The endoscopic resection of colonic polyps is now the standard of care for all benign colonic polyps. This has proved to be very successful and has reduced the need for invasive surgery for the majority of patients. One of the main complications of this approach is delayed bleeding. We aim to investigate the risk factors for delayed bleeding and measures that can be taken to reduce this risk (see Table 1).

Large colonic polyps are generally considered to be any lesion over 2cm in size. There are essentially two main risk factors associated with the endoscopic resection of these large lesions: perforation and bleeding. The established risk for these events is accepted as being around 1%–2% for perforation [1] and around 7%–10% for bleeding [2]. These figures are however overly simplified and do not reflect the wide diversity in complexity of lesions resected and individual patient risk factors which affect this risk.

Bleeding from endoscopic resection of large polyps can broadly be divided into immediate bleeding, occurring during the procedure, and delayed bleeding, which occurs after the patient has been discharged. The risk factors for delayed bleeding after endoscopic resection of polyps have been well described. A study of 330 procedures with a reported delayed bleeding rate of 6.7% identified the presence of visible muscle fibres in the resection base (see Fig. 1) or the presence of a “cherry red spot” as being significant procedural factors which can predict delayed bleeding [3]. This is perhaps unsurprising and is effectively a superficial microperforation. Muscle is well vascularised and this highlights the importance of a good resectional technique with careful inspection of the lesion base post resection.

The location of the lesion within the colon is established as being an independent risk factor for bleeding. A retrospective study of 3253 patients identified that right sided location increased risk of bleeding significantly [4] (OR 2.690, p = 0.001). This finding has been repeated in many studies since, with one retrospective study claiming an odds ratio of 4.67 [5]. Unsurprisingly, size of polyp is a significant risk factor, with a 13% increase in risk of bleeding for every 1mm increase in polyp diameter [5], with lesions >10mm in size having an odds ratio of 3.41 [6].

Morphology of the lesion is also significant. A retrospective study of endoscopic resection of colorectal polyps >20mm in size in 1172 patients identified that lesion morphology (IIa + Is) is an independent risk factor for bleeding (OR 2.2, p = 0.004) [7].

In addition to lesion related factors there are patient related issues which affect bleeding risk. Cardiovascular disease and hypertension may have a modest effect on bleeding risk [6]. A common dilemma is the use of antiplatelet agents and anticoagulants. A large audit of 5593 patients looked at bleeding post polypectomy. Multivariate analysis showed that warfarin usage was an independent risk factor for bleeding (OR 13.27) and use of aspirin as a single agent was not significant [8]. This was supported in a systemic review and meta-analysis which also suggested that bleeding risk was not increased with aspirin although clopidogrel did elevate risk (OR 9.7, CI 3.1–30.8) and the combination of clopidogrel with aspirin and or NSAID increased risk of bleeding (OR 3.4, CI 1.3–8.8) [9]. There is less data available on the direct oral anticoagulants (DOAC) although a comparative study has suggested that apixaban was associated with a significantly lower risk of bleeding than warfarin, dabigatran and rivaoxaban [10].

We can therefore conclude that significant risk factors for bleeding are polyp size, location, intraprocedural muscle injury, cardiovascular comorbidity, and concurrent use of anticoagulants. There are commonly used risk scoring systems that can predict the risk of delayed bleeding post EMR. Both the GSEED-RE model from the Endoscopic Resection Group of the Spanish Society of Endoscopy and the Australian Colonic Endoscopic resection group (ACER) model achieve acceptable prediction levels for predicting risk of delayed bleeding, with proximal location, lesion size, comorbidities, antiplatelet agents and anticoagulant usage all identified as risk factors [11].