Bowel obstruction

Surgical approach

Initial management may be non-operative (esp. partial adhesive SBO): NG decompression, IV fluids, correction of electrolytes, CT to define cause/level, water-soluble contrast challenge in selected cases
- Operate if: peritonism, closed-loop obstruction, strangulation/ischaemia, perforation, failure of conservative management, obstructing tumour, volvulus not amenable to endoscopic decompression
Operative options depend on cause/level
- Adhesive SBO: laparoscopic/open adhesiolysis ± bowel resection if non-viable
- Hernia: reduction and repair ± bowel resection
- Tumour (LBO): resection (e.g. right/left hemicolectomy), Hartmann’s procedure, primary anastomosis ± diverting stoma; or bridge with colonic stent in selected cases
- Volvulus: endoscopic decompression (sigmoid) then definitive surgery; caecal volvulus usually surgery
Intra-op priorities: assess viability, decompress dilated bowel, control contamination, source control for sepsis, stoma formation if high risk anastomosis

Anaesthetic management

Type of anaesthesia: General anaesthesia is usual; neuraxial may be adjunct (epidural) in selected patients after resuscitation and if coagulation OK
Airway: high aspiration risk → cuffed ETT with rapid sequence induction (RSI) in most cases; avoid SGA
- Consider modified RSI if haemodynamically unstable; gentle mask ventilation with low pressure may be safer than prolonged apnoea in hypoxic/septic patients
Duration: variable; ~1–3 h for straightforward laparotomy/adhesiolysis; longer (3–6 h) for complex resections, contamination, difficult adhesions
How painful: moderate–severe (midline laparotomy). Multimodal analgesia; consider epidural or abdominal wall blocks (TAP/rectus sheath) if epidural unsuitable
Key anaesthetic themes: resuscitate first (hypovolaemia, sepsis), manage electrolytes/acid–base, aspiration prevention, invasive monitoring, temperature control, goal-directed fluids, early antibiotics and source control

Definition and classification

Mechanical obstruction: physical blockage (intraluminal, mural, extrinsic)
Functional obstruction (ileus/pseudo-obstruction): failure of propulsion without mechanical block
By site: small bowel (SBO) vs large bowel (LBO); by completeness: partial vs complete; by physiology: simple vs strangulating/closed-loop

Common causes (high-yield)

SBO: adhesions (most common), hernia, tumour, Crohn’s stricture, volvulus, gallstone ileus, intussusception
LBO: colorectal cancer (most common), diverticular stricture, volvulus (sigmoid/caecal), faecal impaction
Ileus/pseudo-obstruction: post-op state, sepsis, electrolyte disturbance (hypokalaemia), opioids, spinal/retroperitoneal pathology, severe illness

Pathophysiology relevant to anaesthesia

Fluid shifts: vomiting + third spacing into bowel lumen/wall/peritoneum → hypovolaemia, tachycardia, hypotension; risk of AKI
Electrolytes/acid–base: early vomiting → hypochloraemic metabolic alkalosis; later/strangulation/sepsis → metabolic acidosis and lactate rise; hypokalaemia common
Aspiration risk: gastric/intestinal distension + delayed emptying + vomiting; NG tube reduces but does not abolish risk
Strangulation/ischaemia: venous congestion → oedema → arterial compromise → necrosis/perforation → sepsis, endotoxaemia, DIC risk
Respiratory mechanics: distension elevates diaphragm → reduced FRC, atelectasis; increased work of breathing; worse in obesity/pregnancy

Clinical features and assessment

Symptoms: colicky abdominal pain, vomiting (early in SBO), distension (marked in LBO), constipation/obstipation
Signs of severity: continuous pain, peritonism, fever, tachycardia, hypotension, altered mental state, oliguria
Investigations: FBC, U&E, CRP, lactate/ABG/VBG, coagulation, group & save/crossmatch; CT abdomen/pelvis is key to define level/cause and detect ischaemia/closed-loop

Pre-operative resuscitation and optimisation

A–E approach; treat as potential sepsis until proven otherwise (especially strangulation/perforation)
IV access: 2 large-bore cannulae; consider arterial line pre-induction if unstable; central access if vasopressors/poor access
Fluids: balanced crystalloid boluses guided by response; aim urine output ≥0.5 mL/kg/h; consider vasopressors early if septic/vasoplegic after adequate filling
Electrolytes/acid–base: correct K+/Mg2+/phosphate; treat severe alkalosis/acidosis; monitor lactate trend
Gastric decompression: NG tube on free drainage (confirm position); reduces vomiting and improves ventilation but does not eliminate aspiration risk
Antibiotics: broad spectrum if strangulation, perforation, ischaemia, or operative management; give within 1 h if sepsis suspected
Analgesia/antiemetics: titrated IV opioids (beware hypotension/ileus), paracetamol; avoid NSAIDs if AKI risk; antiemetic (ondansetron) and consider aspiration prophylaxis
- Aspiration prophylaxis: H2 blocker/PPI; sodium citrate immediately pre-induction in high-risk cases (local practice dependent)

