46 SMALL BOWEL OBSTRUCTION
Joyce A. Majure M.D.

1. Name three mechanisms of bowel obstruction, and give examples and incidence of each type.

Show answer

1. Extrinsic compression: adhesions (60%), malignancy (20%), hernias (10%), volvulus, and others (5%)
2. Internal blockage of the lumen by abnormal materials (obturation): bezoars, gallstone, worms, or foreign body (usually obstructs at the ileocecal valve)
3. Mural disease encroaching on the lumen (inflammatory bowel disease [5%]), fibrous stricture secondary to trauma, ischemia, or radiation, intussusception)

2. What are the most common symptoms of small bowel obstruction (SBO)?

Show answer

1. Abdominal pain-initially nonspecific, often colicky, coinciding with waves of peristalsis trying to pass the point of obstruction
2. Bloating-the more distal the obstruction, the more severe the abdominal distention caused by proximal bowel dilatation
3. Vomiting-bilious, frequent, and profuse with proximal obstruction, less frequent but larger volume and often feculent with distal obstruction
4. Obstipation-failure to pass gas or stool; occasionally, the patient has a few loose stools early on, as the bowel distal to the obstruction empties

3. What are the pertinent questions in the patient’s history?

Show answer

* Any previous abdominal or pelvic surgery?
* Any previous SBO?
* Any history of cancer? What type, and how treated? Any radiation?
* Any previous abdominal infections or inflammation (include pelvic inflammatory disease, appendicitis, diverticulitis, inflammatory bowel disease, perforation, and trauma)?
* Any history of gallstones?
* Current medications, particularly anticoagulants, anticholinergics, chemotherapy, or diuretics?

4. What are the findings on physical examination?

Show answer
The patient is often dehydrated and may have a low-grade fever, postural hypotension, and abdominal distention. Bowel sounds may be hyperactive with “tinkles and rushes” or may be totally silent if the patient has delayed seeking treatment. Percussion usually reveals diffuse tympani, and thin, elderly patients may even have visible loops of distended small bowel. Palpation may increase the abdominal pain, but localized tenderness or peritoneal signs indicate likely strangulation or another diagnosis.

5. Is a rectal examination necessary?

Show answer
Absolutely. The rectal examination may reveal signs of cancer, such as a rigid rectal shelf from carcinomatosis, and blood on hemoccult examination may herald ischemia or strangulation or may indicate inflammatory bowel disease. An obturator hernia can best be palpated transrectally or transvaginally.

6. Where should the examiner look for obstructing hernias?

Show answer
Examine the groins near the pubic tubercle and along the inguinal floor, check the femoral triangles for bulging or tenderness, do a rectal examination to look for obturator hernia (see question 5), and palpate all existing incisions. Check all trocar sites from previous laparoscopic surgeries.

7. What is the most inexpensive way to confirm the diagnosis?

Show answer
The “four-way abdominal series” (flat and upright abdominal films, plus posterolateral [PA] and lateral chest radiographs) is diagnostic about 75% of the time. Look for:

* Air-fluid levels in dilated small intestine (also known as “stair steps” or “string of pearls” sign)
* Absent or minimal air in the distal colon and rectum
* “Ground glass” appearance and obscuring of the psoas shadows by extraperitoneal fluid
* Sometimes a single distended loop of small bowel with a “beak” at each end, indicating a closed loop obstruction in an otherwise gasless abdomen or a single fixed loop that remains in the same location on both supine and upright films
* Chest radiographs may demonstrate an infiltrate, with accompanying ileus, rather than SBO. The lateral chest radiograph is the most sensitive for identifying free air in the abdomen; this necessitates an urgent laparotomy for perforated viscus

8. What other imaging studies can be used?

Show answer
Oral contrast studies with water-soluble contrast (Gastrografin) help to distinguish partial from complete obstruction, intraluminal tumor or foreign body, and inflammatory bowel disease; they may also define the point of obstruction. Recent studies indicate that Gastrografin may actually help resolve partial obstructions by its osmotic effect.
Computed tomography (CT) and magnetic resonance imaging (MRI) can both help delineate bowel obstructions. MRI has the advantage of speed (6-10 minutes using the HASTE [half Fourier single shot turbo spin echo] technique), no need for contrast agent, and a higher accuracy rate. A recent Mayo Clinic series also claims superior accuracy (95% versus 71%).
Ultrasound has not proven useful.

