Bowel Obstruction

Author: Stephen Feltbower / Editor: Janet Skinner / Codes: CAP1, CAP2, HAP1, PAP1, ACCS LO 2, SLO1, SuC12, SuC4, SuP1, SuP2, SuP6 / Published: 08/11/2010

Intestinal obstruction is an important cause of the acute abdomen, accounting for up to 5% of emergency admissions to surgical services. Intestinal obstruction can be classified in several different ways, most traditionally into small and large bowel obstruction. Mortality varies widely according to cause and any associated complications, being 100% in patients with untreated strangulated obstructions1. Morbidity and mortality are particularly high in patients who are managed incorrectly or in whom the diagnosis is delayed,2.

Learning Bite

Bowel obstruction carries a high morbidity and mortality if managed incorrectly.


Small / Large Bowel
Acute / Subacute / Acute-on-chronic / Chronic
Mechanical / Functional
Simple / Strangulated
Partial / Complete


The causes of intestinal obstruction can be broadly divided into mechanical or functional categories, and further subdivided in the following table2:


INTRINSIC (intramural) EXTRINSIC (extramural) LUMINAL (intraluminal)
Congenital atresia
Inflammatory strictures

  • Crohns disease
  • Tuberculosis
  • Diverticular disease


  • Benign
  • Malignant

Radiation stricture
Ischaemic stricture

Congenital bands
Inflammatory masses

  • Benign
  • Malignant
Foreign bodies



  • Hypokalaemia
  • Hyponatraemia
  • Hypothermia
  • Hypoxia
  • Diabetic ketoacidosis
  • Uraemia
  • Drugs (eg anticholinergics)
  • General anaesthesia
  • Dehydration
  • Sepsis (acute pancreatits)
  • Retroperitoneal malignancy (Ogilvies syndrome)
  • Trauma (head injury, spinal injury, pelvic surgery)

  • Intra-abdominal infection / peritonitis
  • Strongyloides

Postoperative (ileus)
Vascular (mesenteric ischaemia)

The most common causes of bowel obstruction are:

  • Small bowel adhesions (60% in UK), hernias, intussusception (paediatric group)
  • Large bowel malignancy (developed countries), volvulus (developing countries)
  • Functional (also referred to as paralytic) obstruction is relatively rare as a presentation to the emergency department.3

In one prospective observational study of 150 consecutive adult patients admitted with acute mechanical bowel obstruction, 114 (76%) presented with small bowel and 36 (24%) with large bowel obstruction. Adhesions (64.8%), incarcerated hernias (14.8%) and large bowel cancer (13.4%) were the most frequent causes of obstruction.4

Learning Bite

Adhesions are the commonest cause of mechanical bowel obstruction.

Basic Science & Pathophysiology

The small bowel bowel extends from the pylorus to the ileocaecal valve and ranges in length from 3 to 9 metres. The diameter of the gut lumen narrows progressively from the duodenojejunal flexure to the ileocaecal valve. The large bowel extends from the ileocaecal valve to the rectum and anus. If the ileocaecal valve remains competent in the presence of colonic obstruction, increasing pressure within the colon may result in perforation.2

Innervation of the intestine is via the parasympathetic and sympathetic nervous systems which form a myenteric plexus. This plexus controls orderly, propulsive contractions of the muscular layers of the gut wall. The sympathetic nervous system mediates the sensation of visceral pain (typically poorly localised, periumbilical and colicky in nature) experienced when the gut contracts against an obstruction.

Intestinal obstruction refers to any form of impedance to the normal passage of bowel content through the small or large bowel. As such, universal findings irrespective of aetiology can be demonstrated in the flow diagram below.

Universal findings of intestinal obstruction5

Screen Shot 2014-11-26 at 15.38.20

Fluid losses are generally greater the more proximal the obstruction. This is because fluids secreted by the upper gastrointestinal tract fail to reach the absorptive areas of the distal jejunum and ileum. Sequestration causes tissue injury, inflammation and capillary leak, manifest as local oedema at the site of injury.2 Such third-space losses can be large and frequently under-estimated, particularly if the obstruction is prolonged.

