Bowel obstruction

The gastrointestinal tract is a tube roughly twenty-five feet long, and like any plumbing, its function depends entirely on things being able to move through it. A bowel obstruction is a mechanical blockage of that tube.

The first distinction to understand is between a true obstruction and an ileus. In an obstruction there is a physical blockage — a band of scar tissue, a hernia, a tumor. In an ileus there is no blockage at all; the bowel has simply stopped propelling, usually after surgery, after certain medications, or in the setting of illness elsewhere in the body. Both produce a distended, quiet, unhappy abdomen and both look similar on an x-ray, but one is a plumbing problem and one is a motor problem. They are managed very differently, and distinguishing them is a significant part of what a surgeon is doing in the first day or two.

What actually happens upstream of a blockage

This is worth understanding because it explains everything about how patients feel and why the treatment is what it is.

Most people assume the distension above a blockage comes from food. It does not, mostly. The gastrointestinal tract secretes something on the order of seven to nine liters of fluid into itself every day — saliva, gastric acid, bile, pancreatic juice, intestinal secretions — nearly all of which is reabsorbed further downstream under normal conditions. When the tube is blocked, that fluid keeps being produced and has nowhere to go. Add swallowed air, and the bowel above the blockage distends rapidly.

Then a cycle sets in. The distended bowel wall becomes edematous and stops absorbing. That worsens the distension. The distension raises pressure in the bowel wall, and as pressure rises it eventually exceeds the pressure at which the small vessels in the wall can deliver oxygen. If that continues, the bowel wall begins to die.

If that mechanism sounds familiar, it should. It is precisely what happens in appendicitis, on a larger scale. Distension is not merely uncomfortable, it is the thing that ultimately kills bowel.

Meanwhile, all of that sequestered fluid is out of circulation. Patients with a bowel obstruction are often profoundly dehydrated even though their abdomen is full of fluid, and they lose large amounts of potassium and chloride through vomiting. A significant portion of the early treatment is simply correcting that.

What causes it?

In the United States and other high-income countries, the leading cause by a wide margin is adhesions — bands of internal scar tissue from prior abdominal surgery. Second is hernia. Third is malignancy.

Globally the order flips. In much of the world where fewer people have had abdominal operations, hernia is the leading cause, followed by volvulus and, in some regions, tuberculosis. I mention this partly because it is genuinely interesting and partly because it illustrates something true about surgical disease: the same organ fails in different ways depending on where you live.

One practical consequence of that ranking: if a patient presents with a bowel obstruction and has never had abdominal surgery and has no hernia, adhesions are unlikely, and the index of suspicion for a tumor or another structural cause goes up considerably.

Adhesions

Any operation inside the abdomen can produce them. The peritoneal surfaces are injured, they heal, and in healing they sometimes stick to each other or form fibrous bands. This is not a complication in the sense of something having gone wrong. It is a normal healing response that occasionally has a bad consequence.

Minimally invasive surgery produces fewer adhesions than open surgery, which is one of its genuine advantages, but it does not eliminate them. And adhesions do not follow a schedule. I have operated on obstructions from an appendectomy performed thirty years earlier.

What it feels like

Crampy, wave-like abdominal pain, distension, nausea and vomiting, and eventually the inability to pass gas or stool. The pattern varies with the level of the blockage. A high, proximal obstruction produces a lot of vomiting and relatively little distension, because there is not much bowel above it to distend. A low obstruction near the colon produces marked distension and vomiting that comes later and, unpleasantly, can become feculent.

A change in the character of the pain matters. Crampy pain that comes in waves is the bowel trying to push against a blockage. Pain that becomes constant, severe, and unremitting is a different and more worrying signal.

Closed loop obstruction

Most obstructions are blocked at one point, which means the bowel above it can at least decompress upward through vomiting or a tube. A closed loop obstruction is blocked at two points, so a segment of bowel is sealed off at both ends with no route of escape.

