A 43-year-old man presents with a 16-hour history of intermittent, crampy abdominal pain and bilious vomiting. He states that the symptoms began approximately 3 hours after lunch on the previous day, improved after vomiting, but returned after 1 to 2 hours. He had a bowel movement shortly after the onset of the pain, but there has been no passage of flatus or stool since then. The patient denies any similar episodes previously and has no current medical problems. He underwent exploratory laparotomy for trauma to the abdomen 3 years previously. On examination, his temperature is 38°C (100.5°F), pulse rate 105 beats/min, blood pressure 140/80 mm Hg, and respiratory rate 24 breaths/min. The abdomen is distended, with a well-healed midline surgical scar. The abdomen is tender throughout with no masses or peritonitis. The bowel sounds are hypoactive with occasional high-pitched rushes. No hernias are identified. A rectal examination reveals no masses and no stool in the rectal vault. Laboratory studies reveal normal electrolyte levels. His white blood cell (WBC) count is 16,000/mm2 with 85% neutrophils, 4% bands, 10% lymphocytes, and 1% monocytes; the hemoglobin and hematocrit values are 18 g/dL and 48%, respectively. The serum amylase value is 135 IU/L (normal, <85 IU/L). An abdominal radiograph was obtained (Figure 6–1).
Figure 6–1. Abdominal radiographs in the supine (A) and upright (B) positions show a dilated small bowel with air-fluid levels. Reproduced, with permission, from Kadell BM, Zimmerman P, Lu DSK. Radiology of the abdomen. In: Zinner MJ, Schwarz SI, Ellis H, et al, eds. Maingot’s Abdominal Operations. 10th ed. New York, NY: McGraw-Hill; 1997:24.)
What is your next step in management?
What are the complications associated with this disease process?
What is the probable therapy?
ANSWERS TO CASE 6: Small Bowel Obstruction
Summary: A 43-year-old patient has signs, symptoms, and radiographic evidence of a high-grade mechanical small bowel obstruction.
• Next step in management: Place a nasogastric (NG) tube to decompress the stomach, begin fluid resuscitation, and place a Foley catheter to monitor urine output and assess his response to the fluid resuscitation.
• Complications associated with this disease process: Mechanical small bowel obstruction may lead to strangulation, bowel necrosis, and sepsis. Vomiting may result in aspiration pneumonitis. When unrecognized or untreated, intravascular fluid loss (from third-space fluid loss and vomiting) can lead to prerenal azotemia and acute renal insufficiency.
• Probable therapy: Exploratory laparotomy after fluid resuscitation.
ANALYSIS
Objectives
1. Learn the clinical and radiographic features associated with mechanical small bowel obstruction and strangulating or complicated disease processes.
2. Learn the management strategy for mechanical small bowel obstruction.
Considerations
An otherwise healthy 43-year-old man presents with typical signs and symptoms associated with mechanical small bowel obstruction, presumably secondary to intra-abdominal adhesions. The change in pain pattern from intermittent to persistent is a concern. Persistent pain in this setting can be produced by severe bowel distension (which produces venous congestion, decreased bowel perfusion, and necrosis) or bowel ischemia secondary to strangulation. Other features of this patient’s presentation suggesting the presence of a complicated bowel obstruction include fever, tachycardia, leukocytosis, an elevated serum amylase level, and radiographic signs of a high-grade small bowel obstruction. Mechanical obstruction of the bowel produces accumulation of fluid in the bowel lumen and bowel wall, in addition to extravasation of fluid into the peritoneal cavity. The net result of these fluid shifts is a depletion of intravascular volume and decreased perfusion of all organs. Therefore, one of the most vital aspects of treatment is early recognition of the problem and restoration of the intravascular volume to reestablish organ perfusion. Restoration of intravascular volume is critical in this patient prior to operative therapy because the induction of general anesthesia in a volume-depleted individual may lead to profound hypotension. Nonoperative therapy is frequently successful for mechanical small bowel obstruction caused by adhesions; however, this approach is inappropriate in a patient exhibiting signs and symptoms suggestive of existing or impending bowel ischemia and/or necrosis. The most appropriate management in this case consists of NG tube placement to prevent further vomiting and potential aspiration of gastric contents, fluid resuscitation, administration of broad-spectrum antibiotics, and urgent laparotomy.
