Anesthesia

GOLD Stage FEV1 Anaesthetic Risk Post-op Recommendation I (Mild) ≥80% Low — near-normal reserve Standard care; consider incentive spirometry II (Moderate) 50–79% Moderate — significant symptom burden Bronchodilators optimised; NIV plan post-op III (Severe) 30–49% High — this patient (42%); PPCs >30% Aggressive preoperative optimisation; HDU/ICU post-op; TEA analgesia IV (Very severe) <30% Very high; consider surgery alternatives MDT decision; ICU post-op; may need post-op ventilation

ARISCAT risk score: incorporates age, SpO₂ (<96% = highest risk — this patient 90%!), anaemia, upper abdominal/intrathoracic incision, duration >2 hours, emergency surgery, respiratory infection; this patient scores very high on SpO₂ alone (90% at rest) PaCO₂ >45 mmHg at rest → severe disease with CO₂ retention → very high post-op ventilatory failure risk; check ABG preoperatively

Intervention Specific Action Smoking Absolute cessation ≥8 weeks before surgery; immediate cessation improves carboxyhaemoglobin within 12 hours and mucociliary function within 2–4 cessation weeks Bronchodilators Optimise existing LABA/LAMA/ICS regimen; add SABA (salbutamol MDI) PRN pre-operatively; continue all inhalers on morning of surgery with sip of water; spirometry re-check 4 weeks post-optimisation Physiotherapy Pre-operative breathing exercises, incentive spirometry (IS), and chest physiotherapy for secretion clearance; IS 10 repetitions hourly pre- and postoperatively reduces atelectasis rate by 30% Treat acute If purulent sputum/fever → antibiotics for ≥4–6 weeks before surgery; elective surgery during active exacerbation is contraindicated (triples PPC risk) exacerbation Pulmonary 4–8 week supervised exercise programme if FEV1 <50% and surgery is semi-elective; improves functional capacity and reduces PPCs rehabilitation

Regional Anaesthesia Preference Thoracic epidural (TEA) T6–T8: provides surgical anaesthesia ± sedation for laparotomy in selected patients; avoids GA and its airway/ventilatory consequences; reduces PPCs by 30% compared with GA; insert epidural preoperatively; combined epidural+GA preferred (epidural → superior post-op analgesia → better respiratory function post-op)

If GA Required (Laparoscopic Colorectal)

Bronchodilator pre-treatment: nebulised salbutamol 2.5 mg before induction via nebuliser

Induction: avoid histamine-releasing drugs (atracurium, morphine, thiopentone — all can cause bronchospasm); propofol (bronchodilator) preferred for induction; rocuronium for intubation

Airway: ETT preferred over LMA (secure airway needed for abdominal surgery + risk of bronchospasm); however LMA can be used for selected procedures if leak pressure >25 cmH₂O Ventilatory Settings for COPD Parameter Setting Rationale Tidal Volume 6–8 mL/kg IBW Lung-protective; avoid overdistension of already hyperinflated lung Respiratory Rate 8–12 breaths/min Lengthens expiratory time → complete exhalation → prevents gas trapping and auto-PEEP build-up (LOW) I:E ratio 1:3 or 1:4 (prolonged Standard 1:2 inadequate for obstructive physiology; prolonged expiratory time allows complete emptying through expiration) narrowed airways PEEP Minimal (3–5 cmH₂O) or Auto-PEEP already present; extrinsic PEEP >auto-PEEP level adds to air trapping; measure auto-PEEP by expiratory zero hold Permissive Accept PaCO₂ 50–60 Avoid normalising PaCO₂ at cost of excessive airway pressures; this patient may normally retain CO₂ (chronic hypercapnia mmHg hypercapnia — check preop ABG baseline) Volatile agent Sevoflurane preferred Bronchodilator properties; avoid desflurane (airway irritant, may trigger bronchospasm)

Epidural analgesia: continue thoracic epidural for 48–72 hours post-op → allows deep breathing and productive coughing → reduces splinting → reduces atelectasis and pneumonia; superior to IV morphine for COPD patients

NIV/CPAP: plan for immediate BiPAP support post-extubation in GOLD III/IV patients; BiPAP settings: EPAP 5 cmH₂O + IPAP 12–16 cmH₂O; reduces reintubation rate; may be used prophylactically for first 24 hours

Early mobilisation: sitting out of bed day 1 post-op; physiotherapy-supervised ambulation; improves FRC and reduces atelectasis

Minimise opioids: opioid-sparing multimodal analgesia (TEA + paracetamol + NSAIDs); opioid-induced respiratory depression is catastrophic in this patient

HDU/ICU: book ICU/HDU bed preoperatively; plan for extended monitoring; daily spontaneous breathing trials if intubated post-op

