The association between lymphocyte-monocyte ratio and postoperative acute kidney injury in patients with acute type A aortic dissection

ATAAD patients undergoing emergency cardiac surgery were recruited from Nanjing First Hospital, Nanjing Medical University. All the patients underwent the surgery within 24 h after the onset of ATAAD. All the ATAAD patients were screened in the intensive care unit (ICU) after surgery and received standard treatments. This study was approved by the Ethics Committee of Nanjing First Hospital, Nanjing Medical University. Informed consent was obtained from participants or their legal representatives. Eligible participants were enrolled in the final analysis if they met the following criteria.

Inclusion criteria:

Exclusion criteria:

All participants enrolled in our study underwent standard assessments of demographic characteristics (age, gender and BMI [body mass index]), past medical history (hypertension, diabetes mellitus, atrial fibrillation, current smoking, coronary heart disease), clinical assessment and baseline laboratory data. Clinical assessment included acute physiology and chronic health evaluation II (APACHE II), European system for cardiac operative risk evaluation (EuroSCORE), systolic blood pressure, diastolic blood pressure, heart rate, operation procedures, blood transfusion, cardiopulmonary bypass (CPB) time, cross-clamp time, deep hypothermic circulatory arrest (DHCA) time, AKI. Baseline laboratory data included serum creatinine (Scr), total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), blood glucose and lactic acid (Lac).

Blood cell counts, including lymphocyte counts and monocyte counts were sampled before emergency cardiac surgery on admission. Then, blood cell counts were analyzed by an auto-analyzer (XE-2100, Sysmex). LMR was calculated as Lymphocyte counts/monocyte counts.

According to the newest consensus-based KDIGO criteria [19], postoperative AKI was defined as (1) small changes in serum creatinine (≥ 0.3 mg/dl or 26.5 mmol/l) when they occurred within 48 h; (2) a maximal change in serum creatinine ≥ 1.5 times the baseline value until postoperative day 7 compared with preoperative baseline values; (3) urine volume < 0.5 ml/kg/h for 6 h. In our study, we did not take urine volume into consideration owing to its inaccuracy, as done in the previous study [7].

After general anesthesia, the arterial blood pressures of both the upper and lower limbs were monitored. For a long time, femoral artery cannulation was the primary choice in ATAAD surgery, the axillary/subclavian arteries (predominantly on the right) are alternative cannulation sites now. In case of hemodynamic instability or severe pericardial tamponade, the femoral artery and femoral vein were used for cannulation and initiation of CPB before sternotomy. Median sternotomy was performed. Right axillary artery and right atrial cannulation was used for CPB and selected cerebral perfusion. A vent catheter via the upper right pulmonary vein was inserted into the left atrium to decompress the left ventricle. Patients were cooled to a nasopharyngeal temperature of approximately 24 °C via CPB. For myocardial protection, an antegrade injection of cold cardioplegic blood solution was used. During the cooling process, the brachiocephalic arteries were exposed, and the proximal aortic surgery was undertaken. When the bladder temperature dropped to 27 °C, the brain continued to be perfused at a rate of approximately 5–10 ml/kg·min through the right axillary artery cannulation. If the right axillary artery was unsuitable for cannulation, the femoral artery was chosen for cannulation, and brachiocephalic arteries were perfused directly for cerebral perfusion during circulatory arrest [20]. The surgical alternatives were numerous, such as limited aortic resection, total aortic arch replacement and stent elephant trunk implantation in the descending aorta. The choice of surgical approach depended on the patient's condition. After the distal anastomosis was completed, systemic blood perfusion was restored, and the patient was gradually rewarmed. The proximal aortic anastomosis and other concomitant operations were carried out during the rewarming period, and then the coronary blood flow was restored. All patients were admitted to intensive care unit for routine postoperative monitoring.

Statistical analyses were performed by R version 4.0.4 software (http://​www.​R-project.​org/​). All participants were categorized into three groups according to levels of LMR. Categorical variables were expressed as n (%) and continuous variables were expressed as means (standard deviation, SD) or medians (interquartile range, IQR). Differences in baseline characteristics between three groups were analyzed using independent sample t tests or Mann–Whitney U tests for continuous variables as well as the Chi-squared test or Fisher’s exact test for categorical variables, as appropriate. Multivariable analysis was adjusted for all potential confounders with a statistically significant association at P < 0.05 in univariate regression analysis. We used the violin plots to show the distribution of LMR between AKI group and non-AKI group. ROC curve analysis was performed to assess the overall discriminative ability of LMR to predict postoperative AKI and to establish optimal cutoff points at which the sum of the specificity and sensitivity was the highest [21]. The NRI and IDI were calculated to estimate the predictive value of adding LMR levels into logistic regression model and evaluate improvement in risk classification. NRI and IDI were calculated with the package nricens and PredictABEL [22]. Model 1 was adjusted for age and gender. All potential confounders with a statistically significant association at P < 0.05 in the univariate analysis for AKI were selected into Model 2. Model 2 was adjusted for age, APACHE II, diastolic blood pressure, Scr. A two-tailed value of P < 0.05 was considered significant.