Epidemiology & Importance in ICU

• Occurs in 15–40% of critically ill patients.
• Often multifactorial (feeds + drugs + infection).
• Associated with ↑ mortality, ↑ LOS, and ↑ ventilator days.
• Frequently under-investigated and misattributed to “tube feeds”.

Pathophysiology (ICU-specific mechanisms)

1. Secretory Diarrhea (most common in ICU)

• ↑ Active secretion or ↓ absorption of electrolytes → water follows.
• Persists during fasting.
• Causes:
• Antibiotics (alter microbiota)
• Clostridioides difficile
• Bile acid malabsorption
• Enteral feed osmolar load
• Sepsis-related gut inflammation

2. Osmotic Diarrhea

• Presence of non-absorbable solutes in lumen.
• Improves with fasting.
• Causes:
• High-osmolar enteral feeds
• Sorbitol-containing medications (elixirs, syrups)
• Lactose intolerance (post-gut injury)

3. Inflammatory / Exudative

• Mucosal injury → protein, blood, pus loss.
• Causes:
• C. difficile colitis
• Ischemic colitis
• IBD flare
• CMV colitis (immunosuppressed)

4. Motility-related

• ↑ Transit time.
• Causes:
• Prokinetics (metoclopramide, erythromycin)
• Autonomic dysfunction
• Post-vagotomy, post-abdominal surgery

Etiology: ICU-Focused Differential Diagnosis

A. Non-infectious (≈70–80%)

1. Enteral nutrition–associated
• Rapid rate, hyperosmolar feeds
• Lack of fiber
• Cold feeds

2. Medications

• Antibiotics (β-lactams, clindamycin, fluoroquinolones)
• PPIs, H2 blockers
• Laxatives, stool softeners
• Magnesium, phosphate
• Sorbitol-based syrups

3. Critical illness–related

• Splanchnic hypoperfusion
• Stress-induced mucosal injury
• Hypoalbuminemia → gut edema

4. Post-surgical

• Short bowel
• Pancreatic insufficiency

5. Endocrine

• Thyrotoxicosis
• Adrenal crisis (rare but exam-relevant)

B. Infectious Causes (always rule out)

1. Clostridioides difficile
• Most important ICU pathogen
• Risk: antibiotics, PPI, prolonged ICU stay

2. Bacterial

• Salmonella, Shigella, Campylobacter (less common ICU-acquired)

3. Viral

• Norovirus (outbreaks)

4. Parasitic

• Rare in ICU unless immunosuppressed

Evaluation of Diarrhea in ICU 

Step 1: Clinical Assessment

• Onset (early vs late ICU stay)
• Stool characteristics (watery, bloody, oily)
• Drug history (last 7–14 days)
• Feeding details (rate, type, osmolarity)

Step 2: Basic Investigations

• Serum electrolytes (Na, K, Mg, Phosphate)
• Renal function
• ABG (metabolic acidosis common)
• Stool charting (volume & frequency)

Step 3: Microbiological Testing

• C. difficile toxin/NAAT (mandatory in ICU diarrhea)
• Stool culture (selective)
• Ova/parasite only if risk factors

Step 4: Imaging (if red flags)

• CT abdomen for:
• Ileus
• Ischemia
• Toxic megacolon

Management 

General Measures (First Principles)

1. Hemodynamic stabilization
2. Fluid & electrolyte correction
• Hypokalemia, hypomagnesemia common

3. Strict stool output monitoring
4. Skin care & pressure injury prevention

Nutrition Management

• Do NOT stop enteral feeds routinely
• Modify instead:
• Reduce rate
• Switch to isotonic or peptide-based feeds
• Add soluble fiber
• Avoid bolus feeds
• Consider post-pyloric feeding

Drug Optimization

• Stop non-essential:
• Laxatives
• Prokinetics
• Sorbitol-containing syrups
• Review antibiotics (de-escalate)

Antidiarrheal Therapy (Use with Caution)

• Loperamide
• Only after excluding infection
• Cholestyramine
• Bile acid diarrhea
• Octreotide
• Refractory secretory diarrhea
• Probiotics
• Not routinely recommended in ICU
• Avoid in immunocompromised (fungemia risk)

Complications of ICU Diarrhea

• Hypovolemia → AKI
• Electrolyte derangements
• Metabolic acidosis
• Malnutrition
• Skin breakdown, infection
• Increased ICU LOS and mortality