Hospital Medicine

Small bowel obstruction

I. What every physician needs to know.

Small bowel obstruction (SBO) presents as a constellation of symptoms including abdominal pain, nausea, vomiting, lack of, or paucity, of bowel movements and signs such as abdominal tenderness and distention. Late in the course of the illness patients are exquisitely tender to abdominal palpation, hypovolemic, febrile, and floridly septic. Complete small bowel obstruction may lead to strangulation, necrosis and eventual catastrophic sequelae of intestinal perforation.

Pathophysiologically, SBO may be secondary to intrinsic or extrinsic interruption of the normal peristalsis of the small intestine. With intra-abdominal adhesions being the most common cause of intestinal obstruction, most patients have a history of previous surgery. An example of intrinsic obstruction is an intraluminal tumor or a bezoar. Extramural obstructions can occur when tumors infiltrate into the mesentery or bowel wall, or kink the bowel externally. As a common consequence to all causes of SBO, intraluminal sodium and water reabsorption decreases whilst intestinal secretion of electrolytes and enzymes increases perpetuating distention and ineffective contraction that lead to intestinal edema and further distention.

It is imperative to have low clinical suspicion for complete obstruction requiring early surgical consultation and a potential laparotomy.

II. Diagnostic Confirmation: Are you sure your patient has small bowel obstruction?

A patient with crampy abdominal pain, obstipation, nausea, periodic vomiting, and history of previous intra-abdominal surgery, Crohns's disease, ovarian or colon cancer are at high risk of having SBO.

A. History Part I: Pattern Recognition:

A typical patient with an SBO is an individual with past history of intra-abdominal surgery who develops progressive abdominal pain, nausea and vomiting. Abdominal pain is usually crampy and paroxysmal. When abdominal pain becomes focal, a concern must be raised that the obstruction is complete.

Emesis may occur repeatedly and will often lead to cessation of oral intake leading to feeling dehydrated and thirsty. In a patient whose level of consciousness is otherwise depressed, abdominal distention may be present for a relatively prolonged period of time resulting in bacterial overgrowth in the proximal small bowel and leading to feculent emesis.

B. History Part 2: Prevalence:

  • Fifteen to forty-two percent of patients who undego intra-abdominal surgery develop intestinal obstruction with 25% of these patients being readmitted in the fist 12 months post surgery. Interestingly, location and direction of the surgical incision and laparascopic versus open surgery may be factors contributing to the differences in incidence of post-operative SBO due to adhesions.

  • Twenty percent of all cases of SBO are attributed to malignant tumors of which ovarian and colorectal carcinomas are the most common ones.

  • Ten percent of the cases are related to hernias with ventral and inguinal being the most common.

  • Patients with active Crohn's disease represent a particularly challenging group of patients since intrinsic intraluminal strictures may result in SBO but surgical intervention is avoided as much as possible due to an increased risk of Crohn's disease recurrence at the surgical site.

  • Other less common conditions leading to intestinal obstruction are strictures due to radiation therapy, mesenteric ischemia and intraluminal tumors such as carcinomas, lymphoma and carcinoid. Intussusception may occur but is much more common in pediatric population. In adults, discovery of intussusception should prompt a search for intraluminal malignancy. Gastrointestinal bezoars and gallstone ileus are rare causes of intraluminal intestinal obstruction.

C. History Part 3: Competing diagnoses that can mimic small bowel obstruction.

Post-operative ileus (also known as paralytic ileus) is a routine and expected finding in most patients recovering from intra-abdominal surgery. It can be distinguished from SBO clinically in that abdominal pain and distention are not as prominent as they are in SBO. Focal pain is usually absent. Patients may complain of nausea but it is usually short lived and not routinely accompanied by vomiting. Since paralytic ileus may be exacerbated by electrolyte abnormalities, routine chemistry profile should be obtained with a particular attention paid to potassium.

Intestinal pseudo-obstruction may also mimic SBO. However, most cases are due to insufficient colonic peristalsis and is frequently found in elderly chronically ill individuals (i.e. Ogilvie syndrome) or in patients with paraneoplastic destruction of the enteric nervous system.

