This retrospective cohort study showed the importance of checking to ensure complete hemostasis by inspecting mucosal defects of the resection stump. Even after instruction, a small number of DPPB events still occurred after HSP. As clipping was an independent risk factor for DPPB, the location of clipping should be further considered to decrease DPPB. To the best of our knowledge, the present study is the first to show the importance of looking at the mucosal defect after polypectomy. Although the procedure time due to inspection of mucosal defect after polypectomy must have been prolonged, any DPPB that arises risks becoming serious because of unpredictable onset often occurring after hospital discharge and requiring intensive management [7].
In a recent meta-analysis of DPPB, the frequency was reported as 0.6-2.8% [25]. Cardiovascular disease, hypertension, polyp size (> 10 mm), and polyps located in the right colon were indicated as significant risk factors for DPPB, whereas age, sex, alcohol use, smoking, diabetes, cerebrovascular disease, pedunculated morphology, and carcinoma histology were not significant risk factors for DPPB [25]. The use of antithrombotic agents is one of the risk factors for PPB and both immediate and delayed PPB occur in patients taking antithrombotic agents. In the present study, interestingly, the rate of DPPB in patients taking antithrombotic agents decreased significantly after instruction. However, the use of antithrombotic agents was still a significant risk factor for DPPB. These data indicate that inspection of the mucosal defect after polypectomy may be effective for patients taking antithrombotic agents, though it is important to note that the inspection cannot fully mitigate the risk of DPPB for these patients.
The experience of the endoscopist might also be associated with the incidence of DPPB. Less than 300 procedures or less than 1 year of experience were reported to correlate with higher rates of DPPB [26, 27]. Conversely, Kwon et al. did not find any association in DPPB rate comparing endoscopists practicing more or less than 10 years [28]. Similarly, Lee et al. found no difference in DPPB rate between procedures performed by fellows versus staff [29]. These data were similar to the present study, in that endoscopist experience did not affect the rate of DPPB. As a unified definition of endoscopic experience was lacking from these studies, whether endoscopic experience affects the incidence of DPPB remains unclear and further studies are warranted.
In a meta-analysis of hot and cold polypectomy, the rates of bleeding were 0.8% and 0% on a per-patient basis, and 0.4% vs. 0% on a per-polyp basis [30]. As indicated before, CSP is safer than HSP. In addition, in the present study, HOT was a significant risk factor for DPPB in multivariate analysis. As the incidence of bleeding was small, we need to be careful before concluding that the method of polypectomy affects the DPPB. However, the procedure itself must be one of the important factors contributing to the incidence of DPPB.
The incidence of clipping after cold polypectomy was 0–6% in previous reports [31-35]. Interestingly, all prospective data showed no DPPB after cold polypectomy, suggesting the safety of CSP. However, the incidence of DPPB after cold polypectomy in the present study could not be ignored before the intervention. The data indicated that we still need to be careful about DPPB even after cold polypectomy, with precise inspection of the mucosal defect. In the present study, no DPPB was seen after instruction in polyps after CSP, even with the increased rate of the procedure. As immediate PPB was higher after CSP compared to HSP in a meta-analysis [36], we also need to be careful regarding DPPB. However, when irrigation with water to make a pseudo-submucosal injection is done and we can confirm hemostasis after CSP by inspection of the mucosal defect after polypectomy, the situation can be considered safe and no DPPB occurs.
Although the rate of clipping increased after instruction in expectation of preventing DPPB in the present study, clipping was indeed an independent risk factor for DPPB. This was unexpected, but as recent reports have indicated, clipping does not appear effective in preventing DPPB [15]. One report showed that clipping after cold polypectomy was more likely to be used in the antithrombotic group. However, no significant difference in rate of DPPB was seen between lesions with and without clipping in that study [7]. One explanation might be related to the target lesions for clipping. Indications for clipping in the present study depended on the endoscopist in charge. When the risk of DPPB is considered high, clipping may be added. Therefore, lesions with clipping might already be at higher risk of DPPB, with clipping not proving effective for preventing DPPB. Another contributor would be ineffective clipping. The location of clipping should be reconsidered for preventing DPPB, because DPPB sometimes occurred next to the residual clips. Further studies are warranted to evaluate the effects of clipping on prevention of DPPB with careful inspection of mucosal defects.
Other than CSP and clipping, no other interventions have been assessed for the prevention of DPPB. In the present study, instruction on inspection of the mucosal defect proved preventive for DPPB, and no DPPB was seen after CSP even with continued use of antithrombotic agents. These data indicate that the intervention presented here would likely already have been enacted in clinical studies assessing the safety and efficacy of CSP, because they tried to avoid DPPB after CSP. Interestingly, no reports have shown the efficacy of clipping after CSP. A study by Kawamura et al. that was not permitted to add prophylactic hemostatic clipping after CSP for 5- to 9-mm polyps did not show any DPPB in 346 polyps [35]. The safety and efficacy of CSP can thus be achieved under strict inspection of mucosal defects with injection of water and without prophylactic clipping [31, 35].
Some limitations to the present study must be considered, and may require attention in further investigations. First, this was a retrospective study from a single institution. We therefore cannot exclude unrevealed confounding factors that affect DPPB. As our institution is a tertiary care center, the doctors would have encountered polypectomy procedures in different institutes earlier in their careers, and may have had different backgrounds and likely show the data of a multicenter study. Although performing a randomized study to examine the effects of inspection of mucosal defects may encounter ethical problems, prospective studies that assess the effect of irrigation of the mucosal defect after CSP might be possible. A second limitation was that the frequency of bleeding was low. As equipment for treatment differs between institutes and is improving quickly, a multicenter prospective study of a larger cohort would provide stronger evidence and reduce the risk of Berkson’s bias.