The decision to manage an ASBO non-operatively is multi-factorial and generally involves an initial period of nasogastric (NG) tube decompression, crystalloid resuscitation, and correcting fluid and metabolic derangements in tandem with diagnostics [18]. Despite nation-wide heterogeneous admissions policies regarding ASBO, patients admitted to surgical services instead of medical services have been shown to receive more cost-effective care, improved triage to the operating room, and decreased length of hospital stay [19].

Once the diagnosis of ASBO is made, those patients presenting with a clinical exam concerning for ischemia or perforation should be managed operatively. In the absence of peritonitis, abdominal tenderness should be considered a relative contraindication to non-operative management in the presence of concerning radiographic findings such as possible closed-loop obstruction, high-grade obstruction, “whirl sign,” mesenteric twisting, stranding, or thickening, poor or absent bowel wall enhancement, pneumatosis, portal venous gas, and free fluid. Laboratory findings such as lactic acidosis, leukocytosis, and significant electrolyte abnormalities may further suggest a need for operation. Other contraindications to non-operative management to consider include a history of gastric bypass (due to inability to decompress the gastric remnant via NG tube alone), history of inflammatory bowel disease (due to intrinsic causes of obstruction from inflammatory bowel disease, i.e. stricture), large bowel obstruction, obstruction caused by hernia, and definitive closed-loop obstruction on imaging. In the unique case of obliterative peritonitis (i.e., “hostile abdomen”) with known dense adhesions, a surgeon may favor non-operative management in the setting of relative contraindications to non-operative management due to an increased risk of accidental bowel injury. A patient presenting with a small bowel obstruction in the setting of carcinomatosis may be presenting with a palliative problem that is best treated with a multi-disciplinary approach that includes a goals of care discussion.

Once a surgeon has decided to attempt non-operative management of an ASBO, there remains a chance that the patient may fail non-operative management and require an operation. The water-soluble contrast challenge (WSCC) has increasingly become the standard of care in differentiating between patients who can be managed non-operatively and those who require surgical intervention, as well as the timing of operating in those patients who fail non-operative management. This approach became widespread after the original 2008 version and 2012 revision of the Eastern Association for the Surgery of Trauma (EAST) small bowel obstruction practice management guidelines [20, 21]. In addition to its predictive value, it is also believed the WSCC may have a therapeutic benefit to reduce bowel wall edema by increasing the luminal osmolar gradient. Sometimes call the “Gastrografin® challenge,” the WSCC uses an ingestible radiopaque contrast medium (diatrizoate meglumine-sodium) which is administered orally (or via enteric tube after a variable period of decompression) and followed by incremental abdominal radiographs. The presence of water-soluble contrast in the right colon predicts successful non-operative management and resolution of an ASBO. While diatrizoate meglumine-sodium solutions are high-osmolar water-soluble contrasts, some centers have shifted to using low-osmolar water-soluble contrast mediums, such as oral iohexol. In one study, using a low-osmolar water-soluble contrast medium had similar outcomes to controls when used in an evidence-based ASBO pathway [22]. Ultimately, the WSCC is thought to be up to 96% sensitive and 98% specific for predicting resolution of the ASBO when contrast reaches the right colon by 24 h [23].

Although previous trials and systematic reviews have described multiple benefits with WSCC in terms of patient-centered and hospital-centered outcomes (i.e. ASBO resolution, operative rates, hospital cost, and hospital length of stay), significant institutional heterogeneity persists regarding the timing of contrast administration and the dosage of contrast. Recent data suggest that contrast administration within 12 h of ASBO presentation following gastric decompression via NG tube is adequate for differentiating non-operative from operative disease, but the duration of adequate decompression is variable throughout the literature and may even be as low as two hours [24,25,26,27,28,29,30,31].

