U-shaped threshold-balanced extensive pleural lavage system for empyema: a retrospective case-control study on drainage efficiency and clinical outcomes

Introduction

Thoracic drainage and irrigation techniques, as the core adjuvant methods in the treatment of empyema, have been widely applied in clinical practice (1-6). Their core objective is to control the infection process by removing residual pus, reducing pleural fibro-purulent adhesions, and reducing the bacterial burden in the pleural cavity. Currently, conventional regimens mostly use closed-drainage systems combined with intermittent or continuous lavage using normal saline, iodine-containing solutions, or antibiotic irrigants. There are mainly two technical approaches: one is the double-catheter system [such as inserting a thin irrigation catheter (e.g., 8 Fr) at the top of the pleural cavity and a thick drainage catheter (e.g., 28 Fr) at the bottom], and the other is the single-tube double-lumen design or temporary modified solutions (such as inserting an infusion needle into the drainage tube). The irrigation modes include open irrigation (irrigation and drainage simultaneously) and intermittent closed-type irrigation (clamping-perfusion-drainage cycle). The former can maintain a low bacterial concentration environment through dynamic fluid exchange, but there is a possibility of the “short-circuiting”, resulting in incomplete coverage of the pleural cavity by the irrigation fluid and poor irrigation effect. The latter can theoretically expand the irrigation coverage area and is currently the mainstream choice, but it requires frequent manual operations (7-9).

In response to the above-mentioned problems, this study proposed a modified drainage system that synergistically regulates based on the U-shaped water-surface balance principle and the siphon effect, which we name the U-shaped threshold-balanced extensive pleural lavage drainage system (UTB-EPLDS). Its core innovations are as follows: the thoracic drainage tube is extended and suspended into a U-shape, making the vertex of the U-shape level with the anatomical position of the top of the pleural cavity in the current body position. The principle of the communicating vessel is used to achieve automatic liquid-level balance. When the irrigation fluid is injected into the pleural cavity and the liquid level exceeds the vertex of the U-shape, the liquid automatically flows out through the U-tube due to the gravity difference. The siphon effect maintains drainage. The U-tube is completely sealed. After the initial negative pressure suction is established, the siphon action is continuously generated by the weight of the liquid, avoiding drainage interruption caused by tortuous tubes in traditional methods. Top-irrigation and bottom-drainage + low-flow continuous irrigation: Continuous low-flow perfusion is carried out through a thin catheter (8 Fr) at the top of the pleural cavity. The liquid infiltrates the pleural cavity from top to bottom under the action of gravity. Combined with the delayed drainage of the U-shaped structure, the contact time between the irrigation fluid and necrotic tissue is significantly prolonged. This system achieves fully automated irrigation-drainage through the dual mechanisms of liquid-level threshold-triggered drainage (with the vertex of the U-shape as the threshold) and self-maintained siphon, ensuring three-dimensional coverage of the pleural cavity while reducing nursing operations. To verify its effectiveness, we collected the data of empyema patients treated in Xiamen University Affiliated Chenggong Hospital from January 2018 to December 2024 and compared the differences in purulent fluid drainage efficiency, infection control speed, and operation efficiency between the new U-shaped system and traditional regimens. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-923/rc).

Methods

Patient selection

We conducted a retrospective case-control study. Adult patients diagnosed with empyema in the Thoracic Surgery Department of our hospital from January 2018 to December 2024 were included. All patients met the following criteria.

• Inclusion criteria: (i) age ≥18 years old; (ii) diagnosed with empyema by chest computed tomography (CT) examination and pleural cavity puncture fluid test [in line with the IDSA/ATS empyema diagnostic criteria (1)]; (iii) considered to be acute empyema caused by pneumonia [Patients presented with symptoms of cough, expectoration, and fever. Moist rales were auscultated during lung auscultation. Chest CT showed an inflammatory image of the lung on the same side as the empyema. Inflammatory markers in the blood, such as C-reactive protein (CRP), interleukin-6, procalcitonin, and white blood cell count, were elevated. In addition, infections in other parts of the body were excluded.]; (iv) only underwent closed-thoracic-cavity drainage and irrigation without surgical intervention. Since stage III empyema often requires surgical intervention, this study only included patients with stage I or stage II empyema (9).
• Exclusion criteria: (i) complicated with lung malignancies, ruptured subpleural pulmonary abscesses, active pulmonary tuberculosis, or immunosuppressive states (such as HIV infection, long-term use of immunosuppressive agents); (ii) empyema caused by chest wall surgery or trauma; (iii) empyema caused by spontaneous rupture, perforation, or surgery of the esophagus; (iv) empyema caused by mediastinal surgery; (v) empyema caused by the spread of subphrenic abscesses through lymphatic vessels to the pleural cavity; (vi) encapsulated effusion with septations in the pleural effusion, forming multiple cavities; (vii) incomplete case data.

