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GI gas pattern. Air is commonly present in the stomach and colon. However, air in the small intestine

is abnormal and suggests an intra -abdominal process.

Paralytic ileus (see II B )

Air that is evenly distributed throughout the small and large intestine usually signifies paralysis of the bowel secondary to a process that is not primarily surgical.

Ileus may be localized to a specific area, such as the “sentinel” loop , an area of localized duodenal ileus adjacent to the pancreas in acute pancreatitis.

Acute gastric dilation is indicated by a markedly dilated gastric bubble. (This condition can result in severe abdominal pain and vasovagal hypotension but is easily treated by nasogastric tube decompression.)

Mechanical obstruction of the intestine (see II A ) is revealed by the presence of distended airand fluid -filled loops of bowel proximal to the obstruction and decompressed intestine distally. This air may be absent in the distal tract, particularly the rectum, unless air has been introduced by an enema given in the past 24 hours.

Mechanical bowel obstruction is an important diagnosis because it may be associated with strangulation of the bowel with resultant ischemia and necrosis. When both ends of a loop of bowel are obstructed, such as occurs with a volvulus, this is termed a closed loop obstruction and represents a surgical emergency due to the high risk of rupture and generalized peritonitis.

Postoperative adhesions, carcinoma of the colon, and inguinal hernias are the three most common causes of bowel obstruction. Specific causes may be diagnosed by the intestinal gas pattern.

Hernias may result in intestinal air located in a nonanatomic location. For example, an inguinal hernia may show gas -filled intestine extended below the inguinal ligament.

Volvulus is a segment of bowel that has twisted upon itself, resulting in both mechanical obstruction and vascular compromise. It may appear on the plain film as an isolated distended loop of bowel with tapered (“bird -beak”) margins. A sigmoid volvulus is treated by sigmoidoscopy and decompression. Other types of volvulus are treated operatively.

An ischemic or gangrenous bowel may produce few radiologic findings. If the colon is affected, however, the mucosal edema may be seen as “thumbprinting” on the wall of a dilated colon.

Isolated distention of the colon by large amounts of air may be seen on radiograph. It may be due to any of the acute processes, such as distal colonic obstruction, which may be secondary to malignancy, profound constipation, stricture, or volvulus; “toxic megacolon,” a massive colonic dilation that is associated with acute colitis; and colonic ileus , a condition of obscure etiology that results in marked distention of the cecum. If the cecum enlarges past 10–12 cm in diameter, there is a significant risk of perforation.

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Heavily calcified vessels may be present in mesenteric ischemia.

Masses , such as teratomas or malignant neoplasms, may calcify.

Soft tissue shadows

Peritoneal fat lines and psoas muscle shadows may be lost in rapidly spreading infections, hematomas, or abscesses.

Margins of solid organs (liver, kidney, or spleen) may be displaced from their normal locations by an abnormal mass.

A distended bladder may be visible and may be responsible for marked abdominal pain.

Contrast roentgenography can be highly useful in patients with an acute abdominal process that remains undiagnosed after other studies.

Intravenous pyelogram (IVP) should be obtained if a renal stone is suspected. It is also useful in identifying acute pyelonephritis, perinephric abscess, or renal infarction. When a patient suspected of having appendicitis has microscopic hematuria, the IVP is particularly useful for verifying that the hematuria is due to the periappendiceal inflammation rather than to a renal stone.

Barium swallow is helpful if it is suspected that the patient's esophagus has ruptured during a violent episode of vomiting. Known as Boerhaave's syndrome , this unusual accident may result in a left pleural effusion, which communicates with the esophageal rent, as demonstrated by the barium swallow.

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Upper GI series, using diatrizoate meglumine (Gastrografin), a water -soluble radiopaque dye, should be performed if a perforation of the stomach or duodenum is suspected but cannot be proven because free air is not visible on the plain film.

Placing contrast materials into the colon and rectum should be done very cautiously when an inflammatory condition or a perforation is suspected because even a small increase in pressure could easily convert friable tissue into a frank perforation.

This procedure is best used when the diagnosis of colon perforation is suspected and especially in a patient taking anti -inflammatory or immunosuppressive drugs, particularly corticosteroids.

In such cases, diatrizoate meglumine should be used because barium sulfate, when it mixes with stool and detritus from an infection, becomes firmly attached to the peritoneal cavity. Extensive abscess formation results, even after the surgeon attempts to irrigate the area thoroughly.

Small bowel follow-through contrast study tracks the barium through the small intestine after an upper GI series. It is useful in identifying a point of small bowel obstruction when either the history, the physical examination, or plain radiography fails to verify the diagnosis of small bowel obstruction.

G

Abdominal ultrasonography is usually of little diagnostic value in the patient with abdominal distention and severe pain, but it can be helpful when acute cholecystitis, cholelithiasis, biliary obstruction, or an abscess is suspected. Computed tomography may also be helpful, but is generally reserved for the patient whose condition

remains undiagnosed after other studies have been exhausted. Some have advocated its use to assist in the diagnosis of acute appendicitis.

H

General principles used in the approach to the patient with acute abdominal pain are discussed below.

A careful and systematic evaluation of the patient should be routinely performed. Most patients will have a well-documented diagnosis if this principle is followed.

Statistically speaking, certain diagnoses are very common , such as appendicitis and gastroenteritis, whereas other diagnoses are quite rare, such as pylephlebitis. The physician should not search for an occult diagnosis when a common diagnosis is more likely to be correct.

When the diagnosis is not initially clear, continued observation and repeated blood studies (complete blood count, arterial blood gases, amylase, and electrolytes) may lead to the correct diagnosis as the disease process evolves.

