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What is Bowel obstruction and explain in detail?
Bowel obstruction, also known as intestinal obstruction, is a mechanical or functional obstruction of the intestines which prevents the normal movement of the products of digestion. Either the small bowel or large bowel may be affected. Signs and symptoms include abdominal pain, vomiting, bloating and not passing gas. Mechanical obstruction is the cause of about 5 to 15% of cases of severe abdominal pain of sudden onset requiring admission to hospital.Causes of bowel obstruction include adhesions, hernias, volvulus, endometriosis, inflammatory bowel disease, appendicitis, tumors, diverticulitis, ischemic bowel, tuberculosis and intussusception. Small bowel obstructions are most often due to adhesions and hernias while large bowel obstructions are most often due to tumors and volvulus. The diagnosis may be made on plain X-rays; however, CT scan is more accurate. Ultrasound or MRI may help in the diagnosis of children or pregnant women.The condition may be treated conservatively or with surgery. Typically intravenous fluids are given, a tube is placed through the nose into the stomach to decompress the intestines, and pain medications are given. Antibiotics are often given. In small bowel obstruction about 25% require surgery. Complications may include sepsis, bowel ischemia and bowel perforation.About 3.2 million cases of bowel obstruction occurred in 2015 which resulted in 264,000 deaths. Both sexes are equally affected and the condition can occur at any age. Bowel obstruction has been documented throughout history, with cases detailed in the Ebers Papyrus of 1550 BC and by Hippocrates.

Signs and symptoms
Depending on the level of obstruction, bowel obstruction can present with abdominal pain, swollen abdomen, abdominal distension, and constipation. Bowel obstruction may be complicated by dehydration and electrolyte abnormalities due to vomiting; respiratory compromise from pressure on the diaphragm by a distended abdomen, or aspiration of vomitus; bowel ischemia or perforation from prolonged distension or pressure from a foreign body.In small bowel obstruction, the pain tends to be colicky (cramping and intermittent) in nature, with spasms lasting a few minutes. The pain tends to be central and mid-abdominal. Vomiting may occur before constipation.In large bowel obstruction, the pain is felt lower in the abdomen and the spasms last longer. Constipation occurs earlier and vomiting may be less prominent. Proximal obstruction of the large bowel may present as small bowel obstruction.

Causes
Small bowel obstruction
Causes of small bowel obstruction include:
Adhesions from previous abdominal surgery (most common cause)
Barbed sutures
Pseudoobstruction
Hernias containing bowel
Crohns disease causing adhesions or inflammatory strictures
Neoplasms, benign or malignant
Intussusception
Volvulus
Superior mesenteric artery syndrome, a compression of the duodenum by the superior mesenteric artery and the abdominal aorta
Ischemic strictures
Foreign bodies (e.g. gallstones in gallstone ileus, swallowed objects such as expandable water toys)
Intestinal atresiaAfter abdominal surgery, the incidence of small bowel obstruction from any cause is 9%. In those where the cause of the obstruction was clear, adhesions are the single most common cause (more than half).

Large bowel obstruction
Causes of large bowel obstruction include:
Neoplasms / cancer
Diverticulitis / Diverticulosis
Hernias
Inflammatory bowel disease
Colonic volvulus (sigmoid, caecal, transverse colon)
Adhesions
Constipation
Fecal impaction
Fecaloma
Colon atresia
Intestinal pseudoobstruction
Endometriosis
Narcotic induced (especially with the large doses given to cancer or palliative care patients)

Outlet obstruction
Outlet obstruction is a sub-type of large bowel obstruction and refers to conditions affecting the anorectal region that obstruct defecation, specifically conditions of the pelvic floor and anal sphincters. Outlet obstruction can be classified into four groups.
Functional outlet obstruction
Inefficient inhibition of the internal anal sphincter
Short-segment Hirschsprungs disease
Chagas disease
Hereditary internal sphincter myopathy
Inefficient relaxation of the striated pelvic floor muscles
Anismus (pelvic floor dyssynergia)
Multiple sclerosis
Spinal cord lesions
Mechanical outlet obstruction
Internal intussusception
Enterocele
Dissipation of force vector
rectocele
Descending perineum
Rectal prolapse
Impaired rectal sensitivity
Megarectum
Rectal hyposensitivity

Diagnosis
The main diagnostic tools are blood tests, X-rays of the abdomen, CT scanning, and ultrasound. If a mass is identified, biopsy may determine the nature of the mass.Radiological signs of bowel obstruction include bowel distension and the presence of multiple (more than six) gas-fluid levels on supine and erect abdominal radiographs. Ultrasounds may be as useful as CT scanning to make the diagnosis.Contrast enema or small bowel series or CT scan can be used to define the level of obstruction, whether the obstruction is partial or complete, and to help define the cause of the obstruction. The appearance of water-soluble contrast in the cecum on an abdominal radiograph within 24 hours of it being given by mouth predicts resolution of an adhesive small bowel obstruction with sensitivity of 97% and specificity of 96%.Colonoscopy, small bowel investigation with ingested camera or push endoscopy, and laparoscopy are other diagnostic options.

Differential diagnosis
Differential diagnoses of bowel obstruction include:

Ileus
Pseudo-obstruction or Ogilvies syndrome
Intra-abdominal sepsis
Pneumonia or other systemic illness

Treatment
Some causes of bowel obstruction may resolve spontaneously; many require operative treatment. In adults, frequently the surgical intervention and the treatment of the causative lesion are required. In malignant large bowel obstruction, endoscopically placed self-expanding metal stents may be used to temporarily relieve the obstruction as a bridge to surgery, or as palliation. Diagnosis of the type of bowel obstruction is normally conducted through initial plain radiograph of the abdomen, luminal contrast studies, computed tomography scan, or ultrasonography prior to determining the best type of treatment.Further research is needed to find out if parenteral nutrition is of benefit to people with an inoperable blockage of the bowel caused by advanced cancer.

Small bowel obstruction
In the management of small bowel obstructions, a commonly quoted surgical aphorism is: "never let the sun rise or set on small-bowel obstruction" because about 5.5% of small bowel obstructions are ultimately fatal if treatment is delayed. Improvements in radiological imaging of small bowel obstructions allow for confident distinction between simple obstructions, that can be treated conservatively, and obstructions that are surgical emergencies (volvulus, closed-loop obstructions, ischemic bowel, incarcerated hernias, etc.).A small flexible tube (nasogastric tube) may be inserted through the nose into the stomach to help decompress the dilated bowel. This tube is uncomfortable but relieves the abdominal cramps, distention, and vomiting. Intravenous therapy is utilized and the urine output is monitored with a catheter in the bladder.Most people with SBO are initially managed conservatively because in many cases, the bowel will open up. Some adhesions loosen up and the obstruction resolves. The patient is examined several times a day, and X-ray images are made to ensure he or she is not getting clinically worse.Conservative treatment involves insertion of a nasogastric tube, correction of dehydration and electrolyte abnormalities