Applied Radiology

Dr. Bender is Director of Education, Radiologic-Pathologic Division, AFIP, Washington, DC. Dr. Maglinte is Chief of Emergency Radiology and the Abdominal Imaging Section, Methodist Hospital of Indiana, Indianapolis, IN. This piece is reprinted in a modified form with permission from Emergency Radiology, Vol. 4, pp 337-339, 1997.

Achieving a high rate of quality imaging studies, if not positive outcomes, is dependent on the timing of the initial decompression. For example, CT is best used prior to gut decompression, while laparoscopic adhesiolysis is best accomplished when the bowel is decompressed.4-6 Timing of the decompression is thus critical; it is not something that should routinely be started as soon as a patient enters the ED. Decompression should only be started in the ED if necessary to control nausea, vomiting, and pain. The potential need for a small bowel study, CT, or decompression in the acute setting mandates that a multipurpose tube, capable of supporting any of these options, should be placed at the time of the initial plain film examination. The commonly used Salem sump nasogastric tube cannot fulfill these functions. If the radiologist places and monitors use of the multipurpose tube, through serial films, diagnostic examination and decompression management can be maximized. To simply allow indiscriminate placement of the standard 18-F nasogastric tube in the ED for decompression defeats an extraordinary opportunity to optimize imaging and subjects the patient to the trauma of having to replace the nasogastric tube. Gut decompression requires a sump and, as such, the multipurpose triluminal catheter is ideally suited for first line management.1,2 This tube not only can serve for gut decompression, but also can be used for enteroclysis or CT-enteroclysis (CT-E) when advanced beyond the pylorus.2

Ideally, CT of the abdomen and pelvis, with both IV and gut contrast, should be performed in the acute setting.7-12 A note of caution: with a fluid-filled, dilated gut, avoidance of introducing any additional fluid volume is critical to patient safety.3,6 The need for gut contrast can often be determined from the initial abdominal plain films. If dilated loops of fluid-filled small bowel are seen, then there is little need for gut contrast.3,6 If the abdominal radiographic series is normal or equivocal in the face of strong clinical evidence for SBO, then gut contrast can be administered easily through the multipurpose tube, which is simply advanced from its initial gastric placement into the jejunum.

Initially determining the grade of obstruction is not as critical as determining whether an obstruction is present or not.3,6,13,14 In fluid-filled gut, the mucosal enhancement that is achieved with IV contrast alone is often sufficient to define the presence or absence of obstruction.3 Once obstruction is determined, decompression is critical over the first 24 to 48 hours to prevent ischemia or other co-morbidities from developing.3,15-17 Following decompression, if subsequent feeding trials are unsuccessful, then a CT with gut contrast, enteroclysis, or a CT-enteroclysis can be performed to assess the severity of obstruction and exclude complications of adhesive obstruction.3,6,7,13,18

When using a nasogastric tube that can be converted into an enteroclysis catheter, CT-E is an immediate option if the patient has not already had a diagnostic CT or if the CT itself was equivocal.6 Early results show that if the SBO patient has a known or suspected malignancy by history, CT-E is more accurate than CT in identifying the site and cause of the obstruction.6,19 With CT-E, the gut must be adequately decompressed so vomiting does not occur with enteral contrast administration. CT-enteroclysis is contraindicated in an SBO with undecompressed, fluid-filled gut. Adding a large volume of fluid to bowel already distended with a large volume of fluid only induces vomiting and increases the risk of aspiration.3 If fluid-filled loops of bowel are seen at fluoroscopy, the enteroclysis portion of the study should be aborted and decompression instituted.2 In malignancy, even tube placement can induce vomiting, so decompression prior to CT-E is imperative.

