Intussusception, ileocolic, air enema reduction, operative management, lead points

Definition / Overview

• The small bowel encompasses the duodenum, jejunum, and ileum, approximately 6-7 metres of bowel responsible for digestion and nutrient absorption.
• Small bowel pathology spans a wide spectrum including obstruction, ischaemia, inflammatory disease, neoplasia, diverticular disease, and motility disorders.
• Timely diagnosis is challenging because symptoms are often nonspecific and the small bowel is not readily accessible by standard endoscopy.
• The consultant surgeon must systematically approach each condition through targeted investigation, appropriate operative or non-operative management, and anticipation of complications.

Anatomy and Surgical Exposure

Relevant Anatomy

• Duodenum: C-shaped, retroperitoneal (D2-D4), adjacent to the head of pancreas, CBD, and superior mesenteric vessels; D1 is intraperitoneal
• Jejunum: Left upper quadrant; thick wall, prominent plicae circulares, short fat-laden mesentery; major site of absorption
• Ileum: Right lower quadrant; thinner wall, longer mesentery, Peyer patches; terminal ileum reabsorbs bile salts and vitamin B12
• Blood supply: Superior mesenteric artery (SMA) via jejunal and ileal branches forming arcades; venous drainage via SMV → portal system
• Lymphatics: Drain to mesenteric lymph nodes and then to para-aortic nodes, critical in oncological resection

Operative Exposure

• Midline laparotomy: Workhorse for emergencies; provides full access
• Laparoscopy: Favoured for adhesiolysis, diagnostic exploration, and elective resection in stable patients
• Kocherisation of duodenum: Mandatory for D2/D3 pathology; mobilise peritoneum lateral to duodenum and rotate medially
• Running the bowel: Systematic hand-over-hand technique from Treitz ligament to terminal ileum; critical in trauma and ischaemia assessment

Pathophysiology and Classification

Clinical Features and Diagnosis

History

• Obstruction: Colicky central abdominal pain, vomiting (bilious early vs faeculent late), absolute constipation, abdominal distension
• Ischaemia: Severe constant pain disproportionate to examination findings; atrial fibrillation, peripheral vascular disease, recent cardiovascular event; post-prandial angina suggests chronic mesenteric ischaemia
• Inflammatory (Crohn's): Chronic diarrhoea, weight loss, RIF pain, perianal disease; extra-intestinal manifestations (uveitis, arthropathy, erythema nodosum)
• Neoplasm: Insidious weight loss, anaemia, occult GI bleeding, obstruction or intussusception in adults (malignancy until proven otherwise)
• Bleeding: Haematochezia or melaena; Meckel's typically presents as painless rectal bleeding in children/young adults

Predisposing Conditions

• Prior abdominal surgery (adhesions), hernias
• FAP, HNPCC/Lynch syndrome, Peutz-Jeghers syndrome, predispose to small bowel neoplasia
• Crohn's disease, coeliac disease, chronic inflammation increases malignancy risk
• Atrial fibrillation, hypercoagulable states, mesenteric ischaemia
• Cystic fibrosis, distal intestinal obstruction syndrome; markedly elevated baseline SB malignancy risk

Physical Examination

• Distension, high-pitched tinkling bowel sounds (mechanical SBO) vs absent sounds (ileus/ischaemia)
• Localised tenderness or peritonism, suggests strangulation or perforation
• Hernia orifices must be examined in every patient presenting with SBO
• Palpable mass, consider neoplasm, abscess, or intussusception
• Haemodynamic compromise, indicates strangulation, ischaemia, or perforation with sepsis

Investigations

Bloods

• FBC: Anaemia (chronic blood loss, Crohn's); leucocytosis (infection, ischaemia, strangulation)
• U&E, creatinine: Dehydration from obstruction; renal function before contrast imaging
• Lactate: Elevated in ischaemia; a late and prognostically poor sign in mesenteric ischaemia, a normal lactate does NOT exclude ischaemia early
• CRP, albumin: Inflammatory burden and nutritional status
• Coagulation: Septic coagulopathy; pre-operative assessment
• Tumour markers (CEA, CA19-9, CgA): Adjunct only; chromogranin A elevated in neuroendocrine tumours

