Acute effects of inhaled nitric oxide in adult respiratory distress syndrome

This study evaluated the dose-response effect of inhaled nitric oxide (NO) on gas exchange, haemodynamics, and respiratory mechanics in patients with adult: respiratory distress syndrome (ARDS). Of 19 consecutive ARDS patients on mechanical ventilation, eight (42%) resp onded to a test of 10 parts per million (ppm) NO inhalation with a 25% incr ease in arterial oxygen tension (Pa,O-2) over the baseline value. The eight NO-responders were extensively studied during administration of seven inha led NO doses: 0.5, 1, 5, 10, 20, 50 and 100 ppm. Pulmonary pressure and pulmonary vascular resistance exhibited a dose-depen dent decrease at NO doses of 0.5-5 ppm, with a plateau at higher doses. At all doses, inhaled NO improved O-2 exchange via a reduction in venous admix ture, On average, the increase in Pa,O-2 was maximal at 5 ppm NO. Some pati ents, however, exhibited maximal improvement in Pa,OL at 100 ppm NO,ln all patients, the increase in arterial O-2 content was maximal at 5 ppm NO, The lack of further increase in arterial O-2 content above 5 ppm partly depend ed on an NO-induced increase in methaemoglobin. Respiratory mechanics were not affected by NO inhalation. In conclusion, NO doses less than or equal to 5 ppm are effective for optim al treatment both of hypoxaemia and of pulmonary hypertension in adult resp iratory distress syndrome. Although NO doses as high as 100 ppm may further increase arterial oxygen tension, this effect may not lead to an improveme nt in arterial O-2 content, due to the NO-induced increase in methaemoglobi n. It is important to consider the effect of NO not only on arterial oxygen tension, but also on arterial O-2 content for correct management of inhale d nitric oxide therapy.