APPROACH TO: Small Bowel Obstruction
DEFINITIONS
CLOSED-LOOP OBSTRUCTION: This can develop when intestinal blockage occurs at both the proximal and distal ends of a bowel segment. Examples include small bowel incarcerated in a tight hernia defect and intestinal volvulus. This situation is associated with more rapid progression to strangulation, and it is unlikely to resolve without operative therapy.
ILEUS: Distension of the small bowel and/or colon from nonobstructive causes. Common causes include local or systemic inflammatory or infectious processes, a variety of metabolic derangements, recent abdominal surgery, and adverse effects of medications.
INTERNAL HERNIA: A congenital or acquired defect within the peritoneal cavity that can lead to small bowel obstruction.
GALLSTONE ILEUS: Mechanical obstruction of the small bowel due to large gallstone(s) in the bowel lumen. This condition generally occurs when a stone or stones in the gallbladder enter the adjacent duodenum. The typical clinical presentation is characterized by intermittent bowel obstruction for several days until the stone lodges in the distal small bowel and causes complete obstruction.
CLINICAL APPROACH
Mechanical small bowel obstruction is a common clinical problem. The cause of the obstruction, treatment considerations, and the approach to the disease differ based on the patient’s age, the duration of symptoms, and whether or not the patient has a history of abdominal operation or trauma. An obstruction in a neonate, an infant, or a young child is more likely to result from a hernia, malrotation, meconium ileus, Meckel diverticulum, intussusception, or intestinal atresia. In contrast, small bowel obstruction in an adult is most commonly caused by adhesions, a hernia, Crohn disease, gallstone ileus, or a tumor. Because a mechanical small bowel obstruction prevents the passage of intestinal luminal contents, the patient develops cramp-like abdominal pain, nausea, and bilious vomiting. It is not uncommon for patients to describe the occurrence of a bowel movement at the onset of an acute obstruction, which generally is caused by the stimulation of peristalsis leading to evacuation of the distal gastrointestinal tract contents. The presence of a bowel movement thus does not rule out bowel obstruction. Whenever the small bowel obstruction is nearly complete or complete (high grade), there may be a cessation of flatus and stool passage following the initial bowel movement. Figure 6–2 outlines the recommended approach to patient evaluation and treatment.
Figure 6–2. Algorithm for the management of small bowel obstruction. CT, computed tomography.
Physical Examination
The physical examination of a patient with small bowel obstruction may initially reveal a low-grade fever and tachycardia as a result of dehydration and inflammatory changes. The persistence of tachycardia after the restoration of intravascular volume may suggest unresolved inflammation from small bowel ischemia and/or necrosis. Similarly, the presence of fever should raise the suspicion for bowel ischemia and/or pulmonary complications due to aspiration of gastric contents. In most patients, abdominal examinations reveal mild, diffuse tenderness. Nonspecific tenderness that improves following successful decompression by the placement of an NG tube is observed commonly in patients with an uncomplicated obstruction. Localized tenderness directly over distended bowel loops suggests the presence of severe distension or bowel ischemia; although a worrisome finding, this localized tenderness is not specific for ischemia. A digital rectal examination (DRE) of patients with small bowel obstruction often reveals little or no stool in the rectal vault, which is because of continued peristalsis and evacuation of stool from the distal bowel. The finding of a large amount of stool in the rectum is unusual and may suggest ileus rather than mechanical obstruction as the cause of distension.
Pathophysiology
Mechanical obstruction of the small bowel reduces bowel absorptive function and causes luminal fluid accumulation. Additionally, there is a fluid shift into the extra-vascular space because of local inflammatory stimulation and venous congestion. As the obstruction continues, transudative fluid loss into the peritoneal cavity occurs. These losses, along with vomiting, generally produce tremendous intravascular volume depletion and place untreated patients at risk for the development of remote organ dysfunction caused by hypoperfusion. Generally, patients with proximal small bowel obstruction have more frequent vomiting, and those with more distal obstruction have more distension and less vomiting. With long-standing distal small bowel obstruction, bacterial overgrowth can develop and lead to feculent vomitus. Prolonged distal small bowel obstruction can lead to further intraabdominal and pulmonary (aspiration) infectious complications.