Radiological studies such as upright chest X-ray and supine and upright abdominal films may be helpful to look for intra-abdominal air, distended loops of small bowel and air-fluid levels. Computerized tomography of the abdomen will assist in identifying a transition point raising suspicion that complete or partial SBO is more likely than paralytic ileus.

D. Physical Examination Findings.

Vital signs and general appearance are important as fever, tachycardia, relative hypotension, dry mucous membranes, and obtundation are all signs concerning for impending circulatory shock in the setting of complete strangulation and impending bowel perforation.

Examination of the abdomen should focus on the degree of distention, focal versus diffuse tenderness, presence of pain on light percussion or gentle shaking of the bed, presence of surgical scars, and presence of inguinal, femoral and incisional hernias.

E. What diagnostic tests should be performed?

N/A

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Although simple laboratory tests are not helpful in the diagnosis of SBO or its cause, complete metabolic panel and complete hematologic profile must be obtained. Electrolyte abnormalities must be corrected and the degree of hypovolemia assessed.

Presence of leukocytosis is seen frequently and is not helpful in differentiating partial SBO from complete strangulation.

Serum lactate is a relatively sensitive marker of impending strangulation.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Typically plain radiographs such as upright chest and supine and upright abdominal films are ordered. Intra-abdominal air, distended loops of small bowel and air-fluid levels may be seen. However, in almost 1/3 of patients such films are not helpful.

Computerized tomography (CT) of the abdomen with dilute barium or water-soluble oral contrast as well as intravenous contrast will assist in identifying a transition point raising suspicion that complete or partial SBO is present. At the very least, radiologist looks for a discrepancy in the caliber of proximal and distal small bowel. Intestinal pneumatosis and hemorrhagic mesenteric changes are ominous signs as they signify advanced bowel wall ischemia.

Small-bowel follow-through series are known to be highly sensitive for SBO but are seldom used in practice.

Ultrasound may be used in the critically ill when a patient cannot be safely transported to the CT suite. Ultrasound may also be used when patient's renal function precludes use of the intravenous contrast for CT.

III. Default Management.

Diagnosis of SBO is most often made on history and physical exam. Radiological studies above are also helpful. However, the importance of early surgical consultation cannot be overemphasized.

The physician caring for a patient with suspected SBO must assess volume status and metabolic abnormalities; replete electrolytes and provide liberal volume resuscitation until the patient is deemed euvolemic. Sufficient intravenous access must be obtained and Foley catheter must be inserted to aid in adequate resuscitation and monitoring of urine output respectfully.

A soft 14 French nasogastric tube (NGT) may provide relief from nausea and repeated vomiting if inserted in patients with partial SBO. It may also be helpful in patients with high-grade SBO thereby decompressing distended stomach. However, it should not replace close monitoring for progressive abdominal distention and frequent clinical re-evaluations.

A. Immediate management.

Volume resuscitation, urine output monitoring via a Foley catheter and early surgical consultation must be accomplished within the first several hours of suspected SBO.

If no improvement is shown within the first 12-24 hours of non-operative management then the patient should be brought to surgery. This delay is unreasonably long in patients who are diagnosed with mesenteric ischemia or complete strangulation.

B. Physical Examination Tips to Guide Management.

After volume resuscitation, adequate urine output are achieved and surgical team is consulted and following along, frequent reassessments are crucial. Hemodynamic stability, decrease in abdominal distention and pain, passage of flatus and stool per rectum are reassuring signs. If, however, abdominal pain becomes constant and more focal then complete obstruction leading to strangulation must be immediately considered and a surgeon re-consulted.

C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

If inserted, NGT position should be confirmed with a plain chest radiograph. It should be connected to intermittent suctioning and NGT output should be monitored. NGT losses may be repleted with intravenous normal saline fluid containing potassium supplements.

Complete metabolic profile should be obtained at least two times within 24 hours especially if NGT output is significant.

Abdominal CT with oral contrast may need to be repeated if there is a change in clinical status such that strangulation is more likely.

If obstruction is deemed to be clinically resolving, NGT may be clamped for four hours before it is removed with a goal of less than 100cc of residuals.

