Small Bowel Obstruction

Distinct from Large Bowel Obstruction. Content below is from a textbook reference chapter (Sabiston Ch50 - Small Bowel Anatomy, Physiology, Obstruction & Crohn Disease), not primary literature — treat as background/orientation rather than critically-appraised evidence.

Causes

By far the most common cause is adhesions (~60%), followed by neoplasms (~20%), hernias (~10%, internal or external), Crohn disease (~5%), and miscellaneous causes (<5%, e.g., intussusception, volvulus, foreign body, bezoar, gallstone ileus, radiation stricture).

Pathophysiology

Mechanical blockage causes proximal bowel dilation from accumulated gas and fluid, increased intraluminal pressure, and progressively impaired venous then arterial blood flow. A closed-loop obstruction — both ends of a bowel segment obstructed simultaneously, classically by an adhesive band or internal hernia — is a particularly dangerous pattern: it can twist to become a volvulus, and ischemia can progress rapidly to infarction with comparatively little warning.

Clinical manifestations and diagnosis

• History: colicky abdominal pain, nausea/vomiting, distension, and obstipation (failure to pass flatus or stool) in varying combinations depending on the level and completeness of obstruction.
• Physical examination: distension, hyperactive (early) or hypoactive (late) bowel sounds, tenderness; peritoneal signs suggest strangulation.
• Laboratory and radiologic studies: no single clinical or laboratory parameter reliably distinguishes simple from strangulating obstruction (see below). Plain abdominal radiographs are diagnostic of obstruction in up to 86% of cases; the remaining 20–30% need further evaluation (CT or barium radiography). CT is particularly useful in patients with a history of abdominal malignancy, prior surgery, or no history of abdominal surgery at all, and can identify the level and (often) the cause of obstruction as well as complications (abscess — Fig. 50.14).
• Enteroclysis (continuous infusion of 500–1000 mL barium/methylcellulose suspension via a duodenal tube) gives detailed double-contrast small bowel imaging and can help characterize low-grade or intermittent obstruction, but requires nasoenteric intubation, is slow, and needs specialized radiologic expertise.
• Ultrasound is useful in pregnant patients (avoids radiation). MRI has been used in obstruction but is not clearly better diagnostically than CT.

Simple versus strangulating obstruction

Most SBO is simple — mechanical blockage without compromised bowel wall viability. Strangulating obstruction involves a closed-loop obstruction with compromised vascular supply, risking infarction, and carries higher morbidity/mortality. Classic signs of strangulation (tachycardia, fever, leukocytosis, constant noncramping pain) have been described, but multiple studies show no clinical parameter or lab test reliably detects or excludes strangulation in all cases — a careful, repeated history and physical examination remain key.

CT findings suggestive of closed-loop/strangulation: U-loop or coffee-bean sign with tapering at both ends, volvulus (mesenteric whirl), bowel wall thickening (>3 mm), mesenteric edema, fluid trapped between loops, decreased bowel wall enhancement, pneumatosis intestinalis, and mesenteric/ portovenous gas. CT findings associated with strangulation specifically reflect irreversible ischemia/necrosis — the decision for emergent surgery in a toxic patient should not be delayed by imaging.

Serum markers (lactate dehydrogenase, amylase, alkaline phosphatase, ammonia, D-lactate, creatine kinase BB isoenzyme, intestinal fatty acid–binding protein) have been assessed for detecting strangulation with no real diagnostic benefit demonstrated; SQUID magnetometer detection of mesenteric ischemia via intestinal electrical rhythm changes remains investigational.

