Bowel Obstruction: Causes, Types, and Physiology

• The document covers info on the small intestine, appendix, and related disorders.
• Surgical indications for small intestines include obstruction, mass, bleeding, perforation, abscess, and fistula.

Small Bowel Obstruction (SBO) Etiology

• Mechanical SBO is the most frequently encountered surgical disorder in the area.
• Etiologies for SBO include a wide range of factors.

Small Bowel Obstruction: Types by Location

• Intraluminal: presence of foreign bodies, gallstones, or meconium

• Intramural: tumors or Crohn's disease-associated inflammatory strictures

• Extrinsic: adhesions, hernias, or carcinomatosis

• Adhesions related to prior abdominal surgery account for up to 75% of SBO cases.

• Intra-abdominal adhesions are a common cause.

• Other less prevalent etiologies include hernias, malignant bowel obstruction, and Crohn's disease.

• Congenital abnormalities causing SBO may become evident during childhood or adulthood.

• Superior mesenteric artery syndrome is a rare etiology involving compression of the third portion of the duodenum.

Pathophysiology of SBO

• Obstruction leads to gas and fluid accumulation in the lumen proximal to the affected site.
• Intestinal activity increases to overcome the blockage, leading to colicky pain and diarrhea.
• This accumulation results in bowel distention, increased intraluminal and intramural pressure, and decreased intestinal motility.
• Impaired intestinal microvascular perfusion can follow, leading to intestinal ischemia and necrosis.

Partial vs. Complete SBO

• Partial SBO involves only a portion of the intestinal lumen being occluded, allowing some gas and fluid passage.
• Pathophysiologic events tend to occur more slowly, and strangulation is less likely.

Strangulated Bowel Obstruction

• Gas and fluid accumulate proximal to the obstruction site.
• Intestinal activity increases, leading to colicky pain and diarrhea.
• Most accumulated gas originates from swallowed air, with some produced in the intestine.
• The fluid consists of swallowed liquids and GI secretions.
• Ongoing gas and fluid accumulation leads to bowel distention and increased pressures.
• Intestinal motility is eventually reduced.
• The luminal flora of the small bowel changes, and bacterial translocation to regional lymph nodes may occur.
• Impaired intestinal microvascular perfusion leads to intestinal ischemia and necrosis which is referred to as strangulated bowel obstruction.

Closed Loop Obstruction

• A particularly dangerous form of bowel obstruction.
• A segment of intestine is obstructed proximally and distally, such as with volvulus.
• Accumulating gas and fluid cannot escape, leading to a rapid rise in luminal pressure.
• This can cause a rapid progression to strangulation.

Clinical Presentation SBO

• Symptoms of small bowel obstruction include colicky abdominal pain, nausea, vomiting, and obstipation.
• Vomiting is a prominent symptom, with feculent vomitus being more suggestive of distal obstruction.
• Continued passage of flatus and/or stool beyond 6 to 12 hours after symptom onset indicates PARTIAL rather than complete obstruction.
• Signs include abdominal distention, most pronounced in distal ileum obstruction, and may be absent in proximal small intestine obstruction.
• Bowel sounds may be hyperactive initially, but minimal sounds may be heard in late stages.
• Laboratory findings reflect intravascular volume depletion, including hemoconcentration and electrolyte abnormalities.
• Mild leukocytosis is common.

Strangulated Obstruction: Clinical Presentation

• Disproportionate abdominal pain relative to physical findings, suggesting intestinal ischemia.
• Patients often have tachycardia, localized abdominal tenderness, fever, marked leukocytosis, and acidosis.

Diagnosis of SBO

• Distinguish mechanical obstruction from ileus.
• Determine the etiology of the obstruction.
• Discriminate partial from complete obstruction.
• Discriminate simple from strangulating obstruction.

SBO vs LBO: Distinguishing Factors

• SBO: paucity of air in the colon.
• LBO: haustral folds/markings.

History and Physical Exam: Key Elements

• Previous abdominal operations (suggesting adhesions)
• Presence of abdominal disorders like intra-abdominal cancer or inflammatory bowel disease.
• Upon examination a search for hernias in the inguinal & femoral regions should be conducted.