Parameter Change by Term Mechanism Anaesthetic Implication Blood ↑ 40–50% (plasma ↑45%, RBC Progesterone → aldosterone activation → Na⁺/water Physiological anaemia of pregnancy (Hb <100 = Volume ↑20%) — dilutional anaemia (Hb retention; oestrogen → renin-angiotensin; plasma pathological); increased blood volume provides falls to 105–110 g/L at term) expansion exceeds RBC production haemorrhage buffer but masks volume depletion Cardiac ↑ 40–50% by 28–32 weeks; CO ↑ Blood volume, ↓ SVR (progesterone → High CO masks underlying cardiac pathology; cardiac Output = HR × SV; HR ↑15–25 bpm; SV vasodilation), ↑ metabolic demand of the feto- disease patients may decompensate in late pregnancy; CO ↑25–30%; further ↑ 15% during placental unit peaks 32–36 weeks not at term labour contractions SVR ↓ 20% (vasodilation from Progesterone → smooth muscle relaxation; Low SVR → relative hypotension; regional anaesthesia → progesterone + prostacyclin) prostacyclin production ↑; results in low-resistance further ↓ SVR → risk of severe hypotension particularly in hyperdynamic circulation pre-existing vasoconstricted states Aortocaval Supine hypotension syndrome in Gravid uterus compresses IVC (right side) and aorta ALWAYS left lateral tilt (15°) for supine procedures after 20 Compression 10–15% at term; IVC (left lateral reduces this) when supine; collateral weeks; for cardiac arrest in pregnancy: manual uterine compression → ↓ venous return circulation (paravertebral, azygous veins) displacement + left lateral tilt during CPR; perimortem CS → ↓ CO → hypotension compensates partially in most patients within 5 minutes if no ROSC

Parameter Change Anaesthetic Implication FRC ↓ 20% (400 mL) — most important respiratory ↓ Oxygen reservoir → rapid desaturation during apnoea; SpO₂ falls faster than in non-pregnant; change; diaphragm is pushed up 4 cm by gravid preoxygenation mandatory and may be less effective; closing capacity may exceed FRC in the uterus supine position → airway closure → shunt → worse oxygenation O₂ ↑ 20–30% at term (metabolic demands of fetus Rapid O₂ consumption + ↓ FRC → very short safe apnoea time; preoxygenate with 100% O₂ for 3–5 Consumption + uterus) minutes ALWAYS before obstetric RSI Tidal Volume TV ↑ 40%; RR ↑ 15%; MV ↑ 50%; driven by Hyperventilation of pregnancy: PaCO₂ falls to 30–32 mmHg (normal for pregnancy); "normal" PaCO₂ + MV progesterone stimulating the respiratory centre 40 mmHg indicates CO₂ retention in a pregnant patient; pH maintained by renal bicarbonate excretion (HCO₃⁻ falls to 18–21 mEq/L) Airway Oedema + hyperaemia of upper airway Smaller ETT (6.5–7.0 mm vs 7.5–8.0 mm standard); use nasal airways with extreme caution mucosa (oestrogen effect); capillary engorgement → (epistaxis); video laryngoscopy first-line for all obstetric intubations; Mallampati class increases as increased bleeding with instrumentation pregnancy progresses

Gastric emptying: progesterone relaxes lower oesophageal sphincter (LOS) → ↓ LOS tone → regurgitation risk; mechanical displacement of stomach by uterus changes gastric axis; opioids during labour dramatically slow gastric emptying → a labouring woman who received opioids should be treated as having a full stomach regardless of fasting time

Gastric acid: ↑ gastric acid production (gastrin from placenta); the combination of ↓ LOS tone + ↑ gastric acid = "at risk for aspiration" from 16–20 weeks gestation

Aspiration prophylaxis: ranitidine 150 mg oral or 50 mg IV (↓ gastric acid pH); sodium citrate 30 mL oral (non-particulate antacid — immediate neutralisation of gastric acid); metoclopramide 10 mg IV (↑ gastric emptying, ↑ LOS tone); RSI protocol for any general anaesthesia after 16–20 weeks; clear liquid fasting 2 hours, light meal 6 hours (but treat as full stomach if in active labour with opioids)

Physiological anaemia: dilutional (plasma ↑45%, RBC ↑20%); Hb 105–115 g/L normal at term; true anaemia in pregnancy = Hb <100 g/L

Hypercoagulability: Virchow's triad complete in pregnancy — hypercoagulability (↑ clotting factors I, VII, VIII, X, XII; ↓ protein S; acquired resistance to protein C), venous stasis (↑ venous pressure in legs; ↓ venous tone from progesterone), and endothelial injury (from placental trauma, delivery); DVT risk ↑5× vs nonpregnant; PE is leading cause of maternal mortality in the UK

VTE prophylaxis: LMWH for high-risk pregnancies (immobility, thrombophilia, previous DVT); graduated compression stockings; early ambulation; timing of neuraxial anaesthesia relative to last LMWH dose (unfractionated 4 hours; LMWH 12 hours prophylactic or 24 hours therapeutic dose)

Platelet count: mild thrombocytopenia of pregnancy (gestational thrombocytopenia — Plt 70–150 × 10⁹/L at term) — benign; does NOT contraindicate epidural; contraindication threshold for neuraxial anaesthesia: Plt <70–80 × 10⁹/L (institution-specific) with normal platelet function

Parameter Change Drug Effect Plasma Albumin ↓ 20–30% → less drug protein-bound → more free (active) Propofol, thiopentone, local anaesthetics: increased free fraction → greater protein drug effect per dose; reduce doses accordingly binding Renal GFR ↑50% → creatinine falls to 0.5–0.6 mg/dL (normal pregnant); Renally-cleared drugs (aminoglycosides, digoxin) have shorter t½ → may need clearance renal tubular secretion ↑ higher/more frequent doses MAC MAC ↓ 25–40% from early pregnancy (high progesterone → Standard MAC concentrations produce deeper anaesthesia in pregnant (volatile GABAergic CNS depression) patients; doses should be reduced; risk of cardiovascular depression agents) Epidural LA Epidural veins engorged (↓ epidural space volume) → same LA volume Reduce epidural and spinal doses by 25–30%; a "standard" dose produces a dose spreads further → blocks are 25–30% more extensive higher block than expected in pregnancy

