Slow-firing mode reduces stump oozing during pulmonary vessel stapling

Introduction

Stump oozing from the central vascular stump is a subtle but clinically relevant challenge in anatomical pulmonary resection. Although major vascular injury during stapling is rare (<1%), minor stump oozing can contaminate a surgical field and prolong operative time (1).

Although modern powered staplers have standardized pulmonary vessel transection and improved procedural speed, the optimal strategy for minimizing stump oozing remains unclear, particularly for thin-walled pulmonary arteries (PAs) that are prone to incomplete staple formation under mechanical stress. Contemporary powered stapling systems automatically adjust firing speed based on tissue resistance, but tend to default to fast-firing for delicate vascular structures (2). This “one-speed-fits-all” approach may overlook subtle anatomical factors that affect staple line integrity. In particular, intraoperative factors, such as stapler lifting or twisting increase the risk of stump oozing (3).

Experimental studies in gastrointestinal stapling have demonstrated that slower firing improves staple line integrity and reduces tissue injury in delicate tissues (4). However, whether this simple intraoperative adjustment can reduce central stump oozing during pulmonary vessel transection has not been systematically evaluated in clinical practice. Importantly, the PA has unique anatomical fragility compared to other tissues, making it especially susceptible to mechanical stress during stapling.

This study aimed to evaluate whether deliberate use of surgeon-controlled slow-firing reduces stump oozing compared with default automatic fast-firing mode during pulmonary vessel transection. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1643/rc).

Methods

Study design and population

This retrospective two-center cohort study included consecutive patients who underwent anatomical pulmonary resection (segmentectomy, lobectomy, bilobectomy, or pneumonectomy) at Seirei Mikatahara and Kariya Toyota General Hospitals from January 2023 to December 2024. All pulmonary vessels were transected using a Signia™ White 30 stapler (Medtronic, Minneapolis, MN, USA). From August 2023, the manual slow-firing mode was selectively used at surgeon’s discretion; the choice was not protocol-driven. The approximate blade traversal times were 12 s (slow), 6 s (medium), and 3 s (fast), measured frame-by-frame from intraoperative video. This study was approved by the Institutional Review Boards of Seirei Mikatahara General Hospital (central IRB approval No. 24-59) and Kariya Toyota General Hospital (approval No. 1082, approved on December 13, 2024). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The requirement for individual informed consent was waived because this was a retrospective study that used anonymized data with an opt-out procedure disclosed on the hospitals’ websites.

Inclusion and exclusion criteria

Eligible patients were aged ≥18 years, had an Eastern Cooperative Oncology Group performance status of 0 or 1, underwent anatomical pulmonary resection, and had preserved major organ function. Patients requiring dialysis or those with a history of cirrhosis were excluded. Additional exclusion criteria included failure to discontinue antithrombotic agents preoperatively, a platelet count of <50,000/µL, prolonged activated partial thromboplastin time or prothrombin time prior to surgery, known bleeding disorders or vascular anomalies, and use of alternative staplers for pulmonary vascular transection. Cases in which no stapler was used for vascular transection or operative video data were missing were also excluded. Medium-firing mode, due to automatic adjustment or partial manual activation, could not be reliably classified from video or device logs and was excluded to ensure a clear dichotomy.

Outcomes

Primary outcome of this study was stump oozing from the central vascular stump lasting ≥15 s following vascular transection. Stump oozing was defined as visible persistent bleeding either from the staple pinholes or from the open lumen of the transected vessel stump for this period after stapler removal. The threshold of 15 seconds was chosen with reference to a similar intraoperative hemostasis assessment used by Khandhar et al. (5). This choice was also consistent with our surgical practice, in which oozing that stopped within 15 seconds was typically regarded as clinically negligible, whereas persistent oozing beyond this interval usually requires surgeon attention and sometimes intervention. We therefore considered ≥15 s to be a practical and reproducible criterion that distinguishes trivial self-limited bleeding from clinically relevant stump oozing in the retrospective video review setting. However, this definition also included cases in which manual compression was applied within the 15-second interval and hemostasis was achieved. It also encompassed very mild oozing that, despite its trivial appearance, happened to persist beyond 15 seconds, as well as events that may not have been noticed intraoperatively.

