3.2 Fecal Diversions: Ileostomy, Loop/End & Continent GI Diversions

Fecal Diversions: Ileostomy, Loop/End & Continent GI Diversions

Fecal diversions originating in the small intestine present distinct physiological, biochemical, and mechanical challenges compared to colonic stomas. Because small bowel effluent is continuous, liquid-to-pasty, and rich in active proteolytic enzymes, the Certified Ostomy Care Nurse (COCN) must understand small bowel transport physiology, stoma protrusion mechanics, fluid-electrolyte adaptation, and the complex management of continent intestinal reservoirs.

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Small Intestinal Anatomy and Specialized Regional Physiology

The small intestine spans approximately 6 meters (20 feet) and consists of three distinct anatomical zones:

1. Duodenum (~25 cm): C-shaped retroperitoneal segment receiving acidic gastric chyme, pancreatic enzymes, and bile. Primary site for trace mineral absorption (iron, calcium, magnesium, folate).
2. Jejunum (~2.5 meters): Characterized by prominent circular mucosal folds (plicae circulares) and tall villi. Main site for carbohydrate, protein, and water-soluble vitamin absorption, absorbing approximately 90% of ingested nutrients and large fluid volumes.
3. Ileum (~3.5 meters): Thinner-walled segment with abundant lymphoid aggregates (Peyer's patches), terminating at the ileocecal valve in the right lower quadrant.

  [Stomach] ---> [Duodenum] ---> [Jejunum] ---> [Ileum] ---> (Ileocecal Valve) ---> [Colon]
                 - Iron          - Major         - Fluid/Electrolytes
                 - Calcium         Macronutrient - Vit B12 (Terminal)
                 - Folate          Absorption    - Bile Salts (Terminal)

Critical Functions of the Terminal Ileum

The terminal 100 cm of the ileum possesses unique transport mechanisms that cannot be compensated for by any other segment of the gastrointestinal tract:

• Vitamin B12 Absorption: Vitamin B12 binds to gastric intrinsic factor (IF) in the duodenum; the intact B12-IF complex is absorbed exclusively via specialized cubam receptor-mediated endocytosis in the enterocytes of the terminal ileum. Resection of $>50\text{ cm}$ of terminal ileum permanently abolishes active B12 absorption, necessitating lifelong monthly intramuscular (1,000 mcg) or high-dose oral/sublingual vitamin B12 supplementation to prevent megaloblastic anemia and subacute combined degeneration of the spinal cord.
• Bile Acid Reabsorption (Enterohepatic Circulation): The apical sodium-dependent bile acid transporter (ASBT) in the terminal ileum reabsorbs $>95%$ of conjugated bile salts, returning them to the liver via portal circulation. Resection of $>100\text{ cm}$ disrupts the bile acid pool:
  • Depleted bile salts impair micelle formation, resulting in steatorrhea and malabsorption of fat-soluble vitamins (A, D, E, K).
  • Unabsorbed fatty acids in the gut bind luminal calcium (forming insoluble calcium soaps). This leaves dietary oxalate unbound and freely absorbed by the colon (in patients with an intact colon), leading to enteric hyperoxaluria and calcium oxalate kidney stones.
  • Diminished bile salt concentration in the gallbladder precipitates cholesterol supersaturation, increasing the incidence of cholelithiasis (gallstones).

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Brooke End Ileostomy: Construction and Spout Mechanics

Introduced by Dr. Bryan Brooke in 1952, the everted end ileostomy revolutionized ostomy care by eliminating stomal serositis, stricture, and severe peristomal chemical erosion.

                 [Abdominal Wall]
               /                \
    =========[Peritoneal Layer]=========
    =========[Fascial / Rectus]=========
    =========[Subcutaneous Fat]=========
    =========[Dermis / Skin   ]=========
              |                |
              |   [Spout]      |
              |  /        \    |
              | |  Lumen   |   |   <--- Protrudes 1.5 to 2.5 cm
              |  \        /    |        Directs proteolytic effluent
              +---[Eversion]---+        into pouch aperture

Surgical Technique

1. The terminal ileum is mobilized with its mesenteric blood supply and passed through the rectus abdominis muscle in the right lower quadrant (RLQ).
2. Approximately 4 to 5 cm of bowel is exteriorized above skin level.
3. The bowel is turned inside out (everted like a turtleneck sweater or cuff) and secured to the dermis with absorbable sutures.