Category Examples Full stomach / known Emergency surgery (<6 hours from last solid meal); trauma (pain + opioids delay gastric emptying); inadequate fasting (non-compliant aspiration risk patient, unknown time of last meal); post-pyloric obstruction (ileus, bowel obstruction); hiatus hernia + severe GORD with symptoms at rest Physiological/anatomical Pregnancy (>16–20 weeks); opioid administration within 4 hours; diabetic gastroparesis (particularly insulin-dependent); renal failure; acute delay in gastric abdominal emergency (pain reflex slows gastric emptying) emptying Raised intra-abdominal Morbid obesity; ascites; peritoneal dialysis; bowel obstruction pressure

1. Preoxygenation: 3–5 minutes 100% O₂ via tight-fitting face mask (SpO₂ ≥99%); 4 vital capacity breaths as alternative if time critical; head-up 20° position increases FRC and tolerance of apnoea 2. Pre-oxygenation assessment: confirm difficult airway assessment completed; DAS algorithm available; team briefed; sugammadex 16 mg/kg drawn and ready if rocuronium used 3. Induction agent (rapid IV): thiopentone 4–5 mg/kg IV (classic choice — extremely rapid and reliable LOC in <30 sec; reduces ICP; propofol 2–2.5 mg/kg is the modern alternative — more cardiovascular depression but associated with less PONV and lower aspiration risk from earlier return of reflexes) 4. Cricoid pressure (Sellick's manoeuvre): applied simultaneously with induction drug injection by a trained assistant; 10 N (cricoid just visibly displaces) during awake phase → 30 N after LOC; maintained until ETT position confirmed; specific technique: steady downward pressure on the cricoid cartilage (not thyroid) compresses the cricoid ring against the vertebral body → occludes the upper oesophagus → prevents passive regurgitation of gastric contents into the pharynx 5. Succinylcholine 1.5 mg/kg IV: the classic RSI NMB; fastest onset (60 seconds) of any NMB; OR rocuronium 1.2 mg/kg (equivalent intubating conditions at 60 sec; sugammadex 16 mg/kg available for reversal if CICO) 6. No bag-mask ventilation between induction and intubation in classic RSI (avoids gastric insufflation); if SpO₂ falls <93% during apnoea → gentle bag-mask ventilation acceptable (modern modification) with cricoid pressure maintained 7. Intubation at 60 seconds: laryngoscopy + intubation at the time of peak NMB effect; no waiting for response to painful stimuli; direct or video laryngoscopy based on anticipated airway 8. Confirm ETT position: ETCO₂ waveform (sustained over 6 breaths) + bilateral breath sounds + SpO₂ maintenance; inflate cuff; release cricoid pressure once position confirmed; secure ETT

Sellick's Manoeuvre — What the Evidence Shows

Arguments FOR: Reduces regurgitation in cadaveric studies; still recommended by RCOA, DAS 2018, and most obstetric guidelines as standard of care

Arguments AGAINST: Reduces LOS competence at 30 N (paradoxically may allow regurgitation); impairs laryngoscopic view in up to 20% of cases; incomplete protection (only works against passive regurgitation, not active vomiting); no randomised controlled trial demonstrating reduced aspiration morbidity; may cause oesophageal rupture if the patient vomits against closed cricoid

DAS 2018 guidance: Cricoid pressure should be applied but must be released immediately if it impairs laryngoscopic view or interferes with intubation attempt; the airway takes priority over aspiration prevention

Rocuronium 1.2 mg/kg provides equivalent intubating conditions to succinylcholine 1.5 mg/kg at 60 seconds; sugammadex 16 mg/kg immediately available for reversal if CICO

Advantages over succinylcholine: no contraindications in burns, denervation, MH susceptibility, pseudocholinesterase deficiency, hyperkalaemia risk; longer clinical duration (30–45 min vs 10 min) which can be an advantage (no recurarisation) or disadvantage (if airway fails and spontaneous recovery is needed)

CICO scenario: rocuronium RSI + CICO → sugammadex 16 mg/kg → spontaneous ventilation returns in 2–3 min → "wake and manage awake" strategy; this converts a catastrophic situation into a recoverable one

Where succinylcholine still preferred: where briefest possible duration is specifically needed (very brief intubation, hyperkalemia acceptable, no CICO concern with established airway plan)

STOP-BANG for OSA: Snoring (loud enough to be heard through closed door?), Tired (tired/fatigued during daytime?), Observed apnoeas (by partner?), blood Pressure (hypertension?), BMI >35, Age >50, Neck circumference >40 cm, Gender male; ≥5 positive = high risk for severe OSA; this patient with BMI 52 + hypertension + female = at minimum moderate risk

Airway assessment: Mallampati class (higher in obese); neck circumference >40–45 cm is the strongest predictor of difficult intubation in obese patients (independently of Mallampati); limited neck extension; LEMON score; plan for video laryngoscopy as first-line tool