Secondary outcomes included the need for additional hemostatic procedures, such as manual compression, topical agents, or suture ligation, and stapler firing time, defined as the interval from closure to reopening of the stapler jaws. Diameter of the compressed vessel was measured using a graduated scale marked at 5-mm intervals on the stapler jaws during vessel clamping. The type of transected vessel [PA or pulmonary vein (PV)] was also recorded. Intraoperative mechanical stress during stapling, including lifting (defined as the upward deviation of the stapler from the vessel axis), twisting, and lung traction (excessive tension applied to the surrounding lung parenchyma during stapling), was also evaluated (Figure 1A-1C). Two independent thoracic surgeons reviewed each video frame-by-frame to assess the presence of these factors. A maneuver was classified as present (positive) only when both reviewers agreed. In cases of initial disagreement, the videos were jointly re-reviewed and resolved by consensus. The overall interobserver agreement was qualitatively high throughout the process. To assess baseline comparability between the groups, we collected data on patient age, sex, surgical side (right vs. left), cumulative smoking exposure (pack years), surgical approach (thoracotomy, multiportal video-assisted thoracoscopic surgery (VATS), or uniportal VATS), and confirmed preoperative discontinuation of oral antithrombotic therapy. Patients who continued antithrombotic therapy at the time of surgery were also excluded. All outcomes were assessed on a per-vessel basis rather than a per-patient basis.

Figure 1 Representative intraoperative illustrations showing three types of mechanical stress that can occur during pulmonary vessel stapling. (A) Lifting: upward deviation of the stapler relative to the vessel axis during firing. (B) Twisting: rotational misalignment of the stapler around the vessel axis. (C) Traction: excessive tension applied to the surrounding lung parenchyma during stapling. Yellow (solid) arrows indicate the direction of tension acting on the stapler, while black (solid) arrows indicate the direction of tension applied to the vessel.

Statistical analysis

Descriptive statistics were used to summarize baseline characteristics (Table 1) and operative findings (Table 2). Continuous variables are presented as medians with interquartile ranges (IQRs) and compared using the Mann-Whitney U test. Categorical variables are summarized as counts (percentages) and compared using the Chi-squared or Fisher’s exact test, as appropriate. To assess the effect of stapling mode on stump oozing, propensity scores were first estimated using logistic regression, incorporating relevant baseline and intraoperative variables. Inverse probability of treatment weighting (IPTW) using stabilized weights was then applied. Covariate balance before and after weighting was evaluated using standardized mean difference (SMD), with an SMD <0.1 indicating acceptable balance (Table 3). Because some residual imbalance remained after weighting (e.g., lifting), we adopted a doubly robust approach, applying weighted regression models with IPTW while additionally adjusting for variables with SMD ≥0.1. This yielded adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for the primary outcome (Table 4). A separate multivariable logistic regression analysis without weighting was also performed in the full cohort to identify the independent predictors of prolonged stump oozing (Table 5). Variables with a P value <0.25 in univariable analysis were included in the multivariable model (6). Pre-specified subgroup analyses were conducted using unweighted logistic regression in the stratified cohorts: fast-firing mode stapling (Table S1), slow-firing mode stapling (Table S2), PA transections (Table S3), and PV transections (Table S4). In these subgroup analyses, the variable “Twisting” was excluded due to the small number of observed events. Sensitivity analyses were conducted to assess the robustness of the primary findings. Specifically, one sensitivity analysis excluded the variable “Lifting” (Table S5), and another included Medium-firing mode stapling reclassified as Fast-firing (Table S6). All statistical analyses were conducted using the R software (version 4.2.1; R Foundation for Statistical Computing, Vienna, Austria). P values were considered statistically significant at two-sided values <0.05. For subgroup and sensitivity analyses, a conservative Bonferroni correction was applied, setting the adjusted threshold for statistical significance at P<0.005 to account for up to 10 simultaneous tests.

Results

A total of 139 patients who underwent anatomical pulmonary resection were initially identified, yielding 338 pulmonary vessel transections for potential analysis. Of these, 62 transections were excluded on the basis of the following criteria: absence of intraoperative video data (n=30); use of medium-firing mode due to automatic adjustment or partial manual activation (n=21); unrecorded stapling process (n=6); and continuation of antithrombotic therapy at the time of surgery (n=5). After exclusion, 276 vessel transections were included in the final analysis; 168 (60.9%) were performed using the manual slow-firing mode and 108 (39.1%) using the automatic fast-firing mode (Figure 2).

Figure 2 Flow diagram illustrating patient selection and pulmonary vessel stapling inclusion process. A total of 139 patients undergoing anatomic pulmonary resection were initially identified, yielding 338 pulmonary vessels stapled. After exclusions, 276 vessel stapling were analyzed in the final cohort. SDR, Small Diameter Reload.

