Chest drainage outcomes by water seal versus low suction on digital drainage systems after lung resection: retrospective study

Introduction

Postoperative air leaks can present a significant challenge after anatomical lung resection, potentially impacting upon patient recovery and healthcare resources (1-6). Water seal methods have long been the cornerstone of thoracic drainage management, offering a simple and effective means of managing air leaks (2,3,7-9). Several meta-analyses have shown the superiority of water seals in reducing the duration of chest drainage compared with continuous suction (4,9,10). Recently, however, digital drainage systems (DDS) have introduced the ability to continuously monitor air leaks and to regulate intrathoracic pressure, potentially simplifying postoperative management and facilitating earlier drain removal (1,6,11-13).

Despite these technological advancements, the optimal approach for managing postoperative air leaks is unclear (5,6,12,14,15). In a previous comparison of DDS set at low and high suction pressures, we observed that low pressure settings may minimize lung parenchymal damage and may accelerate recovery compared with high pressure settings (5); this highlights the advantages of gentler lung handling in the postoperative period. However, even with DDS set to low suction pressure, there remains a risk of intense suction until the intrathoracic pressure reaches the preset level (15). Focusing on gentle lung handling, we therefore hypothesized that the water seal could reduce the durations of air leak and chest drainage compared with DDS set to low suction pressure, particularly in patients with air leak following lung resection.

This study aims to evaluate the optimal drainage method by comparing the air leak and chest drainage durations in patients managed with traditional water seal and low suction on DDS. By concentrating on only patients with initial postoperative air leaks, we aim to identify which specific intervention best improves pulmonary fistula recovery processes. The findings of this research are intended to directly inform the development of detailed clinical protocols, ultimately elevating the standard of care for patients after thoracic surgery. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1069/rc).

Methods

Ethical statement

This retrospective study was conducted at the Department of Thoracic Surgery, Akashi Medical Center, Japan. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study protocol was approved by the Akashi Medical Center Institutional Research Ethics Board (approval No. 2023-5), ensuring compliance with ethical standards. The requirement for written informed consent was waived, but instead the study information and opportunities to opt out were provided on the web site owing to the retrospective nature of this study.

Patient data

We collected postoperative data from the patients at our institution who underwent anatomical lung resection between August 2015 and April 2023. During the 8-year observation period, at least one board-certified thoracic surgeon participated in the surgery and in the postoperative management of almost all cases, ensuring reasonable consistency. Included in the study were individuals who had postoperative chest drainage managed either with a water seal (chest drain bag, SB-KAWASUMI LABORATORIES, Kanagawa, Japan), or DDS set to low suction pressure (−2 to −5 cmH₂O) managed with the Thopaz+ (Medela Healthcare, Baar, Switzerland). Our suction pressure settings were lower than −8 cmH₂O, which is equivalent to passive drainage, because previous reports have shown that low suction pressure significantly shortened the durations of air leak and chest drainage (5,16). We excluded patients who did not exhibit an air leak on the first postoperative morning, those with missing data due to hospital transfers, and those who required reoperation. Reoperations were excluded because they are different procedures adapted to each patient and because they are thought to have limited clinical relevance to the outcomes. Patients with benign disease were also excluded because postoperative course is different from malignant diseases (17). Data taken from an electronic database included sex, age, body mass index, Brinkman index, primary disease, comorbidities, surgical procedure, surgical approach, degree of air leakage on the first operative morning, air leak duration and chest drainage duration. We also collected data on the need for pleurodesis, conversion of drainage methods, and drain reinsertion after removal. We collected air leak volume of the DDS by using ThopEasy+ software (Medela Healthcare).

Operative procedures

All patients underwent anatomical lung resections, including lobectomy or segmentectomy. The surgeries were by video-assisted thoracoscopic surgery (VATS) or posterolateral thoracotomy. Before closing the incision, a sealing test was performed at a pressure of 20 cmH₂O. If an air leak was present, a soft coagulation system was used to ensure minimal air leakage. Staple lines and bronchial stumps were covered using polyglycolic acid sheets (Neoveil, Gunze Medical, Kyoto, Japan) and fibrin glue (Bolheal, KM Biologics, Kumamoto, Japan). An 18 or 20 Fr chest tube was inserted before chest closure.

Postoperative management

Postoperatively, patients received treatment by either the water seal or the low suction pressure DDS. In the water seal group, the chest tube was suctioned at −10 cmH₂O in the operating room to ensure no bleeding, and was changed to water seal the next morning. In the low suction group, the chest tube was connected to the DDS set at −2 to −5 cmH₂O in the operating room. The selection and conversion of either management strategy was based on clinical judgment and the preference of the attending surgeons. The low suction on DDS was introduced in our hospital between November 2019 and September 2022, and during this period it was basically used as standard. However, sometimes water seal was selected when the lungs were deemed to be highly fragile according to intraoperative findings.

