Diferencia entre revisiones de «Small bowel obstruction»

Revisión actual - 23:58 4 ene 2026

Background

Small bowel anatomy with surrounding structures.

Small bowel obstruction without history of surgery or hernia is malignancy until proven otherwise
"Never let the sun rise or set on a small bowel obstruction"

Causes

Adhesions (history of previous abdominal surgeries +LR 3.86 and -LR 0.19)
- Most common cause in developed countries
Hernia
- Port hernias can occur after laparoscopic surgery
Malignancy
Intraluminal strictures
- Crohn's disease
- Radiation therapy
- Mesenteric ischemia
Intussusception (due to lymphoma as lead point)
Foreign body (bezoars)
Trauma (duodenal hematoma)
Gallstone ileus
Small bowel volvulus (3-6% of causes of SBO)^[1]

Clinical Features

Abdominal pain
- Colicky
- Periumbilical or diffuse
- Paroxysms of pain occur q5min
Vomiting
- More common in proximal than distal obstruction
- Bilious (proximal) or feculent (distal ileal)
  - Abdominal pain relieved with vomiting positively predictive +LR (4.50-2.82) -LR (0.78-0.35)
Abdominal distention
- Seen more in distal than proximal obstruction
- +LR (16.8-5.64) -LR (0.43-0.34)
Inability to pass flatus
- May pass flatus/stool initially
  - Takes 12-24hrs for colon to empty
  - History of constipation +LR 8.8 and -LR 0.59
Dehydration
Anorexia
Ischemia (increased intraluminal pressure initially leads to venous obstruction, progresses to frank arterial ischemia)
- Fever
- Leukocytosis
Abnormal bowel sounds
- Studies suggest that auscultating bowel sounds is not clinically useful to differentiate between normal and pathologic^[2]

Differential Diagnosis

Diffuse Abdominal pain

Constipation

Behavioral-related
- Lack of exercise
- Diet-related
Fecal impaction
- Stercoral colitis
Ileus from surgical abdomen
- Appendicitis
- Diverticulitis
Bowel obstruction
- Small bowel obstruction
- Large bowel obstruction
  - Ogilvie's syndrome
- Malignant bowel obstruction
- Specific causes: tumor, stricture, hernia, adhesion, volvulus
Painful anorectal disorders (e.g. anal fissure, hemorrhoids)
Medical causes
- Hypothyroidism
- Electrolytes
  - Hypomagnesia
  - Hypercalcemia
- Hypokalemia
Medication-related
- Opiods, antipsychotics, anticholinergics, antacid, antihistamines
Constipation (peds)

Evaluation

Upright abdominal X-ray demonstrating a small bowel obstruction. Note multiple air fluid levels.

Small bowel obstruction

Ultrasound shows dilated, non-compressible loops of bowel with characteristic to-and-fro motion of bowel contents^[3]

Ultrasound shows dilated loops of bowel steep precipice and tumbling feces^[4]

A small bowel obstruction as seen on CT.

Labs

CBC
- WBC >20K suggests bowel gangrene, abscess, or peritonitis
- WBC >40K suggests mesenteric vascular occlusion
Chemistry - degree of dehydration, evidence of ischemia (acidosis)
Lactate - sensitive (90-100%), though not specific marker of strangulation

Imaging

Use the 3/6/9 rule for bowel imaging
- Upper limit of 3cm for small bowel, 6cm for colon, and 9cm for cecum
Xray
- Acute Abdominal Series
- Upright chest film: rule out free air
- Upright abdominal film: air-fluid levels:
- Supine abdominal film: width of bowel loops most visible (estimate of amount of distention)
- String of pearls sign (small pockets of gas along the small bowel that are trapped between the valvulae conniventes) is virtually diagnostic^[5]
- Small bowel diameter ≥3cm is associated with obstruction
  - Sen 75% Spec 66% +LR 1.6 -LR 0.43
  - Air in colon or rectum makes complete obstruction less likely (esp if symptoms >24hr)
  - If patient does not tolerate upright position left lateral decub abdominal film can substitute
CT A/P with IV contrast
- Consider if plain films are non-diagnostic
- Can show closed-loop obstruction, evidence of ischemia
- Per American College of Radiology PO contrast is no longer indicated
  - Modern CT Scanner (0.75mm slices): Sen 96%, Spec 100%, +LR infinity -LR 0.04
  - Historical CT scanner meta-analysis: Sen 87% Spec 81%, +LR 3.6 -LR 0.18
Ultrasound for SBO
- Sen 97%, Spec 90%, +LR 9.5, -LR 0.04 (four studies, 2 done by EM residents and 2 by radiology residents)
MRI for SBO - Sen 92%, Spec 89% +LR 6.7 -LR 0.11