Clinical Rationale for the 1.5 to 2.5 cm Protruding Spout

Small bowel effluent contains high concentrations of active trypsin, chymotrypsin, carboxypeptidase, lipase, and bile salts. These enzymes rapidly digest epidermal keratin and intercellular lipids upon contact.

• The 1.5 to 2.5 cm (approximately 3/4 to 1 inch) protruding spout acts as an internal spout that drops caustic liquid effluent directly into the center of the pouch opening.
• A flush or retracted ileostomy allows effluent to pool at the stoma base, dissolving the hydrocolloid barrier seal within hours and causing severe peristomal chemical irritant dermatitis (enzymatic erosion).

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Diverting Loop Ileostomy

A loop ileostomy is constructed by exteriorizing a loop of terminal ileum supported by a temporary bridge or rod. It features two openings:

• Proximal Functional Limb: Discharges active small bowel chyme.
• Distal Non-Functional Limb: Leads to the defunctioned colon or pelvic pouch, venting mucus.

Primary Indication: Temporary fecal diversion to defunction and protect high-risk distal pelvic anastomoses (e.g., low anterior resection with coloanal anastomosis, or total proctocolectomy with ileal pouch-anal anastomosis [IPAA]). By diverting the fecal stream for 8 to 12 weeks, loop ileostomies drastically reduce the clinical severity of pelvic sepsis should an anastomotic leak occur.

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Effluent Dynamics, Postoperative Adaptation & Fluid-Electrolyte Balance

Following ileostomy construction, the lost absorptive capacity of the colon triggers profound fluid and electrolyte shifts:

[Immediate Postop: 24-72h]          [Adaptive Phase: 2-12 Weeks]        [High-Output Crisis]
Output: 1,000 - 1,800 mL/day  --->  Output: 500 - 800 mL/day      --->  Output > 1,200 - 1,500 mL/day
Watery green/brown                  Pasty / Oatmeal consistency         Dehydration, Hyponatremia,
High risk of hypovolemia            Compensatory mucosal hyperplasia    Acute Kidney Injury (Pre-renal)

Postoperative Adaptation Timeline

• Immediate Postoperative Phase (Days 1–7): Output is high-volume, watery, and greenish-brown, averaging 1,000 to 1,800 mL/day (and occasionally reaching 2,000 mL/day) as post-surgical ileus resolves.
• Adapted Phase (Weeks 2–12): The remaining small bowel undergoes structural and functional adaptation (mucosal villous hyperplasia, increased microvillus height, up-regulated $Na^+/K^+$-ATPase pumps, and ileal brake hormonal signaling). The effluent thickens to a pasty, applesauce, or oatmeal consistency, and daily volume stabilizes to 500 to 800 mL/day.

Electrolyte Composition of Ileostomy Effluent

• Sodium: $100\text{ to }140\text{ mEq/L}$ (compared to only $10\text{ to }20\text{ mEq/L}$ in normal colonic stool)
• Potassium: $10\text{ to }30\text{ mEq/L}$
• Bicarbonate: $15\text{ to }30\text{ mEq/L}$

Pathophysiology of Dehydration and Acid-Base Imbalance

Because ileostomy effluent contains near-plasma levels of sodium and significant bicarbonate, excessive losses lead rapidly to hypovolemic hyponatremia and normal anion gap (hyperchloremic) metabolic acidosis.

Caution: The Plain Water Trap: Educate patients never to manage high ileostomy output by drinking large quantities of plain, hypotonic water. Ingesting plain water causes an osmotic wash-out in the jejunum, pulling sodium into the bowel lumen and worsening stomal output and systemic hyponatremia. Patients must consume Oral Rehydration Solutions (ORS) containing sodium and glucose in a 1:1 molar ratio to utilize intestinal $Na^+$/glucose cotransporters (SGLT-1).

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Continent Cutaneous Fecal Diversions: Kock Pouch & BCIR

Continent fecal diversions eliminate the need for an external collection appliance by constructing an internal low-pressure ileal reservoir with a continent valve mechanism.

Kock Pouch (Continent Ileostomy)

• Anatomy: Constructed using approximately 45 to 50 cm of terminal ileum. A 30 cm segment is detubularized and folded into a spherical pouch. An adjacent 3 to 5 cm segment of ileum is intussuscepted (invaginated into itself) to create a one-way nipple valve.
• Continence Mechanism: Intra-abdominal pressure and pouch filling compress the nipple valve leaflets against each other, preventing involuntary escape of stool and flatus. The exit conduit terminates as a flush, dime-sized stoma in the right lower abdomen.
• Barnett Continent Intestinal Reservoir (BCIR): A technical modification of the Kock pouch that incorporates an isoperistaltic living collar of bowel around the nipple valve to prevent valve desuccussation (slippage/unraveling), the most frequent mechanical complication of continent reservoirs.