This is a different animal. Pressure in that isolated segment rises fast, the blood supply is often twisted along with it, and the bowel can be dead in hours rather than days. A volvulus is one form of this. A closed loop obstruction is not something we watch. It is an operation.

Strangulation

This is the word that drives urgency. Strangulation means the obstructed bowel has lost its blood supply and is dying.

The honest problem is that there is no single reliable way to detect it before it has happened. Fever, a rising heart rate, an elevated white count, a rising lactate, constant rather than crampy pain, and tenderness on examination all raise concern, and certain CT findings are suggestive. None of them is definitive early on, and by the time all of them are present it is late. Much of the judgment in managing a bowel obstruction is about deciding when the risk of continuing to wait has exceeded the risk of an operation.

Can it be treated without surgery?

Often, yes — and this is where a lot of good surgical care happens.

An adhesive small bowel obstruction without signs of strangulation is typically managed first without an operation. That means nothing by mouth, intravenous fluid, careful correction of electrolytes, and a nasogastric tube.

Patients hate the NG tube, and I understand why, but it is doing something important. It decompresses the stomach and the bowel above the blockage, which breaks the distension cycle described above, relieves the vomiting, reduces the risk of aspirating gastric contents into the lungs, and reduces edema in the bowel wall so that things have a chance to open up on their own. It is the single most useful thing we do for a bowel obstruction that is not an operation.

We also frequently use water-soluble contrast, most commonly Gastrografin, given down the NG tube. This does two jobs at once. Therapeutically it is hyperosmolar, meaning it draws fluid into the bowel lumen and pulls edema out of the bowel wall, and it has been shown to increase the rate of resolution without surgery. Diagnostically, an abdominal x-ray several hours later answers a very useful question: if the contrast has reached the colon, the obstruction is very likely to resolve without an operation. If it has not, the odds shift substantially toward surgery. It is one of the more elegant tests in general surgery because the test and the treatment are the same thing.

How long do we wait?

Most adhesive obstructions that are going to resolve on their own do so within about two to three days. Beyond roughly three to five days without resolution, the calculus changes: continued waiting is no longer buying much and the risk of a complication rises. That is a general rule, not a rigid one.

The situations where we do not wait at all are worth listing plainly: signs of peritonitis on examination, a closed loop obstruction, evidence of strangulation, a hernia containing bowel that cannot be reduced, and an obstruction in a patient with no prior abdominal surgery, where a structural cause is more likely and unlikely to resolve on its own.

The operation

Usually this is lysis of adhesions — dividing the scar bands that are causing the blockage, and running the entire length of the small bowel to be certain nothing else is missed. If a segment of bowel is not viable, it is resected and the two healthy ends are reconnected.

This can often be done laparoscopically, particularly in a patient with a small number of prior operations and a less distended abdomen. In a very distended abdomen or one with dense scarring from multiple prior surgeries, an open approach is safer, because the risk in this operation is making an unintended hole in the bowel while separating it, and that risk goes up substantially in a hostile abdomen.

Recovery, and the part patients find hardest

After an operation for a bowel obstruction, the bowel does not resume working immediately. It has been distended, handled, and injured, and it needs time to wake up. A few days of postoperative ileus is expected and normal, not a sign that something has gone wrong. Patients who have already been in the hospital for several days before surgery find this stretch genuinely demoralizing, and it helps to know in advance that it is coming.

Walking helps. Chewing gum has surprisingly decent evidence behind it. Narcotic pain medication slows the gut down, which is one more reason to use it thoughtfully.

Will it happen again?

Sometimes. That is the uncomfortable truth about adhesive obstruction: the operation performed to relieve it creates new adhesions of its own. Recurrence rates after an episode are meaningful, somewhere in the range of one in five to one in three over subsequent years, and higher in patients who have had multiple abdominal operations.

This is precisely why we work as hard as we do to resolve these without surgery when it is safe to do so. Every operation buys relief now and adds a small amount of risk later.