Bowel obstruction overview

# Overview
Bowel obstruction is a mechanical or functional obstruction of the intestines, preventing the normal transit of the products of digestion.  It can occur at any level distal to the duodenum of the small intestine and is a medical emergency. Although many cases are not treated surgically, it is a surgical problem. Bowel obstruction has been described as far back as 1550 b.c. in ancient Egypt, however, the earliest record of the first successful treatment of small bowel obstruction was in 350 b.c. by Praxagorus. Bowel obstruction  may be classified by 5 different classification methods including; open and closed, incomplete and complete, extrinsic, intrinsic and intraluminal, true and pseudo-obstruction, and finally, small bowel and large bowel. In this chapter, the extrinsic, intrinsic and intraluminal classification method will be used. It is thought that bowel obstruction may occur functionally as a result of abnormal anatomy or impairment of the autonomic nervous system or mechanically, which may occur acutely or chronically. An obstruction that occurs functionally or mechanically can be classified as extrinsic, intrinsic or intraluminal including tumors, strictures and foreign bodies. Excessive bowel distention can lead to ischemia, necrosis and perforation. A functional obstruction may be due to a number of genetic defects including trisomy 21 and the RET proto-oncogene mutation. Associated conditions include post-operative adhesions, complicated hernias, gastrointestinal cancers and endometriosis. Gross pathology may demonstrate adhesions, narrow lumens and volvulus. Microscopic pathology may show evidence of fibrosis, necrosis and ischemia. The incidence of bowel obstruction in the US is 1.47 per 100,000 per year. Colorectal cancer and Crohn's disease are often complicated by bowel obstruction. The mortality rate is about 4% on average with the mortality rate reaching as high as 60% in the presence of bowel ischemia or when surgery is delayed. Bowel obstruction incidence has a median age of approximately 64 years. The incidence in newborns is about 1 in 2000 live births and 1 in 5000 in children above the age of 2. There is no racial predilection in cases of bowel obstruction. Men and women have an equal incidence of bowel obstruction. The highest incidence of bowel obstruction is found in the continent of Africa. If left untreated, 85% of patients with complete bowel obstruction may progress to develop ischemia, necrosis, and gangrene. Common complications of bowel obstruction include bowel ischemia, bowel perforation, gangrene and sepsis. Prognosis is generally excellent for non-ischemic bowel obstruction, and the mortality rate of patients with bowel obstruction is approximately 4%. In contrast, prognosis for ischemic bowel obstruction is approximately 60%. There is no single diagnostic study of choice for the diagnosis of bowel obstruction, but bowel obstruction can be diagnosed based on plain x-ray and CT scan. An x-ray is performed when obstruction is suspected with clinical findings of nausea, vomiting, abdominal pain, abdominal distension and constipation. The results of plain x-ray that confirm of bowel obstruction include dilated bowel loops with air-fluid level, distal collapsed bowel, gasless abdomen or alternatively, "string of pearls" sign. The results of CT that confirm of bowel obstruction include dilated bowel loops with air-fluid level and distal collapsed bowel. Initially, an x-ray is usually performed before surgical intervention. If urgent intervention is not needed and the diagnosis is equivocal, then a CT may be carried out. The mainstay of treatment for bowel obstruction is surgical. Surgery is specifically indicated for complicated bowel obstruction. Complications include: complete obstruction, closed-loop obstruction, bowel ischemia, necrosis, and perforation.

# Historical Perspective
Bowel obstruction has been described as far back as 1550 b.c. in ancient Egypt, however, the earliest record of the first successful treatment of small bowel obstruction was in 350 b.c. by Praxagorus.

# Classification
Bowel obstruction  may be classified by 5 different classification methods including; open and closed, incomplete and complete, extrinsic, intrinsic and intraluminal, true and pseudo-obstruction, and finally, small bowel and large bowel. In this chapter, the extrinsic, intrinsic and intraluminal classification method will be used.

# Pathophysiology
It is thought that bowel obstruction may occur functionally as a result of abnormal anatomy or impairment of the autonomic nervous system or mechanically, which may occur acutely or chronically. An obstruction that occurs functionally or mechanically can be classified as extrinsic, intrinsic or intraluminal including tumors, strictures and foreign bodies. Excessive bowel distention can lead to ischemia, necrosis and perforation. A functional obstruction may be due to a number of genetic defects including trisomy 21 and the RET proto-oncogene mutation. Associated conditions include post-operative adhesions, complicated hernias, gastrointestinal cancers and endometriosis. Gross pathology may demonstrate adhesions, narrow lumens and volvulus. Microscopic pathology may show evidence of fibrosis, necrosis and ischemia.

# Causes
Small bowel obstruction causes include post-adbominal surgery adhesions, foreign bodies and intussusception. Large bowel obstruction causes include neoplasms, hernias and constipation. Miscellaneous causes include, paralytic ileus and Down syndrome. Causes by organ system include, ovarian cancer, bowel strangulation and ascariasis. Mechanical obstruction can be caused by pregnancy, Hirschsprung's disease and Crohn's disease. Non-mechanical obstruction may be caused by ovarian torsion, pancreatitis and lead poisoning. Drug induced bowel obstruction can occur by intake of lanthanum carbonate, methscopolamine bromide, and teduglutide.

