Skip main navigation

New offer! Get 30% off one whole year of Unlimited learning. Subscribe for just £249.99 £174.99. New subscribers only. T&Cs apply

Find out more

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
This article is from the free online

Introduction to Using Total Intravenous Anaesthesia (TIVA)

Created by
FutureLearn - Learning For Life

Reach your personal and professional goals

Unlock access to hundreds of expert online courses and degrees from top universities and educators to gain accredited qualifications and professional CV-building certificates.

Join over 18 million learners to launch, switch or build upon your career, all at your own pace, across a wide range of topic areas.

Start Learning now