169 LOW-DOSE INHALED NITRIC OXIDE (NO) IN INFANTS WITH BRONCHOPULMONARY DYSPLASIA (BPD)

Abstract

BPD is characterised by severe maldistribution of ventilation, hypoxia, hypercapnia and pulmonary hypertension. Similar observations are made in adults with chronic obstructive lung disease (COLD), in whom impairment of endothelium-dependent pulmonary vascular relaxation has been demonstrated. Inhaled NO has recently been demonstrated to improve gas exchange in COLD. The effect of inhaled NO on gas exchange was therefore investigated in 6 infants (26-32 weeks gestation) with BPD receiving mechanical ventilation and with a fraction of inspired oxygen of >0.7. NO at doses of 5-40 parts per million (ppm) was administered into the inspiratory gas for 15 minute periods with 10 minute washout periods. NO administration was continued at the lowest most effective dose when marked improvements in oxygenation were observed. Oxygen saturation (Sa O2), transcutaneous oxygen/carbon dioxide tensions (tc pO2/tc pCO2) and systemic blood pressure (BP) were continuously monitored. Methaemoglobin (MetHB) and nitrogen dioxide (NO2) levels were also measured. Inhalation of NO at all doses produced consistent improvements in the Sa O2 and tc pO2 (confirmed by concurrent arterial blood gases). The tc pCO2 showed a tendency to fall. While 5ppm NO produced a smaller response in oxygenation parameters, 10-40 ppm NO produced similar responses. The percentage changes from baseline values (median and range) in tc pO2, tc pCO2 and Sa O2 at a dose of 10 ppm were +58.2% (25 - 261.5), -15.8% (+2.6 to -21) and +19.8% (5.5 - 52.5) respectively. NO was administered continuously for 9-52 days with no evidence of tachyphylaxis. BP was marginally improved or unchanged. MetHB levels were <2% and NO2 <1ppm. We conclude that inhaled NO improves gas exchange in BPD and speculate that NO synthesis and/or release may be impaired in BPD. (Supported by tne Royal Society).