Learning Bite

Fluid resuscitation is frequently under-estimated in patients with small bowel obstruction.

Adhesions are thought to result from a reduction in peritoneal plasminogen-activating factor (PAA), which in turn leads to a failure to break down the postoperative fibrinous adhesions that follow all intra-abdominal operations. Drying and abrasion of the peritoneum as well as foreign substances such as talc in surgical gloves increase the reduction in PAA, increasing the future risk of adhesion formation.6

Small bowel can become trapped in a pre-existing hernia, causing obstruction. Hernias can be classified in the following table:

Indirect inguinal hernia Bowel passes through inguinal canal via a congenital weakness of the internal inguinal ring most common
Direct inguinal hernia Hernia exits abdominal cavity directly through the deep layers of the abdominal wall uncommon
Femoral hernia Abdominal contents pass through femoral canal just below inguinal ligament rare

Inguinal hernias are the most common type of hernia in both men and women, the indirect type accounting for 2/3 of cases. Almost all femoral hernias occur in women because of the wider bone structure of the female pelvis; however inguinal hernias are still more common in women than femoral hernias.[7,8]

Functional obstruction results from atony of the intestine and loss of normal peristalsis. Atony of the bowel can be localised to a particular segment or generalised throughout the entire bowel. Localised atony is thought to result from an abnormality in the myenteric plexus of the bowel wall, whereas more generalised atony probably results from an imbalance in autonomic nerve supply, although there is little direct evidence for this.[9,10]Different terms are often used to describe functional obstruction of the small or large bowel: paralytic ileus and pseudo-obstruction respectively.2


Initial assessment of the patient should involve concomitant history taking with prompt identification of the shocked patient. Generic treatment incorporating analgesia and fluid resuscitation should be performed alongside the initial history and examination.

Classic symptoms of intestinal obstruction are colicky abdominal pain, abdominal distension, vomiting and constipation. Vomiting is a late feature with large bowel obstruction. The degree of distension depends on the level of obstruction; there may be very little distension with high small bowel obstruction in contrast to gross distension with low small bowel or large bowel obstruction.11 Ask specifically about any previous abdominal surgery and remember to pay particular attention to the12:

  • Reproductive, contraceptive and menstrual history
  • Possibility of pregnancy and its complications
  • Drug history, especially favoured remedies and alcohol consumption
  • Past medical history

Severe pain suggests strangulation and developing ischaemia in a closed loop of bowel.3

Learning Bite

Severe pain in bowel obstruction suggests complications such as ischaemia or perforation.


Begin with baseline observations looking for any physiological evidence of dehydration or shock. Adequately expose the patient to examine the abdomen meticulously, looking for surgical scars, peritonism, masses and not forgetting the hernial orifices.13 It is easy to miss a small femoral hernia in an obese patient.11 Bowel sounds may be high-pitched / tinkling or absent altogether. Careful attention should also be made to look for other causes of the acute abdomen, in particular a ruptured abdominal aortic aneurysm (AAA) or ectopic pregnancy.

A rectal examination must also be performed, perhaps demonstrating an empty rectum or obstructing mass, ideally once only by the clinician making the management decisions. In the same way repeated attempts to elicit rebound tenderness should not be made when evidence of peritonitis has already been established. 12

Many surgeons would advocate that rigid sigmoidoscopy should form part of a complete abdominal examination. An obstructing lesion may be visible and a sigmoid volvulus might be decompressed.2 However, rigid sigmoidoscopy is not generally performed in emergency departments in the UK.

