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.
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