QuestionSBA
QuestionChoice
This would likely present with signs of peritonitis; rebound tenderness, guarding and a rigid abdomen.
10015699
d
Bowel perforation
QuestionChoice
Whilst this could explain an absence of bowel movements post operatively, it would normally present with lower abdominal discomfort and no change in bowel sounds.
10015698
c
Faecal loading
QuestionChoice
Small bowel obstruction would likely present with more predominant nausea and vomiting. Bowel sounds are classically described as “tinkling” rather than absent.
10015697
b
Small bowel obstruction
QuestionChoice
In a post-operative patient with absent bowel sounds and a distended abdomen, ileus is most likely. This is a functional obstruction due to decreased bowel motility. Risk factors for it include manual handling of the bowel during surgery (more likely in open surgery) and certain pre-existing medical conditions, including heart failure.
10015696
a
Post-operative ileus
QuestionChoice
Whilst this could explain some of the symptoms, there would often be more severe pain than described in the scenario above. Bowel sounds are classically described as “tinkling” rather than absent.
10015700
e
Large bowel obstruction
Concept
Chapter
# Summary 

Small bowel obstruction is a mechanical impediment in the small bowel leading to clinical symptoms such as bilious or faeculent vomiting, abdominal pain, and distension. Key causes include adhesions, intra-abdominal hernias, Crohn's disease, malignancy, and foreign body ingestion, among others. Noteworthy signs and symptoms include abdominal pain with distension, vomiting, failure to pass flatus or stool, and possible fever. Primary investigations include blood tests, abdominal and chest X-ray, CT abdomen and pelvis, and possibly a diagnostic laparotomy/laparoscopy. The management involves initial resuscitation, fluid and electrolyte correction, NG tube aspiration for decompression, potential gastrografin administration, and surgery if conservative measures fail.

# Definition

Small bowel obstruction (SBO) is a mechanical disruption in the small bowel, leading to significant clinical symptoms such as bilious or faeculent vomiting, abdominal pain and distension, and complete constipation.

# Epidemiology

SBO is a common clinical issue seen in emergency departments worldwide. Adhesions following abdominal surgery are the leading cause, responsible for approximately 60-70% of all cases in adults. Intra-abdominal hernias, Crohn's disease, malignancy, and foreign body ingestion are other common causes. In children, intussusception, volvulus, and intestinal atresia are more common causes of SBO. The incidence of SBO tends to increase with age due to increasing rates of surgery, malignancies, and other predisposing conditions.

# Aetiology

## Factors outside the bowel

-   Adhesions
    
    -   Most common cause in the Western world
    -   Prior intra-abdominal surgeries increase the risk of adhesion development. The larger the operation, the higher the likelihood of adhesion formation.
-   Intra-abdominal hernia
    
    -   Incarcerated hernias can precipitate acute obstruction

## Factors relating to the bowel wall

-   Crohn's disease - stricturing (rather than fistulating) disease is what specifically causes SBO
-   Appendicitis

## Factors relating to inside the bowel

-   Malignancy
-   Foreign body ingestion
-   Gallstone ileus

## Diseases causing small bowel obstruction in children

-   Intussusception
-   Volvulus
-   Intestinal atresia
-   Appendicitis

# Signs and Symptoms

SBO typically presents with the following:

-   Abdominal pain with distension (Initially colicky pain that becomes continuous)
-   Bloating and vomiting (often bilious)
-   Failure to pass flatus or stool
-   History of abdominal/gynaecological surgery or hernia
-   Tympanic, high-pitched bowel sounds on examination
-   An empty rectum on examination in complete bowel obstruction

Patients may also present with fever and significant fluid depletion. Peritonitis indicates severe bowel obstruction with developing complications (e.g. perforation, especially in closed-loop obstructions), necessitating urgent surgical intervention.

Simple or partial SBO may still result in passing some flatus/stool and present with a mild temperature.

If untreated, SBO can progress to ischaemic or necrotic bowel, leading to perforation.


