An Approach to Bowel Obstruction
Summary
This article attempts to summarize the approach to bowel obstruction.
Basics
Bowel obstruction refers to the blockage of the flow of gastrointestinal content, which may be a solid, a liquid, or a gas. Several terminologies and classifications are used when referring to bowel obstructions. Bowel obstruction, also called intestinal obstruction, may be either complete or incomplete. Complete bowel obstruction usually occurs when there is no flow of content, resulting in obstipation. An obstipation is a severe form of bowel obstruction in which the patient is unable to pass fluids AND gases (flatus).
Classification
- Anatomic
- Small Bowel Obstruction
- Large Bowel Obstruction
- Simple vs Complicated (Strangulated, Perforation, Closed Loop obstruction)
- Course: Acute vs Chronic
- Cause
- Dynamic Bowel Obstruction (Mechanical): The bowel obstruction is caused by a mechanical cause; therefore, the bowel is capable of peristalsis. There is also increased peristalsis proximal to the obstruction.
- Adynamic Bowel Obstruction (Non-Mechanical): The bowel obstruction is caused by a non-mechanical cause; the peristalsis in this type of bowel obstruction is usually absent or it may be present in a manner in which it is inadequate .
Pathophysiology
In the case of mechanical bowel obstruction, there is a blockage secondary due to a particular pathology. This blockage prevents the normal flow of gastrointestinal content from continuing. Peristalsis proximal to the obstruction still occurs. Over some time, the proximal bowel becomes dilated. This proximal dilatation then compromises the blood flow (venous first, then followed by arterial) to the bowel. This compromised segment may also complicate by necrosis. Depending on the pathology, the bowel loop may have also been strangulated. This condition may result in a bowel that is necrotic and susceptible to perforation.
One should also remember that while this process occurs, the intestinal content is accumulating proximal to the obstruction. There is a general decrease in fluid absorption and an increase of fluid loss into the 3rd space. The bowel obstruction may also present with vomiting. These mechanisms are very important because they will result in an electrolyte imbalance. The other concept one must keep in mind is that there will also be an accumulation of bacteria, such as E.coli, Klebsiella, and another microorganism (especially anaerobes). These micro-organisms will result in a septic patient.
In the case of non-mechanical bowel obstruction, there is a particular reason why the bowel loses its ability to have normal peristalsis. The causes are many and some are stated under the differentials.
Presentation
Symptoms
- Vomiting: If the bowel obstruction is at a higher level, for instance at the duodenum, the patient will present with vomiting very early in the disease. However, if the obstruction is lower, such as in the colon, vomiting will not be an early symptom. Lower obstructions will result in feculent vomitus.
- Abdominal Distension: The degree of distension will be greater if there is a lower bowel obstruction.
- Constipation/Obstipation: Refers to the presence of difficulty in defecation. With distal/lower bowel obstruction the patient may complain of a longstanding history of bowel habit changes. In patients who develop a paralytic ileus, there will be no passage of flatus AND no passage of stools.
Physical Exam
On the physical examination, there will be many clinical findings that are important to keep a look out for. Depending on the pathology of the patient, these findings will vary. However, because of the vomiting and abnormal bowel function, these patients may present with signs of dehydration. The patient may also have pallor, a sign suggestive of anemia, and depending on the differentials may suggest gastrointestinal bleeding or anemia due to chronic disease. Lymphadenopathy will raise the suspicion of malignancy or an infectious cause. The patient may also have general signs that are suggestive of sepsis such as pyrexic, tachycardia, tachypnea, and low blood pressure (also secondary to fluid loss).
On the abdomen, one would notice a distended abdomen at a first glance. It is very important to note if the abdomen has any scars as this would suggest the possibility of adhesions secondary to a previous operation, resulting in bowel obstruction (adhesive bowel obstruction). The literature also mentions that in a mechanical bowel obstruction one may also visualize movements secondary to massive peristalsis. On palpation, one may need to discover and need to apply an approach to an abdominal mass. If the bowel obstruction becomes complicated, the signs suggestive of peritonitis (guarding, rigidity, rebound tenderness, absent bowel sounds) may also be present. On percussion, the distended bowel loops will result in a resonant sound. As discussed already, in a mechanical bowel obstruction there may be increased peristalsis and this will be evident with increased bowel sounds on auscultation. In a paralytic ileus, there will be absent bowel sounds. Keep in mind to examine the hernia orifices for signs suggestive of a hernia.
An abdominal examination is not complete without a per rectal examination. In bowel obstruction, one would expect an empty rectum. However, one may find signs suggestive of fecal impaction or malignancy as well (read about Blumer’s Shelf sign). Proctoscopy may also be used to assist in the completion of the examination.