Although this practice might be desirable in a patient with gastroenteritis, delay can be catastrophic in acute appendicitis, ischemic bowel, small bowel obstruction, volvulus, or incarcerated hernia.

If the diagnosis is not certain but the patient may have a potentially lethal condition that could be cured by an early operation, then an early operation should be performed—i.e., a small percentage of negative laparotomies are justified in patients with acute abdomen. This premise is best illustrated by the case of a patient with acute appendicitis. Here, a policy of watchful waiting may convert a simple appendicitis into a perforated appendicitis with generalized peritonitis and septic shock. The risk of death from this complication is many times higher than the risk from a small right lower quadrant incision in a patient who proves to have a normal appendix and mesenteric adenitis.

Analgesics, particularly narcotics, should be withheld from the patient until the diagnosis is established or until the decision to proceed to surgery has been made. Serial physical examinations will be totally useless if the patient has been given narcotics.

Antibiotics should also be withheld until a diagnosis has been made and the antibiotic therapy is needed. The only exception to this is the patient who presents in septic shock from an unknown cause. In that situation, broad-spectrum antibiotics should be part of the patient's resuscitation.

Fluid deficits and electrolyte imbalances should be corrected before surgery. The few exceptions are:

Conditions that threaten immediate exsanguination, such as a ruptured abdominal aortic aneurysm

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Conditions in which the fluid or electrolyte abnormality cannot be corrected in a reasonable amount of time—i.e., conditions that cause profound acidosis, such as necrotic bowel, where the acidosis cannot be corrected until the bowel is surgically removed

Nasogastric tubes should be placed before the induction of anesthesia to empty the stomach, thus minimizing the risk of pulmonary aspiration.

II Intestinal Obstruction

The normal flow of intestinal contents can be blocked by a mechanical obstruction or by a functional obstruction that occurs because of impaired intestinal motility. An acute abdomen often ensues.

A

Mechanical obstructions are common and have various benign and malignant causes. If not treated expeditiously (usually by surgical removal of the cause), mechanical obstructions can rapidly become lethal. Acute obstruction

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Intestinal tumors are the third most common cause of obstruction. The most common obstructing tumor is an adenocarcinoma of the colon or rectum. Benign lesions of the small bowel and colon, such as lipomas, can become the leading point of an intussusception. Other malignant tumors, such as carcinoid or lymphoma, can obstruct the intestinal lumen.

Other intrinsic lesions within the bowel wall or the lumen can cause acute obstruction.

Congenital lesions: webs, malrotations, and atresias

Inflammatory lesions: Crohn's disease, diverticulitis, ulcerative colitis, and infections such as tuberculosis

Luminal foreign bodies: bezoars, parasites, and gallstones

Radiation injury, other trauma , or endometriosis

Other extrinsic lesions , such as large intra -abdominal tumors or abscesses, can compress the intestinal lumen.

Treatment

Intestinal adhesions are treated by surgical lysis of the obstructing bands if the obstruction does not resolve in several days.

Hernias are treated by a reduction of the contents of the hernia and subsequent repair. The bowel must always be examined for necrosis.

Intestinal tumors are treated by surgical removal.

Treatment of intrinsic and extrinsic lesions depend on the lesion.

B

Functional obstructions are blockages in the intestinal flow that result from impaired motility (paralytic or adynamic ileus ). These are usually treated by observation and by fluid and nutritional support until the causal agent resolves. Possible causes include:

Direct irritation of the intestine , such as generalized peritonitis. Irritation may also be a factor in the postoperative adynamic ileus that can last for 3–7 days following surgery.

Extraperitoneal causes, such as retroperitoneal hematoma or nerve root compression. Retroperitoneal dissections, such as a nephrectomy or sympathectomy, can cause a prolonged ileus.

III Upper Gastrointestinal Hemorrhage

A

Causes of massive upper GI hemorrhage as shown by endoscopy are given in Table 9-2.

B Types of bleeding

The diagnosis of hemorrhage is generally obvious, but locating the site of bleeding may be difficult. The type of GI bleeding may give a clue to its source.

Hematemesis is the vomiting of blood that is either bright red or resembling coffee grounds in appearance. Hematemesis usually indicates a bleeding source proximal to the ligament of Treitz. Coffee -grounds hematemesis indicates that the blood has been in contact with gastric acid long enough to become converted from hemoglobin to methemoglobin.

Hematochezia is the passage of bright red blood by rectum. Although it indicates GI bleeding, it does not specify the level within the GI tract.

Melena is the passage of black, usually tarry, stools. Although melena signifies a longer time within the GI tract than bright red blood, it does not guarantee that the bleeding is from the upper tract.

TABLE 9-2 Causes of Upper Gastrointestinal Hemorrhage

Duodenal ulcer

Gastric ulcer

Diffuse erosive gastritis

Esophageal or gastric varices

Mallory-Weiss tear of the gastroesophageal junction

Gastric carcinoma

Arteriovenous malformations

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Blood mixed with stool and mucus can produce a characteristic jellylike or “currant -jelly” stool. This may originate from a Meckel's diverticulum, particularly in children.

C History

The history should include information about previous episodes of GI bleeding, current medications (e.g., aspirin or warfarin use), and related diseases (e.g., hematologic disorders, alcoholism, peptic ulcer disease, and recent episodes of vomiting).

D

Physical examination should specifically include a search for evidence of nasopharyngeal bleeding, portal hypertension, weight loss, malignancy, or systemic diseases such as chronic hepatic or renal failure.

E Diagnosis

The cause and the location of the bleeding must be confirmed unless imminent exsanguination calls for immediate measures (see Chapter 21, I D 3 e [3] [f] ). In less urgent circumstances, once the patient has been stabilized, one