A total of 76 patients were finally included. Among them, 26 patients used UTB-EPLDS and were set as the UTB group; 31 patients used the conventional closed-drainage combined with intermittent irrigation method and were set as the intermittent lavage group (IL group); 19 patients used the conventional closed-drainage combined with open irrigation method and were set as the open lavage group (OL group).

Drainage and irrigation methods

All closed-thoracic drainage procedures were carried out by the resident doctors in charge of the patients. The operation procedures and the types of thoracic catheters used were uniformly standardized, and the doctors performing the operations followed the specified standards.

Conventional closed-drainage combined with intermittent irrigation

After confirming the safety of the puncture site by ultrasound or CT (puncturing through this site will not damage the lungs, diaphragm, etc.), a 28-Fr silicone drainage tube was inserted into the 7th intercostal space at the mid-axillary line, with an insertion depth of approximately 10 cm. It was connected to a water-seal bottle, and the negative pressure of the drainage bottle was maintained at 10 cmH₂O. The needle of the infusion set was inserted into the drainage tube and fixed with sterile tape. During irrigation, the drainage tube was clamped below the insertion point of the needle first. Then, 500 mL of 0.9% normal saline was injected through the infusion set. After the injection, the drainage tube was clamped for another 30 minutes, and the patient was asked to turn over in bed. Subsequently, the drainage was opened. Irrigation was performed twice a day. The daily thoracic drainage volume and its characteristics were recorded. See Figure 1.

Figure 1 Conventional closed-drainage combined with intermittent irrigation.

Conventional closed-drainage combined with open irrigation

An 8-Fr drainage catheter (ABLE drainage catheter, Guangdong Baihe Medical Technology Co., Ltd., Foshan, China) was inserted into the 2nd intercostal space at the mid-clavicular line as the irrigation tube and connected to an infusion pump (flow rate: 200 mL/h) for continuous irrigation with 0.9% normal saline. A 28-Fr drainage tube was inserted into the 8th intercostal space at the posterior-axillary line, with an insertion depth of 10 cm, and connected to a water-seal bottle. The drainage tube was kept open for continuous drainage. During the irrigation and drainage period, the patient was asked to turn over and change positions intermittently. See Figure 2.

Figure 2 Conventional closed-drainage combined with open irrigation.

U-shaped threshold-balanced extensive pleural lavage drainage system

The insertion methods of the irrigation tube and the drainage tube were the same as those in “conventional closed-drainage combined with open irrigation”. The drainage tube was connected to a sterile silicone extension tube and suspended into a U-shape. The end of the extension tube was connected to a water-seal bottle. The height of the vertex of the suspended drainage tube was level with the highest point of the pleural cavity in the patient’s current body position. That is, if the patient stays in a certain position for a long time, the height of the suspended drainage tube needs to be adjusted dynamically to adapt to different positions. Adjusting the height of the suspended drainage tube is relatively easy, and patients or nursing staff can adjust it by themselves after being taught. The irrigation tube was connected to an infusion pump (flow rate: 200 mL/h) for continuous irrigation with 0.9% normal saline. When the irrigation fluid injected into the pleural cavity raised the liquid level to the vertex of the U-shape, the liquid automatically overflowed due to the gravity difference and was continuously drained through the distal end of the U-tube. After the initial negative pressure was activated, a continuous siphon was generated by the self-weight of the liquid column in the U-tube to ensure smooth drainage. During the irrigation and drainage period, the patient was asked to turn over and change positions intermittently. See Figure 3.

