Acute gastrointestinal bleeding: lower GI

"Acute gastrointestinal bleeding" is a Level 1 topic from Section 2.1.6 in the first edition of the CICM Syllabus for the Second Part Examination, where by "gastrointestinal" we mean more "intestinal" than "gastro". For the purposes of having a firm definition, anything below the ligament of Treitz is taken as the "lower" tract, which means this chapter covers the last six or so metres.  

For such a long segment, it has been somewhat neglected by the examiners, with only Question 16 from the second paper of 2023 discussing the management options for lower GI bleeding, whereas the upper GI tract has received much more attention (3 SAQs, or an average of 1 SAQ per every 30cm of hollow viscus). The best references for this would probably have to be large society guidelines, rather than review articles:

• 2021 European (ESGE) guidelines for acute lower GI bleeding
• 2019 British (BSG) guidelines for acute lower GI bleeding

Assessment of lower gastrointestinal bleeding

The following generic list of causes for GI bleeding is reproduced here mainly for convenience, and out of concern that the SEO was becoming too optimised. 

For the exam candidate, the "assessment" question is usually going to arrive in the form of an "Outline" item from the CICM vocabulary, disting from a "list" question because it calls for something more than just the mindless regurgitation of memorised differentials. "Outline" implies some sort of reasoning and structure beyond the usual "history, examination, investigations" routine. For this reason it may be better to design the list of differentials around the need to examine and investigate, or in order of priority in the context of the question. That might mean that the anatomical system offered above might not be suitable. 

Risk stratification

Unstable patients: BSG recommend you stratify according to "stable" or "unstable", on the basis of whether or not the patient is shocked, which means most ICU patients will be definition be in the "unstable" category. Weirdly, the BSG use the shock index to determine whether the patient is shock, which is a strange thing to do as nobody else really uses this measure for anything. In case the reader is wondering about this metric (having themselves never encountered or used it before), it is a value is calculated by dividing the heart rate by the systolic blood pressure, where an SI of >1.0 suggests haemodynamic instability. It is a metric which could theoretically give a reassuring number of 0.7 for a patient with a heart rate of 68 and an SBP of 48 mmHg. The 2021 ESGE guidelines statement instead suggests that "no single risk score should be used in isolation to predict adverse outcomes" and recommends a gestalt clinical assessment to determine risk. 

Value of investigations in lower GI bleeding

CT angiography  is the recommended investigation for the haemodynamically unstable GI bleeder, from both the BSG and the ESGE. It was not even mentioned in the stem of Question 16 from the second paper of 2023, presumably because there was no point in asking about this uncontroversial first step which everyone is in agreement on. The guidelines quote the sensitivity and specificity as 79 %–95 % and 95 %–100 %. The most important role for this is to identify the site of the bleeding so as to guide the decisions around endoscopy and angiography. 

First line colonoscopy is useless. You will never find the bleeder in that mess of blood and stool. Both the BSG and the ESGE seem to believe that unprepped colonoscopy in acute gastrointestinal bleeding is a waste of time. Both sources of guidelines agree that there is a role for colonoscopy at some stage during that admission, but not in the initial acute stages, unless the bleeder is very clearly localised by CT and is well-placed in some easily accessible area of the distal bowel. Rapid bowel prep (4–6 L of PEG solution within 3–4 hours, usually via NG tube because who could possibly), is also an option, with a view to perform colonoscopy within six or so hours. This unpalatable option may be viable where angioembolisation is not possible. Interestingly, both societies recommend upper GI endoscopy as the next stage, if CT has failed to identify an embolisable lower GI source of bleeding.

Angiography is the gold standard, as it can identify a bleeder 85% of the time, and allows one to launch a bunch of Gelfoam into the offending artery, thus putting an end to the bleeding.

In order to see the characteristic "blush" of contrast, you need to be bleeding at a rate of at least 0.5ml/minute. Time is generally accepted to be the most important factor determining outcome here, and both societies suggest the angio happen as soon as possible following the CTA (ESGE actually specify 60 minutes).

Tc-99 Red Cell Scan is a way of radiolabelling RBCs and observing where they go. Apparently, it is identifies a GI bleeder 80% of the time. However it is unlikely that this will be available within the timeframe required to control acute bleeding.

Conservative management of lower GI bleeding

Say, the a

• Octreotide
• Terlipressin
• Bowel rest (eg. TPN)
• Lower BP targets
• Tranexamic acid
• Factor VIIa is also mentioned by the college in their answer to Question 1 from the first paper of 2017, though they themselves moderate their enthusiasm by pointing out that it has "questionable efficacy". If one reads the papers (eg. Bosch et al, 2008) this would certainly seem correct (there was no effect on any primary endpoints). The mention of this option in the college answer is itself questionable, as it is promoted as an option for controlling a lower GI bleed even when trial results "do not support the routine use of rFVIIa in this setting".

Definitive haemostasis in lower GI bleeding

• Colonoscopy is the ideal treatment option for patients in whom the bleeding is minor, and who have been prepped sufficiently. It is probably the least invasive treatment option.
• Angioembolisation is the best option for patients who are bleeding too rapidly to wait for bowel prep. In these people, the rate of bleeding - which makes endoscopy futile - also makes angiography more accurate. The societies are broad;y in agreement that haemodynamically unstable patients should undergo angioembilisation as soon as possible, with the UK guidelines showing a slightly higher preference for this modality. 
• Surgery is the option of choice for diverticular disease, unmanageable polyps and malignancies, and in situations where AVMs or inflammatory bowel disease lesions are not amenable to endoscopic management. It is the option of last resort for patients with bleeding that could not be controlled by other methods. On one hand, definitive control of major bleeding can be achieved by bowel resection, and good samples can be collected intraoperatively to aid diagnosis (eg. of malignancy), but on the other hand it is a laparotomy in an unprepped and unstable patient, with all the attendant risks and morbidity. Risk of perforation, slow recovery, wound infection, etc - but also one needs to consider the possibility that the bit of the bowel they resect was not the one that was bleeding. Determining the source of endoluminal bleeding is actually rather challenging, and the surgeons do not always got it right.