CIRCULATORY AND VENTILATORY EFFECTS OF INTERMITTENT NITRIC-OXIDE INHALATION DURING PORCINE ENDOTOXEMIA

The effects of intermittent inhalation of 57 ppm nitric oxide (NO) wer e studied in eight anesthetized, ventilated pigs given a continuous in fusion of Escherichia coli endotoxin. Seven animals served as controls . By administering NO synchronized with inspiration and close to the o rotracheal tube, measurable amounts of the toxic metabolite, NO2, in t he inspiratory gas mixture were avoided. No direct systemic effects of NO inhalation were seen, but through counteracting pulmonary vasocons triction, a fall in cardiac output was delayed. Nitric oxide effective ly attenuated the initial peak rise in mean pulmonary artery pressure and resistance, both returning to control levels after cessation of NO . These effects were reproduced during later phases of endotoxemia, gi ving further proof to the role of gaseous NO as a selective pulmonary vasodilator. Nitric oxide diminished pulmonary shunting, but unimpaire d oxygenation Was preserved only during the first inhalation period. L eukocyte counts decreased drastically and platelet aggregation was enh anced, but after 1.5 hours of endotoxin infusion, platelet hyperaggreg ation was maintained in the NO group while it decreased in the control group.