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