OXYGEN



The hypoxemia seen in obstructive lung disease has two major deleterious consequences: de­creased 02 delivery to the tissues and hypoxic pulmonary vasoconstriction with resultant cor pulmonale. Oxygen therapy is thus an intergral part of the treatment of patients with obstructive lung disease and should be used whenever the arterial saturation falls below 90 per cent. In some patients 02 may be required only with acute ex­acerbations, but in those with chronic disease it may be needed during sleep, with exercise, or continuously, depending on when desaturation occurs. Because of the mechanism of the hypox­emia, namely ventilation-perfusion inequality, the desaturation can be corrected by small in­creases in the inspired fractional 02 concentra­tions, achieved with less than 4 L/min of nasal flow. It has been clearly demonstrated in patients with chronic obstructive lung disease with a rest­ing Pao2 below 55 torr that long-term 02 therapy markedly improves survival, and maximal benefit is achieved when it is delivered throughout the 24 hours of the day.