A comparative study of the effects of spontaneous ventilation versus one-lung mechanical ventilation on ipsilateral lung injury during thoracic surgery: an empirical analysis based on a rat model

Introduction

Background

Thoracoscopic surgery, since its inception in 1910, has been widely applied in clinical practice. With the continuous development of anesthesia techniques and medical instruments, thoracoscopic surgery has gradually become more minimally invasive and convenient. One-lung ventilation (OLV), a frequently utilized ventilation technique in thoracoscopic surgery, enhances the surgical visibility for thoracic surgeons (1), but it often causes barotrauma and volutrauma during OLV, leading to postoperative complications. Therefore, the ventilation mode of spontaneous breathing emerged. Spontaneous breathing refers to the process where patients, during thoracoscopic surgery, facilitate gas exchange through their own respiratory muscles (such as the diaphragm and intercostal muscles) without external mechanical assistance. Numerous studies in recent years have shown that spontaneous ventilation (SV) can effectively reduce the occurrence of postoperative pulmonary complications (2,3). At the same time, in our (National Center of Respiratory Medicine of China) clinical practice of thoracic surgery, the spontaneous breathing management model has also achieved satisfactory clinical results.

However, there are few relevant animal studies, especially the comprehensive histological and pathophysiological effects, that are not completely clear. Given the similarity between the lung structure of rats and humans, rats can serve as an ideal model for studying human lung diseases. Meanwhile, in rat models of lung injury, we can assess the severity of lung injury through various means such as histological examination, physiological dysfunction evaluation, and inflammatory response assessment. It possesses a well-established and relatively complete evaluation system. Therefore, our study will use rats as experimental subjects for related research.

Rationale and knowledge gap

Numerous studies have highlighted the postoperative complications associated with OLV in thoracic surgeries, including throat discomfort, persistent cough, nausea, vomiting, and damage (such as increased alveolar capillary permeability, pulmonary edema, atelectasis, and lung injury) (4-6). It may also induce biological damage through inflammatory responses in local lung and systemic circulation, cell stretching alters gene expression, upregulating proinflammatory molecules and cytokines (7). These circulating mediators can affect other organs (8), while cytokines can significantly cause and sustain lung injury (9).

Compared to mechanically controlled positive pressure ventilation, SV, a ventilation mode that can reduce the occurrence of complications, has emerged in recent years (10). SV can activate a moderate immune response in the body, mainly indicated by subtle changes in T lymphocytes and natural killer cells (NK cells) during the occurrence of inflammatory responses (11). SV originates from inspiratory muscle movement, causing an increase in negative pressure in the pleural cavity and alveoli, enhancing perfusion redistribution and ventilation homogeneity (12). This method alleviates atelectasis and reduces mechanical stress on the lungs. Compared to intubation surgery, postoperative pain is reduced, and clinical rehabilitation outcomes are favorable (13). Non-intubated anesthesia with spontaneous breathing is widely used in video-assisted thoracic surgery (VATS), including lung cancer (14), mediastinal tumors (15), bullous emphysema (16), lobectomy (17), and bullectomy (18), all of which have been proven to be safe and feasible.

Although in clinical practice, we have found that autonomous ventilation is more conducive to postoperative rehabilitation than mechanical ventilation, there are few animal studies.

Objective

SV in thoracic surgery shows advantages per clinical studies, yet SV’s mechanisms in reducing postop respiratory complications and boosting immunity are unclear, with scarce animal evidence. We postulate SV mitigates lung injury vs. OLV. To validate this hypothesis, we created a rat model to evaluate lung injury under OLV and SV through various detection methods. In this way, the effect of SV on the pathophysiology of lung tissue was further verified, and the theoretical support was better provided for the selection of spontaneous respiratory airway management mode. We present this article in accordance with the ARRIVE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2279/rc).