One prospective observational study of 150 consecutive patients with acute mechanical bowel obstruction reported that absence of the passage of flatus (90%) and/or faeces (80.6%) was the most common presenting symptom with abdominal distension (65.3%) being the most common physical finding.4 A retrospective analysis of 70 consecutive patients presenting with a clinical diagnosis of intestinal obstruction concluded that the classical signs of intestinal obstruction (fever, tachycardia, leukocytosis and local tenderness) are poor indicators for compromised bowel.14 Bohner et al reported a prospective study to determine the value of the AXR in comparison with history and examination.15 The six variables with highest sensitivity for a diagnosis of bowel obstruction were a distended abdomen, increased bowel sounds, history of constipation, previous abdominal surgery, age over 50 years and vomiting.

Learning Bite

constipation and abdominal distension in the patient with a previous history of bowel surgery are strongly suggestive of intestinal obstruction.

Risk Stratification

With particular reference to large bowel obstruction caused by colorectal cancer, a large prospective study found that age over 65 years, higher ASA (American Society of Anaesthesiologists) grade, higher Dukes staging, and greater urgency of operative intervention were associated with increased mortality.16

Learning Bite

age >65, comorbidities, more advanced cancer and emergent surgery are indicators of poor prognosis in patients with large bowel obstruction

The differential diagnosis of the patient presenting with abdominal pain is especially wide. The most common causes in the UK population requiring admission to hospital are:2

Condition Approximate incidence (%)
Non-specific abdominal pain
Acute appendicitis
Acute cholecystitis & biliary colic
Peptic ulcer disease
Small bowel obstruction
Gynaecological disorders
Acute pancreatitis
Renal & ureteric colic
Malignant disease
Acute diverticulitis


  • Blood tests FBC, U+Es, LFTs, glucose, amylase, group and save. Clotting screen if septic or on anticoagulants
  • Plain film x-ray erect chest x-ray and supine abdominal x-ray
  • ECG
  • ABG if signs of sepsis or strangulated bowel
  • Urinalysis

Specific Imaging

  • CT
  • Small bowel follow-through
  • Water-soluble contrast enema

All patients being evaluated for small bowel obstruction should have abdominal x-rays first because of the fact that they are as sensitive as CT to differentiate obstruction from non-obstruction.13 17 Small bowel distension (>2.5cm in diameter) confirms the diagnosis, differentiated from the colon by the valvulae conniventes, which completely cross the bowel wall. The taeniae coli of the large bowel are incomplete across the bowel wall. The relatively central position of the small bowel and restriction in dilatation to 5cm also helps to distinguish small from large bowel on plain films.2 It should be noted that the use of the abdominal x-ray in the undifferentiated patient with acute abdominal pain is not recommended in the emergency department setting,17 with several studies showing that the abdominal x-ray rarely changes the management plan and is often used as a defensive screening investigation.18 19 20


Figure 2 abdominal x-ray showing small bowel obstruction


Figure 3 abdominal x-ray showing large bowel obstruction

The CT scan is the most useful in differentiating the specific cause and location of mechanical obstruction.5 21 22 It is the imaging modality of choice for the investigation of patients with inconclusive plain films for complete or high-grade small bowel obstruction13 23 and for patients with large bowel obstruction.24

A (small) prospective study comparing abdominal x-ray with ultrasound and CT in their ability to diagnose obstruction highlighted CT as the most sensitive (93%) and specific (100%) investigation.25 A retrospective study again comparing abdominal x-ray with CT found that abdominal x-ray had 69% sensitivity and 57% specificity, the main advantage of CT being its ability to diagnose the cause of the obstruction, which it did in 95% of true positives.26


Figure 4 CT abdomen showing small bowel obstruction


Figure 5 CT abdo/pelvis showing large bowel obstruction with apple core constricting lesion

A limitation of CT is its low sensitivity (<50%) in the detection of low-grade or partial small bowel obstruction. There is a variety of literature that suggests that contrast studies should be considered for patients who fail to improve after 48 hours of conservative management as a normal contrast study can rule out operative small bowel obstruction.13 Contrast studies (barium and water-soluble) are therefore rarely indicated in the initial acute setting of the emergency department.

