obesity and general anaesthesia

Last reviewed 10/2021

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