Methods

Animals

All animal experiments were performed under a project license (No. 20230674) granted by the Ethics Committee of The First Affiliated Hospital of Guangzhou Medical University, in compliance with institutional guidelines for the care and use of animals. A protocol was prepared before the study without registration. Based on a previous study (3) and previous experiments, we purchased 42 female Sprague Dawley rats (SD rats) (6–7 weeks, female, 160–220 g) from the Guangzhou Provincial Laboratory Animal Center. All rats were numbered sequentially by the complete randomization method, and 6 random numbers were selected into 1 group by “Numpy” in Python (v3.1.1), and a total of 7 times were selected, and the group names were control (CON), OLV 10 min, OLV 20 min, OLV 30 min, SV 10 min, SV 20 min, and SV 30 min, respectively.

Model establishment

Rats fasted 24 hours were anesthetized with 200 mg/kg chloral hydrate intravenous injection (IV) (19). They were positioned supine, with jugular vein exposed, ligated, and cannulated for venous access. Carotid artery access was also established with a monitoring probe. Trachea was isolated, sprayed with 2% lidocaine, transected, and intubated with a single-lumen tube.

OLV model: rats ventilated with 5 mL/kg tidal volume (VT), pmax ≤20 cmH₂O, respiratory rate (RR) 30/min (20), I: E 1:2, FiO₂ 0.4. Atracurium 0.5 mg/kg IV, followed by midazolam 200 µg/kg/h infusion (21). Endotracheal tube redirected to right lung, inducing open pneumothorax in the left lung, confirming OLV model by observing atelectasis (Figure 1A).

Figure 1 Schematic diagram of experimental model. (A) OLV model (3). (B) SV model. OLV, one-lung ventilation; SV, spontaneous ventilation.

SV model: rats ventilated with FiO₂ 0.4, receiving midazolam 200 µg/kg/h IV (21). Endotracheal tube redirected to right lung and maintain the rats spontaneous ventilation. A 2 cm incision in left axilla allowed non-intubated ventilation of both lungs, confirming SV model (Figure 1B).

In the case of experimental subject mortality resulting from anesthesia or improper handling during the modeling process, it is necessary to conduct a second experiment for the corresponding group. Thus, during the experiment, it is crucial to adhere strictly to operating procedures to prevent accidental deaths of experimental animals. Upon completion of the modeling and the experiment, if the experimental animals are still alive, euthanasia should be carried out using the spinal dislocation technique. Experimental animals that successfully completed all operations were sampled for follow-up experiments.

Wet and dry density (W/D)

Immediately after euthanasia, the left and right lower lung lobes of the rats in each model group were excised and weighed to determine the wet lung weight (22), then the lungs were rinsed thrice with physiological saline to completely remove any blood, and subsequently dried in an oven at 70 ℃ for 48 hours (23), after which the dried lungs were weighed to obtain the dry weight of each sample. The wet-to-dry ratio was calculated by dividing the wet weight by the dry weight. We applied one-way analysis of variance (ANOVA) using Prism software to analyze the W/D data for each group.

Blood gas analysis

Postoperatively, approximately 0.5 milliliters of blood were withdrawn via the carotid artery for blood gas analysis, with the measurement of blood oxygen partial pressure (PaO₂) and carbon dioxide partial pressure (PaCO₂).

Bronchoalveolar lavage fluid (BALF)

At the end of the experiment, BALF was collected from the rat’s right lung. The sternum was cut to access the thoracic cavity and bronchi. The left bronchus was isolated and tied off, allowing flushing of the right lung. A series of saline injections (3 mL initial, followed by 3 mL and finally 1 mL) were administered (24), with 2 mL of BALF removed after each injection to maximize collection. The combined BALF from three washes was stored in a 15 mL tube on ice. Half of the samples underwent centrifugation (4 ℃, 300 g, 10 min) (25) to suspend cells in 50 µL phosphate buffered saline (PBS) for Diff quick staining and inflammatory cell quantification.

