Respiratory acidosis: I. Effects of decreasing respiratory minute volume in patients with severe chronic pulmonary emphysema, with specific reference to oxygen, morphine and barbiturates

In patients with prolonged elevation of P aCO 2 the respiratory center loses its normal degree of sensitivity to carbon dioxide. Hypoxia then becomes the dominant stimulus to respiration. This stimulus to respiration is removed by breathing 99.6 per cent oxygen. The respiratory minute volume and effective alveolar ventilation are then decreased significantly. Subsequently the P aCO 2 becomes elevated and the pH of the blood is depressed to a lower level. Uncompensated respiratory acidosis supervenes. In the more diseased states coma ensues. Morphine and barbiturates in small doses may depress the minute volume and effective alveolar ventilation in patients with pulmonary emphysema. Respiratory acidosis with coma readily develops in these patients because they retain large quantities of carbon dioxide in the pulmonary alveoli and arterial blood.