Figure 3 U-shaped threshold-balanced extensive pleural lavage drainage system. This image is published with the patient’s consent.

Antibiotic use

Broad-spectrum anti-gram-negative-bacteria antibiotics were used first (we generally used piperacillin/tazobactam sodium 4.5 g, intravenous drip, once every 8 hours, Wyeth Pharmaceutical Co., Ltd., Shanghai, China). Then, the antibiotics were adjusted according to the results of pleural fluid bacterial culture and drug sensitivity tests. Antibiotics were used until the body temperature returned to normal, and the blood CRP and white blood cell count returned to normal.

The thoracic irrigation and drainage tube can be removed when the following three criteria are met

(I) The fluid column in the thoracic drainage tube fluctuates normally. The drainage volume has been less than 150 mL for three consecutive days. The drainage fluid is light yellow and clear, without purulent floccules, necrotic tissue, or sediment, and no gas is discharged from the drainage tube. (II) Chest CT shows no significant pleural effusion, empyema cavity, or residual cavity in the thoracic cavity, and the lung is well-re-expanded. (III) After stopping thoracic cavity irrigation, the white blood cell count, pleural lactate dehydrogenase (LDH), and glucose in the drainage fluid remain close to normal levels, and both bacterial and fungal cultures of the drainage fluid are negative.

Observation indicators

The baseline data of patients were collected, including age, gender, smoking history, underlying diseases (hypertension, diabetes), body mass index, side of empyema (left/right), sepsis, pleural white cell count, pleural glucose and pleural LDH, chronic pulmonary diseases, and pathogens causing empyema. The main observation indicators included: drainage tube indwelling time, time for the white blood cell count in the drainage fluid to return to normal, time for the peripheral blood CRP to return to normal (since the white blood cell count did not increase during the infection period in some patients with severe infection, the white blood cell count was not listed as an observation indicator), antibiotic use time, hospital stay, mean daily nursing interventions, complication rate, treatment failure rate, and rate of changing the drainage and irrigation protocol. The definitions of some observation indicators are as follows:

• Sepsis: presence of sepsis at the time of presentation.
• Pleural white cell count, glucose and LDH: test results of pleural fluid obtained from the first thoracentesis or closed-thoracic drainage for laboratory examination.
• Chronic pulmonary diseases included: chronic bronchitis, emphysema, chronic obstructive pulmonary disease, and other chronic pulmonary diseases.
• Drainage tube indwelling time: the time from the placement of the drainage tube to its removal.
• Time for the white blood cell count in the drainage fluid to return to normal: the white blood cell count of the drainage fluid was tested every 3 days. The time from the placement of the drainage tube to the normalization of the white blood cell count in the drainage fluid was recorded.
• Mean daily nursing interventions: the number of times nurses operate the irrigation and drainage system daily, such as changing the irrigation fluid and the water-seal bottle.
• Complication rate: the ratio of complications such as chest tube dislodgement, thoracic hemorrhage, and pneumothorax during the irrigation and drainage period.
• Treatment failure rate: the formation of encapsulated empyema, etc., requiring the injection of urokinase or thoracoscopic surgical intervention.
• Rate of changing the drainage and irrigation protocol: if the chest tube drainage fluid remained purulent without improvement for more than 1 week, the drainage and irrigation protocol needed to be changed.

Statistical analysis

Data analysis was performed using SPSS 26.0 statistical software (Armonk, NY, USA). Measurement data were expressed as mean ± standard deviation (x¯±s) and analyzed by one-way analysis of variance. Enumeration data were expressed as the number of cases or percentages, and group-to-group comparisons were performed using the χ² test or Fisher’s exact probability method. The test level was α=0.05.

Ethical review

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Xiamen University Affiliated Chenggong Hospital (No. 73JYY2024105799). Given the retrospective design of this study, the Ethics Committee waived the requirement for obtaining informed consent from each patient.

