Large Intestine

Background

IBS is a chronic condition that affects approximately 7% to 21% of the general population. It is a disabling disease that can lead to a significant reduction in the quality of life. It is more commonly found in women and is characterized by abdominal pain, bloating, and altered bowel habits. IBS was previously considered a diagnosis of exclusion when no specific anatomical or biochemical abnormalities were found on workup, but new research shows that specific pathophysiological findings are associated with IBS.

There are numerous comorbidities associated with IBS, including functional pain syndromes, psychiatric disorders, as well as other intestinal disorders. This can result in frequent relapses and varying symptoms between relapses. These variable symptoms make both diagnosis and treatment of IBS challenging in the emergency department (ED). This is compounded by the fact that lab and imaging findings are often unrevealing. Patients tend to be discharged from the ED without a specific diagnosis.

Anatomy, Physiology, and Pathophysiology

The pathophysiology of IBS remains unclear, though there are many factors that are thought to contribute to its development. These include intestinal permeability, immune function, alterations in the gut microbiome, motility, and psychosocial status. For example, increased gas production by bacteria in an altered microbiome may result in intestinal reflex responses that create bowel distention. Other theories suggest the possibility of a brain-gut association in certain patients, especially in those with an underlying psychiatric disorder; there is also a potential converse gut-brain association, evidenced by the effect of probiotics in improving symptoms for some patients.

Background

Diverticular disease is one of the most common gastrointestinal diagnoses in the Western hemisphere, affecting 5% of patients younger than 40 years, and up to 60% of patients over the age of 80. There are multiple theories regarding the increasing incidence of diverticular disease including diet, obesity, and bacterial colonization. There was once thought to be a link between fiber intake and the development of diverticular disease, but that theory is now questioned.

Risk factors for diverticular disease include smoking, use of NSAIDs, physical inactivity, obesity, red meat, and a diet high in refined carbohydrates. Diverticular disease involves the development of false diverticula, which is the herniation of the inner mucosal and submucosal layers of the intestinal wall through the muscular layers. Diverticulosis refers to the presence of multiple diverticula. While the sigmoid colon is most often involved, interestingly, in the Japanese population, the right colon tends to be affected. The sigmoid colon is thought to be affected more commonly because of specific anatomic features including noncircumferential muscle layers, along with the location of insertion of the vasa recta (intestinal arteries) ( Box 81.3 ).

Anatomy, Physiology, and Pathophysiology

Diverticulosis refers to the asymptomatic condition of having multiple diverticula. Diverticulitis results from inflammation of the diverticula. Diverticulitis can be uncomplicated, which can most often be managed in the outpatient setting. Complicated diverticulitis can include abscess formation, fistula formation, strictures, along with perforation or acute peritonitis. The pathophysiology of this inflammation is thought to involve changes in gut motility as well as increases in intraluminal pressure in the colon, which can lead to localized perforation. If the perforation occurs into the abdominal cavity, this may result in peritonitis, whereas if the diverticulum is covered by mesentery, perforation can create a phlegmon or abscess.

Diverticulosis is also the cause of 40% of lower gastrointestinal hemorrhages. Severe hemorrhage occurs in 3% to 5% of all patients with diverticulosis. The bleeding is typically painless, as there is no associated inflammation.

Diverticulosis

Most patients with diverticulosis are asymptomatic. It can result in bleeding, and it can also occasionally result in vague abdominal complaints, such as abdominal bloating. Diverticulosis progresses to acute diverticulitis in up to 25% of individuals and results in recurrent episodes of diverticulitis in up to 40%.

Diverticulitis

As the majority of patients develop diverticula in the sigmoid colon, diverticulitis tends to present with persistent left lower quadrant pain. Many patients will present with persistent pain over 24 hours, possibly with a low-grade fever. Other associated symptoms may include nausea, vomiting, or alterations in bowel movements. Physical examination may reveal tenderness in the left lower quadrant and possibly abdominal distention. Patients with more complicated cases may present with high fever or other vital sign abnormalities concerning sepsis.

Patients that are predisposed to developing diverticula in the right colon will present with right lower quadrant abdominal pain and tenderness on examination, which may be difficult to distinguish from appendicitis. There may also be referred pain to the suprapubic region. Additional findings suggest various complications—diffuse tenderness with rebound or guarding may be associated with gross perforation or abscess rupture; dysuria can be present with a colovesical fistula; a palpable mass may be associated with localized abscess formation; vomiting with abdominal distention may suggest proximal obstruction; and feculent vaginal discharge may suggest a colovaginal fistula. Almost any organ adjacent to the colon can be involved in the inflammatory process. Elders and immunocompromised patients may present more subtly despite the potential for having an even more severe disease. Perforation is seen more frequently in this population and is associated with a high mortality rate.