Management

Volume resuscitation

IV fluid resuscitation with electrolyte repletion
Assessment of need for operative vs nonoperative management

Nasogastric tube

14 French
- Intermittent low wall suction
Nasogastric fluid losses can be replaced with NS + KCL (30-40 meq)
There is some evidence to suggest nasogastric tube decompression was not associated with decreased bowel ischemia or need for surgery^[6]

Oral Contrast

Both diagnostic and therapeutic (draws water into the bowel stimulating peristalsis)
Associated with decreased hospital stay, more rapid resolution of symptoms
Repeat CT scan may be helpful to detect early signs of bowel ischemia
- Repeat plain films are not helpful (only detect perforation)

Gastrografin PO

Alternative to operative management if early obstructive process
Gastrografin through NG or OG decreases bowel wall edema and increases bowel motility^[7]
- Diagnostic and therapeutic^[8]
- 100 cc of gastrografin through NG tube
- Transit may be observed through serial radiographs
  - Contrast within the large bowel within 24 hrs suggest partial SBO
  - Contrast failing to reach large bowel within 24-48 hrs suggests complete obstruction, requiring laparotomy
- Therapeutic, may reduce necessary operative rate by ~75%^[9]
Avoid barium as it becomes inspissated in bowel, causing complete obstruction^[10]
- Gastrografin is water-soluble and relatively safer if perforation occurs

Non-operative Management vs. Operative

75% of patients are amenable to non-operative management

Operative Management

25% of patients admitted for SBO require surgery
Surgery is indicated for patients with:
- Increasing pain, distention, or peristent high NGT output
- Necrotic bowel
- Closed-loop obstruction (incarcerated hernia, small bowel volvulus, cecal volvulus)
- Fever, leukocytosis, peritonitis

Antibiotics

Not typically indicated, unless evidence of concurrent ischemia or infection
See peritonitis antibiotics

Disposition

Admit

Prognosis

In the context of advancing malignancy with widespread peritoneal metastases, bowel obstruction is common and often indicates a poor prognosis
A less interventional and more comfort based approach to treatment may be appropriate
See Malignant bowel obstruction for details

References

↑ Roline CE and Reardon RF. Disorders of the Small Intestine. Rosen's. Edition 8. Chapter 92. 2014. 1216-1224.
↑ Felder S, Margel D, Murrell Z, et al. Usefulness of Bowel Sound Auscultation: A Prospective Evaluation. J Surg. 2014; 71(5):768–773.
↑ http://www.thepocusatlas.com/bowel/
↑ http://www.thepocusatlas.com/bowel/
↑ Maglinte DDT, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR 1996; 167:1451-1455
↑ Berman, DJ et al. Nasogastric decompression not associated with a reduction in surgery or bowel ischemia for acute small bowel obstruction. Am J Emerg Med. 2017 Dec;35(12):1919-1921.PMID: 28912083
↑ Assalia A, Schein M, Kopelman D, et al. Therapeutic effect of oral Gastrografin in adhesive, partial small-bowel obstruction: A prospective randomized trial. Surgery 1994; 115: 433-437.
↑ Chen SC, Lin FY, Lee PH, et al. Water-soluble contrast study predicts the need for early surgery in adhesive small bowel obstruction. Br J Surg 1998; 85: 1692-1694.
↑ Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).
↑ Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).

Authors:

[1] Roline CE and Reardon RF. Disorders of the Small Intestine. Rosen's. Edition 8. Chapter 92. 2014. 1216-1224.

[2] Felder S, Margel D, Murrell Z, et al. Usefulness of Bowel Sound Auscultation: A Prospective Evaluation. J Surg. 2014; 71(5):768–773.

[3] ttp://www.thepocusatlas.com/bowel/

[4] ttp://www.thepocusatlas.com/bowel/

[5] Maglinte DDT, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR 1996; 167:1451-1455

[6] Berman, DJ et al. Nasogastric decompression not associated with a reduction in surgery or bowel ischemia for acute small bowel obstruction. Am J Emerg Med. 2017 Dec;35(12):1919-1921.PMID: 28912083

[7] Assalia A, Schein M, Kopelman D, et al. Therapeutic effect of oral Gastrografin in adhesive, partial small-bowel obstruction: A prospective randomized trial. Surgery 1994; 115: 433-437.

[8] Chen SC, Lin FY, Lee PH, et al. Water-soluble contrast study predicts the need for early surgery in adhesive small bowel obstruction. Br J Surg 1998; 85: 1692-1694.

[9] Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).

[10] Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).

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