Laboratory and Radiographic Evaluations
The initial laboratory evaluation should include a complete blood count with a differential count, serum electrolyte and amylase determinations, urinalysis, and arterial blood gas studies (for selected patients). With dehydration and a physiologic response to bowel obstruction, patients with uncomplicated small bowel obstruction may initially present with mild leukocytosis (WBC count 10,000-14,000/mm3) and a left-shifted differential. Generally, the leukocytosis resolves with therapy in most patients with uncomplicated obstruction. Persistent leukocytosis after hydration should raise a suspicion of complicationsand should prompt early surgical intervention or an additional diagnostic evaluation. An elevation in the serum amylase level is most commonly associated with pancreatitis but may also develop with complicated small bowel obstruction.
Plain radiographs of the abdomen are generally obtained during the initial evaluation of patients with suspected bowel obstruction. These usually reveal dilated small bowel with or without colonic air. These findings are not pathognomonic for obstruction and may also be observed in the setting of ileus. Not uncommonly, radiographs of an advanced obstruction demonstrate a fluid-filled bowel with a paucity of air rather than a dilated bowel. Similarly, patients with an obstruction involving the proximal small bowel may have radiographs showing little or no air-filled bowel.
Additional Radiographic Studies
A CT scan may be helpful to identify patients whose bowel obstruction may not resolve with nonoperative treatment and provides additional information for patients in whom the etiology is obscure, such as those with a functional obstruction (ileus), inflammatory bowel disease, internal hernia, intussusception, a tumor, or gallstone ileus. CTs are also being utilized increasingly to determine the severity of small bowel obstruction and for localization of the obstructive site. CT scans can reliably identify the transition from dilated to decompressed bowel, which is diagnostic for mechanical obstruction. A number of CT signs are reported to indicate severe small bowel obstruction, and these include intraperitoneal free fluid, presence of small bowel feces, mesenteric whirl, and decreased bowel wall enhancement (see Figure 6–3). In addition, CT imaging may be useful in visualizing peritoneal tumor spread (carcinomatosis) (Figure 6–4), primary small bowel tumors, Crohn disease, gallstone ileus, and clinically obscure hernias. Alternatively, contrast radiography such as upper gastrointestinal and small bowel follow-through (UGI/SBFT) can be used to differentiate between mechanical obstruction and ileus or to assist in determining the location and severity of a bowel obstruction. It is important to bear in mind that CT scanning and UGI/SBFT require the administration of contrast into the bowel lumen and can aggravate patient vomiting and contribute to aspiration. The goals in patient evaluation are to diagnose the bowel obstruction and identify patients with complicated small bowel obstruction, who may benefit from early operative interventions. Table 6–1 lists some of the more commonly used indicators to identify bowel strangulation.
Figure 6–3. Axial view of CT scan of abdomen of a woman with mechanical small bowel obstruction demonstrating dilated fluid-filled loops of small bowel with decompressed small bowel also present. Note the intraperitoneal free fluid seen adjacent to the space lateral to the liver.
Figure 6–4. CT axial view from the patient with mechanical small bowel obstruction shown in Figure 6–3. This scan demonstrates a “target sign” on the left side of abdomen adjacent to the left iliac crest indicating an intussusception of the small bowel. (This patient’s surgical pathology revealed the presence of a 3-cm gastrointestinal stromal tumor [GIST] causing small bowel intussusception.)
Table 6–1 • INDICATORS SUGGESTIVE OF STRANGULATED SMALL BOWEL OBSTRUCTION
Treatment
Patients with uncomplicated partial small bowel obstruction from adhesions can be initially treated with a trial of nonoperative therapy consisting of nothing by mouth (NPO), placement of an NG tube, close monitoring of fluid status, serial clinical examinations, and laboratory and radiographic follow-up. Most patients who are successfully treated nonoperatively demonstrate improvement within 6 to 24 hours after the initiation of treatment. These improvements include a decrease in abdominal discomfort and decrease distension, decrease in the volume of NG aspirate, and radiographic resolution of bowel distension. The absence of early improvement with nonoperative treatment should prompt evaluation with a CT scan or UGI/SBFT to confirm the diagnosis and/or further define the obstruction for possible surgical therapy. When operative treatment is determined to be necessary, perioperative broad-spectrum antibiotics are administered to prevent wound and intra-abdominal infectious complications. Operative therapy for adhesive small bowel obstruction consists of careful exploration and identification of the obstruction source. Adhesive bands responsible for the obstruction are divided, and ischemic or necrotic bowel is resected.