Intra-operative anaesthetic technique (typical laparotomy for obstruction)

Monitoring: standard + arterial line (often), temperature, urine output; consider CVP/advanced CO monitoring in major sepsis/large fluid shifts/high risk
Induction: RSI with pre-oxygenation; haemodynamic instability common → consider ketamine/etomidate (where available) or reduced-dose propofol with vasopressor support; have push-dose vasopressors ready
- Cricoid pressure: apply if trained assistant; release if impedes laryngoscopy/ventilation
Neuromuscular block: rocuronium (with sugammadex available) or suxamethonium; anticipate prolonged surgery and need for paralysis
Ventilation: lung-protective strategy; higher airway pressures may occur due to distension/retractors; consider recruitment/PEEP; manage aspiration event promptly
Fluids/blood: goal-directed replacement; large third-space losses; crossmatch if likely resection/contamination; correct coagulopathy; consider cell salvage if appropriate (contamination may limit)
Analgesia: epidural (if time and safe) or alternatives (TAP/rectus sheath blocks, wound infiltration, IV lidocaine infusion where used); opioid-sparing to reduce ileus
Antibiotics and source control: ensure appropriate cover and re-dosing; manage sepsis bundle intra-op (lactate, cultures if not already, vasopressors)
Temperature and glucose: active warming; avoid hypothermia (coagulopathy, wound infection); maintain normoglycaemia

Post-operative care

Destination: HDU/ICU if sepsis, vasopressors, significant comorbidity, major resection, ongoing acidosis/lactate, or high fluid requirements
Analgesia: epidural continuation with monitoring; otherwise PCA + paracetamol; consider regional catheters; avoid excessive opioids (ileus, respiratory depression)
Respiratory: high risk atelectasis/aspiration pneumonia; encourage physiotherapy, CPAP if needed; consider NG ongoing until output decreases and bowel function returns (surgical plan)
Fluids/electrolytes: ongoing losses via NG/stoma; daily U&E/Mg/PO4; monitor urine output; early recognition of AKI
Sepsis surveillance: monitor lactate, WCC, CRP, haemodynamics; early escalation for anastomotic leak/perforation

You are asked to anaesthetise a 70-year-old with vomiting and abdominal distension for emergency laparotomy. How will you assess and optimise them before theatre?

Structure: severity/strangulation, resuscitation, aspiration risk, investigations, planning/communication.

Assess severity: continuous pain, peritonism, fever, tachycardia, hypotension, confusion, oliguria; consider strangulation/perforation/sepsis
Resuscitate: 2 large-bore IV lines; balanced crystalloid boluses; target MAP and urine output; early vasopressor if septic after fluids
Investigations: FBC, U&E, CRP, lactate/ABG, coagulation, group & save/crossmatch; ECG; CT findings review (closed-loop/ischaemia)
NG decompression: insert/confirm NG, free drainage; antiemetics; aspiration prophylaxis per local policy
Antibiotics: broad spectrum if ischaemia/perforation or proceeding to laparotomy; within 1 hour if sepsis suspected
Plan monitoring and destination: arterial line (often pre-induction), urinary catheter; discuss HDU/ICU bed early

Why is bowel obstruction a high aspiration risk even if the patient is fasted and has an NG tube?

Key concept: ongoing secretion, delayed emptying, proximal distension, and incomplete decompression.

Obstruction causes gastric and proximal bowel distension with large volumes of fluid/air; fasting does not empty obstructed stomach
NG tube may block, be malpositioned, or fail to drain all compartments; reflux can still occur around the tube
Reduced lower oesophageal sphincter tone (illness, opioids) and raised intra-abdominal pressure increase regurgitation risk
Therefore: cuffed ETT and RSI are usually indicated

Describe your RSI technique for bowel obstruction in a haemodynamically unstable septic patient.

Aim: minimise aspiration while avoiding cardiovascular collapse and hypoxia.

Preparation: senior help, suction ready, difficult airway plan, vasopressors drawn up, arterial line if time; pre-oxygenate thoroughly (head-up if tolerated)
Induction choice: haemodynamically stable agent selection (e.g. ketamine or reduced-dose propofol with vasopressor support; etomidate where available); avoid large propofol doses
Paralysis: rocuronium (with sugammadex available) or suxamethonium; ensure full paralysis for first-pass success
Cricoid pressure if trained assistant; release if it worsens view/ventilation
Ventilation strategy: consider gentle low-pressure mask ventilation if high risk of desaturation (modified RSI), balancing aspiration risk vs hypoxia
Post-intubation: confirm tube, secure, start lung-protective ventilation, ongoing resuscitation, early antibiotics, temperature control

What are the key physiological derangements in bowel obstruction that affect anaesthesia and how do you correct them?

Think: volume, electrolytes/acid–base, sepsis, respiratory mechanics.

