The history of acute onset of colicky abdominal pain, nausea, vomiting, and obstipation in a young patient with prior abdominal or pelvic surgery is highly suggestive of simple mechanical small bowel obstruction (SBO) due to adhesions from prior surgery. This patient presents with uncomplicated, or simple SBO, but treatment is necessary in order to avoid progression and potential complications such as strangulation, bowel necrosis, sepsis, and death. This patient also presents with dehydration as evidenced by dry mucous membranes, prerenal azotemia (high BUN-to-creatinine ratio), and hypochloremic, hypokalemic, metabolic acidosis as a result of volume losses from recurrent emesis secondary to her SBO.

The absence of an abdominal scar suggests that the patient has had no previous surgeries and removes the most common benign etiology of SBO. Since adhesions result from prior surgeries, intra-abdominal adhesions are less likely to be the cause of SBO in a patient without an abdominal scar. This is important because while the majority of SBOs due to intra-abdominal adhesions will resolve with conservative treatment, the other causes of SBO are less likely to resolve without intervention and may need emergent surgical treatment. Additionally, nonadhesive SBOs require further diagnostic evaluation or intervention to assess for malignancy, hernia, or inflammatory bowel disease.

This is suggestive of an obturator hernia and consists of pain in the medial aspect of the thigh with abduction, extension, or internal rotation of the hip due to compression of the obturator nerve by an obturator hernia (pelvic hernias seen mostly in elderly multiparous females and in those with significant weight loss).

Severe abdominal pain and localized tenderness in association with SBO are suggestive of complicated or strangulated SBO. In contrast to a simple SBO where blood flow to the bowel remains intact, strangulated obstruction occurs when vascular perfusion is impaired, leading to intestinal ischemia and ultimately necrosis. Strangulation accounts for almost half of all deaths due to SBO and increases the morbidity rate significantly. Early surgical intervention is essential to avoid morbidity and poor outcomes. Strangulated obstruction typically presents with continuous (as opposed to colicky) abdominal pain, signs of systemic inflammatory response syndrome (fever, tachycardia, leukocytosis), peritoneal signs, acidosis, absence of bowel sounds, localized abdominal tenderness, and occasionally a painful mass or blood in the stool. Unfortunately, these signs are not particularly sensitive or specific for early strangulation, but they should alert one to the possibility of strangulation and the need for early surgical intervention.

A closed loop obstruction is a particularly dangerous form of bowel obstruction in which a segment of intestine is obstructed both proximally and distally. Gas and fluid accumulates within this segment of bowel and cannot escape. This progresses rapidly to strangulation with risk of ischemia and perforation.

In SBO, gas and fluid accumulate proximal to the site of obstruction, causing dilation of the bowel followed by increased motility in attempt to overcome the obstruction. The dilation results in progressive nausea and colicky, visceral pain with subsequent episodes of emesis. The increased peristaltic activity that attempts to overcome the obstruction in the early course of SBO causes the characteristic colicky pain. Initially, bowel sounds are increased and have a high-pitched, tinkling sound, but as the bowel distends and intramural pressures rise, intestinal motility decreases and bowel sounds diminish. Failure to pass gas or stool per rectum is typically due to a complete mechanical obstruction of the small intestine.

The most common cause of SBO in industrialized countries is intra-abdominal adhesions related to prior abdominal surgery. Historically, hernias were responsible for more than half of mechanical SBOs, but with routine elective repair, the incidence of hernias causing SBO has drastically decreased.

Adhesions after pelvic operations are responsible for more than 60 % of all SBO in the USA, with appendectomy being the most common cause, followed by colorectal resection, and then gynecologic procedures. Inflammatory processes such as appendicitis and diverticulitis create adhesions as the omentum and surrounding intestinal loops attempt to contain the source of inflammation and infection. Disruption of the visceral and parietal peritoneum with pelvic operations leads to adhesions, especially in the dependent positions where the loops of small intestine rest. Another possible explanation for this is that the bowel is more mobile in the pelvis than in the upper abdomen, and thus more likely to produce an obstructing torsion.