated inflammatory status. We used the Fisher's exact test to assess whether the preoperative SII was related with adverse outcome. Finally, we included the SII in a multivariable logistic regression controlling for 11 established cardiac surgery mortality risk-factors. Results The median age was 65 years (range 18–88), 361 (29%) were females. The mean ACEF II operative mortality was 3.49%. The median SII before surgery was 576 (IQR 402 - 855). In comparison, the SII of a healthy control non-surgical cohort (N=60) was 434 (IQR 290–559), median difference = 142 [CI95% 84 to 223), p<0.0001. Sub-group analysis revealed that patients who passed away during hospitalisation were admitted with a significantly higher preoperative SII (= 824), median difference 255 [CI95% 143–388], p<0.0001, compared to those patients who were successfully discharged, SII = 569. Contrary to patients with low-grade systemic inflammation (= SII <647), we observed that patients with an elevated SII (≥647) were more likely to have difficulties coming off-pump, Odds Ratio (OR) 1.73, p=0.007; to experience an infection, OR 1.94, p<0.001, or death during postoperative hospitalisation, OR 3.46, p<0.0001. Multivariable logistic regression revealed that an SII ≥647 is an independent risk factor for in-hospital mortality, adjusted OR 2.67, p=0.004. Conclusion A high SII (≥647) is independently associated with postoperative morbidity and mortality following cardiac surgery. The SII may support clinical decision making and stratification of high-risk patients undergoing cardiac surgery. Funding Acknowledgement Type of funding source: None