The Pulmonary Toxicity of Oxygen

Abstract

The direct pulmonary toxicity of O2 contributes significantly to the mortality of the critically ill, the patients in whom its use is most necessary. There are basic questions about O2 toxicity, in particular the mechanism through which it occurs, that are unanswered, largely because of the very fundamental character of the biologic problem. Nevertheless, some provisional conclusions are possible. One is that no toxic threshold exists. Any increase in the 02% of the inspired gas mixture is a threat, but when O2 administration is limited to a few days, percentages over 70% are dangerously high. Opportunities for unintended use of high concentrations have become more frequent with commoner use of mechanical ventilatory assistance. As demonstrated by Bosomworth, pressure-limited ventilators with O2 driven nebulizers that depend on room air entrainment for 40% oxygen may actually deliver concentrations closer to 100%, but this is avoidable by appropriate monitoring. There is need for the development of systems, that will permit delivery of metered concentrations of O2. Still, hypoxemia has to be treated with O2 in the concentration necessary to maintain acceptable arterial PO2; what this must be is a matter of individual clinical judgment, but surely it seldom would be much above 100 mm Hg.