anaesthesia and morbid obesity - wye valley nhs trust · anaesthesia and morbid obesity. facts....
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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?