Response to nitric oxide inhalation in early acute lung injury

Objective: To evaluate the dose response of inhaled nitric oxide (NO) on gas exchange and central haemodynamics in patients with early acute lung injury (ALI). Design: Prospective, multicentre clinical study. Setting: General ICUs in university and regional hospitals. Patients: 18 patients with early ALI according to specified criteria. Interventions: During controlled ventilation an inhalation system was used to deliver NO (1000 ppm in N-2) and O-2/air to the low pressure fresh gas inlet of a Siemens 900C ventilator. Haemodynamics and pulmonary gas exchange variables were measured at baseline and at stepwise increased inspiratory NO concentrations of 0.1, 0.3, 1, 3, 10, 30 and 100 ppm, each dose being maintained for 15 min. Dose testing was repeated the next day, and the response to prolonged (2 h) NO inhalation at 1 and 10 ppm was also tested. Measurements and results: Inhalation of NO produced a significant increase in PaO2 (P<0.0025). The degree of response, as well as the optimal NO dose varied in individual patients and between different days. Venous admixture (Q(VA)/Q(T)) was reduced (P<0.02) from 38% (31-46%) to 33% (26-41%). In our patients with early acute lung injury and only a moderate elevation in pulmonary arterial pressure NO inhalation did not reduce mean pulmonary artery pressure significantly, being 27.0 (21-30) mmHg at baseline and 26.0 (21-30) mm Hg at 100 ppm. Conclusions: This study shows that improvements in arterial oxygenation in response to inhaled NO may show great inter- as well as intraindividual variability, and that improvements in arterial oxygenation occur without any measurable lowering of the pulmonary artery pressure.