Learning Bite

The abdominal x-ray is the initial investigation of choice in patients with suspected intestinal obstruction, followed by a CT scan for further evaluation and identification of the cause of the obstruction.

GENERAL emergency department management

  • Insert an IV cannula taking and sending blood as mentioned above)
  • Start an IVI of 0.9% Saline
  • O2 and fluid resuscitation if the patient is haemodynamically unstable
  • Move the patient to an appropriate area of the department and involve an ED senior in their management
  • Titrate IV analgesia (morphine) with an antiemetic (eg cyclizine)
  • Insert a naso-gastric tube and declare the patient nil by mouth (NBM)
  • Insert a urinary catheter
  • Consider more invasive monitoring if required for accurate fluid resuscitation (CVP and/or arterial line)
  • REFER TO THE SURGICAL TEAM (depending on local policies, this might be to a specific upper or lower GI team for suspected small and large bowel obstruction respectively).

Broad spectrum antibiotics are commonly administered because of concerns that bacterial translocation may occur in the setting of small bowel obstruction; however, there are no controlled data to support or refute this approach.27It would seem prudent however to give systemic antibiotics to patients with signs of strangulation or peritonism at presentation.

The use of a naso-gastric is well established in order to deflate the stomach and proximal small bowel.28 There is no clear published evidence on which patient groups benefit most from naso-gastric tube placement or when such a tube should be placed in the initial management of the patient with intestinal obstruction. Furthermore, there is no additional benefit from using intestinal tubes of longer length.13 28

Learning Bite

Involve the surgical team early in the management of the patient with suspected intestinal obstruction.

SPECIFIC on-going surgical management

Patients with small bowel obstruction generally undergo an initial period of non-operative observation and continued resuscitation, unless there are signs of shock or strangulation at presentation when exploratory laparotomy is indicated. Care must be taken to ensure that strangulation or starvation does not occur; around 3 days is considered the limit of non-operative observation by many surgeons.2

A systematic review and meta-analysis of 14 prospective studies of the role of water-soluble contrast agent (WSCA) in adhesive small bowel obstruction reported that WSCA was effective in predicting the need for surgery (96% sensitivity, 98% specificity in predicting resolution of SBO if contrast appeared in the colon 4-24 hours after administration). In addition, WSCA reduced the need for operation (OR 0.62) and shortened hospital stay (by 2 days).29 Hence WSCA has both a diagnostic and therapeutic role in patients with small bowel obstruction.

In patients with large bowel obstruction, early differentiation from pseudo-obstruction by contrast enema or colonoscopy is essential because the treatments differ. Indeed, a pseudo-obstruction may be relieved therapeutically by colonoscopic decompression.9 In general however, mechanical large bowel obstruction requires operative intervention. Colonic stenting can be used either for palliation in malignant bowel obstruction or as a bridge to surgery.30 31 One-stage primary resection and anastomosis is the preferred choice for low-risk patients.31 32

Colonic pseudo-obstruction can be managed with pharmacological methods as well as colonoscopic decompression. Intravenous Neostigmine is the best-studied pharmacological agent, leading to prompt colon decompression in the majority of patients after a single infusion.9 10 33 However, the underlying cause should always be sought and actively treated wherever possible.

Learning Bite

Small bowel obstruction is often treated conservatively, but large bowel obstruction generally requires operative intervention.