Investigations: ECG (RVH, LVH from chronic hypoxaemia/hypertension); echocardiogram (pulmonary hypertension, RV function); spirometry (restrictive pattern — ↓ FVC, ↓ FRC, ↓ ERV, normal FEV1/FVC; severe OSA with pulmonary hypertension = very high risk); ABG if suspected daytime CO₂ retention (obesity hypoventilation syndrome)

CPAP pre-admission: if OSA diagnosed — patient should be on home CPAP; bring CPAP machine to hospital; use throughout recovery and post-op

Ramped position (HELP position — Head Elevated Laryngoscopy Position): pillows/foam wedge under head and shoulders to align the external auditory meatus with the sternal notch; this optimises the laryngoscopic view (brings glottis into line of sight) in obese patients and simultaneously maximises the FRC benefit of head-up positioning; the HELP position reduces failed first-attempt intubation rates in obese patients by ~50%

Preoxygenation: 3–5 minutes 100% O₂; consider non-invasive ventilation (BiPAP/CPAP 5–10 cmH₂O) during preoxygenation — applies positive pressure to stent open collapsed small airways in obese patients, increasing FRC and O₂ reserve; high-flow nasal O₂ (HFNO) 60 L/min through apnoeic period extends safe apnoea time; target ETO₂ >90% at end of preoxygenation to confirm denitrogenation Safe apnoea time is markedly reduced in morbid obesity — SpO₂ may fall to critical levels within 90 seconds of apnoea vs 8+ minutes in a normal-weight patient; this is the most important practical implication of FRC reduction in obesity

Drug Dosing in Obesity Drug Dose Basis Rationale Propofol Lean Body Weight (LBW) for induction dose; LBW for induction — obese patients have proportionally less increase in central compartment (induction) Total Body Weight (TBW) for maintenance volume vs LBW; TBW for maintenance — larger volume of distribution for fat-soluble propofol infusion Succinylcholine Total Body Weight (TBW) NMBs distribute into extracellular fluid which increases in proportion to TBW in obesity / Rocuronium Sugammadex Actual Body Weight (ABW/TBW) Must encapsulate total circulating rocuronium based on TBW dosing; underdosing causes incomplete reversal Fentanyl / Lean Body Weight (LBW) Opioids should be dosed conservatively in obese patients — increased sensitivity to respiratory Morphine depression; avoid boluses; prefer remifentanil infusion for precise titration Local Ideal Body Weight (IBW) LA does not distribute into fat; TBW dosing would cause LAST; reduce dose as epidural space anaesthetics smaller (fatty infiltration) (regional)

Ventilation Strategy (Laparoscopic — Trendelenburg + Pneumoperitoneum)

Lung-protective ventilation: TV 6–8 mL/kg IBW (NOT TBW — obese lungs are not proportionally larger); using TBW for TV in obesity = massive overventilation = VILI PEEP 10–12 cmH₂O: morbidly obese patients develop rapid atelectasis; higher PEEP than standard needed to prevent alveolar collapse in dependent lung regions; Trendelenburg + pneumoperitoneum → severe FRC reduction → PEEP 10–12 required

Recruitment manoeuvre: 30 cmH₂O sustained inflation for 30 seconds at position change and after pneumoperitoneum then maintain PEEP 10–12; reduces atelectasis significantly

FiO₂: avoid 100% O₂ unnecessarily — absorption atelectasis; target SpO₂ ≥95% with minimum necessary FiO₂

Complication Risk in Obese Prevention Hypoxaemia / Very high; OSA + opioids + supine positioning + upper Semi-recumbent position (30–45° head-up) in recovery; CPAP immediately postObstructive abdominal incision extubation; supplemental O₂; nurse 1:1 in recovery; SpO₂ monitoring ≥12 hours apnoea post-op; avoid opioids DVT/PE ↑ VTE risk 2–3× vs normal weight (venous stasis + LMWH (dose based on TBW for adequate anti-Xa levels — standard prophylactic hypercoagulability + immobility) dose often insufficient); pneumatic compression stockings; early mobilisation; consider extended LMWH prophylaxis for 28 days post-bariatric surgery Wound Impaired wound healing (poor oxygenation of subcutaneous Laparoscopic preferred to open (fewer SSIs); adequate subcutaneous closure; complications fat); SSI 2–3× higher antimicrobial sutures; glycaemic control (<10 mmol/L) Rhabdomyolysis Specific to morbidly obese patients positioned on standard Adequate padding under all pressure points; limit case duration; CK monitoring operating tables; pressure necrosis of dependent muscle post-operatively for cases >3 hours; IV fluids to maintain UO ≥1 mL/kg/hr groups (particularly buttocks in lithotomy, back in supine)