9. Which laboratory studies are indicated?

Show answer

1. Complete blood cell count (CBC) to check for leukocytosis or unexpected anemia
2. Urinalysis to look for urinary tract infection (which may also cause an ileus and present with a similar picture to SBO) and to assess hydration (urine-specific gravity)
3. Chemistry panel to check for electrolyte abnormalities such as hypokalemic or hypochloremic metabolic alkalosis (associated with vomiting of acid gastric contents), hyponatremia, and prerenal azotemia (elevated blood urea nitrogen [BUN] and creatinine levels)
4. Amylase to rule out pancreatitis; this can also be elevated, although not as high, with ischemic bowel

10. What are the initial steps in treatment?

Show answer
Nasogastric suction and intravenous fluids should be instituted to restore electrolyte and fluid balance, and a Foley catheter should be placed to monitor urine output. As soon as resuscitation is complete, prompt surgical intervention is mandatory for complete obstructions and for anyone with signs and symptoms of strangulation.

11. How can I distinguish between a complete and partial obstruction?

Show answer

* Clinically: If partial, the patient may continue to pass small amounts of gas or stool. Pain and distention decreases rapidly with nasogastric suction.
* Radiographically: Radiographs show gas moving into the colon (partial obstruction)
* With oral contrast studies: Barium or water-soluble contrast agent given via the nasogastric tube passes into the colon in partial obstructions

12. What conditions should be included in the differential diagnosis?

Show answer
Ileus from other causes (e.g., as urinary tract infection, pneumonia, hypokalemia), viral gastroenteritis, appendicitis (usually with perforation), ureteral stone, diverticulitis, mesenteric thrombosis, and obstructing colon cancer should be included.

KEY POINTS: SMALL BOWEL OBSTRUCTION

1. Most common cause is adhesive disease, followed by hernias.
2. Malignancy must be considered as a possible cause.
3. Treatment involves NG decompression, fluid and electrolyte repletion, and expectant management.
4. Surgical intervention is required if strangulation or closed loop obstrution is suspected.

13. What are the three types of SBO, based on bowel viability?

Show answer

1. Simple obstruction: Nothing passes the point of obstruction, but the vascular supply is not compromised. It may be partial and resolve with nonoperative management.
2. Strangulated obstruction: The mesentery is twisted or there is so much dilation of the bowel that arterial or venous flow is cut off and the bowel becomes ischemic. Urgent surgery is mandatory.
3. Closed loop obstruction: The bowel is obstructed proximally and distally, usually for a short segment, and that segment becomes massively dilated and susceptible to strangulation as well as perforation. Urgent surgery is mandatory.

14. What are the “five classic signs” of strangulation? How accurate are they?

Show answer

1. Continuous pain (not colicky)
2. Fever
3. Tachycardia
4. Peritoneal signs (localized guarding or tenderness, rebound tenderness)
5. Leukocytosis

These signs usually indicate irreversible ischemia. Persistent pain, progressive fever, and leukocytosis are indications for surgery.

15. What is the mortality rate of SBO?

Show answer

* Simple obstruction: Mortality ∼ 5% if operated within 24 hours
* Strangulated obstruction: Mortality rate ∼ 25%. The mortality depends on the patient’s resiliency (comorbid disease); but strangulation escalates the mortality by fivefold.

16. What operative interventions may be needed for treatment of SBO?

Show answer

* Open or laparoscopic lysis of adhesions at the point of obstruction
* Reduction and repair of hernia
* Resection of obstructing lesions with primary anastomosis
* Resection of strangulated segment with primary anastomosis
* Bypass of obstructing lesions (used mostly for carcinomatosis)
* Placement of long tube down through the duodenum and into the small bowel (a Baker tube is the most commonly used)

17. Describe criteria for distinguishing viable from dead bowel at the time of operation.

Show answer
Pink color, peristalsis, and arterial pulsations are the most obvious way to identify viable intestine. In questionable cases, Doppler ultrasound can detect arterial pulsations, but the most reliable is the intravenous injection of fluorescein dye with use of a Wood’s lamp. Viable bowel fluoresces purple.

