Obesity and general anaesthesia

General anaesthesia in the obese patient is a difficult task because of a number of major complicating factors:

• cardiovascular:
  • majority have moderate to severe hypertension
  • predisposed to atherosclerosis and the complications of ischaemic heart disease
  • right or left ventricular failure
  • increased risk of venous thrombosis
  • difficult intravenous access
• respiratory:
  • poor airway access and management due to reduced neck and mouth mobility, relatively increased size of oropharyngeal tissue - difficult intubation
  • decreased chest wall compliance, inspiratory and expiratory volume, ventilatory effort
  • greater tendency to shunt blood to underperfused parts of lung; increased incidence of sleep apnoea
  • possibly, reliance on hypoxic drive for respiration - "Pickwickian syndrome"
• endocrine:
  • impaired glucose tolerance - a tendency to hyperglycaemia
• biochemistry:
  • deranged lipid levels and hypercholesterolaemia
  • labile LFT's because of lipid infiltration of liver
• abnormal pharmokinetics:
  • greater size of lipid compartment and reduced size of water compartment alters the volume of distribution of a drug depending on whether it is hydrophobic or hydrophilic
  • altered drug binding and clearance
  • excessive degradation of halothane resulting in hepatitis
• miscellaneous:
  • increased risk of wound infection
  • greater frequency of hiatus hernia, higher gastric pH and increased risk of aspiration
  • generally longer operations are needed