# Differential Diagnosis

-   **Adhesions**: Pain, distention, bilious vomiting, constipation, history of previous surgeries.
-   **Intra-abdominal hernia**: Pain, distention, inability to pass flatus or stool, a palpable mass in the abdomen.
-   **Crohn's Disease**: Abdominal pain, diarrhea, weight loss, fatigue, fever.
-   **Malignancy**: Abdominal pain, weight loss, altered bowel habits, possible presence of blood in the stool.
-   **Foreign body ingestion**: Abdominal pain, possible history of foreign body ingestion, altered bowel habits.
-   **Gallstone ileus**: Abdominal pain, distention, bilious vomiting, history of gallstones or cholecystitis.
-   **Paralytic ileus**: Abdominal pain, distension and absent bowel sounds, often a post-operative complication

# Investigations


In a patient presenting with potential intestinal obstruction, peritonitis is a worrisome sign and the consideration to transfer to theatre must be considered.

Basic investigations include:

-   Basic blood tests including FBC, U+Es, and lactate
    -   FBC (To identify leukocytosis or anaemia)
    -   U+Es (To detect organ dysfunction or signs of hypovolaemia)
    -   Lactate (To establish if there is bowel ischaemia or necrosis, though it can be falsely low due to liver metabolism)
    -   Amylase (To rule out acute abdomen conditions)
-   Abdominal and chest X-ray
    -   Performed in an upright position to detect pneumoperitoneum
    -   Absence of air in the rectum can indicate complete obstruction

  
| Feature                        | Small Bowel Obstruction (SBO) | Large Bowel Obstruction (LBO) |
|--------------------------------|-------------------------------|------------------------------|
| **Bowel Wall Thickness**       | May be mildly thickened       | Often markedly thickened      |
| **Valvulae Conniventes**       | May be seen (small intestine) | Not typically seen (large intestine) |
| **Gas Patterns**               | Central or diffuse gas pattern | Peripheral or haustral pattern |
| **Luminal Air Fluid Levels**   | Commonly seen                 | Less frequently seen         |
| **Stool in Colon**             | Minimal or absent             | Often present                |
| **"Bird's Beak" Sign**         | Absent                        | May be seen in LBO (sigmoid volvulus) |
| **Peritoneal Fluid**           | May be seen due to irritation | Less common unless perforation occurs |


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In the absence of peritonitis and given the patient's stable condition, the following investigations may be performed:

-   CT abdomen and pelvis
    -   Best diagnostic test for identifying the underlying cause, the site of obstruction, and whether it's a partial vs. complete obstruction
-   Small bowel contrast study using gastrograffin
    -   Used as a therapeutic measure in partial SBO
    -   Presence of contrast in rectum 24 hours after ingestion signifies a resolving partial SBO, reducing the need for surgery
-   MRI abdomen
    -   Comparable to CT scan, it is useful in young patients to avoid exposure to ionising radiation
-   US abdomen
    -   Not as reliable as CT, but can be used in children to avoid ionising radiation exposure
-   Diagnostic laparotomy/laparoscopy
    -   Used to distinguish between partial and complete obstruction if imaging doesn't provide clear evidence

# Management

-   Begin with resuscitation protocols (ABCDE)
-   Correct fluid and electrolyte imbalances to reduce operative risk before surgery for obstruction
-   Fluid resuscitation and NG tube to aspirate content for decompression ('Drip and suck')
-   Gastrografin can be administered as both a diagnostic and therapeutic measure in cases of partial obstruction. The presence of gastrografin in the rectum 24 hours post-administration indicates a resolving partial SBO, reducing the need for surgical intervention.
-   If conservative measures fail, consider surgery. The type of surgery depends on the cause and may include:
    -   Adhesionolysis
    -   Bowel resection
    -   Closure of hernias
    -   Tumour resection

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Dilated loops of small bowel seen on abdominal x-ray.
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Free air under the right hemidiaphragm.
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Free air under the right hemidiaphragm.
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A 67 year old woman has not opened her bowels 5 days after an emergency open splenectomy. On examination, she has abdominal distension, mild generalised tenderness with no guarding and absent bowel sounds. She has a past medical history of heart failure.

What is the most likely diagnosis?
a