D. Long-term management.

Patients with SBO must be co-managed with general surgeons as 25% of such patients will require surgical exploration. Surgical team must decide on the method of operation (i.e. laparoscopy versus laparotomy), type of incision and lysis of all adhesions or only the ones involved in the current obstruction.

E. Common Pitfalls and Side-Effects of Management

The most important aspects of managing patients with SBO are to consider consequences of a complete SBO with strangulation, volume resuscitation and consult general surgery early.

IV. Management with Co-Morbidities

N/A

A. Renal Insufficiency.

In patients with chronic kidney disease obtaining an initial diagnostic abdominal CT with intravenous contrast may be problematic. Abdominal ultrasound, although less sensitive, may be used to look for intra-abdominal distention and obstruction. Small bowel follow through may also be used. Patients with acute kidney injury should be aggressively volume resuscitated fist and then intravenous contrast-requiring imaging studies considered if renal function shows improvement.

B. Liver Insufficiency.

No change In standard management.

C. Systolic and Diastolic Heart Failure

In patients with heart failure (especially systolic) volume resuscitation and urine output monitoring are particularly crucial in order not to precipitate acute cardiogenic edema.

D. Coronary Artery Disease or Peripheral Vascular Disease

No change in standard management.

E. Diabetes or other Endocrine issues

No change in standard management.

F. Malignancy

Ovarian neoplasm and intestinal carcinomas are the most common malignancies found in patients presenting with an SBO due to cancer. Although surgeons are frequently reluctant to operate on patients with an SBO due to cancer, non-operative management is also associated with high failure rate and mortality. Prolonged medical management including NGT and administration of total parenteral nutrition (TPN) may be offered to patients with a partial SBO and advanced metastatic disease. Antiemetics are helpful for symptomatic relief.

Median survival of patients diagnosed with bowel obstruction due to cancer is between 30 and 90 days. With that in mind, palliative care and discussions regarding goals of care must be considered in patients with SBO due to advanced malignancy.

G. Immunosuppression (HIV, chronic steroids, etc).

Although intussusception is rare in adult population, in patients with AIDS it may result from intraluminal lymphoid hyperplasia, Kaposi's sarcoma and non-Hodgkin's lymphoma - conditions that are more prevalent in this population.

H. Primary Lung Disease (COPD, Asthma, ILD)

No change in standard management.

I. Gastrointestinal or Nutrition Issues

Prolonged medical management including NGT and administration of TPN may be offered to patients with a partial SBO and advanced metastatic disease.

J. Hematologic or Coagulation Issues

No change in standard management.

K. Dementia or Psychiatric Illness/Treatment

Patients with dementia and patients with decreased level of consciousness may develop partial SBO that remains undiagnosed for a period of time secondary to their difficulties verbalizing their complaints. Compete obstruction and proximal intestinal bacterial overgrowth may occur leading to feculent emesis and frank hemodynamic instability and intra-abdominal sepsis at presentation.

Patients with psychiatric illnesses may be found to have complete intestinal obstruction due to bezoars which are composed of hair (i.e. trichobezoar) or pills.

V. Transitions of Care

A. Sign-out considerations While Hospitalized.

  • Complete metabolic profile should be obtained at least two times within 24 hours especially if NGT output is significant.

  • Frequent bedside re-assessments are required to ensure that abdominal pain and distention are not worsening.

  • Intravenous fluid orders should not run out and urine output needs to be monitored and maintained.]#

  • Abdominal CT with oral contrast may need to be repeated if there is a change in clinical status such that strangulation is more likely which would be evident if the patient complains of increased abdominal pain, more focal location of the pain, increased nausea, and vomiting.

C. When is the Patient Ready for Discharge.

If obstruction is deemed to be clinically resolving, NGT may be clamped for four hours before it is removed with a goal of less than 100cc of residuals. Subsequently, diet may be slowly advanced and if the patient tolerates oral nutritional intake without significant nausea, has progressively decreasing abdominal discomfort and is able to pass stool then he may be safely discharged from the hospital.

D. Arranging for Clinic Follow-up

Depending on the cause of SBO patient may need to follow up with surgery, oncology and a primary care physician.

What's the evidence?

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