CT-E has been proposed for use in patients with low grade obstruction, inflammatory bowel disease, and in those with polyposis.6,19-22 Traditional enteroclysis is an alternative; however, cross-sectional imaging (CT-E) may allow for better surgical planning if laparoscopic adhesiolysis is available. In addition, CT-E may have a higher sensitivity and specificity for low-grade partial SBO lesions.6 Regardless, with the initial placement of a multipurpose tube by the radiologist or the emergency physician at the time the patient obtains his or her initial plain film examination, conventional CT with SB contrast, CT-enteroclysis, traditional enteroclysis, simple gut decompression, or surgery all remain easy to perform options without having to subject the patient to the trauma of multiple intubations. For radiologists who prefer blunt end catheters for nasoenteric tube placement, the end of the multipurpose tube can be cut and filed smooth with an emery board. A modified enteroclysis catheter with an end-hole is commercially available (MAG-ENT-120-MAMC, Cook, Inc., Bloomington, IN). Most polyvinyl, blunt enteroclysis catheters lose the function of the balloon but not the sump effect when the end is cut. We have found that use of the balloon is not required in grossly dilated gut, save for possibly helping to maintain a catheter position near the ligament of Treitz.

The proposed "SBO watch", alluded to above, is a useful team approach which bundles the efforts of the emergency room physician, the general surgeon, and the radiologist together. The radiologist must be just as available for patient care as the other two for this approach to work. With more departments starting to use staff radiologists to cover the emergency department in-house at night, this approach should become more palatable and rewarding. The greatest resistance in starting such a clinical pathway, in our experience, is the on-call radiologist's reluctance towards placing nasointestinal catheters and the emergency physician's and surgeon's lack of familiarity with the multipurpose tube. One option is to let the emergency physician, nurse, or physician's assistant place the multipurpose tube into the stomach. The tube functions similarly to the commonly used nasogastric tube if the tip is in the stomach. If necessary to control nausea and vomiting, it should be placed prior to the initial plain film series but should ideally be introduced after the initial plain film study. The health care provider should wait until after the initial CT is performed to place or advance the tube into the small bowel to prevent any tube artifact or premature decompression from interfering with CT interpretation. If the stomach is fluid filled, initial gastric decompression is done. Once the site and etiology of the obstruction is determined, long tube decompression can then occur with advancement of the tube past the ligament of Treitz.1-3

In many patients with obstructive disease secondary to adhesions, decompression is sufficient to alleviate the obstructive symptoms and allow a return to normal bowel function with dietary management. As stenoses or constrictive defects become tighter, eventual surgery can be planned based on enteroclysis criteria for severity of obstruction and the CT criteria for diagnosis of adhesive disease.8-15,19

The "barium-bullet" still practiced in some institutions is to be strictly avoided, regardless of its popularity among general surgeons, as it obviates all other imaging options save for plain films, and all other therapeutic options save for laparotomy.20 Endoscopy is difficult through barium, and stent placement or balloon dilatation cannot be performed. Certainly laparoscopic adhesiolysis is less secure with barium in the gut, lacking full access to the bowel and peritoneal cavity should a spill with barium occur. None of these are as important as the information that can be missed concerning ischemic bowel when using only portable radiographs taken on the ward as opposed to cross-sectional imaging.3,23-27 CT is much more reliable at the time of initial presentation, as opposed to exposing ward personnel to the unnecessary radiation and expense of serial, low quality, portable radiographs that simply increase the length of patient stay (Bender GN: Unpublished data from Madigan Army Medical Center on inpatient SBO review, 1994-1995).

In summary, to become an integral member of the SBO management team, the radiologist must:

1. Offer immediate radiologist services 24 hours/day in making the initial reading for any abdominal radiographs or CT prior to ED management.

2. Be available and willing to place the initial multipurpose tube at the time the patient is in the emergency radiology section after the initial radiographic film series, or immediately after the CT, if obtained.

3. Educate the ED physicians and general surgeons that CT should be obtained during the acute phase of presentation and prior to any initial decompression so that the diagnosis of SBO and the site of obstruction can be confirmed and other causes of the acute abdomen reliably excluded.

4. Be available to ensure tube placement is allowing adequate decompression of the gut, through timely reporting of any serial abdominal radiographs and education of nursing staff on long intestinal tube care.2

5. Be aware of the initiation, and be involved in the follow-up of any post-decompression feeding trials through timely reporting of any serial abdominal films.

6. Be available and capable of performing CT, enteroclysis, or CT-enteroclysis if decompression fails, feeding trials fail, or the persistence or recurrence of symptoms occurs.

This active participation results in optimized imaging work-up and nonsurgical management of small bowel obstructions, fulfilling the radiologist's role as true consultants.

References