Air leak assessment

On the first postoperative morning, we assessed air leaks and divided the patients into two groups according to the chest drainage method. In the traditional drainage system, the leak was observed under −10 cmH₂O suction. According to previous reports (7,15,18), air leaks were defined as mild (cough or forced expiratory only), moderate (resting expiratory only), or severe (inspiratory or continuous throughout respiratory cycle). In the DDS, the degree of air leakage was defined as mild (≤100 mL/min), moderate (101–500 mL/min), or severe (≥501 mL/min), according to previous study (15). Air leaks were assessed twice daily by experienced thoracic surgeons. The criteria for leak cessation depended upon the management strategy. In the case of water seals, the leak cessation was confirmed by the absence of bubbles in the water seal chamber, even when patients engaged in coughing or forced expiratory. For patients treated with DDS, the leak cessation was defined as an air leak <20 mL/min without spikes for at least 8 hours. The chest tube was removed when the criteria for leak cessation had been met and drainage effusion was <200 mL over 24 hours. Pleurodesis was considered if the air leak lasted longer than 5 days, or if the air leak volume was considered to be too large.

Statistical analysis

Time-dependent variables were analyzed using the Kaplan-Meier method, and differences were analyzed using the log-rank test. Fisher’s exact test assessed categorical variables, while Mann-Whitney U tests were used to compare continuous variables. All statistical analyses were performed with EZR software version 1.61 (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria) (19). A P value <0.05 was considered to be statistically significant.

Results

Patient characteristics

We analyzed data from 479 patients who underwent anatomical lung resection during the study period; 281 patients who were managed with either a water seal or DDS set to low suction pressure met the inclusion criteria. Of these patients, 156 patients were excluded from the study owing to having had no air leak on the first postoperative morning. We also excluded the four patients that required reoperations, the three patients that required hospital transfers, and the two patients with benign diseases (Figure 1). This left 116 patients who were eligible for the study, focusing on comparing the effectiveness of water seal (n=59) vs. low suction pressure DDS (n=57). The characteristics and operative data of these patients are detailed in Table 1. Patients comprised 81 males and 35 females, with an age distribution spanning from 45 to 86 years. The most common diagnosis was primary lung cancer (n=112), followed by metastatic lung tumor (n=4). The majority of surgical procedures were lobectomies (n=98), followed by segmentectomies (n=18). The baseline characteristics of the two groups were thus well balanced, and the incidence of mild air leaks on the first operative morning was above 90% in both groups.

Figure 1 Patient flow diagram. DDS, digital drainage system.

Air leak duration and chest drainage duration

We observed a significant disparity in the duration of postoperative air leaks between the groups. The water seal group had a median air leak duration of 2 days [95% confidence interval (CI): 2–2], notably shorter than the 3 days (95% CI: 2–5) observed within the low suction group (P<0.001) (Figure 2A). Additionally, at one week postoperatively, the leak cessation rate was significantly higher in the water seal group at 94.9% (95% CI: 87.2–98.7%) compared with the 80.7% (95% CI: 69.6–89.7%) in the low suction group. Furthermore, the duration of chest drainage also favored the water seal group, with a mean duration of 3 days (95% CI: 2–3) compared with 5 days (95% CI: 4–6) for patients in the low suction group (P<0.001) (Figure 2B).

Figure 2 Kaplan-Meier curve for (A) air leak and (B) chest drainage durations. CI, confidence interval.

Pleurodesis, conversion to another drainage methods, and reinsertion

The incidence of pleurodesis, an indicator of more persistent and challenging air leaks, was notably higher in the low suction group (28.1%) than in the water seal group (6.8%) (P=0.002) (Table 2). Conversion from the initial drainage strategy occurred in 29.8% (n=17) of patients in the low suction group compared with only 6.8% (n=4) in the water seal group (P=0.001) (Table 2). In the low suction group, 15.8% (n=9) of patients were converted to water seal to alleviate high leakage. In addition, 14.0% (n=8) of the low suction group and 3.4% (n=2) of the water seal group required higher suction force due to increasing subcutaneous emphysema or inadequate lung expansion. The rates of drain reinsertion after removal were not significantly different between the two groups (Table 2). In all cases, the reason for reinsertion was that the lung had collapsed after drain removal.

Discussion

In this study, we examined the treatment strategies for postoperative air leaks following anatomical lung resection. Traditional water seal methods were shown to result in shorter durations of air leak and chest drainage compared with low suction pressure DDS for patients with residual postoperative air leak. Water seal management may therefore accelerate lung recovery in such patients. Also, there were significantly more cases of pleurodesis in our low suction group, but no significant difference in the rates of drain reinsertion between the two groups.

