Anaesthesia for morbid obesity

Surgical approach (typical bariatric surgery context)

• Most common operations: laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB); less commonly adjustable gastric band, biliopancreatic diversion/duodenal switch
  • LSG: stapled longitudinal gastrectomy along bougie; removes fundus/greater curvature; leak risk at proximal staple line
  • RYGB: small gastric pouch + gastrojejunostomy + jejunojejunostomy; internal hernia risk; marginal ulcer risk
• Usually laparoscopic: pneumoperitoneum (often 12–15 mmHg) + steep reverse Trendelenburg; occasional conversion to open
  • Physiology: ↓FRC, ↑airway pressures, V/Q mismatch; ↑SVR and potential ↓venous return; CO2 absorption → hypercapnia
• DVT prophylaxis is routine (mechanical + pharmacological) and early mobilisation is a key surgical goal

Anaesthetic management (typical plan for morbid obesity / bariatric surgery)

• Type of anaesthesia: General anaesthesia is standard; neuraxial/RA mainly adjunct (e.g., TAP blocks) rather than sole technique for bariatric laparoscopy
• Airway: cuffed ETT preferred (aspiration risk, pneumoperitoneum, ventilation requirements); SGA generally avoided for bariatric laparoscopy
  • Plan for difficult mask ventilation and difficult intubation; have videolaryngoscope and front-of-neck access plan
• Duration: typically 1.5–3.5 hours (varies with procedure, surgeon, BMI, adhesions, conversion to open)
• Pain: moderate (laparoscopic) to severe (open); multimodal opioid-sparing strategy is important due to OSA/OHS risk
  • Analgesia options: paracetamol, NSAID (if appropriate), ketamine (low dose), dexmedetomidine, magnesium, local infiltration, TAP/rectus sheath blocks
• Post-op destination: PACU with enhanced monitoring; consider HDU/ICU if OHS, severe OSA, significant comorbidity, difficult airway, high opioid requirement, or complications

Definitions and risk stratification

• BMI: obesity ≥30; severe ≥35; morbid ≥40; super-obese ≥50; super-super ≥60 (useful for perioperative planning and equipment)
• Key syndromes: OSA (obstructive sleep apnoea), OHS (obesity hypoventilation syndrome: BMI ≥30 with daytime hypercapnia PaCO2 >6.0 kPa, after excluding other causes)
  • OHS implies higher perioperative risk than OSA alone (pulmonary hypertension, RHF, sensitivity to sedatives/opioids)
• Functional assessment: exercise tolerance, stair climbing, symptoms of heart failure, angina, syncope; consider CPET if available for major surgery

Comorbidities and physiological changes (what matters to anaesthesia)

• Respiratory: ↓FRC and ERV, airway closure, atelectasis; ↑O2 consumption and CO2 production; rapid desaturation during apnoea; asthma/reflux common
• OSA/OHS: difficult mask ventilation, perioperative obstruction, sensitivity to sedatives/opioids; chronic hypoxia/hypercapnia → pulmonary HTN, RHF
• CVS: hypertension, LVH/diastolic dysfunction, IHD; increased blood volume and CO; arrhythmias; pulmonary hypertension in OHS/OSA
• GI: reflux/hiatus hernia; increased aspiration risk; non-alcoholic fatty liver disease (NAFLD) common (affects drug handling and bleeding risk if advanced)
• Metabolic: T2DM, dyslipidaemia; difficult IV access; increased VTE risk; pressure area injury risk; rhabdomyolysis risk with prolonged surgery/poor positioning

Preoperative assessment and optimisation

• History: OSA symptoms (snoring, witnessed apnoeas, daytime somnolence), CPAP use/adherence, previous anaesthetic airway difficulty, reflux, exertional dyspnoea/orthopnoea, VTE history, mobility
• Screening: STOP-BANG for OSA risk; consider ABG or VBG/ETCO2 surrogate if OHS suspected; ECG for all; echo if pulmonary HTN/RHF suspected
  • Clues to OHS: raised serum bicarbonate, resting SpO2 low, polycythaemia, morning headaches, somnolence, signs of RHF
• Investigations: FBC/U&E/LFTs, HbA1c, group & save; consider spirometry if significant respiratory disease; pregnancy test if relevant
• Optimisation: ensure CPAP brought to hospital and used perioperatively; treat wheeze; manage reflux; VTE prophylaxis plan; discuss postoperative monitoring and analgesia strategy
• Fasting and aspiration prophylaxis: follow local guidelines; consider H2 blocker/PPI and sodium citrate in high-risk reflux; avoid heavy premedication

