Bowel obstruction

Definitions & Key takeaways

A bowel obstruction is a blockage of the intestines. It can be caused by many things, including tumors, hernias, or adhesions from surgery. Symptoms can include pain in the abdomen, nausea, vomiting and constipation.

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Introduction0:00–0:40

Bowel obstruction is when the normal flow of contents moving through the intestines is interrupted. The causes of bowel obstruction can be either mechanical or functional, also called ileus.
Mechanical obstruction is caused by actual blockages in the large or small intestine, and it can be defined as partial or complete.
Partial obstruction is when gas or liquid stool can pass through the point of narrowing, while complete obstruction is when nothing can pass.
Functional causes disrupt peristalsis, which are the waves of contraction that move through the smooth muscles of the bowel wall that pushes food through the intestines.
The small and large intestines are tube-shaped structures through which chyme, or food that has been partly digested by the stomach, and stools pass until they’re excreted.

Physiology0:40–1:47

Now if we zoom into a cross-section of the intestinal wall, it’s lined by four layers of tissue: First, there’s the adventitia, or serosa; which is the outermost layer that faces the abdominal or peritoneal cavity.
This is the space between the abdominal wall and the abdominal organs, and it’s lined by peritoneal membranes that contains a thin film of serous fluid.
Moving on, there’s the muscularis externa, which is smooth muscle that contract to move food through the bowel. Deep beneath this layer is the submucosa, which has connective tissue as well as glands, blood and lymph vessels that supply the intestinal wall.
And finally, the innermost layer is the mucosa and it’s composed of a few of its own layers: the muscularis mucosae, which has smooth muscle, the lamina propria, which is rich with blood and lymph vessels, and the innermost layer which is the epithelial lining that faces the lumen.
Okay, so let’s go over some mechanical causes for bowel obstruction. The most common cause in the small intestine is postoperative adhesions.

Causes1:47–3:48

After a surgery, the scar tissue that forms during the healing process can form fibrous bands that cause organs to attach to the surgical site or to other organs, causing the lumen of the bowel to get kinked or pinched tight in certain spots.
Another cause of small intestinal obstruction is hernias, and they can occur when a portion of the bowel protrudes out of the abdominal cavity and can get trapped or tightly pinched at the point where it pokes out.
Mechanical causes for large bowel obstructions, on the other hand, are most often due to a volvulus, which is when a loop of intestine twists upon itself, kinking off the lumen.
Sometimes the volvulus can occur around a mass like in colorectal cancer. Some mechanical causes of both small and large bowel obstruction include inflammatory bowel disease which can cause strictures and adhesions; ingestion of a foreign body, which can get lodged along the gastrointestinal tract; and intussusception, which is where a part of the intestine folds into the lumen of an adjacent section of bowel, kind of like retracting a telescope.
This is the most common cause of bowel obstruction in children under the age of 2.Now, regarding functional obstruction, causes include anything that decreases smooth muscle contractility.
The most common one is postoperative ileus, which is transient paralysis of the smooth muscles in the intestinal wall, and it’s usually caused by trauma during surgery.
Other causes include infection or inflammation, such as appendicitis or peritonitis, hypothyroidism, meaning the thyroid gland does not produce enough thyroid hormones, and electrolyte abnormalities like hypokalemia, meaning low potassium in the blood, or hypercalcemia which is high calcium in the blood, or various medications such as opioids.

