Postoperative Air Leaks With Prompt Improvement of Low Suction on Digital Drainage Devices: a Retrospective Study

Purpose: The aim was to investigate the most effective suction pressure for preventing or promptly improving postoperative air leaks. Methods: We retrospectively analyzed the postoperative data of 242 patients who were monitored with a digital drainage system after pulmonary resection between December 2017 and June 2020. We divided the patients into 3 of group by suction pressure, A (Low-pressure suction group: -5 cm H (cid:0) O), B (Intermediate-pressure group: -10 cm H (cid:0) O), C (High-pressure suction group: -20 cm H (cid:0) O). Duration of air leaks, duration of chest tube replacement, the amount of postoperative air leak, uid volume drained before chest tube removal, and the maximum amount of air leaks during drainage were evaluated. Results: A total 217 patients were included. In the order of A, B, and C groups, duration of air leaks gradually decreased and signicant trend was observed (p=0.019). Duration of chest tube replacement did not signicantly differ among the three groups (p=0.126). The amount of postoperative air leak just after surgery did not signicantly differ among the three groups (p=0.175), however, the amount of postoperative day 1 air leak gradually decreased with statistical signicance in order of A, B, and C groups (p=0.033). The maximum amount of air leaks during drainage gradually decreased in order of A, B and C groups (p=0.036). Fluid volume drained before chest tube removal did not signicantly differ among the three groups (p=0.986). Conclusion: Low-pressure suction after pulmonary resection would be useful for preventing or promptly improving postoperative air leaks. and evaluate postoperative air leak and bleeding after pulmonary resection. There are many studies examining the optimum chest tube management for postoperative air leak after pulmonary resection. Several reports suggested that chest tube drainage followed by water seal could reduce duration of air leak and chest tube replacement after pulmonary resection (4, 5). In recent years, with the advent of the digitally monitored thoracic system (Medela, Healthcare, Baar, Switzerland), quantitative and temporal evaluations of postoperative air leakage and pleural pressure after pulmonary resection became possible. We hypothesized that low negative pressure suction on the chest tube after pulmonary resection could shorten duration of air leakage and chest tube replacement. The purpose of this study was to quantitative and temporal evaluate which suction pressure is most effective in preventing or early improving postoperative air leakage by the use of digitally monitored thoracic system.


Introduction
A postoperative air leak after pulmonary resection is one of the major factors that prevent leaving bed and delay early hospital discharge. Chest tube is critical component for postoperative air leakage management and affect hospital stay and costs (1,2). Moreover, the removal of chest tube reduces pain and improves ventilatory function in early postoperative course (3). Chest drainage tubes are routinely placed in the pleural space in order to promote re-expansion and evaluate postoperative air leak and bleeding after pulmonary resection. There are many studies examining the optimum chest tube management for postoperative air leak after pulmonary resection. Several reports suggested that chest tube drainage followed by water seal could reduce duration of air leak and chest tube replacement after pulmonary resection (4,5). In recent years, with the advent of the digitally monitored thoracic system (Medela, Healthcare, Baar, Switzerland), quantitative and temporal evaluations of postoperative air leakage and pleural pressure after pulmonary resection became possible. We hypothesized that low negative pressure suction on the chest tube after pulmonary resection could shorten duration of air leakage and chest tube replacement. The purpose of this study was to quantitative and temporal evaluate which suction pressure is most effective in preventing or early improving postoperative air leakage by the use of digitally monitored thoracic system.

Material And Methods
We investigate the most effective suction pressure for preventing or promptly improving postoperative air leaks. This is a single-institution, retrospective analysis-based study of data from an electronic database. Study protocol was approved by the Akashi Medical Center Institutional Research Ethics Board (approval number: 2020-9).

Patient Data
We collected the postoperative data of 242 patients who were monitored with a digital drainage system (Thopaz, Medela, Inc, Baar, Switzerland) after pulmonary resection. Included were patients who had lung resection using this digital drainage system between December 2017 and June 2020. We changed the suction pressure depending on periods. We divided the patients into 3 of suction group by observation with re-drainage, those with pleurodesis after surgery, and any patients that died perioperatively. Patients treated by re-drainage or pleurodesis were excluded because they would have remained in the study for a long period of time owing to chest tube replacement time, and their data would have limited clinical relevance to the outcomes.

