A Pilot Study of Regional Alveolar Leukocyte Populations After Robotic-Assisted Laparoscopic Surgery

Document Type

Manuscript

Submission Date

2024

Abstract

A Pilot Study of Regional Alveolar Leukocyte Populations After Robotic-Assisted Laparoscopic Surgery

Background

Ventilation-Induced Lung Injury (VILI) may result from impaired intraoperative lung mechanics despite using lung protective ventilation (LPV). However, few human data exist linking impaired lung mechanics to VILI. Growing evidence shows surgical positioning, particularly Trendelenburg, results in heterogenous mechanics consistent with regional overdistention and cyclic alveolar collapse. We undertook a pilot study examining the relationship between lung mechanics and regional biomarkers of VILI in subjects undergoing robotic assisted laparoscopic surgery (RALS) in Trendelenburg. Here, we examined regional alveolar leukocyte composition before and after surgery to determine if the presence of inflammatory cells changed with impaired lung mechanics.

Methods

In an IRB approved study, we obtained bronchoalveolar lavages (BAL) from apical and anteromedial subsegments before (right upper / RUL and lingula) and after (left upper / LUL and right middle / RML) surgery. Lung mechanics were measured continuously by pneumotachograph and esophageal balloon. Cells were isolated from BAL, cytospin slides were made, and the remainder was frozen. Manual macrophages and neutrophils counts were made from slides. High-resolution differentials were made from frozen cells using 14-color flow cytometry, specific for lymphoid and myeloid cells including monocyte subpopulations. End-expiratory transpulmonary pressures and mechanical power were calculated at relevant surgical time points.

Results

We obtained 59 BAL from 15 patients (7 F / 8 M; average age 59.8 ± 7.0 yrs; mean BMI 34.8 ± 7.0 kg/m^2). Cytospins were made from 45 BAL and flow cytometry from 40 BAL. Before surgery, manual counting showed macrophages composed 86.57 ± 8.34% of all cells, neutrophils constituted 4.23 ± 3.34%, with no differences between BAL regions (p>0.49 for both). Macrophages comprised 85.14 ± 11.54% of BAL cells after surgery and did not differ between regions (p=0.27). Interestingly, there was a trend of increasing neutrophils in RML 7.50 ± 8.15% after surgery compared to 4.40 ± 4.11% in other BAL (p=0.44). By flow cytometry, we found BAL leukocytes were ~70% myeloid and ~30% lymphoid cells. Myeloid populations were composed of 65% alveolar macrophages (CD206+), 24% monocytes (CD14+), 10% dendritic cells, and 1% plasmacytoid dendritic cells. Lymphoid populations were 62% helper T cells (CD4+), 24% cytotoxic T cells (CD8+), 5% B cells, 6% natural killer cells, and 3% natural killer-like T cells. No significant differences in leukocyte populations were noted before or after surgery (p>0.05 for all). There was a trend towards increased classical monocytes in the RML after surgery (65.94% ± 16.13%) compared to 55.46 ± 19.95% in other regions (p>0.05 for all). Percentages of neutrophils and monocytes were not associated with the magnitude of transpulmonary pressures or mechanical power during RALS.

Conclusion

These findings show potential early VILI in patients undergoing RALS in Trendelenburg position. Though we anticipated the apical regions would demonstrate cellular infiltrates from atelectrauma, we observed trends of increased inflammatory cells in anteromedial lung after surgery, suggesting volutrauma. Thus, the heterogeneity of lung mechanics during RALs may lead to lung injury from different local mechanisms. Increased sample size and careful assessment of the BAL for biochemical VILI markers will comprise the next steps.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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