Nationally there is considerable variation in ASBO practice patterns [32]. To standardize our treatment of patients with ASBO on the emergency general surgery (EGS) service at the University of Nebraska Medical Center (UNMC) in Omaha, Nebraska, we perform NG tube decompression for 12 h while performing serial abdominal exams and trending any lab abnormalities to ensure clinical improvement prior to initiating the WSCC. If the patient develops worsening vital signs, physical exam, or labs during admission, we consider operative intervention. A radiographic small bowel follow-through (SBFT) is then performed to serve as the WSCC. During this exam, the patient is administered diatrizoate meglumine-sodium (240 mL) via NG tube, followed by NG tube clamping for the duration of the study where abdominal plain films are obtained at one hour, two hours, four hours, and eight hours post-administration (Fig. 1). As an alternative, iopamidol 61% 200 mL may be used if there is concern for aspiration risk, since diatrizoate meglumine-sodium is known to cause pneumonitis. If contrast reaches the right colon by eight hours, we remove the NG tube and feed the patient. The non-operative management is considered a success if the patient is having bowel function and can tolerate oral diet. If contrast has not reached the right colon by eight hours during the WSCC or the patient cannot tolerate contrast administration, we consider non-operative management to have failed and pursue operative management. This standardized period of NG tube decompression and WSCC duration has resulted in decreased practice variability across the partnership and we have observed reduction in nearly two days of hospital length of stay.

University of Nebraska Medical Center emergency general surgery adhesive small bowel obstruction management pathway. ASBO adhesive small bowel obstruction, WSCC water-soluble contrast challenge

We chose eight hours as the duration of our WSCC after a twelve-hour NG tube decompression period based on our data from a study performed at the Wake Forest School of Medicine in Winston-Salem, North Carolina, where patients who required 24 h of transit time during a WSCC to reach the right colon were more likely to have a higher one-year recidivism of ASBO than those patients who required only eight hours to complete a WSCC [4]. This data indicated that significant adhesions or another process, such as motility dysfunction, were increasing the transit time of contrast during the WSCC in the 24 h population and those processes may be increasing the frequency and chance of ASBO recurrence. In the study, of the ASBO patients who required 24 h for contrast to reach the right colon and who were discharged after successful non-operative management, 40% recurred within one year and a majority (60%) of those recurrences occurred in the first 30 days. That was in comparison to a 21.4% one-year recurrence rate in non-operative ASBO patients who required only eight hours for contrast to reach the right colon, with 33% of those recurrences occurring in the first 30 days. The groups were significantly different at these data points (Fig. 2) [4]. The data also simultaneously found that patients who presented with their first ASBO were at increased risk of one-year ASBO recurrence compared to those whose medical history included multiple previous ASBOs. This was interesting because it is well-established in literature that while operative management of ASBO is associated with fewer future recurrences, it is believed that the more ASBOs a patient has over time, the greater the risk of lifetime recurrence [33].

Wake Forest School of Medicine 1 year ASBO recurrence rates over time. ASBO adhesive small bowel obstruction. This figure was adapted from Terzian et al. [4]

We interpreted this data to mean that if a patient is admitted with an ASBO and does not pass a WSCC within eight hours, he or she may be at increased risk for ASBO recurrence within one year and consideration should be given to exploring his or her abdomen. Furthermore, if a patient is admitted with his or her first ASBO and simultaneously fails to pass a WSCC within eight hours, he or she may be at an even greater risk for ASBO recurrence within one year and serious consideration should be given to exploring the abdomen. This could be useful information to a surgeon who is treating a patient for his or her first ASBO and might be inclined to give that patient greater than eight hours to pass a WSCC; however, the data suggested that this is the very patient who should be intervened upon.

Regardless of how long a surgeon allows a patient to undergo a WSCC, conservative practices should be balanced against a possible increase in 30 day mortality that has been observed in delaying surgery beyond 72 h [34]. Fung et al. concluded that for each additional day managed non-operatively there may be an increased the risk of complication and bowel resection, although this finding has been contested [35, 36].

Bologna guidelines suggest a safe window of non-operative management between three and five days, beyond which an operative intervention should be considered [37]. In support of this, a recent population-based, propensity-matched analysis found that operative intervention at index hospitalization for ASBO is associated with a significant long-term survival improvement and a decreased risk of recurrence [38]. Additional current data nuance this finding, suggesting that, although time to re-admission may be extended by operative intervention, recurrent obstructions are more likely for patients who have experienced multiple prior ASBOs, irrespective of management strategy. Taken together, these studies illustrate a biological propensity for adhesion formation in individuals who suffer multiple episodes of ASBO. In considering elective enterolysis between episodes to prevent ASBO, therapy should be highly individualized in the non-emergent patient.