Key Learning Points

  • Bowel obstruction carries a high morbidity and mortality if managed incorrectly
  • Adhesions are the commonest cause of mechanical bowel obstruction
  • Fluid losses and subsequent resuscitation are frequently under-estimated in patients with small bowel obstruction
  • Severe pain in bowel obstruction suggests complications such as ischaemia or perforation
  • Constipation and abdominal distension in the patient with a previous history of abdominal surgery are strongly suggestive of intestinal obstruction
  • Age > 65, comorbidities, more advanced malignancy and emergent surgery are indicators of poor prognosis in patients with large bowel obstruction
  • The abdominal x-ray is the initial investigation of choice in patients with suspected intestinal obstruction, followed by a CT scan for further evaluation
  • Involve the surgical team early in the management of the patient with suspected intestinal obstruction
  • Small bowel obstruction is often treated conservatively, but large bowel obstruction generally requires operative intervention
  1. Nobie B. Small bowel obstruction.
  2. Smith G, Paterson-Brown S. The acute abdomen and intestinal obstruction. In: Garden O, Bradbury A, Forsythe J (eds). Principles and Practice of Surgery, 4th ed. Churchill Livingston, Edinburgh 2002. Ch 17; p198-220.
  3. Wyatt J, Illingworth R, Robertson C, Clancy M, Munro P. Oxford Handbook of Emergency Medicine, 2nd ed. Oxford University Press, Oxford 2005. Ch 10; p490-1.
  4. Markogiannakis H, Messaris E, Dardamanis D, Pararas N, Tzertzemelis D, Giannopoulous P et al. Acute mechanical bowel obstruction: clinical presentation, etiology, management and outcome. Wrld J Gastro 2007; 13(3): 432-7.
  5. Shelton B. Intestinal Obstruction. AACN Clin Iss 1999; 10(4): 478-91.
  6. Walsh T, Pollock A. Principles of fluid and electrolyte balance in surgical patients. In: Garden O, Bradbury A, Forsythe J (eds). Principles and Practice of Surgery, 4th ed. Chruchill Livingston, Edinburgh 2002. Ch 2; p10-19.
  9. De Giorgio R, Knowles C. Acute colonic pseudo-obstruction. Br J Surg 2009; 96(3): 229-39.
  10. Saunders M, Kimmey M. Systematic review: acute colonic pseudo-obstruction. Aliment Pharmacol Ther 2005; 22(10): 917-25.
  11. Raftery A, Lim E. Churchills Pocketbook of Differential Diagnosis. Chruchill Livingston, Edinburgh 2001. p234-7.
  12. Ford M, Cumming A. The alimentary and genitourinary systems. In: Munro J, Campbell I (eds). Macleods Clinical Examination, 10th ed. Churchill Livingston, Edinburgh 2000. Ch 5; p 145-82.
  13. Diaz J, Bokhari F, Mowery N, Acosta J, Block E, Bromberg W et al. Guidelines for Management of Small Bowel Obstruction. J Trauma. 2008; 64: 1651-64.
  14. Canady J, Jamil Z, Wilson J, Bernard L. Intestinal obstruction: Still a lethal clinical entity. J Nat Med Ass. 1987; 79(12): 1281-4.
  15. Bohner H, Yong Q, Franke C et al. Simple data from history and physical examination help to exclude bowel obstruction and to avoid radiographic studies in patients with acute abdominal pain. Eur J Surg 1998; 164: 777-84.
  16. Tekkis P, Kinsman R, Thompson M, Stamatakis J. The Association of Coloproctology of Great Britain and Ireland Study of Large Bowel Obstruction Caused by Colorectal Cancer. Ann Surg 2004; 240: 76-81.
  17. Smith J, Hall E. The use of plain abdominal x rays in the emergency department. Emerg Med J 2009; 26: 160-3.
  18. Feyler S, Williamson V, King D. Plain abdominal radiographs in acute medical emergencies: an abused investigation? Postgrad Med J 2002; 78: 94-6.
  19. Stower M, Amar S, Mikulin T et al. Evaluation of the plain abdominal X-ray in the acute abdomen. J R Soc Med 1985; 78: 630-3.
  20. McCook T, Ravin C, Rice R. Abdominal radiography in the emergency department: a prospective analysis. Ann Emerg Med 1982; 11: 7-8.
  21. Stoker J, van Randen A, Lameris W, Boermeester M. Imaging patients with acute abdominal pain. Radiology 2009; 253(1): 31-46.
  22. Jaffer U. Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. Computed tomography for small bowel obstruction. Emerg Med J 2007; 24(11): 790-1.
  23. Burkhill G, Bell J, Healy J. The utility of computed tomography in acute small bowel obstruction. Clin Radiology 2001; 56(5): 350-9.
  24. Godfrey E, Addley H, Shaw A. The use of computed tomography in the detection and characterisation of large bowel obstruction. N Z Med J 2009; 122(1305): 57-73.
  25. Suri S, Gupta S, Sudhakar P et al. Comparative evaluation of plain films, ultrasound and CT in the diagnosis of intestinal obstruction. Acta Radiol 1999; 40: 422-8.
  26. Maglinte D, Reyes B, Harmon B et al. Reliability and role of plain film radiography and CT in the diagnosis of small bowel obstruction. AJR Am J Roentgenol 1996; 167: 1451-5.
  27. Sagar P, MacFie J, Sedman P, May J, Mancey-James B, Johnstone D. Intestinal obstruction promotes gut translocation of bacteria. Dis Colon Rectum 1995; 38: 640-4.
  28. Wilson M, Ellis H, Menzies D, Moran B, Parker M, Thompson J. A review of the management of small bowel obstruction. Ann R Coll Surg Engl 1999; 81: 320-8.
  29. Branco B, Barmparas G, Schnuriger B, Inaba K, Chan L, Demetriades D. Systematic review and meta-analysis of the diagnostic and therapeutic role of water-soluble contrast agent in adhesive small bowel obstruction. Brit J Surg 2010; 97(4): 470-8.
  30. Dekovich A. Endoscopic treatment of colonic obstruction. Curr Opin Gastroenterol 2009; 25(1): 50-4.
  31. Trompetas V. Emergency management of malignant acute left-sided colonic obstruction. Ann R Coll Surg Eng 2008; 90(3): 181-6.
  32. Lopez-Kostner F, Hool G, Lavery I. Management and causes of acute large bowe obstruction. Surg Clin North Am 1997; 77(6): 1265-90.
  33. McNamara R, Mihalakis M. Acute colonic pseudo-obstruction: rapid correction with neostigmine in the emergency department. J Emerg Med 2008; 35(2): 167-70.


