Small bowel obstruction

Aetiology of jejunal and ileal SBO

Extra-luminal	Adhesions (65%)	Mostly from surgery, but can also be caused by peritonitis, diverticulitis, radiation enteritis, or PID Can be congenital Likely occurs more for pelvic procedures due to higher mobility of bowel Caused by fibrotic bands which are the end result of inflammation at sites of previous injury/surgery
	Internal hernia
	Midgut (small bowel) volvulus	A huge load of high-fibre, indigestible food which arrives suddenly in an empty bowel, creating rotational-kinking forces. Uncommon in the developed world. Bowel found to be twisted around an unusually long mesentery, containing litres of clay-like undigested food. Can occur in combination with sigmoid volvulus to form the ileosigmoid knot. Urgent operation.
	External hernia (10%)	Typically inguinal or ventral hernia
	Neoplastic	Carcinomatosis Extra-intestinal neoplasm Malignancy accounts for about 20% overall - mostly peritoneal carcinomatosis
	Intra-abdominal abscess	Commonly ruptured appendix, diverticulitis, or dehiscence of an anastomosis
Intra-mural	Primary tumours (carcinoid, GIST, adenocarcinoma)	Rare
	Metastatic tumours (colon, ovarian, gastric, pancreatic, melanoma)
	Malrotation
	Duplications, cysts
	IBD (5%) Acute inflammation and oedema Chronic strictures Also higher risk for malignancy	Close discussion with gastroenterologist regarding when surgery is indicated Remember Crohn's is incurable, and long-term goal is to minimise length of bowel resected Inflammatory strictures may be treatable with steroids Fibrotic strictures - adalimumab, endoscopic dilatation In these patients, consider nutritional status, immunosuppressants may inhibit wound healing and try to optimise 60% of medical treatment of strictures fails and 40% of endoscopic dilatation fails
	Infections	TB Actinomycosis Diverticulitis Mesenteric adenitis
	Traumatic	Haematoma Ischaemic stricture
	Intussusception Rare in adults (1-5% of SBO) Benign lesions Meckel's Polyps Malignant lesions Primary or metastatic tumour Other Anastomotic (e.g. retrograde intussusception of RYGB anastomosis) Adhesions IBD Idiopathic - no lead point 8-20%	Usually secondary to a pathological lead-point such as a polyp or tumour The lead point is pulled forward by normal peristalsis, resulting in telescoping of the intussusceptum (bowel with lead point) within the intussuscipiens (surrounding normal bowel) Malignancy rate varies depending on source - Sabiston says mostly benign in adults, as malignant lesions tend to obstruct via tumour infiltration and adhesions, rather than intussusception. But in the literature, around 60-70% seem to be malignant based on reviews as of 2024. Increased incidence along with AIDS - Kaposi, NHL, lymphoid hyperplasia Generally, resect. Can start laparoscopic and then in most hands exteriorise the segment through a mini-laparotomy. Perform an oncological resection if in doubt. If benign aetiology suspected, can reduce the intussusception prior to resection, to decrease the length of resection.
	Endometriosis
	Radiation enteropathy/stricture
Intra-luminal	Gallstone
	Enterolith	Often originating from a jejunal diverticulum - see separate topic
	Foreign body/bezoar Phytobezoars (vegetables or fruits - persimmons, popcorn) Trichobezoars (hair) Parasitic (ascaris lumbricoides in distal ileum)

Aetiology of duodenal obstructions

• Benign
  • PUD
    • Combination of local inflammation, oedema, pylorospasm and fibrosis
    • Endoscopic balloon dilatation gives good results but patients often require surgery eventually
    • Give PPI and test for H. pylori
  • Crohn's disease
    • Endoscopic balloon dilatation is worthwhile but often need surgery eventually
  • SMA syndrome - reduced angle between SMA and aorta causes entrapment of duodenum
    • See separate topic
    • Develops in severe weight loss and post-surgically
    • Food intolerance with nausea and vomiting and epigastric pain in c/o weight loss
    • Can sometimes be managed conservatively (TPN + NGT) but generally needs surgery
    • Strong's procedure (cutting ligament of Treitz to allow duodenum to fall away) or deuodenojejunostomy
  • Annular pancreas
    • Encircling ring of normal pancreatic tissue
    • Normally diagnosed <1yo by double bubble sign on AXR
• Malignant 50-80% of duodenal obstructions nowadays
  • Most commonly pancreatic cancer with extension to duodenum
  • Small bowel adenocarcinoma
  • Gastric carcinoma
  • Distal cholangiocarcinoma
  • GI lymphoma
  • Often end up requiring pancreaticoduodenectomy

