Anaesthesia and the Obese Patient

1. Anaesthesia and the Obese Patient Lucy SmithConsultant Anaesthetist, St George’s Hospital15th January 2009

2. Outline • Definitions/ Epidemiology • Physiology of Obesity • Comorbidities • Practical Aspects of Anaesthesia • Bariatric Surgery

3. Definitions based on BMI

4. Limitations BMI • Not a direct measure of adiposity • No account of fat distribution • No account of duration of obesity • Inaccurate at extremes of height • Inaccurate with extremes of lean body mass (eg athletes, elderly) • Waist or collar circumference more predictive of cardio-respiratory comorbidity

5. Fat Distribution • Android • Central distribution • High intra-peritoneal fat content • Increased neck circumference • Waist-hip ratio >0.8 women, >1.0 men • Increased morbidity (airway, CVS, metabolic, surgical) • Gynaecoid • Peripheral sites (arms, legs, buttocks)

6. Epidemiology of Obesity • Epidemic in developed world • Increasing prevalence • Major healthcare challenge • DOH reports: Overweight Obese

7. Treatment Strategies • Multidisciplinary approach • Diet • Physical activities • Behavioral interventions • Drugs • Surgery

8. Physiology of Obesity • Multifactorial - genetic, environmental • Complex regulation of appetite and satiety • Multiple humoral and neurological mechanisms • Integrated and processed in hypothalamus • Hormones include leptin, insulin, ghrelin, peptide YY3-36 • Energy balance and appetite reflexes mediated by ANS

9. Pathways of energy balance

10. Models of obesity pathology • Overeating and inactivity simplistic view • Various pathways suggested • Interactions not clearly established • Key features include • Hyperinsulinaemia (fat deposition) • Insulin resistance (type 2 diabetes) • Defective leptin signalling (satiety) • food reward 20 to dopamine clearance in brain (insulin-mediated)

11. Obesity-related Comorbidities • Prevalence increases with BMI and duration of obesity • May be reason to undergo surgery • Severity may be masked by sedentary lifestyle • Major impact in perioperative period

12. Pathophysiology - Respiratory • Higher energy turnover •  O2 consumption,  CO2 production • +/- chronic hybercarbia with renal compensation and altered CO2 sensitivity • FRC, VC, (A-a) O2, shunt • Airway closure (CC greater than FRC) • chest wall compliance and lung compliance  work of breathing

13. Respiratory Comorbidity • Airway • Obstructive Sleep Apnoea • Obesity Hypoventilation Syndrome • Asthma • Pulmonary Hypertension

14. Airway • Difficulty predicted by OSA, short thick neck and BMI • Fatty infiltration pharyngeal wall • pharyngeal wall compliance • Difficult to ventilate by face mask • Rapid desaturation • Consider awake fibreoptic intubation

15. Obstructive Sleep Apnoea • Apnoeic episodes 2˚ to pharyngeal collapse occurring during sleep • Airfow ceases, ongoing effort, closed airway • >10s, >5/hour, >30/night • Snoring, daytime somnolence, am headaches • Hypoxaemia, 2˚polycythaemia, systemic vasoconstriction, hypercarbia, pulmonary vasoconstriction, RVF

16. Obesity Hypoventilation Syndrome • Altered control of breathing • Diurnal variation • PaCO2 >5.9kPa with 1.3kPa asleep • sO2 not explained by obstruction • ventilatory response to CO2 • Often coexists with OSA • (OSAHS- Obstructive Sleep Apnoea Hypopnoea Syndrome)

17. Asthma • Multiple factors • Acid reflux and micro aspiration • Sleep apnoea and partial obstruction • Peripheral airway closure sheer stresses  proinflammatory response • Bariatric surgery  80-100% resolution

18. Pathophysiology - Cardiovascular • blood volume + cardiac output • ventricular workload • myocardial fat content + contractility • Endothelial dysfunction +vascular resistance • 50% moderate HT, 5-10% severe HT • +/- progressive PVR and PAP • Progresses to RVF. Oedema and hepatic congestion

19. Cardiovascular Comorbidity • Hypertension • Obesity cardiomyopathy • Ischaemic Heart Disease (multiple factors) • Arrhythmias (hypoxaemia, hypertrophy, hypokalaemia, coronary art disease, raised catecholamines, OSA, fatty infiltration conducting and pacing systems) • Cor pulmonale

20. Gastrointestinal Comorbidity • Type 2 diabetes • intra-abdominal pressure •  FRC, aortocaval compression, tissue perfusion, risk abdo compartment syndrome • Fatty liver, steatohepatitis, cirrhosis • Hiatus hernia, gastro-oesophageal reflux • Hyperlipidaemia

21. Musculo-skeletal and Other • Osteoarthritis • Compression fractures • Increased risk of injury • Urinary incontinence • Skin infections, candidiasis, poor hygiene • Varicose veins • Lymphoedema

22. Preoperative Assessment • Anaesthetic history • Details of Comorbidities • Drug history (appetite suppressants) • Airway (MP, neck extension, circumference) • Ability to tolerate supine position • Routine and specific investigations (may include baseline ABG, lung function tests, sleep studies, Echo, cardiac cath and PA pressure studies)