Feature Infant/Child Adult Clinical Consequence Laryngeal C3–C4 in neonates (high and anterior) C4–C5 More difficult to align larynx with the line of sight during laryngoscopy; straight position Miller blade preferred in neonates (lifts the epiglottis directly) Epiglottis Long, stiff, omega-shaped (Ω); floppy Short, flat; flexible Miller blade (straight) more effective for direct lift of epiglottis; Macintosh blade (curved, fits vallecular) less reliable in infants Narrowest Subglottis (cricoid ring) — funnel-shaped airway; Glottis (true vocal ETT that passes through the cords may still be too tight at the subglottis; too point the cricoid ring is the non-distensible narrowest cords) large a tube → subglottic oedema → post-extubation stridor; a small air leak at point 15–20 cmH₂O is the correct fit indicator for uncuffed tubes Head and Large occiput → passive neck flexion in supine Smaller occiput; In neonates: a small shoulder roll under the shoulders (not the head) brings the occiput position → relative anterior laryngeal position neck extension larynx into the line of sight; neutral "sniffing" position or slight extension; NO needed for pillow under the head intubation Tongue Relatively large tongue for the oral cavity size → Proportionally Higher aspiration and obstruction risk; jaw thrust more important; LMA insertion more easily obstructs airway; more likely to fall smaller may be more challenging back in unconscious child Rib cage Horizontal ribs → FRC-dependent breathing; Downward- Neonates desaturate extremely rapidly (≤60 seconds in a neonate vs 8+ higher closing capacity relative to FRC → small sloping ribs allow minutes in healthy adults); keep preoxygenation time adequate; work fast during airway closure at FRC → rapid desaturation active increase in apnoea FRC

Parameter Formula Example (5-year-old) Uncuffed ETT internal diameter (Age/4) + 4 = ID in mm (5/4) + 4 = 5.25 → use 5.0 mm uncuffed Cuffed ETT internal diameter (Age/4) + 3.5 = ID in mm (5/4) + 3.5 = 4.75 → use 4.5 mm cuffed ETT length at lips (oral) (Age/2) + 12 cm (5/2) + 12 = 14.5 cm at lip ETT length at nostril (nasal) (Age/2) + 15 cm (5/2) + 15 = 17.5 cm at nostril LMA size <5 kg = size 1; 5–10 kg = 1.5; 10–20 kg = 2; 20–30 kg = 2.5; 30–50 kg = 3; >50 kg = 4 20 kg child = LMA size 2.5

Anticipated difficult airway: plan in advance; assemble the paediatric difficult airway trolley (range of LMAs, paediatric video laryngoscope [Karl Storz DCI or CMAC paediatric blade], paediatric fiberoptic bronchoscope [2.8 mm minimum for ETT loading], paediatric cricothyrotomy kit); experienced paediatric anaesthesiologist; ENT surgeon on standby for possible surgical airway

Inhalational induction (spontaneous breathing maintained): the safest technique for anticipated difficult airway in children — induction with sevoflurane in 100% O₂, maintaining spontaneous ventilation throughout; once adequately anaesthetised, direct laryngoscopy ± video laryngoscopy attempted; if fails → LMA; if LMA → use as conduit for FOI; if all fails → wake up (spontaneous breathing maintained throughout → safe to allow the child to recover)

Video laryngoscopy in paediatrics: paediatric-sized blades (C-MAC size 0, 1, 2; Karl Storz DCI Miller size 0, 1); improving first-attempt intubation success vs direct laryngoscopy; increasingly recommended as first-line for anticipated difficult airway in children

Fibreoptic intubation (awake FOI in paediatrics): rarely practical in young children (unlike adults); infants do not cooperate for topical airway anaesthesia; preferred approach: sedated (dexmedetomidine infusion) or lightly anaesthetised FOI with spontaneous ventilation; technique: 2.8 mm or 3.5 mm paediatric fibrescope through a face mask or LMA while child breathes spontaneously; ETT railroaded over the scope once in trachea

Front-of-Neck Access (FONA) in children: true cricothyrotomy is technically challenging in infants (small cricothyroid membrane); needle cricothyrotomy (14G IV cannula) with jet ventilation is the primary emergency technique in children <8 years; surgical cricothyrotomy and tracheostomy for older children/adolescents

Higher O₂ consumption per kg (6–8 mL/kg/min vs 3 mL/kg/min adults); very small functional residual capacity → rapid desaturation; safe apnoea time in a neonate ≈ 60–90 seconds Higher heart rate (normal neonatal HR 120–160 bpm; infants 100–120 bpm); cardiac output is rate-dependent in neonates (cannot increase SV significantly — immature Frank-Starling mechanism) → bradycardia = fall in cardiac output; ALWAYS give atropine 20 mcg/kg before laryngoscopy in neonates/young infants

Temperature regulation: high surface area:body mass ratio → rapid heat loss; all fluids warmed; warming blanket; theatre temperature 28°C for neonates; temperature monitoring mandatory

Effect Mechanism Intraoperative Management ↑ SVR (early IAP compression → mesenteric vasoconstriction; CO₂ absorption MAP rises initially; may require vasodilators in hypertensive patients; volatile and → sympathetic activation → ↑ catecholamines → vasoconstriction; agents and deeper anaesthesia help manage hypertension from CO₂ absorption sustained) IAP 12–15 mmHg → SVR ↑30–50% ↓ Venous IAP >12 mmHg → IVC compression → ↓ preload; initial ↑ CO from Adequate preloading before insufflation (250–500 mL crystalloid); vasopressors Return → ↓ leg-emptying into central circulation then falls as IVC compression for sustained hypotension; Trendelenburg position modifies venous return (↑ in CO predominates head-down; ↓ further in head-up laparoscopy) (intermediate) ↑ HR Sympathetic activation from CO₂ absorption and surgical stress; Adequate depth of anaesthesia; beta-blocker if needed for rate control (moderate) partially offset by vagal tone from peritoneal stretching Cardiac Hypercapnia (CO₂ absorption) → ↑ catecholamines → arrhythmia; Atropine available; adequate hyperventilation to prevent hypercapnia; if arrhythmia also vagal reflex from peritoneal stretching at insufflation onset → arrhythmia → check ETCO₂ and ABG; consider desufflation bradycardia → asystole (rare)

