Abdominal Pain - 4

Intestinal Obstruction
16.10.06

Causes of obstruction
SMALL INTESTINE
• Adhesions.
• Hernias.
• Neoplasms.
• Miscellaneous.

COLON
• Neoplasms.
• Volvulus.
• Diverticular stricture.
• Miscellaneous.

Intra-abdominal adhesions
• Common cause of small bowel obstruction: 66-75% cases.
• Exacerbated by intra-abdominal infection, ischaemia, foreign bodies.
• Any abdominal/pelvic surgery.
• 1 year post colectomy risk 11%, 10 years 30%.
• Variable interval between surgery and adhesive obstruction (7 months-65 years, average 6 years).

Hernias
• 2nd most common cause of small bowel obstruction (25%).
• Complete obstruction and strangulation related to rigid fascial defect through which hernia passes.

Neoplasms
• Unusual cause of small bowel obstruction (<10%).
• Usually extrinsic compression on local invasion by advanced GI (pancreatic, colonic, gastric)/gynaecological (ovarian) malignancies.

Pathophysiology
• Outcome depends on duration/degree of obstruction.
• Severity of ischaemia determines local and systemic pathophysiological consequences.
• Profound accumulation of fluid and swallowed air within intestinal lumen proximal to obstruction.
• Impaired water and electrolyte absorption and enhanced secretion → movement of isotonic fluid from intravascular space into intestinal lumen.
• Distension due to swallowed air, gases from bacteria and fluid.
• Failure of normal intestinal motility → bacterial overgrowth → translocation of bacteria to lymph nodes and systemic organs → systemic infection.

Presentation
• Acute onset of cramping mid-abdominal pain, vomiting, constipation, abdominal distension.
• Degree depends on degree of obstruction, site and duration.
• Paroxysms of pain every 4-5 minutes for proximal obstruction.
• Proximal obstruction: profuse vomiting, pain, minor abdominal distension.
• Distal obstruction: less frequent vomiting (but faeculent) and greater abdominal distension.

Examination
• Bowel sounds usually described as high-pitched/musical.

Abdominal x-ray
• If suspect obstruction, need AXR.
• Upright AXR: multiple air-fluid levels with loops of distended bowel resembling "U."

Contrast studies and CT
• Definite diagnosis, no obstruction, high-grade/complete obstruction in 50-80% patients studied.

Complete small intestine obstruction
• Complete - urgent laparotomy and broad-spectrum antibiotics.

Adenocarcinoma of colon
• >20% patients with colorectal cancer present with obstructive symptoms.
• Poor prognosis if need emergency surgery.

Volvulus
• Abnormal twisting of segment of bowel on itself along longitudinal axis.
• Results in occlusion of intestinal lumen, often closed loop obstruction → strangulation.

Diverticulitis
• Benign colonic strictures occur as consequence of diverticulitis, ischaemia and post-operative anastomotic strictures.

Pathophysiology
• Competency of ileocaecal valve important in Pathophysiology of colonic obstruction.
• If ileocaecal valve competent → caecum cannot decompress fluid and gas into small bowel → closed loop obstruction, fluid and gas accumulate → intraluminal pressure increased → colonic wall becomes ischaemic.

Presentation
• Periumbilical or hypochondriac pain and abdominal distension.

Benign and malignant colonic strictures
• Change in stool calibre/frequency.
• Malaena (or iron-deficiency anaemia).

Colonic volvulus
• Sigmoid volvulus usually 70-80 years.
• Caecal volvulus - younger sufferers.

Treatment and outcome
• Resuscitate as for small bowel obstruction.
• Obstructions proximal to Splenic flexure usually adenocarcinomas → right hemicolectomy and primary ileocolic anastomosis.
• If unfit → loop ileostomy.
• Obstruction distal to Splenic flexure either adenocarcinomas/Diverticular strictures.

Colonic pseudo obstructions
• Clinical picture suggestive of mechanical obstruction.
• Acute/chronic.
• Acute: symptoms as mechanical.
• Pathophysiology: imbalance in ANS (increased sympathetic and decreased parasympathetic tone).

Treatment
• Treat underlying cause.
• Correct electrolyte abnormalities.
• Drip and suck.
• Neostigmie.

Incidentally, this is the 100th post on this blog. Would you believe it?