1. Anaesthesia and Morbid Obesity

2. Facts 20% adults Obese (1% Morbidly Obese)
BMI >35 with comorbidity / BMI >40 without comorbidity = morbidly obese
BMI > 55 = super-morbidly obese
BMI > 30 – rapid increase in morbidity and mortality
Men – higher risk of CVS problems

3. Apples and Pears BMI poor predictor of difficulty Fat distribution
Android
Gynaecoid

4. Causes of Obesity Multifactorial Genetic and Environmental
Regulation of appetite and satiety (Hypothalamus)
Leptin, Adiponectin – long term (NB dieting)
Insulin = short term (Hypothalamus)
Ghrelin (Stomach Wall), Peptide YY 3-36 (Intestine)
Leptin/Adiponectin – produced by fat cells. Leptin = reduction in food seeking behaviours. Obese people have more leptin but increased leptin insensitivity. Adiponectin doers same but not increased in obesity.
Stretching of stomach wall suppresses Ghrelin – satiety. Peptide YY – food in intestine - satiety

5. Comorbidity

6. Facts Obesity associated with:
Htn DM OA
Liver Disease
Asthma
OSA
Obesity Hypoventilation Syndrome
Risk of cardio-resp comorbidity increases with duration
NB severe comorbidity may be masked by sedentary lifestyle!

7. Respiratory System - OSA
Apnoeic attacks due to collapse of pharynx whilst asleep
Increases with obesity and age
Fat in pharyngeal wall
Features
Snoring
Frequent apnoeic spells whilst asleep (>10s)
Daytime somnolescence
Pathophysiological changes – hypercapnia, polycythaemia, pulmonary htn and cor-pulmonale

8. Obesity Hypoventilation Syndrome
Affects control of breathing
CO2 sensitivity and ventilatory drive partly leptin controlled
Leptin insensitivity = reduced ventilatory response to CO2.
Depressant drugs accentuate
Often combined with OSA

9. Respiratory Compromise
Features
Hypoxaemia at rest (worse supine + depressants)
Rapid desaturation in apnoea
Reduced lung compliance (increased pulm blood volume)
Reduced chest wall compliance
Small airways collapse + diaphragmatic splinting (Decreased FRC)
Increased alveolar-arterial oxygen tension (worse on induction)
Closing volume close to FRC – airway closure and V/Q mismatch (shunting)
Atelectasis
NB Laparoscopy!! Postoperative period
Decreased FRC with increasing BMI - <1L in BMI>40.

10. Cardiovascular System
Circulating Volume (renin-angiotensin. Polycythaemia).
Ventricular Workload
Redistributed to fat beds
Cerebral/Renal flows unchanged
Oxygen Consumption (Increased BMR)
CO2 production
Systemic Htn (LV stress and LVH)
Pulm Htn possible (Cor-Pulmonale)
Increased metabolic demands of adipose

11. Cardiovascular System
Arrythmias – Why?
Myocardial hypertrophy and hypoxaemia
Hyperkalaemia (Htn Rx)
CAD
Increased circulating catecholamines
OSA
Fatty infiltration conducting system
IHD
Htn DM
Cholesterol
Sedentary Lifestyle
DVT/PE

12. Other Sytems Microvesicular Fatty Liver
Steatohepatitis +/- cirrhosis
GORD and Hiatus Hernia (Aspiration)
Insulin resistance and Type 2 DM

13. Preoperative Assessment

14. Planning Ahead Beware the Sedentary Patient Questioning
Symptoms and signs of OSA/Heart Failure
Comorbid disease
Ability to tolerate supine position
Full airway assessment
Mouth opening, Mallampati, Neck movement, Collar circumference
Any airway obstruction whilst awake

15. Pre-Op Investigations
Individual basis
FBC, U+Es, LFTs, Glucose
ABG in suspected OSA/OHS
ECG
Echo – LV/RV function, Pulm Htn
CXR – cardiac failure
PFTs – poor exercise tolerance
RV strain or cor-pulmonale may benefit from elective night NIV pre elective surgery

16. PreMed
Antacids / PPI
Prokinetics
Sodium Citrate
TEDs

17. Conduct of Anaesthesia

18. Pharmacokinetics
Most drugs affected by adipose tissue – lipophilic drugs
How do you calculate doses?!
Volume of central compartment similar (periph increased)
Increased Volume of Distribution (Vd)
Increased redistribution
Increased elimination t1/2

19. Total weight/ideal weight
Benzos/Barbiturates – ideal body weight
Relaxants – Lean body mass (mass of organs, muscle, bone)
Suxamethonium – total body weight
Propofol – total body weight (esp TIVA)
Local anaesthetics – ideal body weight
Epidurals –
Engorged veins and fat impinge on space
Reduced volume of Epidural Space
Reduce dose by 25%

20. Practical Aspects Theatre Table Enough staff to transfer
Correct sized bp cuff
Consider Position
Could they be head-up?
Sniffing position
Pre-oxygenation
The Difficult Airway Ventilatory Issues
Positioning PEEP
Short-handle/Polio blade
Desaturation
Do they need awake fibreoptic?
Temperature Control Volatile choice
Calf Compression
Beware Laparoscopy Epidural?

21. Postoperative Considerations
Extubation
Risk of obstruction
To CPAP?
Location
Post-Op Care
Good analgesia
Early mobilization, TEDS, Enoxaparin
Close monitoring of BMs (Catabolism)
Cardiovascular stability

22. Any Questions?