Imaging

Management

Small Bowel Obstruction (SBO)

Non-operative (First-line for Partial/Adhesive SBO)

1. IV fluid resuscitation: crystalloid; correct electrolyte derangements
2. Nasogastric decompression: large-bore NGT; free drainage
3. Strict nil-by-mouth
4. DVT prophylaxis: LMWH + compression stockings once haemorrhage excluded
5. Serial clinical assessment: 4-6 hourly; escalate if peritonism develops or no resolution at 48-72 hours
6. Water-soluble contrast (Gastrografin) challenge: 100 mL orally/via NGT; appearance in colon on AXR at 24 hours predicts resolution AND has a therapeutic effect; reduces need for surgery and length of stay

Operative Indications

• Immediate: Signs of strangulation (fever, tachycardia, peritonism, leucocytosis, raised lactate), closed-loop obstruction on CT, non-reducible hernia, complete obstruction not resolving
• Elective: Recurrent SBO from adhesions, specific anatomical cause (tumour, stricture, internal hernia)

Operative Approach

• Laparoscopy: appropriate for selected cases (single adhesive band, stable patient, non-distended abdomen); conversion rate higher with matted adhesions
• Open adhesiolysis: sharp dissection preferred; avoid enterotomy; assess bowel viability after release (colour, peristalsis, Doppler, fluorescein)
• Bowel resection: Mandatory for ischaemic or non-viable segments; stapled anastomosis or hand-sewn; primary anastomosis generally safe if no faecal contamination and well-perfused ends
• Damage control: In haemodynamically unstable patients, resect, leave bowel in discontinuity, temporary abdominal closure, return to ICU for resuscitation, relook at 24-48 hours for anastomosis

Mesenteric Ischaemia

Acute (Surgical Emergency)

1. Resuscitation: Large-bore IV access, fluid resuscitation, anticoagulation with UFH (bolus 5000 units then infusion)
2. Antibiotics: Broad-spectrum (e.g. piperacillin-tazobactam 4.5 g 8-hourly) for bacterial translocation and peritonitis
3. CT angiography to delineate occlusion pattern
4. Embolectomy / thrombectomy / thrombolysis: SMA embolus: operative embolectomy via transverse arteriotomy; consider endovascular approach in selected stable patients
5. Bowel resection of non-viable segments; second-look laparotomy at 24-48 hours mandatory to assess anastomotic viability and residual ischaemia
6. NOMI: Intra-arterial papaverine infusion (30-60 mg/hr) via angiography catheter; correct precipitating cause (cardiac failure, sepsis, vasopressors)
7. Venous thrombosis: Anticoagulation first-line; resection if peritonism

Chronic Mesenteric Ischaemia

• Post-prandial pain, weight loss ("food fear"), vascular risk factors
• Revascularisation: endovascular angioplasty ± stenting preferred (lower morbidity); open bypass (aortomesenteric or iliac-mesenteric) for complex anatomy or endovascular failure

Crohn's Disease

Medical Management First

• Induction: corticosteroids (prednisolone 40-60 mg/day), budesonide for ileocaecal disease
• Maintenance: thiopurines (azathioprine 2-2.5 mg/kg/day), methotrexate; biologics (infliximab, adalimumab) for steroid-dependent/refractory disease
• Nutritional support: enteral preferred; TPN for high-output fistulae or pre-operative optimisation

Surgical Indications

• Failed medical therapy, obstruction, fistula/abscess, perforation, haemorrhage, or dysplasia/malignancy
• Principle: bowel-sparing surgery: resect only macroscopically diseased bowel; microscopic margins do not affect recurrence; avoid short gut syndrome
• Strictureplasty: preferred over resection for short strictures (\<10 cm) in the absence of active sepsis or malignancy; Heineke-Mikulicz for short, Finney or Michelassi for longer segments
• Complete obstruction from Crohn's: trial of NGT decompression, IV steroids, and hydration before operative intervention, most resolve and can proceed to elective surgery under safer conditions
• Post-operative recurrence: Endoscopic monitoring at 6-12 months; early reintroduction of biologics reduces recurrence

