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Anaesthesia and the Obese Patient. Lucy Smith Consultant Anaesthetist, St George’s Hospital 15th January 2009. Outline. Definitions/ Epidemiology Physiology of Obesity Comorbidities Practical Aspects of Anaesthesia Bariatric Surgery. Definitions based on BMI. Limitations BMI.

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anaesthesia and the obese patient
Anaesthesia and the Obese Patient

Lucy SmithConsultant Anaesthetist, St George’s Hospital15th January 2009

  • Definitions/ Epidemiology
  • Physiology of Obesity
  • Comorbidities
  • Practical Aspects of Anaesthesia
  • Bariatric Surgery
limitations bmi
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
fat distribution
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)
epidemiology of obesity
Epidemiology of Obesity
  • Epidemic in developed world
  • Increasing prevalence
  • Major healthcare challenge
  • DOH reports:

Overweight Obese

treatment strategies
Treatment Strategies
  • Multidisciplinary approach
  • Diet
  • Physical activities
  • Behavioral interventions
  • Drugs
  • Surgery
physiology of obesity
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
models of obesity pathology
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)
obesity related comorbidities
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
pathophysiology respiratory
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
respiratory comorbidity
Respiratory Comorbidity
  • Airway
  • Obstructive Sleep Apnoea
  • Obesity Hypoventilation Syndrome
  • Asthma
  • Pulmonary Hypertension
  • 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
obstructive sleep apnoea
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
obesity hypoventilation syndrome
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)
  • Multiple factors
  • Acid reflux and micro aspiration
  • Sleep apnoea and partial obstruction
  • Peripheral airway closure sheer stresses

 proinflammatory response

  • Bariatric surgery  80-100% resolution
pathophysiology cardiovascular
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
cardiovascular comorbidity
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
gastrointestinal comorbidity
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
musculo skeletal and other
Musculo-skeletal and Other
  • Osteoarthritis
  • Compression fractures
  • Increased risk of injury
  • Urinary incontinence
  • Skin infections, candidiasis, poor hygiene
  • Varicose veins
  • Lymphoedema
preoperative assessment
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)
practical aspects of anaesthesia
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)

  • 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
  • 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
  • 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
  • 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
bariatric surgery
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
bariatric surgery nice dec 2006 cg43
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
principles of bariatric surgery
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
vertical banded gastroplasty
Vertical Banded Gastroplasty
  • Restrictive
  • ‘Stomach stapling’
  • Smaller pre-stomach pouch
  • Small communication
  • Rapid satiety
  • Upper part may distend over time
adjustable gastric band
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
sleeve gastrectomy
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
roux en y gastric bypass
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
sleeve gastrectomy with duodenal switch
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
jejunoileal bypass
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
laparoscopic bariatric surgery
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


High inpiratory pressure + PEEP

complications of bariatric surgery
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)

risk factors for complications
Risk Factors for Complications
  • M>F
  • Age >65
  • Open Surgery
  • Long operation time
  • Cardiac and Respiratory comorbidities
  • Diabetes
  • Low case load
health benefits
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
  • 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