Bowel Obstruction

Acute bowel obstruction is a common surgical presentation. Delay in identification of bowel obstruction can lead to decreased bowel perfusion, ischaemia, necrosis and perforation. In one study, inclusive of both large and small bowel obstruction, 30-day mortality was as high as 36.6% with in hospital mortality 6.6% and a mean survival of 173 days from hospital discharge (1).


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Miss Nicola Eardley is a Consultant Colorectal and General Surgeon at the Countess of Chester Hospital, UK. We discuss the typical symptoms that particularly define small bowel obstruction, investigations and their interpretation and the important management steps to undertake for general bowel obstruction (both small and large).


Small vs Large


Symptoms differ between small and large bowel obstruction and relate to the differences in the pathologies.

With small bowel obstruction, colicky pain will predominate (2). This is a pain that is episodic and spasmodic in nature.  The pain is more likely to be peri-umbilical or upper abdominal in origin. Vomiting will be an early feature and likely to be feculent. The most common presenting symptoms are (2):

  • Absence of passing faeces (80%) or flatus (90%)
  • Vomiting (78%)
  • Colicky abdominal pain (74%)
  • Abdominal distension (66%)

The absence of distension may represent a closed loop obstruction of a short piece of small bowel or high obstruction. In this setting, there may still be upstream obstruction and significant amounts of pain and vomiting.

Large bowel obstruction has a more insidious onset of pain when associated with a colonic tumour whereas a volvulus would give acute pain (3). Distension is an earlier feature and significant pain should be concerning for a closed loop obstruction with imminent perforation. Similarly, tenderness over the right iliac fossa in the presence of large bowel obstruction may be indicative of imminent caecal perforation.

A history of constant pain, increasing pain or pain that appears out of proportion represents potential ischaemia and possible need for urgent surgery.



The common underlying causes can be considered as intrinsic or extrinsic (4):


  • Adhesions
  • Hernia (both internal and external)
  • Compression by abdominopelvic masses (primary tumours and metastases)
  • Volvulus

Remember, congenital band adhesions can be present and causes obstruction in the virgin abdomen. A lack of previous operations does not make obstruction implausible. Internal hernias will only be detected on CT imaging but it is important to examine for external hernias, especially in the groins for femoral hernias.


  • Inflammatory causes (diverticulitis, Crohn’s disease, ulcerative colitis)
  • Primary bowel cancer (consider a primary caecal tumour obstructing the ileo-caecal calve)
  • Radiation enteritis
  • Post surgical (Especially after gastric bypass)

More unusual causes include: gallstone ileus, bezoar, ingested foreign bodies, endometriosis, impacted medical devices (eg feeding tubes, cameras, stents). This list is not exhaustive and often regardless of the cause, the definitive management is going to be undertaken by the surgical team responsible for the patient.

A particular mention needs to be of Richters type hernias. These are hernias where a portion of the anti-mesenteric bowel wall protrudes through a defect in the abdominal wall, commonly as a femoral hernia. The lumen of the bowel may be narrowed but not completely obstructed. The patient will have significant pain as these easily become strangulated. If not identified they can progress to bowel necrosis and perforation (5).


Investigating Bowel Obstruction

As with any acutely unwell patient, the initial approach should be a structured ABCDE assessment.

Laboratory Studies

  • Full blood count
  • Urea and Electrolytes
  • Liver Function Tests
  • C-Reactive Protein
  • Amylase
  • Lactate
  • Coagulation screen (especially if emergency surgery is expected)
  • Blood Group and Screen (especially if emergency surgery is expected)


No blood test is going to diagnose bowel obstruction for you. The importance of blood tests, at least to me, is to highlight the possibility of complications being present and how unwell the patient may be which should prompt more aggressive treatment and escalation to seniors. In particular, we need to ask ourselves could there be ischaemia? This carries a much higher mortality of approximately 40% (6, 7).