Baseline characteristics

Baseline characteristics were comparable between the slow and fast-firing mode groups (Table 1), including age, sex, surgical side, smoking exposure, surgical approach, and use of antithrombotic therapy. Median patient age was 73 years (IQR, 64–76 years), with no significant differences in age distribution, sex, surgical side, cumulative smoking exposure (pack-years), surgical approach, or oral antithrombotic therapy.

Intraoperative outcomes

Prolonged stump oozing (≥15 s) from the central vascular stump was observed in 64 (23.2%) stapling. The incidence was significantly lower in the slow-firing mode group than that in the fast-firing mode group (17.9% vs. 31.5%, P=0.01) (Table 2). Median stapler firing time was longer in the slow-firing mode group [26 s (IQR, 24–29 s)] than that in the fast-firing mode group [15 s (IQR, 13–19 s); P<0.001]. There were no significant differences in the overall need for additional hemostatic procedures or in the distribution of vessel types. Among 64 cases classified as prolonged stump oozing, 26 underwent manual compression. In nine of these cases, bleeding persisted and further intervention was required: two with suture ligation and seven with topical sealant (TachoSil Tissue Sealing sheet^®, CSL Behring K.K., Tokyo, Japan). The remaining oozing events were very mild and self-limiting without intervention, or were not recognized intraoperatively despite being visible on video review. Lifting during vessel stapling was significantly less frequent in the slow-firing group than that in the fast-firing group (24.4% vs. 41.7%; P=0.003).

Propensity score adjustment

After applying IPTW using stabilized weights, most covariates achieved adequate balance (SMDs <0.1), although some residual imbalance persisted, particularly for lifting (Table 3). To account for this, we applied doubly robust weighted logistic regression models, additionally adjusting for variables that remained imbalanced after weighting. In this analysis, slow-firing mode stapling was independently associated with a reduced risk of prolonged stump oozing (OR, 0.51; 95% CI: 0.28–0.93; P=0.03), while lifting during vessel transection remained a significant risk factor (OR, 2.41; 95% CI: 1.31–4.43; P=0.005) (Table 4).

Multivariable analysis

In the unweighted multivariable logistic regression model (Table 5), slow-firing mode stapling was again significantly associated with a reduced risk of stump oozing (OR, 0.47; 95% CI: 0.24–0.90; P=0.02). Other independent predictors included PA transection (OR, 8.01; 95% CI: 3.47–21.16; P<0.001), lifting (OR, 4.52; 95% CI: 2.22–9.53; P<0.001), and lung traction (OR, 3.94; 95% CI: 1.75–9.03; P=0.001).

Secondary outcomes

Secondary outcomes are summarized in Table 6. The need for additional hemostatic procedures did not differ significantly between the slow- and fast-firing groups (8.9% vs. 10.2%; adjusted OR, 1.06; 95% CI: 0.45–2.53; P=0.89). In contrast, stapler firing time was significantly longer in the slow-firing group [median 26 (IQR, 24–29) vs. 15 (IQR, 13–19) s; adjusted mean difference, +9.95 s; 95% CI: 8.33–11.58; P<0.001].

Subgroup and sensitivity analyses

In the fast-firing mode group (Table S1), PA transection (OR, 8.77; 95% CI: 2.51–32.76; P<0.001) and lung traction (OR, 7.89; 95% CI: 2.10–34.40; P=0.003) remained strongly associated with prolonged stump oozing after conservative Bonferroni correction. Among PA transections (Table S3), lifting (OR, 4.45; 95% CI: 2.04–10.06; P<0.001) and lung traction (OR, 5.12; 95% CI: 2.04–13.34; P<0.001) were also significant predictors. Other factors in subgroup analyses did not retain statistical significance after adjustment for multiple comparisons.

A sensitivity analysis excluding the variable “Lifting” confirmed the robustness of the protective association between slow-firing mode and reduced stump oozing (OR, 0.41; 95% CI: 0.22–0.75; P=0.004) (Table S5). By contrast, a sensitivity analysis including medium-firing mode cases reclassified as fast-firing showed a weaker effect (OR, 0.47; 95% CI: 0.25–0.87; P=0.02) that did not reach significance after correction (Table S6). These subgroup and sensitivity analyses were exploratory and should be interpreted with caution.

Discussion

This retrospective cohort study demonstrated that the deliberate use of the manual slow-firing mode during pulmonary vessel stapling significantly reduced the incidence of prolonged stump oozing from the central vascular stump compared with the default automatic fast-firing mode. Even after adjusting for potential confounding factors using IPTW and logistic regression, slow firing remained an independent protective factor. These findings suggest that stapler firing speed may not necessarily be treated as a fixed device setting but could be considered an adjustable intraoperative variable that influences stump integrity, although this conclusion should be interpreted cautiously given the retrospective single-device design.