Hypovolaemia from vomiting and third spacing → treat with balanced crystalloids, assess response, consider vasopressors if septic
Electrolyte abnormalities: hypokalaemia, hypochloraemia; correct K+/Cl− and magnesium; monitor ECG
Acid–base: early metabolic alkalosis (vomiting) vs later metabolic acidosis (ischaemia/sepsis, raised lactate); treat cause, optimise perfusion/oxygen delivery
Respiratory compromise due to distension → reduced FRC/atelectasis; preoxygenate, use PEEP, consider postoperative respiratory support

How do you recognise strangulation/ischaemia in bowel obstruction and why does it matter to the anaesthetist?

Strangulation predicts sepsis, rapid deterioration, and need for urgent surgery and critical care.

Clinical: continuous severe pain, peritonism, fever, tachycardia, hypotension, systemic toxicity
Biochemistry: rising lactate/metabolic acidosis, high WCC/CRP (non-specific), AKI
Imaging (CT): closed-loop obstruction, reduced bowel wall enhancement, pneumatosis, portal venous gas, free fluid
Anaesthetic implications: treat as septic emergency—aggressive resuscitation, invasive monitoring, early antibiotics, prepare for vasopressors, ICU post-op

Outline an anaesthetic plan for emergency laparotomy for bowel obstruction including monitoring, analgesia and postoperative destination.

A structured plan scores well: pre-op optimisation, RSI/ETT, invasive monitoring, GDFT, analgesia strategy, HDU/ICU.

Monitoring: standard + arterial line, urinary catheter, temperature; consider central line/advanced CO monitoring if septic/major surgery
Airway/induction: RSI with cuffed ETT; haemodynamically appropriate induction; vasopressors prepared
Maintenance: volatile or TIVA; paralysis; lung-protective ventilation with PEEP; active warming
Fluids: goal-directed balanced crystalloids; blood products if required; correct coagulopathy; monitor lactate and acid–base
Analgesia: epidural if suitable; otherwise multimodal + PCA; consider TAP/rectus sheath blocks; minimise opioids where possible
Post-op: HDU/ICU if sepsis/vasopressors/acidosis/major resection; continue antibiotics, electrolyte replacement, respiratory support as needed

A patient with bowel obstruction aspirates during induction. What immediate steps do you take?

Priorities: oxygenation, airway control, suction, ventilation strategy, and postoperative planning.

Call for help; 100% oxygen; suction oropharynx; expedite intubation with cuffed ETT (if not already) and inflate cuff
If severe contamination: consider head-down/left lateral positioning briefly if feasible; suction via ETT after intubation
Ventilate with lung-protective settings; treat bronchospasm/hypoxia; consider PEEP and recruitment cautiously
Bronchoscopy: consider if particulate aspiration suspected and resources available
Antibiotics: not routine for chemical pneumonitis alone, but often indicated anyway due to intra-abdominal sepsis/contamination—coordinate with surgical indication
Post-op: inform team, document, consider HDU/ICU, CXR/ABG if clinically indicated

Discuss analgesic options for laparotomy in bowel obstruction and how they influence postoperative ileus and respiratory outcomes.

Balance: effective analgesia vs hypotension and ileus; choose technique to facilitate breathing and mobilisation.

Thoracic epidural: excellent dynamic analgesia, reduces systemic opioids and may improve respiratory function; risks include hypotension (hypovolaemia/sepsis), failure, contraindications (coagulopathy)
Abdominal wall blocks (TAP/rectus sheath) + multimodal: good opioid-sparing, less hypotension than epidural; may be less effective for visceral pain
PCA opioids: flexible but can worsen ileus, nausea, sedation and respiratory depression; use lowest effective dose with adjuncts
Adjuncts: paracetamol; cautious NSAIDs (avoid in AKI risk); consider IV lidocaine infusion where used (institutional protocols)

What fluid strategy would you use intra-operatively and post-operatively for bowel obstruction with large NG losses?

Replace deficits + ongoing losses; avoid both under-resuscitation and overload.

Replace pre-op deficit and third space with balanced crystalloids guided by haemodynamics, urine output, lactate and (if used) dynamic indices
NG losses: measure and replace (often with balanced crystalloid; consider chloride replacement if hypochloraemic alkalosis—tailor to labs and local practice)
Blood products: if significant bleeding or major resection; correct coagulopathy and hypocalcaemia during transfusion
Post-op: ongoing NG/stoma losses require daily review; monitor U&E/Mg/PO4; avoid salt/water overload (pulmonary oedema, anastomotic oedema)

Differentiate mechanical obstruction from ileus/pseudo-obstruction and explain why it matters peri-operatively.

Management and urgency differ; aspiration risk and surgical need differ.

Mechanical: colicky pain, high-pitched tinkling bowel sounds early, transition point on CT; may need urgent surgery if complete/strangulated
Ileus: diffuse bowel dilatation without transition point; often post-op/sepsis/electrolytes/opioids; treatment is supportive and treat cause
Peri-op relevance: mechanical obstruction often mandates RSI/ETT and emergency laparotomy; ileus may not require surgery but still carries aspiration risk if distended/vomiting