# Differentiating bowel obstruction from Other Diseases
Bowel obstruction must be differentiated from other diseases that cause abdominal pain, nausea and vomiting, and constipation, such as irritable bowel syndrome, volvulus and acute diverticulitis.

# Epidemiology and Demographics
The incidence of bowel obstruction in the US is 1.47 per 100,000 per year. Colorectal cancer and Crohn's disease are often complicated by bowel obstruction. The mortality rate is about 4% on average with the mortality rate reaching as high as 60% in the presence of bowel ischemia or when surgery is delayed. Bowel obstruction incidence has a median age of approximately 64 years. The incidence in newborns is about 1 in 2000 live births and 1 in 5000 in children above the age of 2. There is no racial predilection in cases of bowel obstruction. Men and women have an equal incidence of bowel obstruction. The highest incidence of bowel obstruction is found in the continent of Africa.

# Risk Factors
Common risk factors in the development of bowel obstruction include, abdominal surgery, colorectal cancer, and volvulus. Common risk factors in the development of bowel obstruction include congenital gastrointestinal atresias, colorectal carcinoma and surgical resection of the bowel. Less common risk factors in the development of bowel obstruction include pancreatic cancer, ovarian cancer and lymphoma.

# Screening
There is insufficient evidence to recommend routine screening for bowel obstruction.

# Natural History, Complications, and Prognosis
If left untreated, 85% of patients with complete bowel obstruction may progress to develop ischemia, necrosis, and gangrene. Common complications of bowel obstruction include bowel ischemia, bowel perforation, gangrene and sepsis. Prognosis is generally excellent for non-ischemic bowel obstruction, and the mortality rate of patients with bowel obstruction is approximately 4%. In contrast, prognosis for ischemic bowel obstruction is approximately 60%.

# Diagnosis

## Diagnostic Criteria
There is no single diagnostic study of choice for the diagnosis of bowel obstruction, but bowel obstruction can be diagnosed based on plain x-ray and CT scan. An x-ray is performed when obstruction is suspected with clinical findings of nausea, vomiting, abdominal pain, abdominal distension and constipation. The results of plain x-ray that confirm of bowel obstruction include dilated bowel loops with air-fluid level, distal collapsed bowel, gasless abdomen or alternatively, "string of pearls" sign. The results of CT that confirm of bowel obstruction include dilated bowel loops with air-fluid level and distal collapsed bowel. Initially, an x-ray is usually performed before surgical intervention. If urgent intervention is not needed and the diagnosis is equivocal, then a CT may be carried out.

## History and Symptoms
The hallmark of bowel obstruction is abdominal distension with waxing and waning pain and obstipation. A positive history of previous abdominal surgery and abdominal adhesion is suggestive of bowel obstruction. The most common symptoms of bowel symptoms include abdominal pain with nausea and vomiting, abdominal distension, and obstipation. Common symptoms of bowel obstruction include episodic pain, abdominal distension, and constipation. Less common symptoms of bowel obstruction include constant severe pain, sudden severe pain, and postprandial abdominal discomfort.

## Physical Examination
Patients with bowel obstruction usually appear distressed with a distended abdomen with or without fever. Physical examination of patients with bowel obstruction is usually remarkable for tympanic or hyperresonant abdomen, orthostatic hypotension, tachycardia, and dry mucus membranes.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of bowel obstruction include hyponatremia and hypokalemia, leukocytosis, metabolic alkalosis and elevated serum lactate.

## Imaging Findings

### X Ray
An x-ray is the initial investigation performed in the diagnosis of bowel obstruction. Findings on an x-ray suggestive of bowel obstruction include dilated bowel loops with air-fluid level, distal collapsed bowel,absence of gas in the abdomen or alternatively, "string of pearls" sign indicating trapped flatus.

### CT
Abdominal CT scan may be helpful in the diagnosis of bowel obstruction. Findings on CT scan suggestive of bowel obstruction include dilated bowel loops with air-fluid level, distal collapsed bowel, in addition to, "Target", "Whirl" and "Venous cut-off" signs.

## Other Diagnostic Studies
Other diagnostic studies for bowel obstruction include contrast studies, which demonstrate dilated proximal bowel loops, point of transition, and complete obstruction. Contrast enema is useful in those who have had a previous surgical reconstruction of the bowel. Enteroclysis is a useful study in those with chronic or recurrent bowel obstruction.

# Treatment

## Medical Therapy
The mainstay treatment of bowel obstruction is surgical and non-operative management. The role of medical therapy is supportive and is limited by palliative pain management in cancer patients, fluid and electrolyte replenishment, decreasing abdominal distension, peritumoral edema, intraluminal secretions, peristaltic movements, and control of nausea and vomiting.

## Surgery
The mainstay of treatment for bowel obstruction is surgical. Surgery is specifically indicated for complicated bowel obstruction. Complications include: complete obstruction, closed-loop obstruction, bowel ischemia, necrosis, and perforation.

## Prevention
There are no established measures for the primary prevention of bowel obstruction. However, minimizing the formation of an obstruction is possible. Steroid therapy may be used to minimize the formation of adhesions after bowel surgery, but is controversial. The correction of malrotation early in life, the treatment of Crohn's disease, and the repair of hernia all contribute to minimizing the risk of bowel obstruction development. Recently, laparoscopic surgery has been preferred over open abdominal surgery because laparoscopy reduced the risk for obstruction post-operatively.