↓ FRC and lung compliance: diaphragm displaced cranially by pneumoperitoneum → FRC reduced 10–20% beyond position-related reduction; peak airway pressures rise 40–50% for same TV; atelectasis in dependent lung regions

CO₂ absorption: CO₂ gas diffuses from the peritoneal cavity into systemic blood → ETCO₂ rises 10–20 mmHg above pre-insufflation baseline within 10–20 minutes; must increase MV by 15–25% to maintain normocapnia; in patients with severe COPD or very limited reserve, maintaining normocapnia may not be possible without dangerous airway pressures → accept permissive hypercapnia

Gas embolism risk: direct IV insufflation of CO₂ (rare but catastrophic) → sudden fall in ETCO₂ + cardiovascular collapse; CO₂ is more water-soluble than air → reabsorbed faster from the blood; management: stop insufflation; left lateral Durant's position; aspiration via CVP catheter; CPR

Renal: IAP >15 mmHg → renal vein compression → ↓ renal blood flow → oliguria (transient — resolves on desufflation); not associated with post-op AKI in healthy patients; ensure adequate hydration; monitor urine output; avoid NSAIDs peri-operatively if oliguric intraoperatively

ICP rise: CO₂ absorption → hypercapnia → cerebral vasodilation → ↑ CBF → ↑ ICP; compounded by ↑ CVP from IAP raising venous pressure; head-down Trendelenburg further raises ICP; relevant in patients with pre-existing raised ICP or ventriculoperitoneal shunts

Subcutaneous emphysema: CO₂ tracks along fascial planes from the peritoneal cavity into subcutaneous tissue; presents as crepitus on palpation; may cause extensive tracking to the mediastinum and neck; results in massive CO₂ absorption → very high ETCO₂ → increase MV further; does not require specific treatment unless compromising airway or mediastinal structures

Airway: ETT mandatory (positive pressure needed; aspiration risk from raised IAP; patient may need Trendelenburg); LMA is used for brief, non-obese patients in selected units with second-generation supraglottic devices (higher seal pressure)

Ventilation settings: TV 6–8 mL/kg IBW; PEEP 5–8 cmH₂O; RR adjusted to maintain normocapnia (increase by 15–25% from baseline after CO₂ insufflation); monitor ETCO₂ continuously; check ABG at 30–60 minutes if significant patient complexity; accept permissive hypercapnia in COPD patients rather than use excessive driving pressures

PONV: laparoscopy is one of the highest PONV risk procedures; full multimodal PONV prophylaxis based on Apfel score; TIVA with propofol reduces PONV incidence by 25–30% vs volatile; ondansetron + dexamethasone minimum for all laparoscopic procedures

Analgesia: port-site local anaesthetic infiltration (bupivacaine 0.5% at each port before closure); IV paracetamol + NSAIDs; opioid-sparing; TAP block for larger ports/incisions; intraperitoneal local anaesthetic instillation (bupivacaine) reduces post-operative visceral pain after laparoscopy

Desufflation awareness: sudden desufflation may cause vasovagal reaction (brief hypotension + bradycardia); anaesthesiologist should be informed before desufflation; have atropine ready

Normal MVA = 4–6 cm²; symptoms begin at MVA <2.5 cm²; MVA 1.0–1.5 = severe; MVA <1.0 = very severe

Mechanism: stenotic mitral valve → ↑ LA pressure → pulmonary venous hypertension → pulmonary oedema; chronic LA pressure ↑ → pulmonary arterial hypertension → RV hypertrophy and failure; fixed outflow from LA → any ↑ HR shortens diastolic filling time → less time for blood to cross the stenotic valve → sudden ↑ LA pressure → acute pulmonary oedema (the key clinical insight) AF is almost universal in significant MS (atrial dilation drives AF); loss of atrial systole ("atrial kick") removes 20–30% of ventricular filling → additional haemodynamic compromise

Regional Anaesthesia (Preferred)

Spinal anaesthesia: technically simple but produces sudden sympathectomy → acute hypotension → reflex tachycardia → catastrophic in MS; spinal is RELATIVELY CONTRAINDICATED for major surgery in MS because the sympathectomy is abrupt and may cause severe tachycardia from reflex sympathetic activation; if used → titrated slowly (combined spinal-epidural with very small initial intrathecal dose + epidural top-up) or avoided

Epidural anaesthesia: preferred for regional technique — allows gradual titration of sympathectomy level; maintains more haemodynamic control than spinal; place thoracic epidural for laparoscopic hysterectomy; slow top-up in 5 mL increments; use vasopressor (phenylephrine) to maintain SVR; monitor closely for tachycardia

General Anaesthesia (for Laparoscopic Case)

Induction: etomidate (most cardiovascularly stable) or carefully titrated propofol; AVOID ketamine (↑ HR → ↑ LA pressure → pulmonary oedema); fentanyl 1–2 mcg/kg with induction to blunt laryngoscopy response

Maintenance: sevoflurane preferred (moderate rate reduction; preconditioning); avoid desflurane (sympathetic activation → tachycardia)

Intraoperative tachycardia management: esmolol 0.5–1 mg/kg IV bolus; or digoxin if not already digitalised; metoprolol 1–2 mg IV bolus