Pathophysiology

• Early, intestinal motility and contractile activity increases in an attempt to push past the obstructing point, both above and below the obstruction (this accounts for the diarrhoea that is often present)
• Later, the intestine becomes fatigued and dilates, with contractions becoming less frequent and less intense
• Distension contributed to by accumulation of gas from fermentation as well as sequestration of secreted fluid
• Water and electrolytes accumulate intra-luminally and in the bowel wall itself. This third-space loss accounts for the dehydration and hypovolaemia
  • Proximal obstructions - dehydration, hypochloraemia, hypokalaemia, and metabolic alkalosis
  • Distal obstruction - dehydration, but less severe electrolyte disturbances
  • Renal hypoperfusion will activate RAAS, causing more sodium preservation at expense of H+, and leading to metabolic alkalosis
• Increased intra-abdominal pressure
• Decreased venous return
• Elevation of the diaphragm, compromising ventilation
• Strangulation occurs as increased intra-luminal pressure decreases mucosal blood flow
  • Commonly seen with closed-loop obstructions due to greater intra-luminal pressures
• Greatly increased concentration of bacteria in the intestine, and associated increased bacterial translocation, causing systemic inflammation and potentially even leading to sepsis. E. coli, S. faecalis and Klebsiella are also much more likely to be isolated from the gut during SBO.

Presentation

• Typical presentation:
  • Colicky abdominal pain - crampy, paroxysms every 4-5 minutes but less frequently with distal obstructions
  • Nausea/vomiting - more common with a higher obstruction. Vomitus becomes more faeculent as the obstruction becomes more complete and bacterial overgrowth occurs.
  • Abdominal distension - as the intestine becomes more dilated - more prominent with distal obstructions
  • Obstipation - often have associated small-volume diarrhoea, so bowels opening cannot exclude SBO
• Signs of strangulation - need to be interpreted together and in context
  • Continuous pain (most important)
  • Fever
  • Tachycardia
  • Localised tenderness and peritonism (not as useful)
  • Leucocytosis (not sensitive or specific)
  • Metabolic acidosis secondary to hyperlactataemia
• Key points on review
  • History
    • Surgical history
    • Hernias
    • Malignancy
  • Exam
    • Distension with often visible peristalsis early on
    • Surgical scars
    • Auscultate borborygmi (hyperactive bowel sounds with audible rushes from the vigorous peristalsis)
    • Percussion - tympany
    • Check for hernias
    • You could technically do a PR exam to check for distal obstruction and blood, which could indicate malignancy, intussusception or infarction
• Bloods
  • Often have a hypokalaemic, hypochloraemic, metabolic alkalosis
  • High haematocrit expected due to dehydration

Imaging

AXR - sensitivity 66%

• Best role is for follow-up of patients with chronic obstruction being managed non-operatively
• Supine/prone signs:
  • Dilated gas or fluid-filled small bowel >3cm
  • Dilated stomach
  • Small bowel dilated out of proportion to colon
  • Stretch sign
  • Absence of rectal gas
  • Gasless abdomen
  • Pseudotumour sign
• Upright/left lateral decubitus signs:
  • Multiple air fluid levels
  • Air fluid levels longer than 2.5cm
  • Air fluid levels in same loop of small bowel of unequal lengths
  • String of beads sign

CT - SBO is a CLINICAL diagnosis, CT is to find the cause and evaluate for strangulation