Diverticulosis

Patients with diverticulosis are recommended to initiate a high-fiber diet in order to reduce abdominal symptoms. Physical activity has been associated with a decreased risk for developing acute diverticulitis, although the mechanism behind this benefit is unclear. Patients were previously instructed to avoid foods that may obstruct diverticula, such as nuts, small seeds, and popcorn, but this has been largely discredited due to the lack of evidence.

Uncomplicated Diverticulitis

There is more evidence to suggest that acute diverticulitis is an inflammatory process and not an infectious process. In fact, guidelines published by the American Gastrointestinal Association in 2015 advocate for the selective (as opposed to routine) use of antibiotics in treating uncomplicated diverticulitis. If antibiotics are utilized, oral antibiotics should cover both Gram-negative aerobic and anaerobic bacteria ( Box 81.5 ). The vast majority of patients with uncomplicated diverticulitis can be managed on an outpatient basis. Studies have shown no benefit in the use of IV antibiotics when compared with oral antibiotics for uncomplicated diverticulitis. Liquid diets with instructions to advance as tolerated should be recommended for patients that are managed as outpatients.

Hospitalization for IV antibiotics and bowel rest is often required for elders, patients who are immunocompromised or have multiple comorbidities, and individuals who cannot tolerate oral liquids or have poor social support in the outpatient setting.

Complicated Diverticulitis

Patients with complicated diverticulitis should generally be admitted for IV antibiotics ( Box 81.6 ) and bowel rest. Surgical consultation is indicated when there is concern for peritonitis or perforation, continuing clinical decline, or sepsis resistant to medical management. Small abscesses (4 cm or less) may resolve with IV antibiotics alone, whereas larger abscesses are often treated with percutaneous drainage, with possible surgical management if unsuccessful. Fistulae are usually repaired surgically on an elective basis. Surgical resection may be considered in patients with recurrent episodes of diverticulitis.

Background

Large bowel obstruction (LBO) is not as common as small bowel obstruction but is a more ominous condition frequently associated with malignancy. Most cases of LBO are due to a progressive narrowing of the intestinal lumen from intrinsic lesions within the lumen. Approximately 50% of all cases of LBO are eventually found to be secondary to underlying colorectal malignancy. Diverticular disease and volvulus are the next most common causes of LBO. Other less common intrinsic causes of LBO include IBD, ischemia, adhesions, endometriosis, or radiation. Extrinsic lesions can also cause LBO from an impingement of the intestinal lumen. The most common causes of extrinsic lesions causing LBO include ovarian cancer, followed by hernias.

Anatomy, Physiology, and Pathophysiology

The most common location for LBO is the sigmoid colon. Anatomically, it is important to note if the obstruction is proximal or distal to the splenic flexure for management purposes. Approximately 75% of colonic tumors are located distal to the splenic flexure. LBO along the left side of the colon may manifest sooner than obstruction along the right side of the colon due to the smaller lumen of the sigmoid and descending colon.

When mechanical obstruction is caused by an obstructing lesion, either intrinsic or extrinsic, the bowel proximal to the lesion becomes increasingly dilated. As the distention progresses, intraluminal pressure increases. When intraluminal pressure approaches systolic blood pressure, blood flow to the bowel wall is compromised, causing edema and subsequent transudation of fluid into the lumen. Transudation, along with decreased reabsorption of intraluminal fluid, further increases intraluminal pressure and decreases arterial flow to the bowel wall, which can lead to ischemia and gangrene. The translocation of bacteria from compromised bowel can lead to sepsis. Perforation of the bowel wall follows if the process is left uninterrupted.

Acute colonic pseudo-obstruction (ACPO), also known as Ogilvie syndrome, may mimic LBO. It refers to acute colonic dilation without evidence of mechanical obstruction. ACPO tends to affect the cecum and right hemicolon, although dilation can extend all the way to the rectum. It is thought to be a functional obstruction that results from either increased sympathetic tone or decreased parasympathetic tone. ACPO is often associated with other conditions that can affect autonomic intestinal innervation. ACPO tends to affect elders, chronic opioid users, postoperative patients, and those with severe electrolyte disturbances or other significant acute comorbid conditions.

Laboratory Tests

A chemistry panel is important to identify electrolyte derangements, as fluid and electrolyte replacement therapy tend to be the mainstay of ED treatment for LBO. An elevated white blood cell (WBC) count should raise suspicion for gangrenous bowel. Anemia may suggest the possibility of colorectal cancer. An elevated serum lactate level may point toward ischemic bowel as a complication.

Imaging Studies

Plain Radiography

Both supine and upright plain films are advised for the workup of LBO and ACPO ( Fig. 81.4 ). A distended colon (>6 cm diameter) is the hallmark of LBO, although the small bowel may be distended as well (>3 cm diameter) if the ileocecal valve is incompetent. A cecal diameter >6 cm is abnormal and when >12 cm is associated with a higher risk of perforation, although perforation has been known to occur at smaller diameters. The actual location and cause of the LBO are usually not evident on plain films.