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Emergency Ultrasound

Tips & Tricks:  Early Small Bowel Obstruction Identification

Laleh Gharahbaghian, MD, FACEP and Ryan Horton, MD

Brief Case:

Chief complaint: Abdominal Pain

A 75-year-old male with history of a laparoscopic cholecystectomy more than ten years prior presented with three hours of suprapubic abdominal pain and tenesmus. The patient was non-toxic, and his abdominal exam was remarkable only for mild suprapubic tenderness on deep palpation; the patient did not have guarding, rebound or abdominal distension. Bedside ultrasound revealed forward and backward peristalsis, as well as mildly dilated proximal loops of bowel (Clip 1 and Clip 2), concerning for a small bowel obstruction. The patient was prioritized for CT scan which showed a closed loop bowel obstruction with compromised perfusion. The patient was taken to the operating room emergently for surgical decompression.

Clip 1 and Clip 2 both show anterograde and retrograde flow of intraluminal contents. Clip 2 overlies the bladder.

Introduction:

Small bowel obstructions are a common cause of abdominal pain leading patients to present to the emergency department. The clinical picture of a patient with bowel obstruction varies depending on the location, form, etiology, and degree of the obstruction.1 Small bowel obstructions are associated with high rates of morbidity and mortality if not identified and treated in a timely manner.2,4,6

 
The diagnosis of intestinal obstruction in the emergency department has been estimated to be around 2% of all patients who present with symptoms of abdominal pain and 15% of all patients who ultimately get admitted to a surgical unit from the emergency department.3 Given these statistics, it is important that emergency physicians be able to identify obstructions and their causes and institute treatment early.


Far and away the most common cause of small bowel obstructions are adhesions, with one study finding adhesions accounted for 75% of all obstructions. Many other causes for small bowel obstruction exist, including neoplasms, hernia, inflammatory bowel disease, foreign bodies, etc.4 Regardless of the cause, the complication rate for small bowel obstructions remains high, with one study finding 30% of small bowel obstructions suffered strangulation and 15% having a complication of bowel necrosis.4,5

 
Point of care ultrasound has been shown to contribute to faster time to diagnosis in many various disease states and likely will contribute to more rapid diagnosis of small bowel obstructions, as well.7,8 In a recent meta-analysis, Taylor, et al, found point of care ultrasound performed by emergency medicine residents to be more accurate than plain abdominal radiographs, CT, or MRI based on likelihood ratios.2,6

 
Different criteria exist for making a diagnosis of small bowel obstruction by ultrasound. The most common findings cited in literature are dilated loops of bowel (>25 mm) [Clip 3], anterograde and retrograde movement of intraluminal contents [Clip 4], or absent peristalsis [Clip 5].3,4,6,9,10


Clip [3]


Clip [4]


Clip [5]

Regardless of the criteria used, the more familiar an emergency physician is with normal bowel anatomy, the more likely they are to recognize a small bowel obstruction.

Tips for ultrasound evaluation of small bowel obstructions:

  1. Patient comfort: if the patient is in too much pain to allow compression with the probe, then the exam will be quite limited. If the patient appears in pain on manual palpation of the abdomen, then to be successful with bowel ultrasound, the patient’s pain should be treated, typically by the parenteral route with an appropriate analgesic.
  2. Probe selection: we’ve found that the curve-linear probe provides the best penetration and image resolution for identifying small bowel obstructions in most patients. In select adult patients and children, with minimal adipose tissue, a linear probe can be an acceptable probe selection given its high resolution. Keep in mind the depth with which the linear probe can visualize will be limited.
  3. Examine the abdomen in a systematic fashion, so that the bowel is ‘run’ with the ultrasound probe to ensure that a dilated and distended segment is not missed. On initial assessment in a patient with classical findings for a small bowel obstruction, it is reasonable to begin at the point of maximal tenderness, where it is more likely for a mechanical obstruction to be identified.
  4. On initial examination, it is common to identify intraluminal air and resulting scatter. If this is the case, use gentle, graded compression of the bowel to displace air and compress the segment until intraluminal contents and bowel wall are seen in the field of view. Once gas has been displaced, slide the probe while continuing to compress to prevent re-accumulation of gas in the visualized segment.
  5. Be patient. Many of the earliest findings of a small bowel obstruction will only be identified when the bowel is viewed over time. The findings include lack of peristalsis over five minutes (consistent with an ileus)5 and anterograde along with retrograde movement of intraluminal contents.
  6. If an obstruction is identified, continue your examination of the bowel to attempt to identify the cause! Hernias, masses, intussusception and intra-abdominal abscesses can all be identified by point of care ultrasound.
  7. Know your limitations! Like an abdominal plain film, POCUS can identify a small bowel obstruction but will not rule it out and might not readily identify the cause. Additionally, closed loop bowel obstructions with ischemic bowel need to be quickly identified, given that their management is surgical. For all but the most skilled sonographers, once a bowel obstruction is identified, the concern for ischemic bowel must remain high.


References:

  1. Ma OJ, Mateer JR, Blaivas M. (2008). Emergency ultrasound. New York: McGraw-Hill Medical.
  2. Taylor MR, Lalani N. In: Carpenter CR, editor. Adult small bowel obstruction Academy of Emergency Med 2013;20(6):527–44.
  3. Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013 Jun;20(6):528–44. doi: 10.1111/acem.12150.
  4. Menzies D, Ellis H. Intestinal obstruction from adhesions–how big is the problem? Ann R Coll Surg Engl. 1990 Jan;72(1):60–3.
  5. Wale A, Pilcher J. Current role of ultrasound in small bowel imaging. Semin Ultrasound CT MR. 2016 Aug;37(4):301–12. doi:10.1053/j.sult.2016.03.001
  6. Fevang BT, Fevang J, Stangeland L, et al. Complications and death after surgical treatment of small bowel obstruction: a 35-year institutional experience. Ann Surg. 2000 Apr; 231(4):529–37.
  7. James V, Alsani FS, Fregonas C, et al. Point-of-care ultrasound in pediatric small bowel obstruction: an ED case series. Am J Emerg Med. 2016 Dec;34(12):2464. e1 - 2464.e2
  8. Blaivas M, Harwood RA, Lambert MJ. Decreasing length of stay with emergency ultrasound examination of the gallbladder. Acad Emerg Med. 1999 Oct;6(10):1020–3.
  9. Melniker LA, Leibner E, McKenney MG, et al. Randomized controlled clinical trial of point-of-care, limited ultrasonography for trauma in the emergency department: the first sonography outcomes assessment program trial. Ann Emerg Med. 2006 Sep;48(3):227–35.  
  10. Ünlüer EE, Yavaşi Ö, Eroğlu O, et al. Ultrasonography by emergency medicine and radiology residents for the diagnosis of small bowel obstruction. Eur J Emerg Med. 2010 Oct;17(5):260–4.
  11. Ogata M, Mateer JR, Condon RE. Prospective evaluation of abdominal sonography for the diagnosis of bowel obstruction. Ann Surg. 1996 Mar;223(3):237–41.
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