• IV contrast only (PO contrast takes time, interferes with view of the colonic wall, and may be poorly tolerated)
• Small bowel faeces sign - immediately proximal to transition point, caused by stasis
• Transition point DOES NOT predict need for operation (although controversial)
• Free fluid commonly present, however large volume ascites is concerning
• Indications for immediate intervention - ischaemia, closed loop obstruction, perforation
• Complete SBO - significantly distended bowel, failure to pass stool or flatus, lack of air in distal small bowel or colorectum
  • Virtually always leads to operation
• Closed-loop obstruction - concerning for ischaemia due to increased intra-luminal pressures - evaluate for other signs of ischaemia
• CT findings associated with ischaemia:
  • Bowel wall - decreased, delayed enhancement; mural thickening >3mm; pneumatosis intestinalis
  • Mesentery - venous congestion and engorgement; mesenteric oedema; mesenteric haemorrhage
  • Other - portal or mesenteric venous gas; free fluid or ascites
  • Note that these are all late signs compared to the clinical findings of strangulation above

Barium enteroclysis

• Continuous fluoroscopy or radiographs at frequent intervals
• Theoretically allows details imaging of the entire small bowel
• Has been suggested for patients with low-grade recurrent SBO

MRI

• No better than CT

USS

• Has been described for use in pregnant patients

Differential diagnosis

• LBO
  • SBO more often acute, LBO progresses over days/weeks
  • SBO - high-pitched bowel sounds
  • Vomiting seen earlier in SBO
  • If incompetent ICV - may see faeculent vomiting
• Ileus
  • See separate topic

Classification

• Simple or strangulating
  • Strangulation usually involves a closed loop obstruction with a compromised vascular supply, and can lead to intestinal infarction
  • All known clinical parameters are non-sensitive and non-specific
• High or low
• Partial or complete
  • Gastrografin in colon within 24hrs indicates partial, if it is not possible to confirm obstipation from patient
  • Also see whether any gas in colon/rectum
• Low-grade or high-grade
• Closed loop
  • Both ends of a segment of bowel are obstructed, either by an adhesive band or an internal hernia, which may result in ischaemia and necrosis
  • Look for a U loop or coffee bean sign with tapering of both ends of bowel, and volvulus (mesenteric whirl)

Management principles

• Evaluate need for immediate operation (signs of strangulation or other specific aetiologies)
• If no indication for surgery, manage conservatively, with constant reassessment

Indications for surgery (based on Bologna guidelines 2017 for adhesive SBO)

• On admission
  • Clinically suspected strangulation/peritonitis (fever, tachycardia, leucocytosis, metabolic acidosis, continuous pain, radiological signs)
  • Surgery in past 6/52 (UTD says trial non-op in these patients)
  • Irreducible hernia (or internal hernia)
  • No signs of resolution within 72hrs (in practice, this belongs to 'ongoing')
• Ongoing
  • Evolving peritoneal signs
  • CRP >75
  • WBC > 10 (persistently)
  • Free intraperitoneal fluid > 500mL on CT
  • Reduction of CT small bowel wall contrast enhancement
• Day 3
  • Failed Gastrografin challenge
  • Pain lasting 4 days or more
  • Persistent ileus >72hrs
  • NGT drainage volume >500mL on day 3

Non-operative management

• NBM + ice chips for comfort
• NGT 14 or 16Fr (check position ASAP to allow Gastrografin)
• IVF and electrolyte replacement
• Consider IDC
• Rationalise medications
• Antibiotics only if surgery is required
• Gastrografin given once outputs have settled to the point where it's safe to spigot NGT for 4-5 hours
  • Note that GG does not increase the proportion of patients that avoid an operation, but does decrease time to resolution (in patients that would have resolved anyway) and hospital stay. There is not strong evidence that it acts therapeutically.
  • 100mL Gastrografin neat then spigot NGT until either patient opens bowels or patient has refractory nausea
  • If no contrast in colon in 24/36hrs - surgery
    • Presence of GG in colon at 24 hours predicts non-op resolution with 97% specificity and 96% sensitivity
  • Schein suggests give it 1-2 hours after NGT decompression

Specific situations:

