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&amp,E, CRP, lactate/ABG/VBG, coagulation, group &amp, 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&amp,E/Mg/PO4, monitor urine output, early recognition of AKI
Sepsis surveillance: monitor lactate, WCC, CRP, haemodynamics, early escalation for anastomotic leak/perforation

Test yourself…

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&amp,E, CRP, lactate/ABG, coagulation, group &amp, 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&amp,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