Immunohistochemical staining for tumor necrosis factor-α (TNF-α)

To evaluate TNF-α protein expression in lung tissues across experimental groups, immunohistochemistry was performed on rats hilum lung tissue samples, which underwent deparaffinization, antigen retrieval, peroxide and serum blocking, overnight incubation with a TNF-α primary antibody (Servicebio, China), followed by a secondary antibody incubation. The sections were then stained with diaminobenzidine (DAB) to visualize TNF-α and hematoxylin for nuclei, dehydrated, cleared, and mounted. Quantitative analysis of the staining was conducted using ImageJ (v1.53) to measure the intensity of optical density per area (IOD/Area) and %Area of positive staining.

Hematoxylin and eosin (HE) and morphological analysis

Rat right upper lung tissue (ventilatory lung) was fixed, embedded, and sectioned for HE staining (Servicebio, China). HE-stained images were analyzed with ImageJ. A semi-quantitative pathological scoring system (0–4; 0= normal, 4= severe 75% lung involvement) (26) assessed lung injury, including neutrophil infiltration, aggregation in alveolar, vessel walls and alveolar congestion.

In clinical practice at our center, mechanically ventilated patients exhibit increased sputum production post-surgery and are more prone to atelectasis. This may be attributed to the shear stress of mechanical ventilation causing injury to terminal bronchioles, manifested primarily by morphological changes and increased inflammatory exudation in the terminal bronchiole walls.

To evaluate the area of inflammatory exudation from the terminal bronchiole wall, representative cross-sections of terminal bronchioles were selected to quantify the terminal bronchial wall area (WAt, µm²) and terminal bronchial basement membrane perimeter (Pbm, µm). The WAt/Pbm ratio served as an indicator for assessing morphological changes, including airway collapse (27). To quantify the degree of terminal bronchiole collapse, the circularity index was employed to characterize the shape of the airway lumen. The circularity index ranged from 1 (perfectly circular airway) to 0 (completely collapsed airway with no lumen) (28). The calculation formula is presented below.

Circularity=4π×AreaPerimeter2[1]

Statistical analyses

If there is an obvious data anomaly during the experiment, that is, there is a significant difference from the general change trend, this data needs to be extracted. However, this did not occur in this study. All analyses were performed using Prism 9 (v9.5.1). For the specific representation of the data, please refer to the legend. The data were processed using one-way ANOVA as well as two-way ANOVA. A P value of <0.05 was considered statistically significant.

Results

W/D analysis

At 10 min, there was no significant change in the wet-dry ratio of each group (Figure 2A). At 20 min, both SV and OLV had more W/D than CON (P<0.0001, Figure 2B). At 30 min, SV and OLV had more W/D than the CON, and OLV had a higher W/D than SV, which was statistically significant (Figure 2C).

Figure 2 Lung tissue W/D and mean arterial PaO₂ and PaCO₂. Comparison of W/D of rats at 10 min (A), 20 min (B), and 30 min (C). n=6, results are presented as mean ± SEM. ****, P<0.0001 vs. CON; ^##, P<0.01 vs. SV. Comparison of mean arterial PaO₂ (D) and PaCO₂ (E) during surgery between two groups. *, P<0.05, SV vs. OLV. CON, control; OLV, one-lung ventilation; PaO₂, arterial oxygen pressure; PaCO₂, partial pressure of carbon dioxide; SEM, standard error of the mean; SV, spontaneous ventilation; W/D, wet and dry density.

Blood gas analysis

As the control group did not undergo ventilation intervention, only the blood gas analysis of the OLV and SV groups was compared here. As surgery progressed, PaO₂ declined, lowest at 30 min, with SV significantly higher than OLV (P<0.05) at 30 min but not at 10/20 min (Figure 2D). Meantime, PaCO₂ increased, peaking at 30 min, significantly higher in OLV vs. SV (P<0.05) at 30 min but not at 10/20 min (Figure 2E). Therefore, we believe that the reason for this increase in PaCO₂ and decrease in PaO₂ may be because the mechanical ventilation group is more likely to cause greater alveolar shear without positive end-expiratory pressure (PEEP) support.