Results

All the enrolled patients had no conditions that could put their bodies in an immunosuppressed state, such as co-existing tumors, human immunodeficiency virus infection, or taking immunosuppressive agents. No statistically significant differences were observed in baseline indicators such as age, gender, smoking history, underlying diseases (hypertension, diabetes), body mass index, side of empyema (left/right), sepsis, pleural white cell count, pleural glucose and pleural LDH, chronic pulmonary diseases, and pathogens causing empyema among the UTB group, the intermittent irrigation group, and the open irrigation group (P>0.05). See Table 1.

The drainage tube indwelling time, time for the peripheral blood CRP to return to normal, antibiotic use time, and hospital stay in the UTB group were significantly shorter than those in the intermittent irrigation group, and those in the intermittent irrigation group were significantly shorter than those in the open irrigation group (P<0.05 for all inter-group comparisons). See Table 2.

No statistically significant differences were observed in the time for the white blood cell count in the drainage fluid to return to normal and the mean daily nursing interventions between the UTB group and the open irrigation group (P>0.05), but both were significantly less than those in the intermittent irrigation group (P>0.05). See Table 2.

No statistically significant differences were observed in the complication rates (7.7% vs. 3.2% vs. 5.3%, P=0.75) and treatment failure rates (3.8% vs. 16.1% vs. 21.1%, P=0.20) among the UTB group, the intermittent irrigation group, and the open irrigation group. See Table 2.

No one in the UTB group changed the drainage protocol. In the intermittent irrigation group, 19.4% (6/31) changed to the UTB-EPLDS protocol, and in the open irrigation group, 26.3% (5/19) changed to the UTB-EPLDS protocol. See Table 2.

Discussion

Empyema, as a severe complication of pleural cavity infection, has a long treatment period and high cost, imposing a huge burden on both patients and medical institutions (10-12). The core of its treatment lies in thoroughly removing pus, relieving pleural adhesions, and controlling the infection. Efficient thoracic drainage and irrigation may be the key to shortening the treatment time. However, there are currently no targeted research reports on which drainage and irrigation protocol is more effective and its improvement measures. In our clinical work, we found that open irrigation of the pleural cavity has a “short-circuiting” (incomplete irrigation due to rapid fluid outflow). After the irrigation fluid is injected through the top-placed catheter, due to the continuous opening of the bottom-placed drainage tube, the liquid quickly flows out through the low-position drainage tube under the action of gravity, only flushing the bottom of the pleural cavity or areas with less resistance. The top, side walls, and fibrous septum areas of the pleural cavity are difficult to be effectively covered due to insufficient liquid residence time (i.e., “low retention”). The intermittent irrigation of the pleural cavity also has the problem of “intermittent blind areas”. Although the intermittent mode of clamping-perfusion-drainage prolongs the contact time of a single irrigation, the frequency of manual operations (twice a day) makes it impossible for the irrigation fluid to dynamically fill the changes in the shape of the pleural cavity (such as the newly exposed purulent adhesion areas after a change in body position).

In response to the deficiencies of traditional empyema drainage and irrigation methods, we designed the UTB-EPLDS. Its innovation lies in reconstructing the spatiotemporal distribution characteristics of the irrigation fluid through the synergistic mechanism of “low-flow continuous perfusion + U-shaped delayed drainage”. Low-flow continuous perfusion (200 mL/h): compared with the rapid drainage of open irrigation or the pulsed perfusion of intermittent irrigation, low-flow perfusion can reduce the mechanical impact of the liquid on the pleural cavity, making the irrigation fluid more dependent on gravity and surface tension to gradually infiltrate the complex structures in the pleural cavity (such as fibrous septa and concave areas). U-shaped threshold drainage and delayed effect: The dynamic alignment of the vertex of the U-shape with the top of the pleural cavity ensures that the irrigation fluid triggers drainage only after filling the top of the pleural cavity (threshold-triggered). This mechanism forces the liquid to fully fill the anatomical high-position areas of the pleural cavity (such as the lung apex) before drainage. The delayed drainage promotes the dissolution or suspension of purulent secretions and necrotic tissues in the irrigation fluid by prolonging the contact time between the liquid and infected tissues, enhancing the dilution and clearance of pathogens and accelerating the infection control process. The synergistic benefits of dynamic positional adjustments: When the patient turns over intermittently (such as lateral position, prone position), UTB-EPLDS adjusts the height of the vertex of the U-shape in real-time, keeping the liquid level with the highest point of the pleural cavity, ensuring that the irrigation fluid can preferentially fill the newly exposed pleural cavity areas in different positions. This cycle of “dynamic filling-delayed drainage” essentially simulates the “autologous lavage” process of the pleural cavity, breaking through the dependence of traditional methods on static body positions.