Fluid management: conservative; avoid large volume crystalloid boluses; pulmonary artery catheter or TOE for haemodynamic monitoring in MVA <1.0 cm²

CO₂ pneumoperitoneum in MS: ↑ IAP → ↑ SVR (helps maintain MAP) and initial ↑ CO₂ absorption → sympathetic activation → tachycardia (harmful); maintain ETCO₂ strictly in normal range (increase MV to manage absorbed CO₂)

Trendelenburg position: increases venous return to an already volume-loaded right heart → may precipitate acute pulmonary oedema; head-down tilt must be gradual; monitor closely

Post-desufflation: sudden ↓ IAP → venous pooling → ↓ preload → ↓ CO; prepare vasopressor

HDU/ICU level monitoring for 24 hours post-op; cardiac monitoring (continuous ECG); resume rate-control medications immediately post-op; watch for AF with rapid ventricular rate; fluid balance (restrict fluids post-op; furosemide if signs of pulmonary congestion); anticoagulation for AF (warfarin or DOAC — check thromboembolism vs bleeding balance post-surgery); resume warfarin/DOAC within 24 hours if haemostasis adequate

Item Fasting Period Rationale Clear liquids (water, black 2 hours before Clear fluids empty from the stomach within 30–60 minutes; gastric pH improves with fluid consumption (dilutes coffee, clear fruit juice without induction acid); preoperative carbohydrate drink (200–400 mL of 12.5% carbohydrate solution 2 hours before surgery) pulp, sports drinks, carbonated reduces insulin resistance and anxiety, improves postoperative outcomes — integral to ERAS protocols drinks) Breast milk (infants) 4 hours Breast milk empties from the stomach faster than formula or cow's milk due to its whey-dominant protein composition and lower fat content Infant formula / non-human milk 6 hours Higher fat and protein content → slower gastric emptying Light meal (toast, crackers, 6 hours Light meals typically empty within 4–5 hours; 6-hour fasting ensures adequate buffer simple carbohydrate meal — low fat, low protein) Full/fatty/fried meal (heavy meal 8 hours High-fat meals significantly slow gastric emptying; fat delays gastric acid secretion reduction; high-protein meals — high fat, meat, fried food) minimum are digested slowly; in practice: a large evening meal → fast from midnight (8+ hours) is appropriate (some guidelines: overnight fast)

Patient Modification Rationale Group Pregnancy Treat as full stomach regardless of fasting time (in active labour + opioids); RSI mandatory; Progesterone reduces LOS tone; opioids (>16–20 sodium citrate 30 mL oral + H₂ blocker before all GA dramatically slow gastric emptying; risk persists weeks) through full postoperative period Morbid Apply standard fasting times; however, gastric emptying may be delayed; some centres treat Obesity associated with raised intra-abdominal obesity morbidly obese patients with raised aspiration risk as "full stomach" for GA pressure and higher gastric residual volumes; GORD common Diabetes Establish surgery as first on the list (shortest fasting); monitor blood glucose hourly; variable rate Diabetic gastroparesis delays gastric emptying; mellitus insulin infusion (VRIII) if glucose >14 mmol/L; resume oral agents when eating and drinking; omit prolonged fasting → hypoglycaemia; insulin on the metformin if GA with fasting (standard glucose-containing fluids in prolonged fasting) morning of surgery without food → severe hypoglycaemia Emergency Treat as full stomach regardless; RSI if GA; aspiration prophylaxis; check last oral intake as part Emergency surgery cannot wait for fasting to surgery of pre-operative history complete; RSI is the mechanism for managing fullstomach risk when anaesthesia must proceed Gastro- Continue proton pump inhibitor (PPI) preoperatively (omeprazole 20 mg oral OD); consider PRN GORD with severe symptoms/hiatus hernia → oesophageal antacid pre-operatively; apply RSI if severe symptoms/hiatus hernia with regurgitation at rest elevated aspiration risk even with adequate fasting reflux disease (GORD)

200–400 mL of a specialised clear carbohydrate drink (12.5% maltodextrin — e.g., PreOp, Nutricia) given 2–3 hours before induction as part of the ERAS protocol

Evidence: reduces insulin resistance by 50%; reduces preoperative thirst, hunger, anxiety; reduces length of hospital stay by 0.5–1 days in colorectal ERAS programmes

Safe: gastric emptying is complete within 90 minutes for this formulation; not associated with increased aspiration risk vs water; contraindicated in: diabetics with gastroparesis; morbid obesity with delayed gastric emptying; immediate emergency surgery

Property Desflurane Sevoflurane Blood-gas partition 0.42 (lowest of all volatile agents) 0.65 coefficient (λ) MAC (O₂, 40-year adult) 6.0% 2.0% Boiling point 23.5°C (near room temp → requires heated pressurised TEC-6 vaporiser with 58.5°C (standard draw-over TEC-7 vaporiser; no electrical power) heating required) Global Warming Potential 2540 (most potent greenhouse gas anaesthetic); atmospheric lifetime 14 years 130; atmospheric lifetime 1.1 years (GWP 100-year)

Inhalational induction NOT suitable — pungent; causes coughing, laryngospasm, breath-holding; cannot Suitable — non-pungent, pleasant odour; gold suitability be used for gas induction standard for paediatric gas induction; smooth and rapid

