Effects of inhaled nitric oxide on gas exchange and acute lung injury in premature lambs with moderate hyaline membrane disease.

OBJECTIVE: The purpose of this study was to examine whether inhaled nitric oxide (iNO) may change lung injury in moderate hyaline membrane disease (HMD). METHODS: Fifteen moderately premature lambs (128 days gestation, term=147 days) were randomly assigned to treatment with 20 ppm inhaled NO (n=7) from the onset of ventilation or control (n=8). Except for inhaled NO, treatments were intentionally similar to those applied in clinical situations. After porcine surfactant administration (Curosurf, 100 mg/kg), mechanical ventilator settings were modified during the course of the study to maintain PaCO(2) between 40 and 50 mmHg and post-ductal SpO(2) between 90 and 95%. The main studied parameters were gas exchanges parameters, respiratory mechanics (static compliance and functional residual capacity) and pulmonary vascular permeability and/or filtration rate indices. RESULTS: We found that 20 ppm of inhaled NO for 5 h significantly reduce ventilatory and oxygen requirements, but only during the first hour of mechanical ventilation. No increase in extravascular lung water content (5.41+/-0.96 vs. 5.46+/-1.09 ml/g bloodless dry lung in the control group and in the NO group, respectively) and no impairment of the respiratory mechanics could be found in the NO-treated group. However, inhaled NO increased the albumin lung leak index in this model (6.09+/-1.51 in the NO-treated group vs. 4.08+/-1.93 in the control group; P<0.05). CONCLUSIONS: Our results do not therefore support a detrimental effect of short-term exposure to low doses of NO inhalation in moderate HMD. However, it may induce an increase in lung vascular protein leakage. The pathophysiological consequences of this finding remain to be elucidated.