Small bowel obstruction: Clinical sciences

Small bowel obstruction, or SBO, occurs when intraluminal contents like chyme and gas are unable to pass through the small intestine due to a blockage. Blockages can be mechanical, which is a physical obstruction, such as adhesion, hernia, or tumor; or functional, which is caused by reduced or absent peristalsis, also called an ileus. Some SBOs resolve with conservative management, but others may require surgical intervention.

When approaching a patient with signs and symptoms suggestive of small bowel obstruction, first perform an ABCDE assessment to determine if the patient is stable or unstable.

Let’s start with what to do if the patient is unstable.

Start acute management immediately to stabilize their airway, breathing, and circulation. This means that you might need to intubate the patient, obtain IV access, administer fluids, and monitor their vitals before continuing with your assessment. Your next step is to obtain a focused history and physical exam, as well as labs. Labs will include CBC, CMP, and lactate.

Now, history might reveal bloating, abdominal pain, obstipation, and nausea and vomiting.

Here’s a high-yield fact! You can suspect some causes of SBO based on history. For example, ask your patients about any prior abdominal surgeries or known hernias. Both are common causes of mechanical SBO.

Okay, let’s move on to the physical examination. The exam may reveal tachycardia and hypotension, as well as abdominal distension and signs of peritonitis, like diffuse tenderness to palpation, rebound pain, and guarding. Remember to look for surgical scars and hernias during your exam! An incarcerated ventral or inguinal hernia often presents as a tender palpable mass, sometimes with overlying inflammatory skin changes. Finally, labs may show leukocytosis, as well as lactic acidosis from bowel ischemia. If you see these signs and symptoms, suspect SBO.

The next step is to start supportive care. You should initiate IV fluid resuscitation, electrolyte replacement, broad-spectrum antibiotics, and bowel rest, as well as nasogastric tube placement for bowel decompression if the patient has nausea and vomiting. Once you initiate supportive care, order an abdominal x-ray.

Alright, let’s discuss abdominal X-ray findings that indicate SBO. Findings may include small bowel dilatation with distended loops and air-fluid levels; as well as pneumoperitoneum, meaning that perforation has already occurred. When you encounter any of these signs, you should quickly think of complicated small bowel obstruction and obtain surgical consultation for emergent laparotomy.

Here’s a clinical pearl! The surgical team may order a CT scan to confirm the diagnosis. If there’s complicated SBO, CT may typically show signs of bowel ischemia, such as pneumatosis and portal venous gas. Additionally, CT helps reveal a transition point, where the small bowel is distended to the point of obstruction but collapsed beyond it; and absence of gas in the colon and rectum. Having two or more transition points is called a closed-loop obstruction, and this can quickly progress to bowel ischemia and perforation. Common causes of closed-loop obstruction include small bowel volvulus, adhesions, and hernias.

Okay, now that the unstable patients are taken care of, let’s talk about stable patients.

Keep in mind that patients who present as stable might develop complicated SBO and become unstable if not promptly treated. So again, start with your ABCDE assessment. Your next step is to obtain a focused history and physical exam, as well as labs like CBC, CMP, and lactate. Stable patients typically report bloating, abdominal pain, and obstipation, often with nausea and vomiting. Again, remember to ask about prior abdominal surgeries and hernias.

On the other hand, the physical exam often reveals abdominal distension, tenderness to palpation, and sometimes high-pitched hyperactive bowel sounds on auscultation. Note any surgical scars or hernias. Finally, labs might show leukocytosis or lactic acidosis.

At this point, you can suspect SBO, so start supportive care. As before, supportive care includes IV fluid resuscitation, electrolyte replacement, bowel rest, broad-spectrum antibiotics, and nasogastric tube placement for bowel decompression if the patient is having nausea and vomiting.

Once the supportive care is initiated, order an abdominal and pelvic CT with oral and IV contrast to diagnose the condition and identify the underlying cause. Alright, let’s consider possible CT findings of mechanical SBO.

Once again, you might encounter small bowel dilatation with distended loops and air-fluid levels, as well as evidence of one or more transition points, and an absence of gas in the colon and rectum.