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2025 PACUPrep BCCCP Preparatory Course Ileus and Acute Intestinal Pseudo-obstruction Foundational Concepts in Ileus and Acute Intestinal Pseudo-Obstruction

Lesson 30, Topic 1

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Foundational Concepts in Ileus and Acute Intestinal Pseudo-Obstruction

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Ileus and Acute Intestinal Pseudo‐Obstruction: Principles and Risk Stratification

Foundational Principles and Risk Stratification of Ileus and Acute Intestinal Pseudo‐Obstruction

Learning Objective

Describe the foundational principles of ileus and acute intestinal pseudo‐obstruction, including pathophysiology, clinical presentation, and risk factors.

Key Learning Points:

Summarize the epidemiology and incidence of ileus and acute intestinal pseudo‐obstruction in critically ill patients.
Explain the pathophysiology underlying ileus and acute intestinal pseudo‐obstruction.
Analyze how pre‐existing chronic diseases impact the risk and presentation of ileus and acute intestinal pseudo‐obstruction.
Analyze how social determinants of health (e.g., medication access, health literacy) can be precipitating risk factors.

1. Introduction and Importance

Ileus and acute intestinal pseudo‐obstruction (AIPO) are common in ICU patients and drive morbidity, length of stay, and costs. Critical care pharmacists are central to early detection, risk stratification, and prevention of complications.

Roles of Pharmacists:

Medication review
Electrolyte optimization
Protocol development
Interdisciplinary coordination

Impact of Ileus/AIPO:

Delays in enteral nutrition
Increased diagnostic procedures
Risk of perforation, sepsis, thromboembolism

Key Pearl

Early pharmacist involvement in identifying at‐risk patients and modifying therapies can reduce ICU days and prevent adverse outcomes.

2. Epidemiology and Incidence

Incidence varies by ICU population and diagnostic criteria. Postoperative patients and those with severe systemic illness are at highest risk.

Postoperative ileus occurs in 10–30% of major abdominal surgeries; also seen in medical ICUs due to sepsis, medications, metabolic disturbances.
AIPO (Ogilvie’s syndrome) affects 0.1–0.5% of all hospital admissions; incidence rises after orthopedic, cardiac, or pelvic surgery.
Risk of spontaneous colonic perforation in AIPO: ~3%; associated mortality >50% if perforation occurs.
Under‐recognition and variable definitions lead to incidence underestimation in critically ill cohorts.

Key Pearl

Vigilant monitoring is essential in postoperative and severely ill patients to detect early signs of hypomotility.

Controversy

Lack of standardized ICU criteria for ileus and AIPO leads to diagnostic delays and inconsistent reporting.

3. Pathophysiology

Multifactorial mechanisms converge on autonomic imbalance, interstitial cell dysfunction, neurotransmitter alterations, and inflammation to impair motility.

Autonomic nervous system: Sympathetic overactivity and parasympathetic suppression lead to colonic atony and small‐bowel hypomotility.
Interstitial cells of Cajal: Pacemaker cell dysfunction disrupts slow‐wave generation.
Neurohormonal mediators: Decreased acetylcholine, increased nitric oxide, inflammatory cytokines, and endotoxins impair smooth muscle and enteric neurons.
Functional vs. mechanical: Ileus/AIPO are functional (no physical blockage) but mimic obstruction clinically.

Autonomic Imbalance

(↑ Sympathetic, ↓ Parasympathetic)

Interstitial Cell of Cajal (ICC)

Dysfunction (Pacemaker)

Neurohormonal Mediators

(↓ Acetylcholine, ↑ Nitric Oxide)

Inflammation & Endotoxins

(Cytokines, Sepsis)

↓

Impaired Gut Motility

(Ileus / AIPO)

Figure 1: Key pathophysiological factors contributing to ileus and acute intestinal pseudo-obstruction.

Key Pearl

The dramatic response of AIPO to cholinergic therapy (e.g., neostigmine) underscores the pivotal role of parasympathetic pathways.

Controversy

Relative contributions of myopathic versus neuropathic processes in chronic pseudo‐obstruction remain debated.

4. Impact of Pre‐existing Chronic Diseases

Comorbidities like diabetes, kidney disease, neurologic and cardiovascular disorders modulate baseline motility and complicate management.

Diabetes mellitus: Autonomic neuropathy delays gastric and intestinal transit.
Chronic kidney disease: Electrolyte derangements (hypokalemia, hypomagnesemia, hypocalcemia) and uremic toxins impair contractility.
Neurologic disorders: Parkinson’s disease, spinal cord injury disrupt central and enteric autonomic control.
Cardiovascular disease: Hypotension, vasopressors, and low perfusion exacerbate gut hypomotility.

Key Pearl

Tailor pharmacotherapy and monitoring based on comorbidities to avoid drug accumulation and exacerbation of ileus.

5. Social Determinants of Health (SDOH)

Nonclinical factors influence chronic disease management and adherence to prevention strategies, affecting ileus/AIPO risk.

