EFFICACY OF INHALED NITRIC-OXIDE IN A PORCINE MODEL OF ADULT-RESPIRATORY-DISTRESS-SYNDROME

Objective: To assess the efficacy of inhaled nitric oxide (NO) in redu cing pulmonary hypertension in a porcine model of adult respiratory di stress syndrome.Design: Nonrandomized, controlled experiment without b linding. Setting: Surgical research laboratory. Participants: Twelve p igs, matched equally for bodyweight. Intervention: Acute lung injury w as induced by intravenous injection of oleic acid. Animals were then d ivided into either a control group, for monitoring without any further intervention, or a NO-treatment group, in which NO was administered a t concentrations of 10 to 80 ppm, with each step separated by a NO-fre e interval to assess duration of effect. Main Outcome Measures: Pulmon ary artery pressure, systemic blood pressure, paO(2) intrapulmonary sh unt fraction, and extravascular lung water. Nitrosylated hemoglobin, a rterial methemoglobin, and plasma nitrite and nitrate concentrations. Results: All animals responded to oleic acid injection with rapid deve lopment of pulmonary hypertension and deterioration of paO(2) and intr apulmonary shunt fraction. Inhaled NO reversed these changes in a conc entration dependent manner. Cessation of NO administration led to a pr ompt return of pulmonary hypertension. A small but significant drop in systemic blood pressure was observed only at the highest concentratio n of NO administered (80 ppm). Extravascular lung water almost doubled following oleic acid injury. This increase was sustained in all anima ls for the remainder of the experiment. Significant increases in circu lating methemoglobin and plasma nitrite and nitrate concentrations wer e measured during NO inhalation. Conclusion: Inhaled NO appears to be a selective pulmonary vasodilator and may prove to be useful in improv ing gas exchange in adult respiratory distress syndrome.