Leonard Karel

THE INFLUENCE OF DENITROGENATION ON THE RESPONSE OF ANESTHETIZED DOGS TO INTRAVENOUSLY INJECTED OXYGEN

A marked clinical improvement in critically ill human subjects after the intravenous administration of oxygen has been reported by a number of investigators (1 to 5) despite the fact that only about 1.5 to 10 per cent of the calculated basal oxygen requirement was injected. However, in normal and in anoxemic experimental animals, other workers (6 to 10) have observed not only rapid, shallow breathing but also decreased rather than increased oxygen content of the arterial blood following the intravenous injection of oxygen at rates of 0.21 to 2.3 ml. per kgm. per minute. The paradoxical anoxemia has been attributed to interference with the pulmonic oxygenation of the blood by the formation of multiple oxygen emboli in the pulmonary capillaries (7). The accompanying respiratory changes, which are abolished by bilateral vagotomy, have been considered (10) as similar to the tachypnea observed in dogs after the production of pulmonary capillary emboli by the intravenous injection of starch granules (11). Recently, in seeking a simple and effective means of extra-pulmonic oxygenation for supportive treatment in severe, acute pulmonary edema, we became interested in the possibilities of intravenous oxygen administration, and particularly in the cause and prevention of the hypothesized emboli resulting from this procedure. From theoretical considerations, it became apparent that, since the nitrogen tension of the blood and tissues normally is high (573 mm.), gaseous nitrogen present in the blood must enter intravenously injected oxygen bubbles, as in a tonometer. Consequently, if all the oxygen injected were absorbed by the reduced venous hemoglobin before the blood reached the right heart, residual nitrogen bubbles would remain to obstruct the pulmonary capillaries. In recent years, the analogous role of dissolved nitrogen in the bubble formation of decompression sickness and aero-embolism has been demonstrated and the value of prophylactic denitrogenation by inhalation of 99.6 per cent oxygen has been well established (12 to 18). To explore the interrelationship between nitrogen tension and intravascular bubble formation and the anoxemia following intravenously administered oxygen, in the present experiments, comparisons were made between the effects of oxygenadministered intravenously to anesthetized dogs without prior denitrogenation and after the nitrogen saturation of the blood and tissues was reduced by continuous intratracheal exposure to 99.6 per cent oxygen before and during the intravenous administration of oxygen.