Treatment

• Fluid resuscitation and antibiotics: isotonic IV fluids (e.g., lactated Ringer solution) to correct dehydration and electrolyte depletion (sodium, chloride, potassium); Foley catheter for urine output monitoring; potassium chloride added once adequate urine output is established. Prophylactic antibiotics are used by some surgeons given concern for bacterial translocation, but there is no substantial evidence supporting antimicrobial therapy in simple mechanical obstruction absent suspected overgrowth; antibiotics should be reserved for when surgery is required.
• Tube decompression: nasogastric suction remains standard supportive care — empties the stomach, reduces aspiration risk, limits further distension from swallowed air. Long intestinal tubes (Cantor, Baker) have not shown benefit over NG tubes in randomized trials and are associated with longer hospital stay and more complications.
• Partial obstruction: often managed conservatively with resuscitation and tube decompression alone — resolution without surgery reported in up to 85% of patients. Enteroclysis can help grade partial obstructions; higher-grade partial obstructions warrant earlier operative intervention. Clinical deterioration or increasing distension during a nonoperative trial warrants prompt surgery.
• Contrast challenge: for lower-grade obstructions not resolved after 48 hours of NG suction — 100 mL water-soluble contrast via NG tube, follow-up films at 8 and 24 hours; if contrast has not reached the colon by 24 hours, conservative management will probably fail and surgery is likely needed.
• Operative management: reserved for those who fail conservative management or show vascular compromise, strangulation, or perforation. Retrospective data suggest a 12–24 hour nonoperative trial is safe, but strangulation and other complication rates rise significantly beyond that window. Adhesive obstruction is treated with lysis of adhesions, handling bowel gently to avoid serosal trauma and inadvertent enterotomy; incarcerated hernias by manual reduction plus defect closure. For obstruction from malignancy with widespread metastasis, nonoperative management (if successful) is often best; for complete obstruction, intestinal bypass may be preferable to a long, complicated resection. Crohn-related obstruction from acute inflammation often resolves with conservative management; a chronic fibrotic stricture typically needs resection or strictureplasty (see Crohn Disease).
• Laparoscopic management is effective and associated with lower morbidity/mortality, shorter stay, shorter operative time, lower reoperation rate, and fewer complications in a selected patient group — ideal candidates have mild proximal/partial distension, an anticipated single-band obstruction, and low risk of strangulation or perforation; matted adhesions/carcinomatosis or advanced/complete/distal obstruction are better managed with open laparotomy.
• Intraoperative bowel viability assessment: if questionable after release of a strangulation, wrap the bowel in a warm, saline-moistened sponge for 15–20 minutes and reexamine; return of normal color and peristalsis indicates it is safe to retain. Doppler probe added little to clinical judgment in a prospective trial; fluorescein fluorescence may help in difficult/borderline cases. Indocyanine green near-infrared angiography shows promise but is not yet in wide clinical use. A second-look laparotomy at 18–24 hours is an alternative approach and is clearly indicated if the patient deteriorates after the initial operation.

Management of specific problems

Recurrent intestinal obstruction

Patients with multiple prior operations and a “frozen abdomen” who present with yet another obstruction usually warrant an initial nonoperative trial, which is often safe. Reoperation in these patients can be long and arduous, with real risk of enterotomy or adjacent organ injury. Various adhesion-prevention strategies have been tried: external plication procedures (largely abandoned due to fistula/leak/peritonitis/death risk), long intestinal tubes for internal fixation/stenting (moderate success but risk of prolonged drainage, intussusception, difficult removal), pharmacologic agents (corticosteroids, cytotoxics, antihistamines, anticoagulants, proteinase instillation, hyaluronidase, fibrinolytics — largely of limited or unproven efficacy), and hyaluronate-based bioresorbable membranes (mixed trial results on severity vs. incidence of adhesions). The most effective proven strategy remains good surgical technique: gentle bowel handling, minimizing unnecessary dissection, avoiding foreign material and excessive gauze/starch exposure in the peritoneal cavity, adequate irrigation/debris removal, and omental preservation.

Acute postoperative obstruction

Challenging to diagnose because pain/nausea/emesis may be attributed to ordinary postoperative ileus. CT and enteroclysis can help distinguish true obstruction from ileus and determine the level if obstruction is present. More than 90% of early postoperative obstructions are partial and resolve spontaneously with bowel rest, fluid resuscitation, electrolyte replacement, and parenteral nutrition if needed; complete obstruction or signs of strangulation mandate reoperation. Postoperative obstruction after laparoscopic surgery is more often associated with a definitive point (port site, hernia, internal hernia) and should prompt a high index of suspicion for the need to reoperate.

Ileus (differential diagnosis)

An ileus is intestinal distension and slowing/absence of luminal content passage without a demonstrable mechanical cause — drug-induced (opiates, anticholinergics, antihistamines, psychotropics), metabolic (hypokalemia, hyponatremia, hypomagnesemia, uremia, diabetic coma, hypoparathyroidism), neurogenic (after abdominal, spinal, or orthopedic procedures; retroperitoneal irritation), or infectious (pneumonia, peritonitis, sepsis) — see Box 50.3 in the source. Presents similarly to mechanical obstruction (distension predominates over colicky pain); passage of flatus/diarrhea can help distinguish ileus from mechanical obstruction. Plain films are often unhelpful in distinguishing the two; CT/enteroclysis can help. Treatment is entirely supportive — NG decompression, IV fluids, aggressive treatment of the underlying cause. Pharmacologic agents (cholinergic/anticholinergic manipulation, cholecystokinin, motilin analogues such as erythromycin, cisapride) have shown inconsistent or ineffective results. Chewing gum was proposed as a cheap way to stimulate the cephalic phase of digestion/vagal cholinergic activity, but a more recent randomized trial found no benefit on return of bowel function or length of stay, and raised concern that sugared gum could worsen postoperative ileus.

Open items / gaps

• No primary trial data yet in the wiki independently appraising the adhesion-prevention strategies above (hyaluronate membranes, Kono-S-style technique, etc.) — currently only the textbook’s summary of single studies.
• ICG angiography for intraoperative viability assessment is flagged as promising but not yet in wide use — worth revisiting if primary literature is ingested later.
• Cross-link to Large Bowel Obstruction for the colonic-obstruction analog once the two pages’ overlap (e.g., closed-loop physiology, general resuscitation principles) is worth spelling out explicitly rather than duplicating.