X-Ray in Diagnosing SBO

• Advantages: readily available and inexpensive.
• Disadvantages: Sensitivity and specificity 70%-80%
• Abdominal series consists of chest (upright) and abdomen (upright and supine) radiographs.
• The most specific finding for small bowel obstruction is the triad of:
• Dilated small bowel loops (>3 cm in diameter)
• Air-fluid levels seen on upright films
• Paucity of air in the colon

CT Scanning in Diagnosing SBO

• Increasingly the imaging of choice; ideally done with oral contrast.
• Offers a global evaluation of the abdomen and may reveal the obstruction etiology.
• Findings include- discrete transition zone, proximal bowel dilation, distal bowel decompression, & intraluminal contrast not passing the transition zone.
• Colon contains little gas or fluid.
• Closed-loop obstruction is suggested by a U- or C-shaped dilated bowel loop with mesenteric vessels converging toward a torsion point.

CT Scanning Features Suggestive of Strangulation

• Thickening of the bowel wall
• Pneumatosis intestinalis (air in the bowel wall)
• Portal venous gas
• Mesenteric haziness
• Poor uptake of IV contrast into the wall of the affected bowel

CT with Contrast and Limitations

• Usually performed after oral water-soluble contrast or dilute barium administration.
• Contrast appearance in the colon within 24 hours predicts nonsurgical resolution.
• Limitation: low sensitivity (<50%) in detecting low-grade or partial small bowel obstruction.

Contrast Examinations of the Small Bowel

• Small bowel series (SBS) or enteroclysis
• Helpful but more labor-intensive and less rapidly performed than CT scanning.
• May offer greater sensitivity in detecting luminal and mural obstruction etiologies.

Therapy: Non-operative & Operative

• NPO (nothing by mouth)
• Fluid Resuscitation
• Usually associated with a marked depletion of intravascular volume, fluid resuscitation is integral to treatment.

Therapy: Small Bowel Obstruction

• Small bowel obstruction is usually associated with a marked depletion of intravascular volume due to decreased oral intake, vomiting, and sequestration of fluid in bowel lumen and wall.
• Fluid resuscitation is integral to treatment.

Initial Conservative Treatment

• NG decompression and fluid resuscitation
• NPO(Nil per Os)
• Partial SBO
• Early SBO secondary to post-operative adhesions (POA)
• Intestinal obstruction due to Crohn's disease and Carcinomatosis.

Complete SBO secondary to POA

• The standard therapy has been expeditious surgery.
• Clinical signs and available tests don’t reliably distinguish simple obstruction from strangulated obstructions before irreversible ischemia.
• The goal is to operate before the onset of irreversible ischemia.

Partial SBO secondary to POA

• Nonoperative management (with monitoring) is warranted.
• Nonoperative management is successful 65 to 81% of patients.
• Most patients that don’t improve need surgery.
• Patients need to be monitored by surgical intervention.

Early Post-operative SBO

• Incidence: 0.7%
• Highest in pelvic/colorectal surgery
• It is considered obstruction for the first return of bowel function or 3-5 days after abdominal surgery.

High Incidence/Mortality

• Non-stringulating < 5%
• Stringulating: 8-25%

Prevention & Adhesions

• Use good surgical technique
• Handle tissue with care
• Avoid foreign bodies

Viability

• Examine and nonviable bowe should be reselected
• Normal color, peristalsis, and marginal arterial pulsations should be considered/assessed

Laparoscopic Surgery

• Used
• Quick recovery
• Less Postoperative discomfort
• Single adhesion is best suited

Ileus

• Impaired Intestinal motility
• Absence of a lesion-causing mechanical obstruction
• Reversible namas to once cause away

Post Operative

• Most frequently implicated cause of delayed following abdominal operations
• Temporary Malatility that is resolved with time
• Etologies include
• infections
• sepsis
• Intra infection
• elcectrolyte abnormality
• Medication
• Surgery

Return of GI Motility

• Small Bowel
• Gastric
• Colonic
• Important Indicator to see patients passing flatus or if bowel movements are occuring

Therapy

• Limiting oral intake
• NPO
• Check and monitor Electrolytes

Short Bowel Syndromes

• Inadequare small vowel in adult patients
• The presence of less than 200cm of residual small Bowel in Adults Population

Intussusception

• Refers to a condition where one segment of the intestine segment gets drown in to the Lumen

Pmeumotasis Intestinalis

• Presence of gas with In the Bowel Wall
• In the Idiophathic
• Intestinial and non intestinal disorders
• Usually Jejunum is most common

Symptoms for Duodenal perforations

• Abdominal Peritoneal
• Fever and tarchcadia Direct re bound

Daignosis

• Cscanning.
• Can determine presence of perforations

Explore the causes, types, and physiological responses associated with bowel obstruction, including gas accumulation, post-operative complications, and intraluminal factors. Learn about the colicky pain and different classification of obstruction.