Cardiovascular effects — Causes marked sympathetic activation (tachycardia + hypertension) when Minimal sympathetic activation with concentration abrupt concentration concentration rapidly increased → dangerous in ischaemic heart disease; requires changes; smoother cardiovascular profile increase gradual titration Metabolism Minimal (<0.02%) — essentially no hepatic metabolism; no nephrotoxic metabolites 2–3% hepatic metabolism → inorganic fluoride + HFIP; Compound A from soda lime degradation Recovery speed Fastest of all volatile agents; significant time advantage in long cases (>6–8 hours); Rapid — marginally slower than desflurane; in (emergence) clinically meaningful in very long procedures procedures <6 hours: discharge time equivalent to desflurane Vaporiser Expensive TEC-6 heated and pressurised vaporiser required; electrically powered; Standard TEC-7 vaporiser; no power required; not portable portable; cheaper Anaesthetic Less data than sevoflurane; some evidence of preconditioning Well-documented ischaemic preconditioning effect preconditioning (mitoKATP channels); benefit in cardiac surgery

When desflurane might be preferred: cases expected >8 hours (morbid obesity, hepatobiliary surgery) where the faster emergence from desflurane provides meaningful time advantage; patients with high risk of prolonged emergence where rapid assessment is clinically important; very long neurosurgical cases requiring rapid wake-up testing

When sevoflurane is clearly preferred: paediatric anaesthesia (gas induction); cardiac surgery (preconditioning benefit); all routine cases (<6 hours, which is the vast majority) where recovery times are equivalent; all environmentally-conscious practice; any patient with ischaemic heart disease (desflurane sympathetic activation on concentration changes is contraindicated)

Environmental decision: UK NHS has banned desflurane from formulary (2021); ESA recommends desflurane should be reserved for exceptional clinical indications only; for the same MAC-hour, desflurane produces 19× more CO₂ equivalent emissions than sevoflurane; switching a department from desflurane to sevoflurane is among the highest-impact individual actions an anaesthesiologist can take for environmental sustainability

Mechanism: NMDA receptor antagonism (the primary mechanism for analgesia and sedation); inhibits nicotinic ACh receptors; modulates opioid receptors (μreceptor agonist — contributes to analgesia and some physical dependence); activates TREK-1 two-pore potassium channels (contributes to sedation)

Properties: colourless gas; sweet smell; no hepatic metabolism; excreted unchanged by the lungs; blood-gas partition coefficient = 0.47 (low — rapid onset and offset); MAC = 105% (requires hyperbaric conditions for surgical anaesthesia as sole agent; clinically used at 50–65% to provide MAC-equivalent of approximately 0.6 MAC)

Analgesia: significant analgesic effect at 30–50% concentrations — equivalent to moderate-dose opioids for procedural pain; the mechanism: endogenous opioid release + NMDA antagonism; Entonox (50% N₂O/50% O₂) provides effective labour analgesia, dental analgesia, and procedure analgesia

Cardiovascular: mild myocardial depression (direct) but sympathomimetic (↑ catecholamines) → net: relatively stable BP and HR; less vasodilatory than volatile agents; suitable for cardiac surgery supplementation

Controversy Mechanism Clinical Evidence Expansion of N₂O is 34× more blood-soluble than N₂; diffuses into gas-filled spaces faster than Strong evidence; absolute contraindication in known gas-filled N₂ leaves → expanding gas volumes (pneumothorax, bowel obstruction, middle pneumothorax, bowel obstruction, middle ear surgery (Jobsonspaces ear, pneumocephalus, intraocular gas bubbles post-vitreoretinal surgery) Horne tympanoplasty), intraocular gas (>3 months after vitreoretinal surgery with gas tamponade), pneumocephalus, and air embolism; N₂O triples/quadruples trapped gas volume PONV N₂O activates opioid receptors in the gut → ↑ PONV; also activates vomiting ENIGMA trial (Myles PS, Lancet 2007; n=2050): N₂O-free increase centre directly; meta-analyses confirm N₂O increases PONV incidence by anaesthesia significantly reduced severe PONV; eliminating N₂O approximately 20–30% relative to N₂O-free anaesthesia from routine practice is one of the most effective PONV prevention strategies Vitamin B12 / N₂O irreversibly oxidises cobalt (Co²⁺→Co³⁺) in the active site of vitamin B12 Clinically relevant in: prolonged exposures (>6 hours); patients Methionine (cobalamin) → inactivation of methionine synthase → impaired methionine with pre-existing B12 deficiency (vegans, elderly, pernicious synthase synthesis → impaired DNA synthesis (folate-methyl trap); single anaesthetic anaemia, malabsorption); ICU patients on prolonged N₂O; patients inhibition exposure → 50% reduction in methionine synthase activity within 2–6 hours; bone on antifolate drugs (methotrexate); subacute combined marrow depression with megaloblastic changes within 24 hours after prolonged degeneration of the cord reported in N₂O abuse and chronic exposure occupational exposure Environmental GWP = 265; atmospheric lifetime 114 years; also depletes stratospheric ozone Multiple hospitals have eliminated N₂O from routine use without impact (similar mechanism to CFCs); N₂O pipeline systems leak 10–30% of delivered patient outcome impact; the ENIGMA trial in fact showed improved gas into building; healthcare N₂O accounts for approximately 5% of all healthcare outcomes in the N₂O-free arm; environmental + PONV evidence greenhouse gas emissions globally together strongly support N₂O elimination from routine anaesthesia