Thursday, April 22, 2010

INTESTINAL OBSTRUCTION

INTESTINAL OBSTRUCTION

Intestinal obstruction is significant mechanical impairment or complete arrest of the passage of contents through the intestine. Symptoms include cramping pain, vomiting, obstipation, and lack of flatus. Diagnosis is clinical, confirmed by abdominal x rays. Treatment is fluid resuscitation, nasogastric suction, and, in most cases of complete obstruction, surgery.
Mechanical obstruction is divided into obstruction of the small bowel (including the duodenum) and obstruction of the large bowel. Obstruction may be partial or complete. About 85% of partial small-bowel obstructions resolve with nonoperative treatment, whereas about 85% of complete small-bowel obstructions require operation.

 Clinical features :
• Pain.
• Vomiting.
• Distention.
• Constipation.
 Features vary according to :
• Site of obstruction .
• Age of Presentation.
• Underlying pathology.
• The presence or absence of intestinal ischemia.
 Other manifestations:
• Dehydration.
• Hypokalemia.
• Pyrexia.
• Abdominal distention.

ETIOLOGY
Overall, the most common causes of mechanical obstruction are adhesions, hernias, and tumors. Other general causes are diverticulitis, foreign bodies (including gallstones), volvulus (twisting of bowel on its mesentery), intussusception (telescoping of one segment of bowel into another and fecal impaction. Specific segments of the intestine are affected differently.

PATHOPHYSIOLOGY
In simple mechanical obstruction, blockage occurs without vascular compromise. Ingested fluid and food, digestive secretions, and gas accumulate above the obstruction. The proximal bowel distends, and the distal segment collapses. The normal secretory and absorptive functions of the mucosa are depressed, and the bowel wall becomes edematous and congested. Severe intestinal distention is self-perpetuating and progressive, intensifying the peristaltic and secretory derangements and increasing the risks of dehydration and progression to strangulating obstruction.
Strangulating obstruction is obstruction with compromised blood flow; it occurs in nearly 25% of patients with small-bowel obstruction. It is usually associated with hernia, volvulus, and intussusception. Strangulating obstruction can progress to infarction and gangrene in as little as 6 h. Venous obstruction occurs first, followed by arterial occlusion, resulting in rapid ischemia of the bowel wall. The ischemic bowel becomes edematous and infarcts, leading to gangrene and perforation. In large-bowel obstruction, strangulation is rare (except with volvulus).
Perforation may occur in an ischemic segment (typically small bowel) or when marked dilation occurs. The risk is high if the cecum is dilated to a diameter ≥ 13 cm. Perforation of a tumor or a diverticulum may also occur at the obstruction site.

SYMPTOMS AND SIGNS
Obstruction of the small bowel causes symptoms shortly after onset: abdominal cramps centered around the umbilicus or in the epigastrium, vomiting, and—in patients with complete obstruction—obstipation. Patients with partial obstruction may develop diarrhea. Severe, steady pain suggests that strangulation has occurred. In the absence of strangulation, the abdomen is not tender. Hyperactive, high-pitched peristalsis with rushes coinciding with cramps is typical. Sometimes, dilated loops of bowel are palpable. With infarction, the abdomen becomes tender and auscultation reveals a silent abdomen or minimal peristalsis. Shock and oliguria are serious signs that indicate either late simple obstruction or strangulation.
Obstruction of the large bowel usually causes milder symptoms that develop more gradually than those caused by small-bowel obstruction. Increasing constipation leads to obstipation and abdominal distention. Vomiting may occur (usually several hours after onset of other symptoms) but is not common. Lower abdominal cramps unproductive of feces occur. Physical examination typically shows a distended abdomen with loud borborygmi. There is no tenderness, and the rectum is usually empty. A mass corresponding to the site of an obstructing tumor may be palpable. Systemic symptoms are relatively mild, and fluid and electrolyte deficits are uncommon.

Volvulus


Volvulus often has an abrupt onset. Pain is continuous, sometimes with superimposed waves of colicky pain.

After your initial assessment, the patient's health care provider will order a number of diagnostic tests to determine the location, extent, and severity of the obstruction. These tests include:
 a complete blood cell (CBC) count to look for signs of infection and dehydration. An elevated white blood cell count (15,000 to 20,000/mm3) is a sign of infection and may indicate bowel strangulation or perforation. An increased hematocrit level may mean dehydration.
 an electrolyte panel and urinalysis to evaluate fluid and electrolyte imbalance and/or sepsis
 C-reactive protein and serum lactate levels to assess renal function and inflammation as well as rule out other problems
 creatinine and blood urea nitrogen (BUN) levels; an increase in these serum levels indicates that your patient may be dehydrated
 type and crossmatch (if there's a chance the patient needs surgical intervention)
 abdominal X-rays, flat and upright views to determine the location, pattern, and types (mechanical or nonmechanical, partial or complete) of the obstruction
 computed tomography can also determine the location and degree of the obstruction; it's about 90% sensitive and specific in diagnosing small-bowel obstruction and is the preferred diagnostic imaging test
 barium enema to determine the exact location and confirm the presence of an obstruction (barium is used with great caution, and not at all if a perforation is suspected)
 colonoscopy to help in the assessment and diagnosis of a large-bowel obstruction
 oral barium/gastroscopy tests, which can indicate an upper gastrointestinal mass.


DIAGNOSIS• Abdominal series
Supine and upright abdominal x-rays should be obtained and are usually adequate to diagnose obstruction. Although only laparotomy can definitively diagnose strangulation, careful serial clinical examination may provide early warning. Elevated WBCs and acidosis may indicate that strangulation has already occurred.
SMALL-BOWEL OBSTRUCTION (SUPINE)


SMALL-BOWEL OBSTRUCTION (UPRIGHT)


On plain x rays, a ladderlike series of distended small-bowel loops is typical of small-bowel obstruction but may also occur with obstruction of the right colon. Fluid levels in the bowel can be seen in upright views. Similar, although perhaps less dramatic, x ray findings and symptoms occur in ileus (paralysis of the intestine without obstructiondifferentiation can be difficult. Distended loops and fluid levels may be absent with an obstruction of the upper jejunum or with closed-loop strangulating obstructions (as may occur with volvulus). Infarcted bowel may produce a mass effect on x ray. Gas in the bowel wall (pneumatosis intestinalis) indicates gangrene.
In large-bowel obstruction, abdominal x ray shows distention of the colon proximal to the obstruction. In cecal volvulus, there may be a large gas bubble in the mid-abdomen or left upper quadrant. With both cecal and sigmoidal volvulus, a contrast enema shows the site of obstruction by a typical “bird-beak” deformity at the site of the twist; the procedure may actually reduce a sigmoid volvulus. If contrast enema is not done, colonoscopy can be used to decompress a sigmoid volvulus but rarely works with a cecal volvulus.

TREATMENT
• Nasogastric suction
• IV fluids
• IV antibiotics if bowel ischemia suspected
Patients with possible intestinal obstruction should be hospitalized. Treatment of acute intestinal obstruction must proceed simultaneously with diagnosis. A surgeon should always be involved.
Supportive care is similar for small- and large-bowel obstruction: nasogastric suction, IV fluids (0.9% saline or lactated Ringer's solution for intravascular volume repletion), and a urinary catheter to monitor fluid output. Electrolyte replacement should be guided by test results, although in cases of repeated vomiting serum Na and K are likely to be depleted. If bowel ischemia or infarction is suspected, antibiotics should be given (eg, a 3rd-generation cephalosporin, such as cefotetan

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