Small Bowel Neoplasms

Work-up

• CT chest/abdomen/pelvis with contrast for staging
• MRI for liver lesions (hepatic metastases from NETs)
• Octreotide scan / $^{68}$Ga-DOTATATE PET for NETs
• Staging laparoscopy for locally advanced disease

Management by Histology

Meckel's Diverticulum

• Symptomatic: Always resect, diverticulectomy (stapled or wedge) if base is narrow and uninvolved; segmental ileal resection if base is wide, inflamed, or contains ectopic mucosa
• Incidental: Resection debated; generally indicated in children, patients <40 years, symptomatic history, or anatomically at high-risk features (wide base, heterotopic mucosa suspected)
• Laparoscopic approach appropriate for elective resection

Motility Disorders and Ileus

• Post-operative ileus: Multimodal analgesia (minimise opioids), early enteral feeding, gum chewing, alvimopan (mu-opioid antagonist, 12 mg pre-operatively then 12 mg BD for up to 7 days; evidence-based reduction in ileus duration); early mobilisation; correct electrolytes
• Adynamic ileus (generalised): Address systemic cause (sepsis, metabolic derangement); NGT decompression; neostigmine not indicated (colonic pseudo-obstruction agent); avoid pharmacologic agents until mechanical obstruction excluded
• Chronic intestinal pseudo-obstruction: MDT approach; nutritional support; prokinetics; exclude mechanical cause; surgical decompression rarely required

Complications and Special Considerations

Anastomotic Leak

• Risk factors: Tension, ischaemia, malnutrition, immunosuppression, distal obstruction, steroids
• Clinical: Day 3-7 fever, tachycardia, rising CRP, ileus, drain output change, abdominal pain
• Diagnosis: CT with oral ± rectal contrast
• Management: Small contained leak, IV antibiotics, radiological drain; large uncontained or peritonitis, return to theatre; proximal diversion (defunctioning stoma) or resection with end stoma

Post-operative Haemorrhage

• Early return to theatre if haemodynamically unstable despite resuscitation; identify source (mesenteric vessel, anastomosis); angioembolisation for non-operative candidates

Short Bowel Syndrome

• Occurs when functional intestinal length <100-150 cm; common after extensive resection for ischaemia, Crohn's, or trauma
• Management: TPN initially, intestinal rehabilitation (glutamine, GLP-2 agonist teduglutide), enteral adaptation, and ultimately intestinal transplantation in select cases

DVT Prophylaxis

• Pharmacological: LMWH (e.g. enoxaparin 40 mg SC daily) commenced 12-24 hours post-operatively; extended course 28 days for oncological resections
• Mechanical: Graduated compression stockings + intermittent pneumatic compression devices intraoperatively and post-operatively
• High-risk (cancer, prolonged bed rest): Combined pharmacological and mechanical; consider pre-operative insertion of IVC filter only in exceptional circumstances

Perioperative Management and MDT Considerations

Pre-operative Optimisation

• Correct nutritional deficits: albumin <30 g/L warrants pre-operative enteral or parenteral nutritional support for at least 7-10 days in elective cases
• Optimise immunosuppression: withhold biologics (infliximab, adalimumab) 4-6 weeks pre-operatively where possible; steroids, do not abruptly stop; consider stress dosing
• Bowel preparation: not routinely required for small bowel surgery
• Consent: stoma possibility, short bowel risk, anastomotic leak, re-operation

MDT Decision-Making

• All small bowel malignancies discussed at a multidisciplinary tumour board including surgical oncology, medical oncology, gastroenterology, radiology, pathology, and clinical nurse specialist
• Neoadjuvant therapy (e.g. imatinib in GIST) considered to facilitate R0 resection of borderline-resectable disease
• Palliation vs curative intent established early to guide operative planning

Enhanced Recovery

• Carbohydrate loading pre-operatively, multimodal analgesia (minimise opioid), early mobilisation, early enteral feeding (day 1 post-operative), targeted IV fluid strategy
• Aim for early transition from IV to oral medications

Key viva point: In any patient presenting with SBO, always examine hernia orifices, assess CT for a transition point and signs of strangulation, and apply a water-soluble contrast challenge for partial adhesive obstruction, this has both diagnostic and therapeutic value and is supported by level I evidence.