Medication access: Cost, insurance coverage, pharmacy availability impact control of diabetes, CKD, and other risk factors.
Health literacy: Patient and caregiver understanding of risk signs and adherence to bowel regimens.
Socioeconomic status: Nutritional deficits, food insecurity, limited follow‐up care increase vulnerability.

Key Pearl

Incorporate SDOH screening into care plans to identify barriers and implement targeted interventions.

6. Clinical Application for Pharmacists

Critical care pharmacists integrate epidemiologic, pathophysiologic, and social risk factors into daily practice to prevent and manage ileus/AIPO.

Routine medication review: Identify and discontinue or adjust opioids, anticholinergics, calcium‐channel blockers.
Risk stratification protocols: Flag high‐risk patients for abdominal girth monitoring and early nutrition planning.
Prevention strategies: Implement opioid‐sparing analgesia, maintain electrolyte balance, initiate early ambulation when feasible.
Interdisciplinary communication: Lead rounds with surgery, nutrition, nursing to ensure timely decompression and escalation.

Key Pearl

Proactive pharmacist‐driven protocols reduce incidence and severity of ICU ileus and AIPO by addressing modifiable risk factors.

References

Catena F, De Simone B, Coccolini F, et al. Bowel obstruction: a narrative review for all physicians. World J Emerg Surg. 2019;14(1):20.
Batke M, Cappell MS. Adynamic ileus and acute colonic pseudo‐obstruction. Med Clin North Am. 2008;92(3):649–670.
Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013;20(5):528–544.
Vanek VW, Al‐Salti M. Acute pseudo‐obstruction of the colon (Ogilvie’s syndrome): an analysis of 400 cases. Dis Colon Rectum. 1986;29(3):203–210.
Saunders MD, Kimmey MB. Systematic review: acute colonic pseudo‐obstruction. Aliment Pharmacol Ther. 2005;22(10):917–925.
Ponec RJ, Saunders MD, Kimmey MB. Neostigmine for the treatment of acute colonic pseudo‐obstruction. N Engl J Med. 1999;341(3):137–141.
Mann SD, Debinski HS, Kamm MA. Clinical characteristics of chronic idiopathic intestinal pseudo‐obstruction in adults. Gut. 1997;41(5):675–681.
Kamm MA. Intestinal pseudo‐obstruction. Gut. 2000;47(Suppl IV):iv84.
Ogilvie H. Large‐intestine colic due to sympathetic deprivation: a new clinical syndrome. BMJ. 1948;2:671–673.
Vantrappen G. Acute colonic pseudo‐obstruction. Lancet. 1993;341(8837):152–153.
Kamm MA. Primary and secondary disorders of gut muscle and nerve. Scand J Gastroenterol. 1996;31(suppl 220):91–93.
Smith VV, Lake BD, Kamm MA, et al. Intestinal pseudo‐obstruction with deficient smooth muscle alpha‐actin. Histopathology. 1992;21(6):535–542.
Debinski HS, Kamm MA, Talbot IC, et al. DNA viruses in the pathogenesis of sporadic chronic idiopathic intestinal pseudo‐obstruction. Gut. 1997;41(1):100–106.
Hutchinson R, Griffiths C. Acute colonic pseudo‐obstruction: a pharmacological approach. Ann R Coll Surg Engl. 1992;74(6):364–367.
Cronnelly R, Stanski DR, Miller RD, Sheiner LB, Sohn YJ. Renal function and the pharmacokinetics of neostigmine in anesthetized man. Anesthesiology. 1979;51(3):222–226.

2025 PACUPrep BCCCP Preparatory Course

Pulmonary

Participants 432

Foundational Concepts in Ileus and Acute Intestinal Pseudo-Obstruction

Foundational Principles and Risk Stratification of Ileus and Acute Intestinal Pseudo‐Obstruction

Learning Objective

Key Learning Points:

1. Introduction and Importance

Roles of Pharmacists:

Impact of Ileus/AIPO:

2. Epidemiology and Incidence

3. Pathophysiology

Autonomic Imbalance

Interstitial Cell of Cajal (ICC)

Neurohormonal Mediators

Inflammation & Endotoxins

Impaired Gut Motility

4. Impact of Pre‐existing Chronic Diseases

5. Social Determinants of Health (SDOH)

6. Clinical Application for Pharmacists

References

2025 PACUPrep BCCCP Preparatory Course

Pulmonary

Participants 432

Foundational Concepts in Ileus and Acute Intestinal Pseudo-Obstruction

Learning Objective

Key Learning Points:

1. Introduction and Importance

Roles of Pharmacists:

Impact of Ileus/AIPO:

2. Epidemiology and Incidence

3. Pathophysiology

Pathophysiology of Ileus/AIPO

Autonomic Imbalance

Interstitial Cell of Cajal (ICC)

Neurohormonal Mediators

Inflammation & Endotoxins

Impaired Gut Motility

4. Impact of Pre‐existing Chronic Diseases

5. Social Determinants of Health (SDOH)

6. Clinical Application for Pharmacists

References