Large and Small Bowel Obstructions

In medical vernacular, small intestines (duodenum, ileum, and jejunum) are referred to as bowel or just the intestines, and the large intestines (ascending, transverse, descending, and sigmoid) are referred to as the colon. However, the phrase, bowel obstruction can mean both small (intestinal) and large (colon) bowel.

BOWEL OBSTRUCTION (both small and large bowel) is defined as mechanical or functional obstruction, partial or complete, that stops the normal progression of fecal waste along the gastrointestinal tract.

The real problem with obstruction:

Failure to eliminate the waste is not the immediate problem with obstruction: it is the risk to the structural integrity of the entire intestinal tract and abdomen, due to perforation and spillage of fecal contents into the peritoneal cavity.

Since the intestines are covered over with an extension of the very distention-sensitive peritoneum, called the "serosa," and since obstruction causes distention at the site of the blockage, obstruction is extremely painful, the most informative sign that a dangerous condition is present.

Bowel obstruction by percentage:

• 3/4 small bowel;
• 1/4 large.

In the small bowel (intestines), adhesions, Crohn's disease, and hernia are common causes.

In the large bowel (colon), about 70% of obstructions are at the transverse or lower (descending colon and rectum), usually due to malignancy (see below), the most common etiology of large bowel obstruction in the developing world.

Serious business: morbidity rates of bowel obstructions range from 12%-16% of all hospital admissions for complaints of abdominal pain, and mortality rates range from 2%-8% but can increase to as high as 25% if ischemia occurs (bowel death).

Causes of Mechanical Obstruction

• Adhesions caused by previous surgery, hemorrhage, or infection. This is the most common cause of small bowel obstructions in adults, typically caused by previous surgeries or other disease processes like Crohn's disease.
• Malignancy. The most common cause overall for large bowel obstructions is malignancy, including colorectal cancer. Cancer involves tissue growth independent and at the expense of other tissue, and it can mechanically block the lumen of the intestines anywhere in the GI tract, from the esophagus to the anus, as well as interfere with peristalsis even when outside of the bowel/colon walls. This is the most common etiology of large bowel obstruction in adults. 
  • Source: Large Bowel Obstruction 
• Inflammatory diseases, such as Crohn's disease (more than ulcerative colitis), with repeated bouts of intestinal inflammation.
• Strictures due to repetitive bouts of diverticulitis.
• Hernia is complicated by the incarceration of the bowel when the bowel becomes entrapped.
• Severe constipation with fecal impaction occurs with opioid use and abuse.
• Sigmoid volvulus, when an air-filled loop of the sigmoid colon twists about its mesentery, with possible impairment of vascular perfusion, leading to bowel death.

The above are mechanical obstructions. There is also a "functional" type of obstruction when the normal propulsive peristaltic mechanisms are ineffective due to abnormal intestinal physiology.

 

Causes of Functional Obstruction

• Post-op ileus (or "stunned bowel syndrome"), which is temporary and benign. Most surgery patients are discharged home after post-op ileus has resolved, but those discharged too soon, as in these days of same-day surgery and cost-containment, may present at home with this.

NOTE: In the field, it is impossible to differentiate between post-op ileus and acute mechanical bowel obstruction, so transport is the default position.

• Intestinal shut-down that accompanies generalized dangers in the abdomen, such as peritonitis or internal hemorrhage. Inflammation plays havoc with the orderly peristalsis of the GI tract.
• Abnormalities in peristalsis, called "pseudo-obstruction," from problems of the bowel nerves or smooth muscle within bowel walls.

This can be seen in diabetes, degenerative Parkinson's disease, and immune disorders.

• Bowel death from vascular compromise due to embolus or volvulus.

NOTE: People especially at risk for embolizing and blocking the blood supply to the bowel are those being treated for atrial fibrillation. Migrating clots along the arterial system can lodge in the superior mesenteric artery, causing ischemia or infarction to portions or to all of the intestines or to other arteries, causing ischemia or infarction to portions or to all of the colon.

 

Perforation

Perforation can occur due to the following:

• From over-distension: the devastating end point of obstruction is perforation, but this is well after the pain of obstruction has begun.

At some point, the distension outpaces the elasticity of the serosa, resulting in a breach of the wall, with the perforation spilling intestinal contents into the abdomen, further resulting in peritonitis (an acute abdomen).

• Infection: an abscess is designed to wall off infection and rupture its contents into the outside world.

Unfortunately, the "outside" of an intestinal abscess is the sterile abdomen, so a rupture that spills its contents into the peritoneal cavity will cause an acute abdomen. 

• Bowel ischemia: loss of blood supply leads to bowel ischemia and patch(es) of dead bowel.

This is not only a functional obstruction, which is painful in its own right, but non-viable serosa can perforate spontaneously. The most likely causes of bowel ischemia are volvulus and embolus.

 

Signs and Symptoms of Obstruction

In the field, the average patient with obstruction is usually seen after 5 days of progressive obstruction, so transport is the default decision for this surgical emergency, as the damage and danger is well underway.

They will present with:

• Pain
• Distention

Both the pain and/or distention will be either with or without fever.

• Decreased bowel sounds: there can be a complete absence of bowel sounds or "rushes" (high-pitched) or "tinkling" bowel sounds.
• Intermittent cramping.
• Loss of appetite.
• Vomiting.
• Constipation.
• Inability to have a bowel movement or pass gas.
• With perforation, there will be signs of the acute abdomen: rigidity/guarding and rebound tenderness.

While it might seem logical that where the obstruction will manifest itself is a specific area of the abdomen, the reality is that obstruction leads to generalized pain due to the distention of the bowel all above the level of obstruction, which can involve many feet of bowel.

►Call to Action: TRANSPORT. Any suspicion of bowel obstruction, impossible to differentiate from post-op ileus, perforation, or an acute abdomen, requires transport.

Transport and pre-hospital management should focus on

• strict attention to BSI and PPE,
• airway and circulatory support (ABC),
• IV fluid replacement,
• medication administration, and
• transport to definitive care.