Pathological changes in lung tissue

To assess lung injury and inflammation caused by two ventilation techniques in rats, we utilized HE and Masson staining on lung tissues. HE staining revealed that as ventilation time increased, both SV and OLV groups showed escalating inflammatory cell infiltration, alveolar capillary congestion, with OLV displaying more severity (Figure 3A). As shown in Figure 3B, we found OLV led to progressive inflammatory cell accumulation, inflammatory exudation from the terminal bronchiole, and bronchial collapse. Conversely, SV showed minimal changes. Notably, at 30 min, OLV had significantly higher inflammatory scores (3.8±0.2) and alveolar congestion scores (3.8±0.45) than SV (2.8±0.2 & 2.6±0.55, P<0.01) (Figure 3C,3D).

Figure 3 HE staining of ventilated lung tissue. Schematic diagram of ventilated lung tissue infiltrating inflammatory cells (A, scale bar =100 µm) and terminal bronchiole (B, scale bar =50 µm). Quantitative analysis of inflammatory cell infiltration score (C) and semi-quantitative analysis of lung inflammation based on alveolar congestion score (D) in Figure (A). Quantitative analysis of Wat/Pbm (E) and lung inflammation based on bronchiolar circularity (F) from Figure (B). n=6, results are presented as mean ± SD. *, P<0.05; ***, P<0.001; ****, P<0.0001 vs. CON. ^##, P<0.01; ^###, P<0.001; ^####, P<0.0001 SV vs. OLV. ⁺⁺⁺⁺, P<0.0001 SV vs. OLV. CON, control; HE, hematoxylin and eosin; ns, no statistical significance; OLV, one-lung ventilation; SD, standard deviation; SV, spontaneous ventilation; Wat/Pbm, the terminal bronchial wall area/terminal bronchial basement membrane perimeter.

Compared to controls, OLV exhibited abundant inflammatory infiltration with time-dependent aggravation (Figure 3E). Moreover, at 30 min, OLV bronchiolar circularity significantly decreased, differing from SV (Figure 3F).

As shown in Figure 4A, the distribution of collagen fibers in the normally ventilated lung is confined to a single layer with minimal recruitment of inflammatory cells. In contrast, OLV and SV groups show increased collagen fiber extravasation and inflammatory cell recruitment. Quantitative analysis confirms higher collagen fiber areas in OLV and SV vs. CON (Figure 4B). Notably, at 30 min, OLV had significantly more collagen extravasation than SV (P<0.001). Inflammatory cell counts were also significantly elevated in OLV and SV compared to control (P<0.0001), with OLV consistently higher than SV across all time points (Figure 4C).

Figure 4 Masson staining of ventilated lung tissue. (A) Extravasation of collagen fiber in lung tissue (scale bar =100 µm). Quantitative analysis of collagen fibers (B) and inflammatory cell counts (C). n=6, results are presented as mean ± SEM. ***, P<0.001; ****, P<0.0001 vs. CON. ^##, P<0.01 vs. OLV 10 min. ⁺, P<0.05; ⁺⁺⁺, P<0.001 vs. OLV 20 min. ^§§§, P<0.001 vs. OLV 30 min. CON, control; ns, no statistical significance; OLV, one-lung ventilation; SEM, standard error of the mean; SV, spontaneous ventilation.

BALF

BALF of SV and OLV groups was observed under light microscope (Figure 5A). In Figure 5B, red blood cell counts in SV and OLV increased significantly at 30 min, suggesting that the damage worsened over time. Figure 5C suggests that damage caused by ventilation leads to the aggregation of inflammatory cells over time. The most severe symptoms occurred at 30 min, with infiltration of inflammatory cells. OLV was more serious than SV at 30 min.

Figure 5 BALF analysis of model rats. (A) Images of white blood cells in BALF (the scale is shown in the figure). The number of red blood cells (B) and inflammatory cells count (C) in BALF. n=6, results are presented as mean ± SD. **, P<0.01; ****, P<0.0001 vs. CON, ^#, P<0.05; ^###, P<0.001 vs. OLV 30 min. BALF, bronchoalveolar lavage fluid; CON, control; OLV, one-lung ventilation; SD, standard deviation; SV, spontaneous ventilation.