We propose two primary mechanisms for the cessation of postoperative air leaks: one is by reducing the amount of airflow through the pleural fistula, promoting healing of lung injuries and closure of pulmonary fistulas through alveolar epithelial cell induction (2,3,8,15,20,21). The other mechanism is using negative thoracic pressure to encourage lung expansion and adhesion of the damaged visceral pleura (2,3,8,15,20). However, excessive continuous suction has been suggested to aggravate air leaks and to hinder the pulmonary healing process. Previous meta-analyses did not demonstrate the superiority of continuous suction over the use of a water seal for shortening the duration of air leakage following lung resection (4,9,10).

Several meta-analyses of the use of DDS have shown significantly shorter drainage durations compared with traditional chest drainage systems (6,12,13). Water seal methods, which are still used in many clinical settings, require the surgeon to frequently observe the bag at the bedside to check the amount of bubbles and the up-and-down movement of the water-filled bottle, so there is some reliance upon the clinician’s subjective judgement (6,11,13,22). The emergence of DDS, offering precise air leak quantification and 24-hour monitoring functions, represents a significant technological advancement over traditional chest drainage systems, especially benefiting inexperienced clinicians and co-medics (1,6,11-13,22). Furthermore, there is an added problem when patients cannot forcefully cough due to postoperative pain: it is difficult to accurately assess air leaks with traditional chest drainage systems. However, with DDS, air leaks can be more accurately assessed because they are automatically set to the pre-set intrathoracic pressure. Indeed, in this study, 3.4% (n=2) of patients in the water seal group had difficulty with forced coughing and were converted to DDS for more accurate leak assessment.

On the other hand, the question of the optimal pressure setting for DDS is critical. The duration of drain placement at −5 and −20 cmH₂O settings were concluded to be equivalent in one study (14), while three other studies (5,16,23) all indicated that the low suction pressure setting showed a shorter air leak duration compared with high suction pressure settings. Maintaining a low-pressure environment in the chest cavity, thereby minimizing lung stress, may be therefore more conducive to leak resolution than applying strong negative pressure. However, even using low suction pressure settings, suction with DDS may be continued until the pre-set pressure is reached, potentially leading to unexpectedly strong lung suctioning and hindrance of pulmonary fistula healing (15). In a previous comparison of continuous suction, DDS and water seal, the water seal was found to be the most effective of the three in eliminating air leaks (15), which is consistent with our results.

Notably, we observed increased subcutaneous emphysema and inadequate lung expansion in 14.0% of the low suction group and 3.4% of the water seal group, necessitating higher suction pressure settings. Another report also noted that there was a need to increase suction pressure in 7% of patients on low suction pressure due to poor control of subcutaneous emphysema (16). Gentle management with low suction pressure DDS or water seal is beneficial for limited leaks, but larger leaks may require more aggressive interventions (7,10,16). These findings underscore the importance of patient-specific management strategies based on daily assessments of imaging studies and leak volumes.

A strength of this study is its comparison of two groups with a focus on the minimization of lung stress. While numerous studies have compared water seals to continuous suction or DDS with various pressure settings, few have specifically directly compared DDS at low suction pressure settings to water seals. This distinction allowed us to explore the most suitable drainage management strategy.

Our study has several limitations. Its retrospective, single-center design and lack of randomization potentially introduce selection biases. Additionally, decisions regarding conversion of the drainage method and pleurodesis timing are to some extent based on the surgeon’s preference, and this may have influenced the outcomes. The continuous monitoring capability of DDS also introduces discrepancies in leak cessation timing compared with the twice-daily checks of water seals, potentially affecting the accuracy of our findings. In addition, there is no clear consensus on the leak cessation criteria for the low suction DDS, so we applied the same criteria as for standard suction (−8 to −20 cmH₂O), which may have influenced the results. Further research is needed on the management of the low suction setting on DDS.

Conclusions

In conclusion, water seal management was suggested to be safe and comparably effective to low suction on DDS in reducing air leak and chest drainage durations after lung resection. Further research, ideally through randomized controlled trials, is needed to validate these findings and to refine postoperative air leak management protocols.

Acknowledgments

We acknowledge proofreading and editing by Benjamin Phillis.

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1069/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1069/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1069/prf

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1069/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 (as revised in 2013). The study was approved by the Akashi Medical Center Institutional Research Ethics Board (approval No. 2023-5). The requirement for written informed consent was waived, but instead the study information and opportunities to opt out were provided on the web site owing to the retrospective nature of this study.

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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