23. Practical Aspects of Anaesthesia • Location: Operating theatre only • Staff: plenty of strong, trained people! • Equipment: appropriate trolleys + table, electric beds, large BP cuffs, pillows, patslide/ hover mattress, airway • Premed: H2 antagonist/ PPI • Positioning: Patient climb onto table, head up tilt 30˚, ‘ramped’- wedge under shoulders (sternum to thyroid cartilage - horizontal level)

24. Induction • iv access (dorsum hand, flexor aspect forearm, central with US guidance) • Consider arterial line • Preoxygenation at least 5 mins • +/- RSI (dose sux 1mg/kg real body wt) • Intubation (short handle, long blade,) • Awake fibreoptic intubation if indicated

25. Maintenance • Short acting agents eg sevoflurane, desflurane, remifentanil • Temperature maintenance • Neuromuscular monitoring • Ventilate with PEEP • Pressure areas and skin • Calf compression • Fluids - insensible losses  BSA • SV/ pulse pressure optimisation

26. Recovery • Aim: rapid emergence with good airway control • Risks: loss of airway control, inadequate respiration, aspiration, postop chest complications, CVS stress and instability • Extubate wide-awake and sitting up +/- CPAP recruitment procedure prior to extubation • Appropriate postop environment

27. Analgesia • Multimodal - paracetamol, NSAIDs, opioids, LA, regional • Paracetamol - central compartment so normal dose, clearance dose frequency • NSAIDs - risk renal dysfunction • Opioids - risk respiratory depression • Regional - higher failure rate

28. Bariatric Surgery • Weight loss surgery • Procedures to treat obesity by modification of GI tract to reduce nutrient intake and/or reduce absorption • ‘Tool’ enabling patient to alter lifestyle and eating habits to achieve effective and permanent management of obesity and eating behaviour

29. Bariatric SurgeryNICE Dec 2006 (CG43) • Recommended as option if: • BMI>40 (or 35 with significant comorbidity or severe DM) • All non-surgical measures tried and failed • Specialist obesity service involved • Fit for anaesthesia and surgery • Committed to long-term follow up • First line option when BMI>50

30. Principles of Bariatric Surgery • Reduction of stomach size (restrictive) food enters small upper gastric pouch passes into lower stomach or intestine early filling, discomfort on eating more • Restriction of size of gastric outlet pouch or stomach remain full for longer • Induction of malabsorption by intestinal bypass

31. Vertical Banded Gastroplasty • Restrictive • ‘Stomach stapling’ • Smaller pre-stomach pouch • Small communication • Rapid satiety • Upper part may distend over time

32. Adjustable Gastric Band • Restrictive • Silicone band • Small upper pouch approx 25ml • Inject saline via s/c port to adjust band to early satiety • Upper pouch can distend • Band can become displaced

33. Sleeve Gastrectomy • Restrictive • Reduces stomach to 15% original size • Remove large portion following greater curve • Open edges joined to form sleeve or tube • Early fullness, no outflow obstruction • May be converted in 2nd stage procedure to gastric bypass or duodenal switch

34. Roux-en-Y Gastric Bypass • Mixed restrictive and malabsorptive • Small stomach pouch • Connect pouch to small intestine • Upper small intestine re-attached in y-shape approx 45cm below stomach outlet

35. Sleeve Gastrectomy with Duodenal Switch • Mixed restrictive and malabsorptive • Stomach disconnected from duodenum • Connected to distal small intestine • Duodenum and upper small intestine attached 75-100cm from colon

36. Jejunoileal Bypass • Malabsorptive procedure no longer performed • Proximal jejunum anastomosed to distal ileum, 10cm before caecum • Short length functional bowel • Long blind loop • Problems with severe malabsorption, dumping, liver failure, cardiac failure, renal stones

37. Laparoscopic Bariatric Surgery • Head-up position (up to 45˚) venous pooling in lower limbs venous return, cardiac output • Pneumoperitoneum venous return, cardiac output intra-abdominal pressure migration gas into tissues progressive pCO2 activation SNS - arrythmias, SVR, BP PAP, ICP High inpiratory pressure + PEEP

38. Complications of Bariatric Surgery • General infection, haemorrhage, incisional hernia, bowel obstruction, VTE • Specific anastomotic leak, anastomotic stricture, dumping syndrome, nutritional deficiencies (iron, vit B12, thiamine, protein malnutrition, vit A)

39. Risk Factors for Complications • M>F • Age >65 • Open Surgery • Long operation time • Cardiac and Respiratory comorbidities • Diabetes • Low case load

40. Health Benefits • Sustained loss of 65-80% excess body weight • Diabetes resolves very rapidly • Asthma resolves early on • OSA - most asymptomatic in 1 year • Hyperlipidaemia resolved in >70% • Essential hypertension resolved in >70% • GOR relieved in most • Low back pain and joint pain relieved in most • self esteem, participation in social activities

41. Summary • Obesity is a major healthcare challenge • Daily challenge for anaesthetists • Obese patients are at risk from comorbidities and pathophysiological changes of obesity • Bariatric surgery is a beneficial and cost-effective healthcare intervention