Immunohistochemical staining assessment of lung TNF-α

We studied TNF-α expression in rat lung tissue after OLV vs. SV (Figure 6A). Both groups showed higher TNF-α than controls, which may indicate that the inflammatory response is systemic in the case of contralateral open or pneumothorax, and that the healthy lungs are not completely normal, but also have a small amount of increased inflammatory expression. Notably, OLV induced significantly higher TNF-α, indicating greater injury and inflammation than SV (Figure 6B,6C).

Figure 6 TNF-α expression in lung tissues. (A) TNF-α levels in lung tissues (scale bar =100 µm). Quantitative analysis of TNF-α IOD/Area (B) and %Area (C). n=6, results are presented as mean ± SEM. *, P<0.05; ***, P<0.001; ****, P<0.0001 vs. CON. ⁺⁺, P<0.01; ⁺⁺⁺, P<0.001; vs. SV 20 min. ^§§, P<0.01; ^§§§, P<0.001; vs. SV 30 min. CON, control; IOD/Area, the integrated optical density/area; ns, no statistical significance; OLV, one-lung ventilation; SEM, standard error of the mean; SV, spontaneous ventilation; TNF-α, tumor necrosis factor-α.

Discussion

Key findings

Our findings indicate that during unilateral pneumothorax surgery, OLV significantly upregulates the recruitment of inflammatory cells and cytokines, as well as collagen fiber cell exudation, in the ventilated lung tissue compared to SV. Furthermore, as the duration of surgery increases, the lung tissue injury caused by OLV becomes more severe. These results are significant for selecting appropriate ventilation modes during clinical surgery and actively preventing adverse complications when adopting OLV.

Strengths and limitations

There are two limitations to this study. Firstly, in the experimental design, the ventilation durations for the model rats were set at 10, 20 and 30 min, respectively, with the possibility that the shorter duration may have resulted in insufficient ventilation, thereby leading to less pronounced injury effects. However, it is evident from the comparison of our experimental results that, after 20 min of ventilation with both OLV and SV modes, OLV caused more severe damage to the ventilated lungs. We chose 30 minutes as our time point due to the fact that, in clinical practice, at our center, the National Center of Respiratory Medicine of China, some minor surgeries including lung wedge resection or thoracoscopic exploration and biopsy, when the surgeon is highly skilled, the duration of surgery from thoracotomy to skin suturing, which is approximately the time required for OLV, and in some cases, even less than 30 minutes. Hence, we aim to utilize the 30-minute time point to further validate and investigate whether there are differences in lung injury induction between the two ventilation techniques in animal models. Admittedly, there are still numerous thoracoscopic surgeries that necessitate over 30 minutes. Thus, we intend to incorporate additional time points in our future research to delve deeper into prolonged thoracoscopic surgeries.

Secondly, the study primarily concentrated on the damaging effects of two ventilation modes on the ventilated lungs during surgery, without comparing the postoperative conditions of the rats. The research scope is limited, potentially affecting the comprehensiveness of the study results. However, to assess the damaging effects of the two ventilation modes on the ventilated lungs, we conducted relevant experiments to demonstrate the in vivo conditions, gross changes, local pathological alterations, and overall inflammatory effects, thereby confirming the presence of lung injury. Certainly, in subsequent research, the underlying mechanisms of lung injury can be explored to aid in the use of intraoperative ventilation. For example, we have also noticed lung protective ventilation strategies including PEEP. In the case of OLV, would adding PEEP improve this injury.

Explanations of findings and comparison with similar research

OLV is used in thoracic surgeries, to isolate the affected lung. However, during clinical application, OLV can cause lung complications like hypoxia, stretch-induced injury, ventilator-induced lung injury (VILI) (29), and postoperative atelectasis (6).

It is well-established that VILI can affect anatomy, physiology, and clinical outcomes, mainly from mechanical stretch. This includes ventilation, lung tissue collapse/re-expansion. SV improves air-dependent lung regions (12), optimizing blood flow and reducing VILI. Histology of lung injury shows atelectasis and inflammation (30).