  1. Charlotte Walker says:

    Useful module and nicely consolidated.

  2. Katherine Clarke says:

    Very concise module. Thank you

  3. Allan says:

    Excellent module.

  4. Christopher Roots says:

    Great module

  5. Dr. Muhammad Umer Khayyam Sayyed says:

    Interesting about role of AXR in ED settings

  6. Mr. Robert Daniel Jennings says:

    Interesting read

  7. Dr. Imran Khalid says:

    well constructed module

  8. Miss Katie Louise Hemmings-Trigg says:

    Great module and update on causes of bowel obstruction. Thank you.

  9. daranijoo870 says:

    Very well laid out

  10. Andrew Scott-Donkin says:

    Useful revision. Well structured module

  11. Anne Snoddy says:

    well constructed and informative, good revision of subject

  12. Bassem Alhadi says:


  13. Dr. Aravindhan Asokan says:


  14. Dr. Emma Ridings says:

    Very useful & concise module, clear categorisation of causes of bowel obstruction mechanial vs functional.

  15. Chandani Sharma says:

    Thank you. Great learning session.

  16. Israel Oserohwovo says:

    very useful module. helpful in my surgical referrals!

  17. Mr. Daniel Haider says:

    Good concise and clinically applicable,thanks.

  18. Gagandeep Kaur says:

    Concise and very useful

  19. Dr. Olubusola Mojisola Odesanya says:


  20. Jonathan Holliday says:


  21. Dr. Rachel Louise Angell says:

    useful module

  22. Dr. Waleed Metwally Nassar says:

    very concise

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