Preoperative Neutrophil and Lymphocyte Ratio as a Predictor of Mortality and Morbidity After Cardiac Surgery

Background Inflammatory markers, such as neutrophils and lymphocytes, for risk stratification of postoperative morbidity and mortality in patients with cardiovascular disease may provide benefit for patient selection for cardiac surgery. This study aimed to investigate the association between preoperative neutrophil to leucocyte ratio (NLR) after cardiac surgery. Methods A retrospective study from September 2014 to November 2017 undergoing cardiac surgery at Waikato Hospital was conducted. Preoperative haematological profiles, patient factors and primary and secondary endpoints were obtained. The primary endpoint was 30-day new postoperative atrial fibrillation requiring treatment, new neurological insult, readmission within 30 days and 30-day mortality. The secondary endpoint was long-term all cause mortality. Results Of the 1,694 patients included in the study, 21% (356/1,694) of patients had new atrial fibrillation (AF), 3.0% (51/1,694) strokes, 10.6% (180/1,694) readmissions and 2.8% (47/1,694) deaths within 30 days were observed. Receiver operator curve (ROC) returned a cut-off value of NLR equal to or greater than 3.23 (high NLR) to be associated with greatest mortality. Subsequently, a high NLR was compared to the endpoints. High NLR was associated with higher postoperative (p<0.001) and discharge creatinine, longer ICU stay (p=0.012), prolonged intubation and ventilation (p<0.001), new neurological status (p=0.002) and increased risk of returning to theatre (p=0.009). After logistic regression, high NLR was associated with increased mortality (OR 3.36, p=0.001). Conclusions The interpretation and utilisation of readily available haematological markers can provide further risk stratification data to the surgeon when considering the postoperative cardiac surgery risks.