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Changes associated with obesity

Join us this week to discuss how obesity affects our body in terms of physiology, pharmacokinetics and pharmacodynamics


  • Physiology
    • ↑ Blood volume,
    • ↑ Systolic volume
    • ↑ Cardiac output
  • Presents as
    • Ischaemic heart disease
      • obesity is an independent risk factor for ischaemic heart disease
    • Hypertension
      • ↑ Extracellular volume and cardiac output are characteristic of obesity‐induced hypertension.
    • Cardiac failure
      • Left ventricular hypertrophy and ↓compliance, combined with ↑ blood volume
Weighted adjusted metabolic, blood volume and cardiac output are decreased when per kg values are used
  • Blood volume 50ml/kg vs 75ml/kg non obese
  • Pharmacokinetics (PK)
    • Drugs with narrow therapeutic indices may cause adverse effects if administered according to their actual body weight
    • ↑ Initial drug distribution
    • ↑ Loading dose required
    • ↑ Maintenance requirements
    • ↑Renal and hepatic blood flow
    • Using linear per kg dosing schemes designed for non-obese patients overestimates volumes and clearances
      • ↑ Overdose adverse effects
    • Obesity-related cardiovascular compromise
      • ↓ Distribution
      • ↓ Clearance for drugs that have high intrinsic clearance and are perfusion limited (e.g. propofol)


  • Difficult Airway
    • Incidence of difficult airway approximately 13%
    • Increased neck circumference
    • Fatty infiltration of the pharynx and peri glottic area
      • Increased risk of airway obstruction
    • Consideration to AFOI
  • Obstructive sleep apnoea (OSA)
    • 5%
    • Screening Test: STOP BANG criteria
      • Snoring: Snore loudly
      • Tiredness: Day time somulence
      • Observed: Stop Breathing or Choking/Gasping during your sleep
      • Pressure: High Blood Pressure
      • BMI: Body Mass Index more than 35 kg/m2
      • Age: >50years
      • Neck Circumference: Shirt collar 16 inches / 40cm or larger
      • Gender: Male
    • Polysomnography in a sleep laboratory
  • Obesity hypoventilation syndrome
    • The acid–base disturbance of OSA
    • Progressive desensitization of the respiratory centres
    • Ventilation reliance on hypoxic drive for ventilation
  • Pickwickian syndrome: Hypoventilation syndrome in an obese persons – Diminished to absent ventilatory chemoresponsiveness, – Chronic hypoxia, – Hypercapnia – Polycythemia – Hypersomnolence
  • Lung volume – Fatty deposits in the chest wall and increased intra-abdominal fat – Decrease thoracic compliance – Decrease lung volume – Functional residual capacity (FRC) – Rapid desaturation post-induction despite pre‐oxygenation. – Expiratory reserve volume (ERV)
  • Gas exchange
    • PEEP improves the PaO2 but only at the expense of cardiac output and oxygen delivery
    • Increased V/Q mismatch
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