Pathology3:48–7:19

So, when there's a bowel obstruction, whatever the cause, the bowel contents distal to the obstruction get passed; but after that happens, proximal to the obstruction, gas and stool start to accumulate, causing the bowel to dilate, and therefore, the overall abdominal cavity to distend.
Over time, all this gas and stool causes pressure inside the bowel lumen to increase, so the intestinal contents push towards the intestinal wall, compressing the mucosal blood and lymphatic vessels.
Since the walls of veins and lymphatics are weaker and easier to compress compared to arteries, venous and lymphatic drainage are the first ones to get blocked.
The pressure pushes the water in these vessels into the surrounding tissue, leading to mucosal edema. If pressure inside the lumen gets even higher, it also compresses mucosal arteries, leading to ischemia or reduced blood flow to the intestinal wall.
In turn, ischemia causes hypoxia, or low oxygen supply. At the cellular level, this is accompanied by the production of reactive oxygen species; which can damage DNA, RNA, and proteins of the cells in the epithelial layer and lamina propria of the mucosa, leading to cell death, or mucosal infarction.
So, when the mucosa becomes damaged and capillary blood vessels in the lamina propria rupture, blood enters the bowel lumen.
All this stool and blood in the lumen becomes a nutritious feast for bacteria that normally reside in the intestines, and they start growing out of control.
These bacteria can then get into the intestinal wall, where they get attacked by macrophages rushing into the mucosa. These macrophages then release inflammatory cytokines like tumor necrosis factor-alpha, which cause blood vessels to become more permeable to fluid and to more immune cells, further increasing mucosal edema, inflammation, and damage.
The overall result is the compromised ability of the mucosa to absorb food and water, which may lead to dehydration and loss of electrolytes, like sodium, potassium and chloride.Now, as all these lumen contents continues to build up, intraluminal pressure rises even higher, making the problem even worse if not corrected.
And if this pressure becomes high enough, even larger arteries get compressed, meaning that the arterial supply to more layers of the bowel wall is compromised.
In other words, bowel ischemia and infarction extend from just the mucosa to all layers bowel wall, known as a transmural infarction.
This may result in perforation, so there’s basically a hole in the bowel wall that connects the lumen to the peritoneal cavity.
And all the bacteria that have been accumulating inside the lumen, can now easily leak out, causing peritonitis. Now, since the layers of the peritoneum are very rich in blood vessels, large numbers of bacteria from the peritoneal cavity can sneak into the bloodstream, triggering a massive inflammatory response called sepsis.
In sepsis, blood vessels throughout the body can get leaky, letting the water in blood escape into the interstitial space.
If too much fluid is lost, blood volume drops and so does the blood pressure. This leads to a decrease in the amount of blood reaching vital organs to deliver oxygen and we call this shock.
Ultimately, this can cause organ failure and death.Generally speaking, symptoms of bowel obstruction include cramping, abdominal pain, constipation, vomiting, and abdominal distention.

Signs and symptoms7:19–8:57

In individuals with partial obstruction, symptoms typically appear more gradually and are milder, including abdominal discomfort after meals and constipation.
On the other hand, in complete obstruction, symptoms usually appear suddenly and include obstipation, which is a more serious version of constipation where there’s a complete inability to pass stool or gas.
Now, in small bowel obstruction, vomiting is more common and the pain tends to be periumbilical, or around the belly button.
The pain is often described as cramping, and intermittent, with bouts that last for a few minutes at a time. In large bowel obstruction, vomiting is less common, the pain is lower in the abdomen and the bouts of pain are less frequent but last a bit longer.
When there’s progression from cramping and vague pains to more focal and constant pain it can indicate peritoneal irritation due to a perforation of the intestine.
Finally, bowel obstruction can cause abdominal distention which pushes on the diaphragm, making it hard for the lungs to expand.
This causes some individuals to develop respiratory distress, presenting with symptoms like shortness of breath, tachypnea, and cyanosis, which is a bluish color of the skin due to poor oxygenation of the blood.
They can also develop shock if sepsis is present, with symptoms like fever, fatigue or weakness, tachycardia, and tachypnea.Diagnosis of bowel obstruction begins with auscultation or listening to the bowel sounds with a stethoscope.

Diagnosis8:57–9:56

High pitched, tinkling sounds typically indicate mechanical obstruction, while the absence of normal bowel sounds suggests functional obstruction.Imaging studies are also important, starting with an upright abdominal X ray.Dilated loops of bowel with multiple air-fluid levels on the x-ray suggest mechanical bowel obstruction.
On the other side; generalized, uniform distention of the large and small bowel suggest functional bowel obstruction. Free air under the diaphragm means there's perforation, so emergency surgery is needed.
Otherwise, we can proceed to an abdominal CT scan with contrast in order to identify the potential cause of obstruction.
Abdominal ultrasonography may be useful for individuals with contraindications to CT scanning, like those with contrast allergies and pregnant females.Most bowel obstructions resolve on their own, so treatment typically focuses on relieving the symptoms.

Treatment9:56–10:21

This might involve administering intravenous fluids, or nasogastric suction, which is inserting a tube through the nose to the stomach to remove the fluid and gases that have built up.
If symptoms don’t improve or there’s complications such as perforation; then surgery might be needed.##SummaryAll right, as a quick recap… Bowel obstruction is when the normal flow of contents moving through the intestines is interrupted.

Review10:21–11:05

Causes can be mechanical, which can result in partial or complete bowel obstruction, or functional. Complications include dehydration, electrolyte abnormalities, bowel perforation and peritonitis.
Symptoms include cramping abdominal pain, constipation, abdominal distention and vomiting. Diagnosis of bowel obstruction requires imaging studies, like X ray, and CT scan with contrast or abdominal ultrasonography.
Treatment depends on the cause and severity of the obstruction. There’s conservative management, surgery.