Differentials
Keep in mind that small bowel obstruction [SBO] (80%) is more common than a large bowel obstruction [LBO] (20%). The most common cause of SBO is adhesion while for LBO is malignancy, followed by volvulus. There are several ways to come up with differentials, however this is the one I feel most comfortable with.
| Dynamic (Mechanical) | Adynamic (Non-Mechanical) |
|---|---|
-Meconium -Foreign body (infestations with parasites) -Bezoars -Gall stones -Inflammatory strictures – Chrons, diverticulitis -Malignant strictures -hernias -volvulus (midgut and sigmoid) -intussusception -Pelvic inflammatory disease |
>Pain >Peritonitis >Post-traumatic >Post-operative >Pills (Medication) >Potassium low >Peritoneal blood (hemoperitoneum) -Mesenteric vascular occlusion -Pseudo-obstruction (Ogilvie’s syndrome) -Toxic Megacolon |
Investigations
- Bloods
- Formal Bloods:
- Urea and Electroyltes, Creatinine – Electrolyte imbalance
- Full Blood Count – Increased WCC in infective pathology, rule out an anemia
- Blood Gas: Patient may have findings such as a metabolic acidosis secondary to fluid loss, a metabolic alkalosis if there is too much vomiting, elevated lactate, low Hb
- Formal Bloods:
- Imaging
- X-Rays
- Chest X-Ray: Erect Chest X-Ray to view any air under the diaphragm (complicated bowel obstruction – perforation)
- Abdominal X-Ray: Erect and Supine. This type of X-ray is diagnostic, and will help you identify several characteristics of bowel obstruction: Dilated bowel loops, air-fluid levels (seen in erect x-rays), absence of air in the rectum (complete bowel obstruction).
- X-Rays
| X-Ray Findings | |
|---|---|
| Large Bowel Obstruction | Small Bowel Obstruction |
|
- Dilated bowel loops are located peripherally - Presence of Haustration - Diameter follows the 3-6-9 rule (>6cm) |
- Dilated bowel loops are located more central - Jejunum (valvulae conniventes), ileum (featureless) - Diameter follows the 3-6-9 rule (>3cm) |
- Imaging (Continued)
- Abdominal Ultrasound: This is usually not useful in bowel obstruction. Unless there is a mass that you’d want to investigate further. Remember that is user dependent.
- CT-Abdomen: This investigation is very useful because it is much more sensitive and specific than an abdominal ultrasound.
- Endoscopy: G-Scope or a C-scope may assist with identifying a pathology, as well as the decompression of an obstruction.
Management
Emergency Management
- Insert a IV line and provide the patient with fluids (Ringer’s Lactate): Remember that these patients may also have an electrolyte imbalance and this needs to be corrected.
- Insert a urinary catheter: To monitor the urine output. One should maintain a target of ≥ 1ml/kg/hr.
- Medications (ideally IV/IM, not PO):
- Antibiotics to cover gram-negative and anaerobic organisms.
- Analgesia (Opiods such as Morphine)
- Antiemetics (Promethazine, Ondasetron)
- Insert an nasogastric tube: This helps with decompression of the stomach and the proximal bowel. It will also reduce the risk of vomiting and aspiration.
- Inform consent: Provide the patient with the necessary information and ask for consent for any procedure that requires their consent.
- Perform basic investigations: Formal Bloods, Blood Gas, and X-Rays. Further imagining with a CT scan may be required.
- Decision: Decide whether the patient needs immediate surgery or not. The following are indications for surgical management.
- Findings suggestive of peritonitis
- Findings suggestive of bowel ischemia/strangulation
- Findings that suggest a complete or a closed loop bowel obstruction (the bowel is obstructed along two points, resulting in a closed loop).
- If the patient requires surgical intervention then we should attempt to correct any major electrolyte imbalances as best as possible. Ideally, the patient’s hemodynamic status should also be optimized. Otherwise, if the patient is not for surgical intervention then we should treat the patient conservatively.
Non-Surgical (Continue Stabilizing the patient)
- Continue the administration of fluids and correction of electrolyte imbalances.
- Continue with observation of the patient every 1-2 hours
- Continue monitoring the patient for signs of complications, such as perforation, sepsis
- If the patient has not been done specific investigations such as CT-Scans then this can be done at this stage.
- Continue monitoring the patient for 24-72 hours. If the condition has not improved within 24-48 hours or the patient’s condition deteriorates then on should consider surgical intervention.
Surgical
- At this time, it is likely that the pathology is still unknown and the surgical procedure that one would perform is an “Explorative Laparotomy”.
- The surgical procedure aims to treat the underlying pathology, commonly: Adhesions, Hernias, and Tumors. If the operation is done and the patient has a particular complication such as a necrotic bowel, this bowel will need to be resected. Other procedures will follow this depending on the pathology such as anastomosis of the bowel loops, or formation of a stoma. During the consent, these procedures need to be included in the initial discussion.
Complications
| Due to Bowel Obstruction | Due to the Surgery |
|---|---|
|
1. Perforation 2. Peritonitis 3. Shock: Hypovolemic, Septic 4. Renal 5. ARDS |
1. Abscess – Pelvic, Sub-phrenic 2. Fistulas – Biliary, Fecal 3. Post operative adhesions, bands 4. Incisional hernias 5. Burst Abdomen |
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