A major strength of this study was that it quantified an often-overlooked aspect of thoracic surgery: subtle but persistent stump oozing. Although catastrophic vascular injury is rare during pulmonary vessel transection, low-grade stump oozing can contaminate the surgical field, prolong hemostasis time, and necessitate unplanned intervention. Such minor events may cumulatively affect operative efficiency and surgeon focus; however, they are often underreported. By systematically recording bleeding duration and standardizing its definition (≥15 s) through video review, this study provides an objective metric that can be used to improve surgical quality.

A key finding was the apparent difference in oozing risk between PA and PV transections. PA transection consistently emerged as an independent risk factor for prolonged stump oozing in the present study. This likely reflects anatomical differences, as the PA has a thinner wall and adventitia, making it more vulnerable to mechanical stress during stapling. In contrast, the PV has a thicker adventitia that may help maintain staple line integrity even with faster firing (7). Subgroup analysis supported this finding; the benefit of slow firing was most evident in the PA transections, showing a trend toward a lower bleeding risk that approached statistical significance.

Mechanical factors are also important. Lifting and lung traction were identified as significant independent predictors of stump oozing. These maneuvers can disrupt the alignment between the stapler and vessel, thereby increasing the risk of incomplete staple formation and tissue tearing. Lifting was less frequent in the slow-firing group, likely because slower blade advancement allows for steadier handling and more precise alignment, thereby reducing unintended deviations. This supports that safe staple formation depends on pre-compression and stable blade motion during firing. Even when both lifting and lung traction were absent, the incidence of stump oozing in the slow-firing mode group remained at 11.1%. This suggests that factors other than mechanical stress, such as inherent vessel wall fragility, local tissue characteristics, or intraoperative medial disruption, may contribute to stump oozing. Moreover, vessel diameter alone may not fully represent wall thickness, and further research is needed to clarify these relationships.

These observations align with experimental data from gastrointestinal stapling. Previous studies have shown that extending precompression time before firing improves staple formation quality (8), and that slower blade progression reduces tissue injury and enhances staple line security (4). More recent work also demonstrated that deliberate slow-firing can improve staple leg alignment and reduce malformation, although the effect may vary depending on the stapler platform (9). Collectively, these findings support the biomechanical rationale that gradual compression and slower blade advancement allow more even distribution of stress, reducing tissue tearing and staple malformation. Although the pulmonary vasculature is thinner and more fragile than gastrointestinal tissue, the same principles are likely to apply: gradual and stable compression minimizes micro-injury at the staple line and reduces oozing from the vascular stump.

Practically, any benefit of the slow-firing mode must be weighed against its effect on the operative time. In this study, the median firing time was approximately 11 s longer in the slow-firing group, which may appear minor, but can accumulate when multiple vessels are stapled. However, this small amount of time investment may be offset by the reduced intraoperative bleeding, fewer unplanned interventions, and less surgical field contamination. Improving staple security upfront is preferable for managing unexpected bleeding. Importantly, although slow firing significantly prolonged stapler firing time and reduced the incidence of prolonged stump oozing, this did not translate into a lower frequency of additional hemostatic procedures, indicating that most oozing events in both groups were minor and often self-limiting.

These findings are also relevant to the expanding use of minimally invasive thoracic surgery. Narrow working spaces, restricted visualization, and limited maneuverability can increase the risk of misalignment and mechanical stress. Newer powered staplers with slimmer reloads, such as the Signia™ system with its Small Diameter Reload, allow better access to small or deep hilar branches, but at the cost of fewer staple rows. This trade-off may increase the risk of incomplete closure, particularly when combined with fast firing in fragile arteries. The deliberate use of slow-firing mode may help mitigate this risk without incurring additional costs or requiring new equipment. This simple adjustment may be particularly useful in narrow-access procedures such as uniportal VATS, where stable stapling is technically more demanding due to limited working angles.

Despite the benefits of powered staplers with automatic tissue sensing (2), this study highlights the limitations of fully automated algorithms. Current systems default to fast-firing mode when they detect low resistance, which is precisely the scenario in which slow-firing might be more beneficial. Surgeons should remain attentive and override the default when the anatomy suggests that fast firing could compromise staple formation. This challenges passive reliance on automatic modes and emphasizes the surgeon’s role in adjusting the technique to match tissue conditions.

