[Physiopathology of acute decompensation in chronic obstructive respiratory insufficiency]

The acute decompensation of chronic obstructive respiratory failure is characterised by a deterioration of the respiratory mechanics which leads to a reduction of maximum ventilatory output, the respiratory muscles are placed at a mechanical disadvantage and in attempting to compensate are vulnerable to muscle fatigue. A large part of ventilation is wasted in ventilatory dead space. Total ventilation is normal but tidal volume is shallow and respiratory rate rapid. This type of breathing is partially responsible for the large dead space effect. Respiratory centre activity is greatly increased. The prescription of bronchodilators is debatable because there is a risk of increasing the dead space effect. The hypoxic and hypercapnic stimuli have a weak and roughly similar effect on ventilatory control, but the effect of pure oxygen on PaCO2 is due to factors other than those relating to respiratory centre activity.