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Anaesthesia and the Obese Patient

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1 Anaesthesia and the Obese Patient
Lucy Smith Consultant Anaesthetist, St George’s Hospital 15th January 2009

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

3 Definitions based on BMI
BMI (kgm-2) Definition <18.5 Underweight Ideal Weight Overweight Obese or with obesity-related comorbidity Morbidly Obese Super Obese Super Super Obese >70 Hyper Obese

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 Gynaecoid 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 M F 2001 43% 29% 13% 16% 2006 33% 22% 23%

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  % 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 Surgery NICE 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 cm 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 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

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