18. What is the risk of development of SBO after initial laparotomy? After previous laparotomy for SBO? Which operations are associated with high rates of SBO?

Show answer
Approximately 15% of all patients undergoing laparotomy eventually develop an SBO. About 12% of patients with a prior SBO develop another. The more recurrences, the higher the recurrence rate. Total or subtotal colectomy has a 1-year rate of 11% and a 30% rate at 10 years. Hysterectomy also carries a high rate of SBO: about 5% for routine procedures and up to 15% after radical hysterectomy.

19. What can surgeons do to decrease the risk of SBO?

Show answer

* Use powderless gloves or wash off glove powder from gloves.
* Avoid suturing through the peritoneum at closure.
* Use barrier film between the incision and small intestine.

20. What is the role of laparoscopy in SBO?

Show answer
Laparoscopic lysis of adhesions is usually reserved for patients who have not had multiple previous laparotomies. Approximately one third of them can be treated successfully by laparoscopy alone, one third require a minimal laparotomy (”lap-assisted”), and about one third require a full open laparotomy. Recent series claim more than 80% success.

21. What can be done for patients with multiply recurrent bowel obstructions for adhesions? S

how answer
Long tube placement, either via nasogastric, gastrostomy, or jejeunostomy with the tube advanced through to the ileocecal valve, can be done. The long tube is left in position for approximately 7 days and reportedly allows the bowel to reform adhesions in more gentle curves. Many other techniques have been tried and abandoned, including Noble plication (i.e., suturing the bowel in orderly loops) and adding various irrigants (e.g., heparin, Dextran, saline) to the peritoneal cavity before closure.

22. Name five complications associated with surgery for SBO.

Show answer

1. Enterotomy
2. Prolonged ileus
3. Wound infection
4. Abscess
5. Recurrent obstruction

23. Name products purported to decrease adhesion formation.

Show answer

* Oxidized cellulose (Interceed)
* Sodium hyaluronate and carboxymethylcellulose (Seprafilm)
* Icodextrin (Adept; investigational)
* 0.5% Ferric hyaluronate gel (Intergel; investigational)

References
WEB SITEs

1. http://www.acssurgery.com/abstracts/acs/acs0305.htm
2. http://www.emedicine.com/EMERG/topic66.htm

BIBLIOGRAPHY
1. Bass BN, Jones B, Bulkley GB: Current management of small-bowel obstruction. Adv Surg 31:1, 1997.
2. Beall DP, Fortman BJ, Lawler BC, Regan F: Imaging bowel obstruction: A comparison between fast magnetic resonance imaging and helical computed tomography. Clin Radiol 57:719-724, 2002. Medline Similar articles Full article
3. Beck DE, Opelka FG, Bailey HR, et al: Incidence of small-bowel obstruction and adhesiolysis after open colorectal and general surgery. Dis Colon Rectum 42:241-248, 1999. Medline Similar articles
4. Choi HK, Chu KW, Law WL: Therapeutic value of Gastrografin in adhesive small bowel obstruction after unsuccessful conservative treatment: a prospective randomized trial. Ann Surg 236:1-6, 2002.
5. DeCherney AH, diZerega GS: Clinical problem of intraperitoneal postsurgical adhesion formation following general surgery and the use of adhesion prevention barriers. Surg Clin North Am 77:671-688, 1997. Medline Similar articles
6. Helton WS: Intestinal obstruction. In ACS Surgery: Principles and Practice. New York, WebMD Professional Publishing, 2003, pp 263-280.
7. Leon EL, Metzger A, Tsiotos GG, et al: Laparoscopic management of small bowel obstruction: Indications and outcome. J Gastrointest Surg 2:132-140, 1998. Medline Similar articles