THE EFFECTS OF NITRIC-OXIDE INHALATION ON RESPIRATORY MECHANICS AND GAS-EXCHANGE DURING ENDOTOXEMIA IN THE PIG

Background: Ln the adult respiratory distress syndrome, nitric oxide ( NO) inhalation improves oxygenation through reducing ventilation-perfu sion mismatching, but detailed information on the pulmonary effects of NO inhalation in septic shock is scarce. The present study investigat ed the effects of inhaled NO on alveolar dead space (Vdalv) and venous admixture as well as on respiratory system compliance (Crs) and respi ratory system resistance (Rrs) in a porcine model of septic shock. Pro tective effects of NO are discussed. Methods: Thirteen anaesthetised a nd ventilated pigs were given an infusion of endotoxin for an observat ion time of 220 min to induce acute lung injury (ALI). In the NO-early group (n=6), an inhalation of 60 ppm NO was started simultaneously wi th the endotoxin infusion and continued for 190 min. In 7 control/NO-l ate animals, 60 ppm NO was administered for 30 min following 190 min o f endotoxin infusion. Haemodynamics, single-breath CO2-, pressure-, an d now signals were recorded. Results: Endotoxin induced haemoconcentra tion, pulmonary vasoconstriction, and a decrease in Crs, while venous admixture, Vdalv, and Rrs increased. Ln the NO-early group, the pulmon ary vasoconstriction was attenuated, no increase in pulmonary venous a dmixture or in Vdalv was seen before cessation of NO, and the improvem ents in oxygenation outlasted the NO inhalation. In the control/NO-lat e group, the NO inhalation reversed the changes in dead space and veno us admixture. NO had no effect on the changes in respiratory mechanics . Conclusion: In porcine ALI, 60 ppm NO diminishes pulmonary vasoconst riction and improves gas exchange by reducing pulmonary venous admixtu re and alveolar dead space, but does not prevent a fall in Crs. NO inh alation may help prevent longlasting pulmonary failure.