The findings that should make you suspicious for ischaemia include:

  • Pyrexia
  • Haemodynamic compromise
  • Significant, constant pain
  • Peritonitis
  • Leucocytosis
  • Raised CRP
  • Raised Amylase
  • Metabolic acidosis (whether decreased pH or Base Excess)
  • Raised lactate

In the case of lactate, multiple studies have sought to evaluate it’s diagnostic performance. The end result is that lactate is influenced by multiple variables. A systematic review found a positive likelihood ratio of 2.64 and negative likelihood ratio of 0.23 with no specific cut off value (8). Whilst these numbers suggest some usefulness, they also reveal that a low or normal lactate does not rule out bowel ischaemia. Indeed, two studies have sought to evaluate lactate’s diagnostic accuracy and produced the results of a sensitivity of 90-100% but a specificity of only 42-87% (6, 10). One study retrospectively investigated the lactate values preceding surgery and found they were higher immediately before surgery (7). Whilst this does not explore the decision making process, it reinforces that a worsening patient whether clinically or biochemically needs urgent attention and action.

Imaging Studies

Traditional imaging studies undertaken initially include the Chest and Abdominal X-ray. Often, chest X-rays are ordered to investigate for perforation and look for air under the diaphragm. Abdominal films are ordered to diagnose bowel obstruction.

Both are imperfect but provide good, quick and low radiation methods for early diagnosis. In the case of the plain abdominal film, it has a reported sensitivity of 77% and specificity of 50% with an accuracy of 75% (10). The common signs to look for include:

  • Dilated loops of bowel with air-fluid levels. Air-fluid levels would only be seen on upright films and mostly, AXRs are performed supine. In this case we see the entirety of the bowel as air filled.
  • Bowel dilatation. The appearance is different for small and large bowel. Small bowel would tend to be more central, smaller in diameter with valvulae conniventes presented (simply put, lines that extend across the whole diameter). Large bowel is generally located more peripheral, is larger and possesses tinea coli (step wise lines that do not extend across the entire diameter).
  • Gasless abdomen. This causes issues sometimes and you may be tempted to describe it as a “non-specific pattern”. This may represent dilated bowel loops that are completely filled with fluid, therefore no gas is seen.


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The most accurate tool we have for diagnosing obstruction and it’s complications is CT with IV contrast. If you are a junior seeing these patients acutely, the bear in mind these patients are likely to have fluids losses and may have an AKI. As such, radiologists may be weary of giving contrast to these patients. If the diagnosis is critical and cannot wait for some rehydration then discuss with your seniors about the risk vs benefit of undertaking these procedures.

Does everyone need imaging?

Uncommonly, you may come across a cohort of patients, especially with small bowel obstruction, who are well known to the surgical team. They may have a classical history and previous attendances with the same issue and known to have recurrent obstruction. As Nicola describes, these people may just be managed expectantly and imaged only if there was suspicion of something more sinister at play. Having said this, rather than working on assumptions in these patients, discuss them with your seniors first.

There may be some patients who are simply too sick to wait for imaging. They may have clinical signs of obstruction and a dire clinical picture that necessitates surgery before imaging. In this situation your seniors should be involved with the patient from the beginning.

If you are worried about the patient or uncertain, discuss with the surgical seniors.

Initial Management

Initial management should be focussed on the immediate clinical problems you are faced with. There are specific areas to consider:


Patients with bowel obstruction will invariably have pain as a predominant symptom (2). Sometimes, you may encounter other professionals reluctant to give morphine in the context of bowel obstruction. The justification is usually that morphine will decrease gut motility and so worsen obstructive symptoms. Despite searching, I cannot find anything that either supports or refutes the use of opiates in the setting of acute intestinal obstruction. Certainly, as Nicola mentions, if the patient is in pain then they need pain relief. You can use alternatives such as IV paracetamol and NSAIDs such and ketorolac but if they need morphine, they need morphine.

If you are finding yourself administering morphine to any patient then you need to consider is the underlying problem severe and if so does it need more urgent and aggressive management?


IV Fluids

Patients with bowel obstruction can have significant fluid losses due to “third space losses”. Third space losses essentially mean the sequestration of fluid into the intestinal wall and lumen and other spaces. We cannot quantify these losses accurately. Patients will often be clinically dry and may have biochemical evidence such as an AKI. When undergoing anaesthetic induction, if these patients are inadequately resuscitated, cardiovascular collapse can occur.

Patients with bowel obstruction need fluid resuscitation, however bear in mind that large volumes of fluids administered to patient who undergo major bowel surgery can have a negative impact on outcomes (11).

IV fluids need to be titrated to effect against monitoring available by reviewing the patient. No two patients will need the same regime.

