Leukocyte cell population data in patients with cardiac surgery and cardiopulmonary bypass: A potential readily available tool to monitor immunity

Abstract

Purpose: Cardiac surgery with cardiopulmonary bypass triggers sterile inflammation that is responsible for post-operative morbidity. Automated flow cytometry devices used for leucocyte count provide cell population data (CPD) regarding fluorescence intensity, size and granularity of leukocytes that have never been studied in the context of sterile inflammation. Our objective was to explore leukocyte cell population data in patients undergoing cardiac surgery with cardiopulmonary bypass in order to determine whether CPD could be used to monitor immune cell activation.

Methods: This is an ancillary study of a cohort of patients undergoing cardiac surgery with cardiopulmonary bypass. Cell population data (CPD) extracted from a routine automated flow cytometer were analyzed (Fluorescence targeted to nucleic acids). The time points of interest were: pre-operative, postoperative and 5 days after surgery. The variations in those parameters were studied. Data were then compared between patients according to the occurrence of a composite criteria (supra-ventricular arrythmia, stroke, acute renal failure, and/or death).

Results: Data from 1453 patients were analyzed. The neutrophil count, fluorescence granularity (NE-SCC), intensity (NE-SFL) and size (NE-FSC) increased with surgery. Heterogeneity of neutrophils decreased in terms of fluorescence granularity (NE-WX) and size (NE-WZ) but increased in terms of intensity (NE-WY). The lymphocyte count decreased with surgery. While fluorescence granularity (LY-X) and size increased (LY-Z), Lymphocyte intensity decreased (LY-Y). Lymphocytes were less heterogeneous in terms of their granularity, size and intensity after surgery (LY-WX, LY-WY, LY-WZ). Patients who developed the composite complication criteria had a higher pre-operative neutrophil count (5.08 [3.89;6.95] vs 4.76 [3.60;6.13], p = 0.02; AUC = 0.56 [0.51;0.60]), and more heterogeneous neutrophils in terms of fluorescence granularity (NE-WX, AUC = 0.57 [0.52;0.62]) and intensity (NE-WY, AUC 0.61 [0.56;0.65]). Those patients also had lower pre-operative lymphocyte count (1.49 [1.10;1.14] vs 1.81 [1.39;2.39], p<0.01, AUC = 0.61 [0.57;0.66]) and fluorescence granularity (LY-X, AUC = 0.57 [0.53;0.62]). NE-WX, NE-WY and LY-X were associated with post-operative complications after adjustment on the EuroSCORE 2 (adjusted odd ratio of 1.01 [1.00;1.02]; 1.01 [1.00;1.01] and 1.08 [1.02;1.15] respectively).

Conclusion: Cardiac surgery with cardiopulmonary bypass was associated with substantial alterations of CPD probably reflecting leukocytes activation in sterile inflammation. Pre-operative NE-WX, NE-WY and LY-X biomarkers levels were associated with post-operative complications, independently of the EuroSCORE 2. Such routine, unexploited and low cost parameters might represent useful tools likely to monitor immune function and predict outcomes for patients undergoing cardiac surgery. Our findings requires validation on a larger external cohort.

Keywords: acute kidney injury; biomarker; cardiac surgery; cardiopulmonary bypass; cell population data; immunity; inflammation; post-operative outcome.

Figure 1

Cell population data parameters as visualized on the analyzer SCC: Granularity, SFL: Fluorescence.

Figure 2

Study flow chart. CPD, Cell Population Data.

Figure 3

White blood cell count are modified by cardiac surgery and are associated with post-operative complications. (A) Neutrophils, (B) Lymphocytes, (C) Monocytes Dotted line represent normal range for each parameter * above the plot refers between groups significant difference (non-parametric test, p-value were corrected using Bonferroni’s method). * on the x-axis report significant differences from baseline (intragroup comparison with p < 0.05). Red represent patient that developed the composite complication criteria and blue patient who did not.

Figure 4

Neutrophil cell populations data are modified with cardiac surgery and are associated with post-operative complications. (A) Neutrophil cell complexity, (B) Heterogeneity in cell complexity, (C) Neutrophil fluorescence intensity, (D) Heterogeneity in fluorescence intensity, (E) Neutrophil cell size, (F) Heterogeneity in neutrophil cell size. Results are presented as median and interquartile range. * above the plot refers between groups significant difference (non-parametric test, p-value were corrected using Bonferroni’s method). * on the x-axis report significant differences from baseline (intragroup comparison with p < 0.05). Red represent patient that developed the composite complication criteria and blue patient who did not.

Figure 5

Lymphocyte cell populations data are modified with cardiac surgery and are associated with post-operative complications. (A) Lymphocytes cell complexity, (B) Heterogeneity in cell complexity, (C) Lymphocytes fluorescence intensity, (D) Heterogeneity in fluorescence intensity, (E) Lymphocytes cell size, (F) Heterogeneity in lymphocytes cell size. Results are presented as median and interquartile range. *: between groups significant difference (non-parametric test, p-value were corrected using Bonferroni’s method). * on the x-axis report significant differences from baseline (intragroup comparison with p < 0.05). Red represent patient that developed the composite complication criteria and blue patient who did not.