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2025 PACUPrep BCCCP Preparatory Course Acute Lower Gastrointestinal Bleeding Foundational Concepts in Acute Lower Gastrointestinal Bleeding

Lesson 27, Topic 1

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Foundational Concepts in Acute Lower Gastrointestinal Bleeding

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Epidemiology of Acute Lower Gastrointestinal Bleeding in Critical Care

Epidemiology and Incidence of Acute Lower Gastrointestinal Bleeding in Critically Ill Patients

Learning Objective

Analyze the epidemiology, incidence, and resource implications of acute lower gastrointestinal bleeding (LGIB) in general and ICU populations; appraise data limitations and research gaps in the critically ill.

1. Incidence and Prevalence

Acute lower gastrointestinal bleeding (LGIB)—defined as bleeding distal to the ligament of Treitz—affects approximately 20–33 per 100,000 adults annually. Incidence rates are observed to be rising, particularly in older individuals and those with multiple comorbidities. While critically ill cohorts often present with more severe manifestations of LGIB, precise incidence estimates within this specific population are lacking, necessitating careful extrapolation from general population data.

A. General Population

Annual incidence: 20–33 cases per 100,000 adults.
Median age at presentation: Typically between 70–75 years.
Leading causes: Diverticular bleeding accounts for 20–34% of cases, while hemorrhoids and other anorectal diseases contribute to 12–21%.
Diagnostic challenges: Approximately one-quarter of admissions for LGIB have no identified source of bleeding despite comprehensive evaluation.

B. ICU/Critically Ill Population

True incidence: Undefined, though it is generally extrapolated to exceed rates observed in the general population due to the concentration of risk factors.
Risk factors: Critically ill patients often present with advanced age, polypharmacy (including anticoagulants, antiplatelets, and NSAIDs), and multi-organ dysfunction, all of which predispose to LGIB.
Severity: Bleeding episodes in the ICU tend to be larger in volume, more persistent, and more frequently associated with hemodynamic instability compared to the general population.

Clinical Pearl: ICU Predisposition

Critically ill patients are inherently predisposed to severe LGIB due to the high prevalence of coexisting comorbidities and frequent exposure to anticoagulant and antiplatelet therapies. ICU-specific epidemiologic data remain sparse, highlighting a significant knowledge gap and necessitating cautious extrapolation from general population studies when assessing risk and prognosis in this vulnerable group.

2. Trends in Morbidity, Mortality, and Resource Utilization

Mortality for LGIB in general hospital wards is estimated at 2–4%, with rebleeding occurring in 10–14% of patients during their hospitalization. In the intensive care unit (ICU), both mortality rates and resource requirements escalate markedly, reflecting the increased severity of illness and complexity of care in this patient population.

A. Morbidity and Mortality

General mortality: Ranges from 2–4%. In-hospital rebleeding occurs in 10–14% of patients, with this figure rising to as high as 25% at one year post-discharge.
ICU mortality: Substantially higher than in the general ward population, although precise rates are not well-defined. Mortality in ICU patients with LGIB is often driven by underlying shock, multi-organ failure, and the burden of comorbidities.
Rebleeding risk: Amplified in the ICU setting due to factors such as ongoing anticoagulation requirements for other conditions and persistent hemodynamic instability.

B. Resource Utilization

Transfusion: Approximately 42% of general LGIB admissions require red blood cell transfusions. ICU patients frequently need multiple units of blood products due to more severe bleeding and coagulopathies.
Endoscopy/Radiology: Around 16% of patients in the general population undergo interventional procedures (e.g., endoscopic hemostasis, angiographic embolization). ICU patients are more likely to require advanced interventions such as embolization or surgical management.
Length of stay: LGIB in the ICU significantly extends both overall hospital and ICU lengths of stay, thereby increasing healthcare costs and demands on staffing.

Clinical Pearl: Transfusion Strategy

Evidence suggests that a restrictive transfusion strategy, targeting a hemoglobin threshold of 7 g/dL, is associated with reduced mortality and rebleeding rates in hemodynamically stable patients with LGIB. However, a higher threshold of 8 g/dL may be considered for patients with active cardiovascular disease or ongoing signs of ischemia.