Early Postoperative Small Bowel Obstruction
Early postoperative small bowel obstruction is defined as bowel obstruction symptoms developing within 30 days following an abdominal operation. This condition can result from narrowing of the lumen because of mechanical causes or ileus from intraperitoneal inflammatory sources. An exact determination of the cause is generally not necessary because nonoperative observation is the usual treatment for both. A CT scan may be useful in some patients to identify or rule out an intra-abdominal infection as the cause.
Outcome
The mortality associated with small bowel obstruction has improved over the past 50 years with improved medical technology and supportive care. Despite this overall improvement in patient outcome, a significant increase in morbidity and mortality continues to be associated with complicated small bowel obstruction. Therefore, one of the major goals in patient treatment is early diagnosis and treatment of uncomplicated small bowel obstruction to prevent a progression to strangulation and bowel necrosis. Patients with a high-grade bowel obstruction or suspected of having a strangulated bowel should undergo prompt resuscitation and early operative therapy, which may prevent the development and/or progression of bowel necrosis.
COMPREHENSION QUESTIONS
6.1 A 79-year-old woman who has had no previous abdominal surgery presents with intermittent abdominal distension and pain of 1 week’s duration and persistent vomiting for the past 1 day. Her physical examination does not reveal any hernias and is consistent with that of distal small bowel obstruction. She is afebrile. Her WBC count is 4000/mm2. Which of the following is the most appropriate next step?
A. Attempt nonoperative treatment for 48 hours.
B. Perform upper gastrointestinal tract endoscopy.
C. Proceed with an immediate exploration laparotomy.
D. Obtain a serum carcinoembryonic antigen (CEA).
E. Perform a CT scan.
6.2 Which of the following situations is most likely to respond to nonsurgical management?
A. A 72-year-old woman with a bowel obstruction due to midgut volvulus
B. Small bowel obstruction caused by gallstone ileus
C. A 45-year-old woman who has small bowel obstruction after open gallbladder surgery 20 days previously
D. A 2-day-old male infant who has small bowel obstruction because of jejunal atresia
E. A 20-year-old man with partial small bowel obstruction associated with an incarcerated inguinal hernia
6.3 A 72-year-old white man arrives in the emergency department with nausea and vomiting following an appendectomy performed at the age of 25. He is afebrile. The abdomen is slightly tender and distended. The WBC count is 18,000/mm2. Electrolyte studies reveal a sodium level of 140 mEq/L, potassium 4.2 mEq/L, chloride 105 mEq/L, and bicarbonate 14 mEq/L. Which of the following is the best therapy for this patient?
A. Placement of an NG tube and observation
B. Colonoscopy for possible intussusception
C. A barium enema to relieve a volvulus
D. Broad-spectrum antibiotics and supportive care
E. Surgical therapy
6.4 A 33-year-old woman with a history of three previous C-sections presents to the hospital with her third bout of small bowel obstruction over the past 2 years. She has been managed with nonoperative treatment consisting of NG suction, NPO, and IV fluid for the past 4 days. With her course of management, the patient has had a decrease in abdominal distension, but her NG-tube output has diminished but continues to be bilious and voluminous (currently 600 mL/24 h). Which of the following is the most appropriate management option?
A. Place a central venous catheter for total parenteral nutrition (TPN) administration and continue her nonoperative treatment for an additional 2 weeks.
B. Obtain a CT scan.
C. Perform a laparotomy.
D. Remove her NG tube and initiate PO feedings.
E. Prescribe an enema to stimulate bowel activity.
6.5 A 32-year-old white man arrives in the emergency department with nausea and vomiting following an appendectomy performed 20 days previously. He is afebrile. The abdomen is slightly tender and distended. The WBC count is 12,000/mm2. Electrolyte studies reveal a sodium level of 140 mEq/L, potassium 4.2 mEq/L, chloride 105 mEq/L, and bicarbonate 14 mEq/L. Which of the following is the best therapy for this patient?