In the results of this study, the UTB group had significant advantages. The drainage tube indwelling time, time for the peripheral blood CRP to return to normal, antibiotic use time, and hospital stay were significantly shorter than those in the intermittent irrigation group, indicating that UTB-EPLDS can control the infection more quickly and effectively reduce therapeutic duration of empyema. It can also be seen that the data of the intermittent irrigation group were significantly better than those of the open irrigation group in the above-mentioned indicators. However, the time for the white blood cell count in the drainage fluid of the open irrigation group to return to normal was significantly shorter than that of the intermittent irrigation group. This indirectly proves the existence of the “short-circuiting” of open irrigation. That is, open irrigation cannot effectively irrigate the entire pleural cavity. However, due to continuous irrigation, the white blood cells in the drainage fluid are diluted, resulting in the abnormal phenomenon that the white blood cell count in the drainage fluid drops to normal quickly while the peripheral blood CRP drops slowly.

The research results show that among the three groups of patients, the treatment failure rates, that is, the rates of patients developing encapsulated empyema and requiring the injection of urokinase or thoracoscopic surgical intervention, were 3.8% vs. 16.1% vs. 21.1%. Although there was no statistical difference, in terms of the ratios, more patients in the intermittent irrigation group and the open irrigation group developed encapsulated empyema. This is considered to be related to incomplete drainage and irrigation, and the fibrin of the inflammatory exudate in the pleural cavity cannot be removed in time, resulting in the accumulation and formation of fibrous septa.

On the other hand, there was no statistically significant difference in the complication rates (7.7% vs. 3.2% vs. 5.3%, P=0.75) among the UTB group, the intermittent irrigation group, and the open irrigation group. However, in terms of the number of patients who needed to change the drainage protocol, no one in the UTB group needed to change, while 19.4% (6/31) in the intermittent irrigation group and 26.3% (5/19) in the open irrigation group changed to the UTB-EPLDS protocol. This indicates that the UTB-EPLDS has better stability and adaptability in clinical applications.

It must be emphasized that this study has several limitations. To simplify comparisons among the three irrigation-drainage protocols and minimize bias, we excluded patients with concurrent lung malignancies (13), subpleural pulmonary abscess rupture (14), active tuberculosis (15), or empyema secondary to thoracic surgery, trauma (16), spontaneous esophageal rupture/perforation (17), mediastinal procedures, subphrenic abscess spread via lymphatic pathways (18), as well as multiloculated empyema (19,20). These conditions often require management of comorbidities more complex than empyema itself, which would significantly prolong hospitalization and confound comparisons of this critical outcome. Consequently, the etiological spectrum of included empyema cases was relatively homogeneous, though UTB-EPLDS may still achieve favorable outcomes in the excluded scenarios. Additionally, the single-center retrospective design limits the reliability and generalizability of findings, as results may not fully represent broader clinical contexts. Furthermore, outcome measures focused predominantly on short-term therapeutic efficacy, lacking long-term evaluations such as pulmonary function recovery, pleural thickening severity, or quality-of-life improvements. These longitudinal metrics are essential for comprehensively assessing the clinical value of UTB-EPLDS.

Conclusions

The UTB-EPLDS presents remarkable superiority in treating empyema when juxtaposed with conventional drainage and irrigation techniques. It can effectively curtail the treatment duration, rein in the infection, and boasts better stability and adaptability. Nevertheless, in light of the limitations of this study, more extensive large-sample, multi-center, and prospective research is required to comprehensively appraise its clinical worth.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-923/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-923/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-923/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-923/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. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Xiamen University Affiliated Chenggong Hospital (No. 73JYY2024105799). Given the retrospective design of this study, the Ethics Committee waived the requirement for obtaining informed consent from each patient.

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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