3. Data Limitations and Research Gaps

Current research on LGIB largely omits or underrepresents ICU subgroups. Furthermore, studies often lack standardized definitions for bleeding severity and vary considerably in their diagnostic and management approaches, limiting comparability and the ability to draw firm conclusions for the critically ill population.

A. Key Limitations

Lack of uniform criteria for defining bleeding severity or ICU-specific outcomes, hindering comparative research.
Significant underrepresentation of critically ill patients in major LGIB clinical trials and registries.
Heterogeneous application of diagnostic modalities, particularly regarding the timing and choice between early colonoscopy versus computed tomography angiography (CTA).
Inadequate statistical adjustment for critical confounders prevalent in ICU patients, such as polypharmacy (especially anticoagulants and antiplatelets) and the severity of underlying organ dysfunction.

Controversy: Timing of Diagnostic Evaluation

The optimal timing and initial modality for diagnostic evaluation (e.g., urgent colonoscopy versus CTA) in acute LGIB remain subjects of ongoing debate, particularly in the ICU setting. Clinical decisions should be individualized, hinging on factors such as hemodynamic stability, the suspected rate of bleeding, local resource availability, and patient-specific risk factors.

B. Research Priorities

Conducting prospective, multicenter epidemiologic studies specifically focused on LGIB in ICU populations to accurately define incidence, risk factors, and outcomes.
Validating existing risk stratification tools (e.g., Oakland score, Blatchford score) or developing new ICU-specific scores for predicting rebleeding, mortality, and need for intervention.
Assessing the impact of standardized management algorithms, including diagnostic pathways and transfusion strategies, on clinically relevant outcomes such as mortality, rebleeding rates, and resource utilization in critically ill patients with LGIB.

Clinical Pearl: Addressing Data Gaps

Addressing the current epidemiologic and outcome data gaps specific to ICU populations is essential for advancing the care of critically ill patients with LGIB. Such research will enable more accurate risk stratification, guide the development of evidence-based interventions, and ultimately improve patient outcomes.

4. Summary Table: Key Epidemiologic Parameters

Comparison of Key Epidemiologic Parameters for Acute Lower Gastrointestinal Bleeding
Parameter	General Population	ICU/Critically Ill Population
Incidence (per 100,000)	20–33	Higher, undefined
Median age (years)	70–75	Often >75
Leading etiology	Diverticular (20–34%)	Diverticular, often more severe presentations; other causes related to critical illness
In-hospital mortality	2–4%	Elevated; exact rate unknown but significantly higher
Rebleeding (in-hospital)	10–14%	Higher (up to 25% at 1 year for general population, likely higher in ICU)
Transfusion requirement	~42% (often single/few units)	Higher; frequently multi-unit transfusions
Interventional therapies	~16% (endoscopy, some embolization)	Increased need for advanced interventions (embolization, surgery)

References

Triantafyllou K, Gkolfakis P, Gralnek IM, et al. Diagnosis and management of acute lower GI bleeding: ESGE Guideline. Endoscopy. 2021;53(9):850–868.
Sengupta N, Feuerstein JD, Jairath V, et al. Management of patients with acute lower GI bleeding: updated ACG clinical guideline. Am J Gastroenterol. 2023;118(2):208–231.
Oakland K, Guy R, Uberoi R, et al. Acute lower GI bleeding in the UK: patient characteristics, interventions and outcomes in the first nationwide audit. Gut. 2018;67(4):654–662.
Gralnek IM, Neeman Z, Strate LL. Acute lower gastrointestinal bleeding. N Engl J Med. 2017;376(18):1054–1063.
Nagata N, Niikura R, Aoki T, et al. Recurrence and mortality among patients hospitalized for acute lower GI bleeding. Clin Gastroenterol Hepatol. 2015;13(3):488–494.e1.
Strate LL, Liu YL, Huang ES, et al. Use of aspirin or NSAIDs increases risk for diverticulitis and diverticular bleeding. Gastroenterology. 2011;140(5):1427–1433.
Villanueva C, Colomo A, Bosch A, et al. Transfusion strategies for acute upper GI bleeding. N Engl J Med. 2013;368(1):11–21.

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