Alteration in respiratory physiology in obesity for anesthesia-critical care physician.

Obesity is known to be a major risk factor of a whole range of cardiovascular, metabolic and respiratory disorders. The pattern of regional fat distribution plays an important role in the pre-disposition of obese subjects to respiratory complications. Obesity is responsible for important changes in respiratory function both during spontaneous breathing as well as during general anesthesia and mechanical ventilation. The most characteristic abnormalities consist of decreased functional residual capacity, reduced expiratory reserve volume, decreased compliance and increased resistance of the respiratory system. Breathing at low lung volume promotes airway closure in the dependent lung zones with consequent gas exchange abnormalities even though lung carbon monoxide-diffusing capacity is normal or increased. Weight loss can reduce many of the alterations in pulmonary function related to obesity.