Intervention
Patients underwent lobectomy, segmentectomy, and wedge resection for benign and neoplastic diseases.
Surgery was performed by video assisted thoracoscopic surgery (VATS) and posterolateral thoracotomy. Before closing a surgical incision, a sealing test was performed. The methods of sealing air leaks was managed with soft coagulation system. Additionally, we covered stapler line and bronchial stump with polyglycolic acid sheets and brin glue to prevent further air leaks in patients undergoing lobectomy or segmentectomy. One chest tube (18-20 Fr) was inserted before closure of the chest. After the surgery, the digital drainage system (Thopaz) was connected. The suction pressure in each group was set as follows: -5 cm H O for Low-pressure suction group (group A), -10 cm H O for Intermediate-pressure group (group B) or -20 cm H O for High-pressure suction group (group C) immediately after the operation until removal of the chest tube. The chest tube was removed when an air leak was < 20 ml/min and there were no spikes for at least 8 hours, and when the uid drainage was < 200 ml over 24 h. In patients undergoing lobectomy or segmentectomy, chest tubes were removed after at least two postoperative days. Clinical outcomes were duration of air leaks, duration of chest tube replacement, the amount of one-day postoperative air leak, uid volume drained before chest tube removal, and the maximum amount of air leaks during drainage. We analyzed clinical outcomes with ThopEasy software (Thopaz, Medela, Inc, Baar, Switzerland).

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Demographic characteristics of the patients were described using the mean with standard deviation (SD) for continuous variables and the frequency with proportion for categorical cariables. The Kruskal-Wallis test was used to compare the continuous outcomes, and Wilcoxon test with Holm adjustment was used to compare the three group pairwise. Moreover, to assess the trends of the chest and outcomes, we performed Jonckheere-Terpatra trend tests. All statistical analysis were performed with EZR software version 1.40 (Saitama, Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Stastistical Computing, Vienna, Austria) (6). A p value < 0.05 was considered statistically signi cant.

Results
We analyzed data from 242 consecutive patients who were digitally monitored by Thopaz system after undergoing pulmonary resection during the study period ( Fig. 1). Patient characteristics and operative data are presented in Table 1. Of these patients, 25 met the exclusion criteria; nine patients underwent reoperation because of postoperative air leaks (n = 7) or bleeding (n = 2), thirteen patients required pleurodesis, and two patients treated by re-drainage needed additional thoracostomy because of severe subcutaneous emphysema leading to lung expansion failure after surgery. One patient died of perioperative cardiac disease. Clinical outcomes are presented in Table 2. Assessment of air leaks of patients was performed every morning. The mean duration of air leaks was 0.57 days in group A, 0.78 days in group B, and 1.13 days in group C. In the order of A, B, and C groups, duration of air leaks gradually decreased and signi cant trend was observed (p = 0.019 by the Jonckheere-Terpstra test). This analysis indicates that chest tube suction pressure was signi cantly associated with duration of air leaks and low suction pressure promptly improves postoperative air leaks. However, the mean duration of chest tube replacement was 2.12 days in group A, 2.17 days in group B, and 2.35 days in group C and did not signi cantly differ among the three groups (p = 0.126 by the Jonckheere-Terpstra test). The amount of postoperative day 1 air leak gradually decreased with statistical signi cance in order of A, B, and C groups (p = 0.033 by the Jonckheere-Terpstra test). The amount of postoperative day 2 air leak did not signi cantly differ among the three groups (p = 0.520 by the Jonckheere-Terpstra test). The amount of postoperative air leak just after surgery did not signi cantly differ among the three groups (p = 0.175 by the Jonckheere-Terpstra test). The maximum amount of air leaks during drainage gradually decreased in order of A, B and C groups (p = 0.036 by the Jonckheere-Terpstra test). The mean uid volume drained before chest tube removal was 304.5 mL in group A, 289.7 mL in group B, and 289.0 mL in group C. Fluid volume drained before chest tube removal did not signi cantly differ between among three groups (p = 0.986 by the Jonckheere-Terpstra test). Clinical outcome in patients who underwent anatomical resection are presented in Table 3. The mean duration of air leaks was 0.90 days in group A, 1.55 days in group B, and 1.94 days in group C. In the order of A, B, and C groups, duration of air leaks gradually decreased with statistical signi cance (p = 0.010 by the Jonckheere-Terpstra test). The mean duration of chest tube replacement was 2.72 days in group A, 3.10 days in group B, and 3.15 days in group C and did not signi cantly differ among the three groups (p = 0.141 by the Jonckheere-Terpstra test). The amount of postoperative air leaks just after surgery and postoperative day 1 gradually decreased with statistical signi cance in order of A, B, and C groups (p = 0.017 and 0.008 by the Jonckheere-Terpstra test). The amount of postoperative day 2 air leak did not signi cantly differ among the three groups (p = 0.389 by the Jonckheere-Terpstra test). The maximum amount of air leaks during drainage decreased in order of A, B and C groups (p = 0.010 by the Jonckheere-Terpstra test). The mean uid volume drained before chest tube removal was 424.6 mL in group A, 459.3 mL in group B, and 477.7 mL in group C. Fluid volume drained before chest tube removal did not signi cantly differ between the three groups (p = 0.288 by the Jonckheere-Terpstra test). Clinical outcome in patients who underwent wedge resection are presented in Table 4. All category did not signi cantly differ among the three groups.