Although the absolute magnitude of stump oozing is modest and typically manageable with gentle compression or topical agents, these findings are relevant. Even minor bleeding can obscure the surgical field and increase the risk of serious bleeding or inadvertent injury if not properly controlled. As major vascular complications are rare, addressing these subtle but common events offers a meaningful way to refine surgical safety without relying on new technologies. In contrast, rare but catastrophic cases have also been reported, in which staple-line failure led to massive vascular rupture and life-threatening hemorrhage requiring reoperation (10). Such tragic events underscore the critical importance of secure staple formation, and deliberate adjustments such as slow firing may help reduce not only minor stump oozing but also, potentially, the risk of severe bleeding complications.

This study has several limitations that must be acknowledged. First, the retrospective and non-randomized design carries a risk of residual confounding despite robust adjustment methods. Second, all procedures were performed using a single powered stapler platform (Signia™, Medtronic); therefore, the findings should be considered exploratory and their generalizability to other stapler systems remains uncertain. Third, the definition of prolonged stump oozing was based on intraoperative videos and visual estimations, which may have introduced subjectivity. Although intraoperative videos were carefully reviewed, it was extremely difficult to precisely classify the exact bleeding source (such as staple pinholes, stump edge, or staple line depth) due to the limited resolution and field of view, and this was not systematically recorded. In Addition, although medium-firing mode cases were initially excluded due to classification uncertainty, they were included in a sensitivity analysis, which confirmed the consistency of our main results. Although a conservative Bonferroni correction was applied for key subgroup and sensitivity analyses, the risk of residual type I error remains due to the exploratory nature and the multiple statistical tests performed.

Fourth, conditions that may increase PA pressure, such as pulmonary hypertension or advanced emphysema, could potentially affect the risk of stump oozing specifically from the central PA stump; however, relevant clinical data were not available, and these factors were not systematically evaluated. Fifth, although hemostatic interventions such as compression, suture ligation, or topical sealant were predefined as secondary outcomes, the majority of oozing events were minor and judged by the surgeons to stop spontaneously without intervention. Only 26 of 64 oozing cases underwent initial compression, and 9 required further measures (2 suture ligations and 7 topical sealants). This reflects the subjective nature of intraoperative decision-making in managing minor stump oozing. Finally, the choice of firing mode was left to the discretion of the surgeons. Most fast-firing cases were performed before the study was conceived; therefore, the frequency of compression in the fast-firing group was unlikely to have been influenced by surgeon awareness of the study. After the study was conceived, slow-firing mode was routinely applied irrespective of patient characteristics, and the few fast- or medium-firing cases that occurred thereafter were due to inadvertent activation of the automatic mode or technical handling rather than deliberate surgeon preference. In addition, more experienced surgeons may have used fast firing in straightforward cases and preferentially selected slow firing for more fragile vessels where they anticipated a higher bleeding risk. This potential selection bias is an inherent limitation of our retrospective design and warrants careful interpretation of the results.

Moreover, the subgroup analyses should therefore be regarded as exploratory. Although some associations appeared significant before correction, the statistical significance did not remain after Bonferroni adjustment. Accordingly, these findings should be interpreted with caution and considered hypothesis-generating rather than confirmatory.

Future studies should build on these findings by conducting prospective trials, ideally multicenter, randomized trials comparing firing modes across different stapler platforms and various pulmonary vessel conditions. Further cost-benefit analyses could help clarify whether lower bleeding risks and fewer unplanned hemostasis measures balance the slight increase in time with slower firing.

Conclusions

This study suggests that the selective use of slow-firing mode may be a simple and feasible method for reducing subtle yet clinically relevant stump oozing during pulmonary vessel transection, especially in certain anatomical contexts such as the PA. By considering stapler firing speed as an adjustable factor rather than as a fixed device setting, surgeons may better tailor their technique to the anatomy and intraoperative situation. However, these findings should be regarded as exploratory and interpreted with caution, as they were derived from procedures performed with a single powered stapler platform. Their generalizability to other stapler systems remains uncertain. Nevertheless, this adjustment did not require new equipment, additional training, or additional costs, and may represent a practical strategy to optimize staple line security. Future multicenter trials are warranted to validate these results and guide optimal intraoperative stapling strategies.

Acknowledgments

We gratefully acknowledge Miyuki Abe for her invaluable contribution to this study through the creation of original illustrations, which significantly enhanced the clarity and visual quality of the manuscript.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1643/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1643/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1643/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-2025-1643/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. This study was approved by the Institutional Review Boards of Seirei Mikatahara General Hospital (central IRB approval No. 24-59), and Kariya Toyota General Hospital (approval No. 1082, approved on December 13, 2024). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The requirement for individual informed consent was waived because this was a retrospective study that used anonymized data with an opt-out procedure disclosed on the hospitals’ websites.

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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