Mechanical Ventilation and Obesity

• Obesity is defined as a BMI of 30 - 34.99 kg/m2, with class II obesity defined as 35 - 39.9 kg/m² and extreme obesity as > 40 kg/m²
• In obese patients:
  • oxygen consumption is increased with a high proportion going to the work of breathing
  • lung volumes are abnormal with reduced expiratory reserve
  • the alveolar - arterial oxygen difference is increased
  • respiratory system compliance is markedly reduced
• These changes are futher exacerbated in the supine position
• To overcome the effects of reduced compliance, higher levels of PEEP are generally needed
• In addition, higher plateau pressures may be necessary to achieve adequate tidal volumes

References

Lapinsky SE, Posadas-Calleja JG, McCullagh I. Clinical review: Ventilatory strategies for obstetric, brain-injured, and obese patients. Crit Care 2009;13:206.