NG tube and Catheter

Traditional teaching is that nasogastric decompression is needed for patients with acute bowel obstruction. Anecdotally, NG tubes in patients with significant vomiting and distension can provide a lot of relief in the acute period. To some extent, they can help quantify the amount of fluid sequestered into the bowel. However, this will always be an under-estimate. If you do place a NG tube, it should be aspirated and then left on free drainage. It is a procedure that is uncomfortable for patients but the benefits should be clearly explained to them. At the time of anaesthetic induction, NG tubes will often be suctioned to fully empty the stomach to avoid regurgitation in this period.

NG tubes are associated with risks. A patient with a NG tube may be more at risk of pneumonia and an increased length of stay (12, 13). However, the patient will likely not want to continue being in pain and vomiting so there is a risk vs benefit to be considered. NG tubes can be removed once they are no longer necessary but they do form part of the standard treatment for obstruction and should not be delegated to nursing staff unless they are capable of doing this.

If the patient does refuse then this should be clearly documented in the notes.


Urinary catheters are useful in the setting of bowel obstruction. Remember, these patients are often hypovolaemic and need fluid replacement and the response to this fluid can be measured by the urine output. A falling urine output may be representative of a worsening patient or even abdominal compartment syndrome.

Urine output may be a poor surrogate for cardiac output but it can help guide fluid therapy by showing us the response when fluid is given. A falling or no urine output is a worrying sign.

VTE Prophylaxis

Patients with bowel obstruction are high risk for venous thromboembolic events (VTE). They are often older patients with comorbidities who are set to spend a prolonged period in bed post-operatively. Unless contraindicated, these patients should have TED stockings applied and receive low molecular weight heparin. Try to take into account timings for surgery with LMWH. Depending on the agent used, it might prevent an epidural being used as part of the anaesthetic technique for up to 24 hours. If in doubt, ask a surgical or anaesthetic senior.


Even with NG tubes, patients may continue to feel nauseated and require treatment. Agents such as metoclopramide should be avoided as these increase intestinal motility and may worsen the patient’s symptoms. Ondansetron is a commonly used alternative.


Antibiotics do not need to be routinely given to patients with simple bowel obstruction. If there is any concern about underlying sepsis or ischaemia then antibiotics should be given. Your own hospital will have a preferred regime for these patients and you should consult their antibiotic policies. Typical agents would be cefuroxime or tazobactam/piperacillin and metronidazole.


What if the investigations are normal?

As we have discussed already, the investigation we use initially are imperfect but very useful.

Rarely, you will come across patients without distension but with other symptoms of obstruction and normal initial investigations. These are the patients that your clinical judgement will be what guides the treatment. I have treated patients with a small closed loop obstruction or very proximal high small bowel obstruction. These patients have significant pain and other symptoms of small bowel obstruction but lack the classical distension and plain X-ray findings and the diagnosis will be made by CT.


Significance of VTE

In a large retrospective review that was investigating risk factors for VTE, 183000 patients undergoing vascular and general surgery were analysed (14). Of this cohort, 0.63% of patients developed VTE and nearly a quarter of these were emergency cases. Within the population studied specifically focussed on abdominal surgery 0.93% of patients developed VTE. Those patients who were found to have VTE had a 11.19% mortality compared to 2.54%. Whilst this is a retrospective review looking at data from another study, this association is quite startling. It doesn’t give any details about VTE prophylaxis prescribing in the cohort studied however so it is difficult to generalise to our patients in the UK.

That may seem a bit data heavy, but the point is:

Venous thromboembolism is an uncommon, preventable complication of surgery that potentially impacts negatively on patient outcomes.



Acute bowel obstruction is a common presentation to surgical teams. It carries significant morbidity and mortality especially when associated with ischaemia. We should be actively suspecting ischaemia in these patients and escalating any concerns to senior members of the surgical team. Investigating patients is straightforward but the investigations need to be taken in context with the patient in front of us and negative results may not rule out obstruction. CT is the best imaging available acutely. Patients with bowel obstruction will often be dehydrated and fluid therapy needs titrating to response. NG tubes do carry risks but are an important step in the management of bowel obstruction. VTE prophylaxis is a simple but important intervention to undertake to prevent potentially significant mortality within this group of patients.


Thank you to Miss Nicola Eardley for her time and help with producing this. As always, we encourage you to discuss what you hear and read with your seniors and colleagues, especially if it involves a change in practice. Please read the underlying evidence in order to appraise it for yourself.


Speak soon,




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