Equipment, staffing, and theatre preparation

• Environment: bariatric operating table (weight limit), wider trolley/bed, hover-mat/air-assisted transfer, adequate staff for moves, pressure-relieving surfaces
• Airway kit: videolaryngoscope, bougie/stylet, 2nd-gen SGA as rescue, fibreoptic scope, ramping aids, suction, difficult airway trolley, FONA kit
• Vascular access: ultrasound for IV and arterial/central access; long cannulas; consider arterial line if severe OHS/pulmonary HTN/major comorbidity or expected instability
• Monitoring: standard + consider capnography quality, temperature, neuromuscular monitoring mandatory; consider BIS/processed EEG if TIVA or high risk of awareness

Airway strategy (key FRCA content)

• Predictors: obesity alone is a poor predictor of difficult intubation, but increases risk of difficult mask ventilation; neck circumference and OSA correlate with difficulty
• Positioning: ramped/head-elevated laryngoscopy position (HELP) to align external auditory meatus with sternal notch; improves preoxygenation and laryngoscopy
• Preoxygenation: tight seal, 100% O2, head-up 25–30°, consider CPAP/pressure support; aim EtO2 >0.85–0.90; consider apnoeic oxygenation (nasal cannula)
• Induction: plan for rapid desaturation; have two-person mask ventilation; consider modified RSI (gentle ventilation) if high aspiration risk vs hypoxia risk
  • Cricoid pressure: may worsen laryngoscopy/ventilation; apply correctly and release if impeding ventilation/intubation
• Extubation: fully awake, head-up, ensure full reversal and good respiratory mechanics; consider extubation to CPAP/NIV in OSA/OHS; plan for reintubation risk

Intraoperative ventilation and pneumoperitoneum

• Ventilation goals: maintain oxygenation, avoid atelectasis, avoid excessive pressures, manage CO2 load from pneumoperitoneum
• Strategy: lung-protective ventilation (e.g., tidal volume based on predicted/ideal body weight), moderate PEEP, recruitment manoeuvres as needed, adjust RR to maintain ETCO2/PaCO2
  • Be cautious with recruitment/PEEP in haemodynamic compromise; consider arterial line/ABGs if severe OHS or CO2 retention
• Reverse Trendelenburg improves FRC and oxygenation but may reduce venous return; secure patient to avoid sliding and nerve injuries

Drug dosing in obesity (high-yield)

• Use the right size descriptor: Total body weight (TBW), Ideal body weight (IBW), Lean body weight (LBW), Adjusted body weight (AdjBW) depending on drug properties
• Induction agents: propofol induction often closer to LBW (avoid overdose); maintenance requirements can increase with TBW due to increased clearance/volume—titrate to effect
• Opioids: fentanyl/alfentanil often dosed to LBW and titrated; remifentanil uses IBW/LBW in most models (avoid TBW dosing to prevent hypotension/bradycardia)
• Neuromuscular blockers: suxamethonium dose to TBW (↑pseudocholinesterase and Vd); rocuronium/vecuronium often to IBW/LBW (avoid prolonged block); always monitor and reverse appropriately
• Reversal: sugammadex is typically dosed to actual body weight (TBW) per manufacturer (2/4/16 mg/kg depending on depth); ensure availability and cost considerations
• Antibiotics and thromboprophylaxis: may require weight-based dosing; follow local bariatric protocols (under-dosing risks SSI/VTE)

Fluids, haemodynamics, and monitoring

• IV fluids: avoid both hypovolaemia (AKI, hypotension) and overload (worsens oxygenation); consider goal-directed therapy for higher-risk cases
• Blood pressure cuff sizing is critical (miscuffing causes error); consider arterial line if non-invasive readings unreliable or rapid changes expected
• Temperature: active warming; hypothermia increases wound complications and delays recovery

Analgesia and PONV

• Analgesia: multimodal, opioid-sparing; consider local infiltration + TAP block; avoid long-acting opioids where possible in OSA/OHS
• PCA: if used, avoid background infusion in OSA; ensure monitoring (SpO2 ± capnography) and clear escalation plan
• PONV: high risk (laparoscopy, opioids, female, non-smoker); use multimodal prophylaxis (e.g., dexamethasone + ondansetron ± droperidol) and minimise volatile/opioids

Postoperative care and complications

• Respiratory: high risk of hypoventilation, obstruction, atelectasis; nurse head-up; early CPAP/NIV if indicated; encourage incentive spirometry and mobilisation
• VTE: very high risk; ensure mechanical + pharmacological prophylaxis and early mobilisation; consider extended prophylaxis per bariatric protocol
• Surgical complications to recognise: anastomotic/staple line leak (tachycardia, pain, fever, sepsis), bleeding, bowel obstruction/internal hernia, aspiration
• Rhabdomyolysis/pressure injury: prolonged surgery, extreme BMI, poor padding; monitor pain, CK, renal function if suspected