Discussion
A postoperative air leaks after pulmonary resection is one of the major factors in the cooperative period. Generally, postoperative air leakage stops spontaneously after a few hours up to few days (4, 5, 7). However, prolonged air leaks can cause various complications such as atrial brillation, thromboembolism, empysema, pneumonia, and respiratory failure which lead to prolonged hospital stay and increasing costs (1, 2). Our predecessors have tried various approaches to chest drain management for postoperative air leaks. Alphonso and colleagues and Brunelli and colleagues have described in their randomized study on the patients who underwent pulmonary resection that there are no differences between suction group and non-suction group concerning duration of air leaks (8,9). Although Leo et al, have described the routine use of external suction reduces the rate of prolonged air leaks after anatomic lung resection (10), Gocyk et al, have reported in their retrospective study that non suction drainage is more effective than suction drainage with regard to drainage volume, drainage duration, and the rate of prolonged air leak (5). The optimum postoperative suction pressure remains controversial.
Until recently, it is di cult to evaluate the amount of air leak by traditional closed chest tube drainage system. However, in recent years, with the advent of the digitally monitored drainage system, quantitative and temporal evaluations of postoperative air leaks and pleural pressure after pulmonary resection became possible. Goto M, et al, have reported that digitally monitored drainage system was useful predicting postoperative air leaks after pulmonary resection (11). Additionally, digitally monitored drainage system showed a signi cant reduction in duration of air leaks, chest tube replacement, and hospitalization compared to traditional closed chest tube (12). The main strength of our study is that the effect of chest tube suction pressure on the postoperative air leaks was quantitatively evaluated.
In our present study, it became so clear that duration of air leaks tends to be short signi cant as the suction pressure has decreased. It is suggested that low-pressure suction shortened duration of air leaks.
Holbek et al. report similar ndings in a prospective randomized study that a low suction pressure signi cantly shortened duration of air leaks and chest drain replacement (13). This study supports the study above-mentioned, however, duration of chest tube replacement did not signi cantly differ among the three groups. This is thought to be due to the chest tube removal after at least two postoperative days in patients undergoing lobectomy or segmentectomy. In addition, low-pressure suction tends to make the amount of air leak just after surgery and on postoperative 1 day fall, while there are no signi cant difference on postoperative 2 day in our analysis of anatomical pulmonary resection. In concluded, we suggest that low-pressure suction at least postoperative 1 day have the possibility of early improvement of air leakage on the patients whose air leakage can be expected to stop spontaneously. Handing the lung in kind way by low-suction pressure probably cause promoting early improvement of damage of lung parenchyma and preventing new tears in lung parenchyma by keeping a lung in the rest. There is no signi cant difference in uid volume drained before chest tube removal between three types of suction pressure. We believe that it is not necessary to perform high-pressure suction drainage considering postoperative pleural effusions and hemorrhage. The difference of all category between low-suction pressure group (group A) and intermediate-suction pressure group (group B) was not clear, but there is a good possibility that more accumulation was signi cant due to differences in the number of cases. Clinical outcome in patients who underwent wedge resection did not signi cantly differ between three groups. Given the lower numbers of postoperative air leakage appeared in the patients who underwent wedge resection, this may be attributable to a lack of power.
This study has several limitations. Our retrospective study was performed without the randomization of patient selection in a single center. Patients characteristics has no signi cant difference in all category between three groups, however, we could not deny some sample bias could distort our result because of no randomization. In addition, the number of excluded cases has increased to 25 cases because next treatment criteria for postoperative air leakage has not been decided. In some cases, pleurodesis and surgery were performed early after surgery, and in some cases second treatment were performed after one week, therefore, we have no choice to exclude all cases of second treatment for postoperative air leakage and bleeding.

Conclusion
Results of this analysis indicated that low suction pressure (-5 cm H O) shortened the duration of air leaks after pulmonary resection compared to other groups (-10 cm H O and − 20 cm H O). In addition, uid volume drained before chest tube removal did not signi cantly differ among the three groups. Lowpressure suction after pulmonary resection would be useful for preventing or promptly improving postoperative air leaks.

Declarations
Ethical Approval and Consent to participate Study protocol was approved by the Akashi Medical Center Institutional Research Ethics Board (approval number: 2020-9).

Consent for publication
Not applicable.

Availability of supporting data
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors have declared that they have no con ict of interest.