SV, however, originates from the subject (animal) itself, with the fundamental driving force being the negative pressure resulting from thoracic expansion during normal breathing. It is primarily accomplished through the active descent of the diaphragm during inspiration, the assistance of respiratory muscles, and the enlargement of the pleural cavity. Unlike positive pressure mechanical ventilation, this type of respiratory activity maintains a negative pressure within the thorax. Thus, the RR of subjects in this model is self-determined, potentially influenced by factors such as medications.

To assess the extent of lung edema in rats from various groups, we conducted a wet-to-dry weight ratio analysis of their lung tissues post-experimentation. The results indicated that SV mitigated lung injury in rats during simulated thoracic surgical procedures. The wet-to-dry lung weight ratio serves as an indicator of both the severity of lung edema and the integrity of the alveolar barrier. Our data suggest that the W/D ratio exhibits a time-dependent pattern. Although no notable disparity was evident between the groups at 20 min, a statistically significant difference emerged in the SV at 30 min, demonstrating a reduced lung injury compared to the OLV.

Blood gas analysis, crucial in thoracic surgery, assesses hypoxemia, respiratory failure. In our findings, OLV vs. SV at 30 min showed SV had higher PaO₂. During OLV, excessive perfusion leads to capillary shear stress, which, coupled with high strain due to the loss of non-physiological tidal volume and normal functional residual capacity in the ventilated lung, induces lung injury. Additionally, the re-expansion of collapsed lungs inevitably induces time-dependent ischemia-reperfusion injury. Consequently, this ultimately results in lower PaO₂ and higher PaCO₂ in OLV compared to SV. Although in actual human surgery, during thoracic surgery with OLV, PaCO₂ may remain low and PaO₂ can maintain normal levels, we believe this is due to the fact that when patients are in the lateral position, the ventilated lung (lower lung) receives relatively more blood flow, leading to a slight improvement in the V/Q ratio, and the use of PEEP in human applications often reduces alveolar shear forces, further reducing lung injury. In this study, the rats were in the supine position and PEEP was not used, therefore, the damage caused by mechanical positive pressure ventilation was significantly exacerbated, ultimately reflected in the blood gas analysis results.

Furthermore, studies have raised the question of whether hypoxic pulmonary vasoconstriction (HPV) contributes to lung injury, attributed to airway pressure disparities between ventilated and non-ventilated lungs, causing blood flow surges to collapsed lungs. HPV-influenced augmented blood flow redirects to ventilated lungs. Blood flow to non-ventilated lungs decreases within 5 minutes of OLV, with the impact on lung injury during OLV still uncertain (31). Mild hypercapnia poses minimal risk and may enhance parenchymal compliance, optimize ventilation/perfusion (12), and mitigate ALI by reducing mechanical stress (32). There is research to prove it that link neuromuscular blocking agents during anesthesia to increased postoperative pulmonary complications (33). Meanwhile, SV can preserve respiratory muscle function and reducing lung injury by avoiding muscle relaxants.

HE staining clarifies histopathological alterations, visualizing cellular and tissue structures. Our findings showed SV reduced atelectasis, with terminal bronchiole circularity in SV groups resembling controls, supporting SV’s role in atelectasis reduction at end-expiratory pressure (34). A previous study have demonstrated that OLV-induced inflammatory cell accumulation heightens alveolar-vascular permeability, surfactant dysfunction, alveolar collapse, worsening atelectasis (35). With increasing ventilation time, OLV groups exhibited heightened inflammatory cell infiltration and alveolar collapse, potentially contributing to VILI via atelectasis. Histological scores revealed higher inflammatory cell infiltration and alveolar congestion in OLV vs. SV groups, indicating that lung damage was more severe in OLV.

Masson staining visualizes collagen fibers and inflammatory factors in tissues, critical for the extracellular matrix (ECM) maintenance, organ and tissue structuring, cytokine signaling, and tissue repair/remodeling (36). In healthy lungs, collagen fibers uphold normal structure and lung compliance for respiratory motion. Mechanical ventilation utilizes lung compliance/resistance to ensure respiratory movement via positive pressure. However, OLV exacerbates parenchymal stress through alveolar collapse/overdistension, activating mechanotransduction, converting stress into chemical signals. This repair and damage signal interplay promotes VILI (37). Studies show VILI mechanisms disrupt ECM homeostasis (38), accelerating VILI progression (39,40).

