Anaesthesia and Morbid Obesity

Facts

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

Apples and Pears

BMI poor predictor of difficultyFat distribution

Android Gynaecoid

Causes of Obesity

MultifactorialGenetic and EnvironmentalRegulation of appetite and satiety (Hypothalamus)Leptin, Adiponectin – long term (NB dieting)Insulin = short term (Hypothalamus)Ghrelin (Stomach Wall), Peptide YY 3-36 (Intestine)

Comorbidity

Facts

Obesity associated with:HtnDMOALiver DiseaseAsthmaOSAObesity Hypoventilation Syndrome

Risk of cardio-resp comorbidity increases with durationNB severe comorbidity may be masked by sedentary lifestyle!

Respiratory System - OSA

Apnoeic attacks due to collapse of pharynx whilst asleepIncreases with obesity and ageFat in pharyngeal wallFeatures

SnoringFrequent apnoeic spells whilst asleep (>10s)Daytime somnolescencePathophysiological changes – hypercapnia, polycythaemia, pulmonary htn and cor-pulmonale

Obesity Hypoventilation Syndrome

Affects control of breathingCO2 sensitivity and ventilatory drive partly leptin controlledLeptin insensitivity = reduced ventilatoryresponse to CO2.Depressant drugs accentuateOften combined with OSA

Respiratory Compromise

FeaturesHypoxaemia at rest (worse supine + depressants)Rapid desaturation in apnoeaReduced lung compliance (increased pulm blood volume)Reduced chest wall complianceSmall 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)AtelectasisNB Laparoscopy!! Postoperative period

Cardiovascular System

Circulating Volume (renin-angiotensin. Polycythaemia).

Ventricular WorkloadRedistributed to fat bedsCerebral/Renal flows unchanged

Oxygen Consumption (Increased BMR)CO2 productionSystemic Htn (LV stress and LVH)Pulm Htn possible (Cor-Pulmonale)Increased metabolic demands of adipose

Cardiovascular System

Arrythmias – Why?Myocardial hypertrophy and hypoxaemiaHyperkalaemia (Htn Rx)CADIncreased circulating catecholaminesOSAFatty infiltration conducting system

IHDHtnDMCholesterolSedentary Lifestyle

DVT/PE

Other Sytems

Microvesicular Fatty LiverSteatohepatitis +/- cirrhosis

GORD and Hiatus Hernia (Aspiration)Insulin resistance and Type 2 DM

Preoperative Assessment

Planning Ahead

Beware the Sedentary PatientQuestioning

Symptoms and signs of OSA/Heart FailureComorbid diseaseAbility to tolerate supine position

Full airway assessmentMouth opening, Mallampati, Neck movement, Collar circumferenceAny airway obstruction whilst awake

Pre-Op Investigations

Individual basisFBC, U+Es, LFTs, GlucoseABG in suspected OSA/OHSECGEcho – LV/RV function, Pulm HtnCXR – cardiac failurePFTs – poor exercise tolerance

PreMed

Antacids / PPIProkineticsSodium Citrate

TEDs

Conduct of Anaesthesia

Pharmacokinetics

Most drugs affected by adipose tissue –lipophilic drugsHow do you calculate doses?!

Volume of central compartment similar (periph increased)Increased Volume of Distribution (Vd)

Increased redistributionIncreased elimination t1/2

Total weight/ideal weightBenzos/Barbiturates – ideal body weightRelaxants – Lean body mass (mass of organs, muscle, bone)Suxamethonium – total body weightPropofol – total body weight (esp TIVA)Local anaesthetics – ideal body weight

Epidurals –Engorged veins and fat impinge on spaceReduced volume of Epidural SpaceReduce dose by 25%

Practical Aspects

Theatre TableEnough staff to transferCorrect sized bp cuffConsider Position

Could they be head-up?Sniffing position

Pre-oxygenationThe Difficult Airway Ventilatory Issues

Positioning PEEPShort-handle/Polio bladeDesaturationDo they need awake fibreoptic?

Temperature Control Volatile choiceCalf CompressionBeware Laparoscopy Epidural?

Postoperative Considerations

ExtubationRisk of obstructionTo CPAP?Location

Post-Op CareGood analgesiaEarly mobilization, TEDS, EnoxaparinClose monitoring of BMs (Catabolism)Cardiovascular stability

Any Questions?