                  [Kock Pouch Internal Architecture]
                  
                     Terminal Ileum Inflow
                              |
                              v
                   +---------------------+
                   |   Spherical Ileal   |
                   |   Pouch Reservoir   |
                   |   (45 cm ileum)     |
                   +----------+----------+
                              |
                       [Nipple Valve]  <--- 3-5 cm intussuscepted valve
                              |             Compresses under pressure
                       [Flush Stoma]   <--- Intubated with catheter

Postoperative Catheterization Protocols

• Acute Phase (Weeks 1–4): A wide-bore catheter (e.g., 28–30 Fr Medina catheter) remains anchored inside the pouch on continuous gravity drainage for 3 to 4 weeks to prevent reservoir distension, protect internal suture lines, and allow mature fibrous bonding.
• Intubation Schedule Retraining: Once pouch integrity is confirmed via pouchogram, the catheter is removed and intermittent intubation begins:
  • Weeks 4–6: Catheterize every 2 to 3 hours during the day and once or twice overnight.
  • Maintenance: Catheterize 3 to 4 times daily (upon waking, midday, evening, bedtime) or whenever a sensation of pelvic fullness or mild pressure occurs.
  • Mucus Lavage: Routine daily irrigation with 30 to 50 mL of warm tap water or saline clears thick accumulated mucus and prevents catheter blockage.

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Ileal Pouch-Anal Anastomosis (IPAA / J-Pouch)

Total proctocolectomy with Ileal Pouch-Anal Anastomosis (IPAA) is the surgical gold standard for patients with ulcerative colitis (UC) or familial adenomatous polyposis (FAP) who wish to avoid a permanent stoma while maintaining transanal fecal elimination.

             [IPAA / J-Pouch Construction]

             Terminal Ileum (15-20 cm limbs)
                     |          |
                     +----+-----+  <--- Folded side-to-side (J-shape)
                          |             and stapled
                     [ J-Pouch ]
                          |
                 [Anal Transition Zone]
                          |
                [Anal Sphincter Complex] <--- Preserves voluntary continence

Surgical Staging Approaches

1. 1-Stage Procedure: Proctocolectomy, J-pouch creation, and ileoanal anastomosis without a diverting stoma. Reserved for young, non-immunosuppressed, hemodynamically stable elective patients.
2. 2-Stage Procedure (Standard): Proctocolectomy, J-pouch creation, ileoanal anastomosis, and creation of a diverting loop ileostomy. The loop ileostomy is closed (takedown) 8 to 12 weeks later following pouchogram confirmation of anastomotic integrity.
3. 3-Stage Procedure: Subtotal colectomy with end ileostomy (Stage 1 for acute severe toxic colitis or high-dose steroid therapy), followed months later by completion proctectomy and J-pouch with loop ileostomy (Stage 2), followed by ileostomy takedown (Stage 3).

Pouchitis: Pathophysiology and Clinical Management

Pouchitis is a nonspecific idiopathic inflammatory condition of the ileal reservoir and the most common long-term complication of IPAA, affecting 30% to 50% of patients with ulcerative colitis.

• Clinical Presentation: Abrupt increase in stool frequency ($>6\text{ to }10\text{ liquid stools/day}$), severe fecal urgency, tenesmus, nocturnal soiling, pelvic cramping, malaise, and occasional low-grade fever or hematochezia.
• Diagnostic Confirmation: Diagnosed using the Pouchitis Disease Activity Index (PDAI), which combines clinical symptoms, endoscopic visualization (erythema, mucosal friability, loss of vascular pattern, ulceration), and histological evidence of acute mucosal inflammation. A PDAI score $\ge 7$ confirms acute pouchitis.
• Pharmacotherapy:
  • First-Line Therapy: Ciprofloxacin (500 mg PO BID) or Metronidazole (500 mg PO TID) for 14 days. Ciprofloxacin is widely preferred due to higher efficacy and fewer adverse effects (avoiding metronidazole-induced nausea and peripheral neuropathy).
  • Maintenance / Probiotics: High-potency, multi-strain probiotic formulations (e.g., De Simone formulation / VSL#3) are administered to maintain remission in chronic recurrent or refractory pouchitis.

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Comprehensive Comparison of Fecal Diversions