Influence of catecholamines on arterial oxygen tension in the anesthetized dog

¹ Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire

Catheter oxygen pressure (PO₂) electrodes for continuous recording of blood oxygen tension in vivo were inserted into the aorta of dogs anesthetized with pentobarbital and ventilated with constant volume and frequency. Femoral arteries were cannulated for pressure recording and arterial sampling for arterial oxygen tension (Pa_OO2) calibration by polarography. Epinephrine in doses between 0.002 and 133 µg/kg and norepinephrine between 1.25 and 133 µg/kg were injected intravenously. With both agents two types of Pa_OO2 response, without change in alveolar oxygen tension (Pa_OO2) were observed: Type I occurred with high doses and consisted of three phases, a rise of 10–20 mm Hg, then a decrease of up to 100 mm Hg, and eventually an increase of 15–30 mm Hg. Type II was found with doses below 5 µg/kg and showed only a Pa_OO2 increase of 10–70 mm Hg. Doses below 0.05 µg/kg were without effect. The reactions were most pronounced with breathing of 100% oxygen. This suggests an influence of the agents on true venous admixture. The effects might be due to a differential action on pulmonary and systemic (bronchial) circulation, perhaps combined with differences of action on the two sides of the heart and blood shifts.

Note:
With the Assistance of J. S. Picken