• Complete SBO - monitor closely, generally needs OT
• Partial high-grade SBO (some gas in rectum) - initial observation, closely watched, may need theatre
• Partial low-grade SBO (bowels opening/passing flatus, but symptomatic on fluid intake) - can be safely watched in hospital
• SBO in virgin abdomen - Ask again about surgery, and check carefully for scars and hernias. Ask about history of trauma, and cancer that may have metastasised, and recent ingestion of bezoar-forming foods. According to one meta-analysis: 54% de novo adhesions, 11% malignancy, 2% internal hernia. The vast majority of patients will safely be managed non-operatively. It's worth thinking about outpatient workup for malignancy if non-op management is successful. This could be CT +/- MRI enteroclysis.
• SBO post-op - Mostly resolves with conservative management, consider TPN. >90% of early post-op obstructions are partial and will resolve spontaneously. However, need to be sure there are no signs of strangulation and no technical errors. Technical errors are more common after laparoscopic surgery, such as port site hernias.
• Recurrent SBO shortly after operation for same - initial non-op management. Very careful surgical technique. Many would advocate for prolonged non-op management and TPN until adhesions mature and the obstruction resolves.
• Obstruction secondary to Crohn's - attempt conservative management with gut rest, TPN and steroids, involve medics, try to avoid OT. If have to operate, limited bowel resection or stricturoplasty.
• SBO with known intra-abdominal malignancy/potential recurrent malignancy - 30% have simple band adhesion, 30% need bowel resection, 30% inoperable - therefore probably deserve a laparotomy (aborting an operation may be better in many cases than not offering an operation that would have been simple). If they are already receiving palliative care input, and not far away from death, then less likely to offer an operation.
• Malignant SBO (either primary or metastatic): median survival even with operation is 3-7 months, lower without (retrospective data), so a palliative procedure is not out of the question. Probably two types of patients - those with late cancer (do not operate), and those with first presentation of peritoneal disease (consider operating and debulking if good physiological reserve; think about patient's peritoneal carcinomatosis index (PCI)). Can sometimes offer bypass procedure.
• SBO secondary to abscess - percutaneous drainage may be sufficient, but laparotomy and washout may be the better option for large and established abscesses.
• SBO secondary to radiation enteropathy - follows a progressive course of gradually worsening partial obstructions, leading to a complete obstruction. Attempt to treat non-operatively, often with steroids. Can be a very difficult operation - paper-thin bowel, glued together and onto adjacent structures; accidental enterotomies are common and lead to fistulas. When longer segments are involved, bail out with an entero-enteric or entero-colic bypass. Poor prognosis no matter what you do.

Operation

• Midline laparotomy, taking care to avoid adhesions
• Lyse all adhesions necessary for safe visualisation of bowel
  • It is not necessary to completely free the entire bowel - focus on the area of TP (and distal to that point if a bowel resection is performed)
  • With frozen abdomen/bowel, you probably do need to release the entire bowel though.
  • Enterotomies: leave superficial serosal tears alone, but repair anything where the mucosa pouts through the defect
• Run small bowel - start with a collapsed loop, and follow it proximally until the TP is identified. If no collapsed bowel is seen, start at ICV.
  • If mass or neoplasm is encountered, needs to be resected with 8-10cm margins + lymphatics, and remember to look at abdomen for evidence of metastases
• Repair hernias - biologic mesh if contamination, otherwise synthetic as normal
• Evaluate bowel for ischaemia
  • Fluoroscein dye - 500 to 1000mg IV in 10% solution - then use Wood's lamp to check perfusion
  • Leave dusky bowel for 10 minutes and reassess before resecting
• Decompress the bowel by milking it back to the stomach

Selection criteria for laparoscopic surgery:

• Haemodynamic stability
• Absence of peritonitis or severe intra-abdominal sepsis
• Proximal (small bowel) obstruction - less distended
• Localised distension on radiography
• Absence of severe abdominal distension
• Anticipated single band
• Low anticipated Peritoneal Adhesion Index (i.e.: safe place to access abdomen)
  • First episode SBO
• Experience/skill of surgeon
• Left upper quadrant/left flank usually the safest places to access abdomen. Use Hasson technique.

Adhesion prevention

• Saline irrigation - INEFFECTIVE
• Anticoagulants - INEFFECTIVE
• Anti-inflammatories - INEFFECTIVE and may interfere with healing
• Fibrinolytics - recombinant t-PA may have some promise, but needs more study
• Barriers - effective - has been shown to reduce adhesion severity and volume, and subsequent risk of bowel obstruction

Many others have been studied - none that achieve holy grail of reduced adhesions, cheap and easy, no effect on wound healing