Efficacy of Inhaled Nitric Oxide in a Porcine Model of Adult Respiratory Distress Syndrome

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Abstract
Objective: To assess the efficacy of inhaled nitric oxide (NO) in reducing pulmonary hypertension in a porcine model of adult respiratory distress syndrome. Design: Nonrandomized, controlled experiment without blinding. Setting: Surgical research laboratory. Participants: Twelve pigs, matched equally for body weight. Intervention: Acute lung injury was induced by intravenous injection of oleic acid. Animals were then divided into either a control group, for monitoring without any further intervention, or a NO-treatment group, in which NO was administered at concentrations of 10 to 80 ppm, with each step separated by a NO-free interval to assess duration of effect. Main Outcome Measures: Pulmonary artery pressure, systemic blood pressure, PaO2, intrapulmonary shunt fraction, and extravascular lung water. Nitrosylated hemoglobin, arterial methemoglobin, and plasma nitrite and nitrate concentrations. Results: All animals responded to oleic acid injection with rapid development of pulmonary hypertension and deterioration of PaO2 and intrapulmonary shunt fraction. Inhaled NO reversed these changes in a concentration-dependent manner. Cessation of NO administration led to a prompt return of pulmonary hypertension. A small but significant drop in systemic blood pressure was observed only at the highest concentration of NO administered (80 ppm). Extravascular lung water almost doubled following oleic acid injury. This increase was sustained in all animals for the remainder of the experiment. Significant increases in circulating methemoglobin and plasma nitrite and nitrate concentrations were measured during NO inhalation. Conclusion: Inhaled NO appears to be a selective pulmonary vasodilator and may prove to be useful in improving gas exchange in adult respiratory distress syndrome. (Arch Surg. 1994;129:158-164)