Masson staining aids in exploring the link between ventilation modes, collagen fiber expression, and lung damage, assessing collagen fiber exudation and inflammatory cell recruitment in rat lungs under OLV and SV over time. Results reveal both modes enhance collagen fiber exudation and inflammatory cell recruitment, suggesting a correlation with inflammation. Compared to controls, OLV and SV elevations hint at stress-mediated anesthesia effects on inflammation, supporting collagen’s repair role. Prolonged ventilation led to significantly higher collagen fiber exudation and inflammatory cell recruitment in OLV vs. SV, indicating greater lung damage. Thus, when possible, SV may reduce collagen-induced lung damage, protect lung structure, and minimize surgical impacts on lung function.

To delve into pathophysiological states in ventilated rat lungs, we analyzed BALF neutrophils. Both ventilation modes raised neutrophil counts vs. controls, with OLV significantly higher than SV, notably at 30 min. This hints at stress-induced inflammatory response upregulation during surgery (41), stimulating the immune system to enhance resistance to infection and reduce the probability of infection. However, accurately speaking, the upregulation of inflammatory response is a double-edged sword for surgical procedures. Studies have shown that OLV may amplify inflammation, recruiting inflammatory cells and cytokines, hastening VILI onset (42-44).

To investigate OLV impact on VILI via cytokine upregulation, we assessed TNF-α in ventilated lungs. TNF-α, a key inflammatory mediator, triggers inflammatory cascades, boosting immunity and reducing infection. Both OLV and SV groups showed TNF-α upregulation due to stress-induced inflammation (41). However, excess TNF-α disrupts immune balance, fueling inflammation and organ damage (45). Our quantitative analysis at various timepoints under OLV & SV found that TNF-α upregulation by mechanical ventilation was significantly higher than SV. This implies TNF-α overexpression aggravates lung inflammation via multiple pathways, crucial in VILI (46). Additionally, SV consistently induced lower TNF-α than OLV, suggesting weaker inflammatory effects. This may mitigate excessive inflammation-induced damage, aiding in intraoperative lung protection and postoperative recovery.

Implications and actions needed

This study provides experimental data on the reduction of intraoperative lung injury by SV compared to OLV and offers supportive evidence for the clinical application of SV mode. Our research results indicate significant differences between the OLV group and SV group at the 20 and 30 min time points during surgery. Furthermore, our data suggest that with prolonged ventilation time, the inflammatory response induced by OLV in the ventilated lung will intensify, and the extravasation of collagen fibers may lead to lung fibrosis. Thus, OLV may increase the risk of postoperative ventilator-associated lung complications. Therefore, clinically, by adopting a tailored approach to SV based on patient-specific conditions, the occurrence of VILI, atelectasis, and other postoperative complications of thoracoscopic surgery can be effectively reduced. It can somewhat promote the postoperative recovery of patients and enhance their postoperative survival outcomes.

Conclusions

Our study showed that during unilateral pneumothorax surgery, at 30 minutes of ventilation, OLV caused more severe ventilated lung injury than SV. Therefore, choosing the ventilation mode of SV during surgery may be more beneficial in mitigating the injury of the ventilated lungs.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the ARRIVE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2279/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2279/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2279/prf

Funding: This work was supported by National Natural Science Foundation of China (No. 82272160), Guangzhou Municipal Science and Technology Bureau, The Project of Basic and Applied Basic Research Jointly Funded by Municipality and University (Hospital) (Fund Nos. 202201020584 and 2023A03J0345) and GMU Undergraduate Innovation Ability Enhancement Project and Plan on Enhancing Scientific Research.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2279/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All animal experiments were performed under a project license (No. 20230674) granted by the Ethics Committee of The First Affiliated Hospital of Guangzhou Medical University, in compliance with institutional guidelines for the care and use of animals.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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