Oxygen therapy and oxygen toxicity.

When oxygen therapy is warranted, the minimum effective dose generally should be given. Hypoxemic patients who have normal baseline ABG may be treated initially with an intermediate to high FiO2 in the range of 35% to 100%, depending on the severity of the respiratory distress. The majority of patients with exacerbations of COPD who are not in extremis may be given an initial FiO2 of 28%, especially if their previous response to oxygen is known. When treating patients who have chronic severe hypercapnia (eg, those requiring chronic home oxygen), the initial FiO2 should be 24% even though renal compensation of the respiratory acidosis has occurred. Further mild elevation of the PaCO2, due mainly to the V/Q mismatch that oxygen therapy induces, may be sufficient to precipitate unacceptable hypercapnia. Patients with exacerbations of COPD who are obviously in extremis, with severe hypoxemia and acidosis, should start with an FiO2 of 24% unless they are being mechanically ventilated. The severity of the hypoxemia and acidosis is more predictive for the development of CO2 narcosis and respiratory failure than is the degree of hypercapnia in these patients. The FiO2 can be increased to 28% and incrementally higher if low FiO2 is tolerated. The use of a high FiO2 is subject to the following guidelines for prevention of clinically significant oxygen toxicity: 100% oxygen at atmospheric pressure is safe if given for less than six hours; 70% oxygen is probably safe for 24 hours; and after this time, 45% should be the approximate upper limit to the FiO2.(ABSTRACT TRUNCATED AT 250 WORDS)