A. Placement of an NG tube and observation
B. Colonoscopy for possible intussusception
C. A barium enema to relieve a volvulus
D. Surgical therapy
ANSWERS
6.1 E. Patients without previous abdominal surgery or hernias who present with symptoms and signs of bowel obstruction may benefit from CT imaging (to identify the cause of obstruction that may include malignancy, gallstone ileus, or internal hernia), and most patients with this presentation would ultimately require exploratory laparotomy to diagnose and correct the cause of obstruction. CT in these patients may also help differentiate mechanical obstruction from an ileus. Serum CEA elevation may occur with colorectal cancers; however, serum CEA should not be obtained to determine the cause of bowel obstruction.
6.2 C. Early small bowel obstruction (within 30 days) following abdominal surgery is generally caused by early adhesions or persistent inflammation that frequently resolves with NG decompression and supportive care. All of the other described causes of obstruction should be treated by operations.
6.3 E. The patient has anion gap acidosis as evidenced by the low bicarbonate level, which is probably caused by lactic acid, reflecting ischemic bowel or severe fluid depletion. Elderly patients, age 65 or older, often have a minimum of symptoms and are often afebrile in the face of inflammatory or infectious conditions. Surgical therapy may be indicated if CT imaging confirms intra-abdominal sepsis or high-grade obstruction.
6.4 B. This patient is a difficult patient from the management standpoint because although she is demonstrating some signs of improvement, such as decreased distension and decreasing NG output, she continues to have a fairly high NG output that is bilious. A CT scan may be highly appropriate to look for signs of continued mechanical obstruction and it also may be useful to quantify the degree of obstruction and plan the next step in treatment. Laparotomy is a reasonable option, if the patient has not made any progress with conservative management. NG removal and PO feeding could be attempted but may not be successful given the volume and quality of the patient’s NG output. Continued nonoperative treatment without further assessment is not appropriate in this patient who is without any prohibitive risks or contraindications for surgery. Enemas should not be given to patients with mechanical obstruction because they can worsen the patients’ conditions.
6.5 C. Early small bowel obstruction (within 30 days) following abdominal surgery is generally caused by early adhesions or persistent inflammation that frequently resolves with NG decompression and supportive care. A CT scan can be considered prior to nonoperative therapy in this patient because it would help identify any potential intra-abdominal infectious source (eg, abscess) as a cause of the obstructive picture.
CLINICAL PEARLS
A significant proportion of patients with small bowel obstruction can be treated conservatively (NPO, placement of an NG tube, close monitoring of fluid status, serial clinical examinations, and laboratory and radiographic follow-up) while constantly being assessed for bowel ischemia or strangulation.
Persistent pain, fever, tachycardia, leukocytosis, an elevated serum amylase level, and radiographic signs of high-grade small bowel obstruction are often signs of complicated bowel obstruction and the need for surgical therapy.
CT imaging plays an important role in patient evaluation. The exceptions to this rule include patients with simple adhesive obstruction and an absence of indicators of complicated small bowel obstruction (see Table 6–1), as well as patients in whom early operative intervention is clinically indicated.
Patients with closed-loop obstruction require early operative treatment.
REFERENCES
Evers BM. Small intestine. In: Townsend CM Jr, Beauchamp RD, Evers BM, et al, eds. Sabiston Textbook of Surgery. 18th ed. Philadelphia, PA: Saunders Elsevier; 2008:1278-1332.
Mallo RD, Salem L, Lalani T, Flum DR. Computed tomography diagnosis of ischemia and complete obstruction in small bowel obstruction: a systematic review. J Gastrointest Surg. 2005;9:690-694.
Tavakkolizadeh A, Whang EE, Ashley SW, Zinner MJ. Small intestine. In: Brunicardi FC, Andersen DK, Billiar TR, et al, eds. Schwartz’s Principles of Surgery. 9th ed. New York, NY: McGraw-Hill; 2010: 979-1012.