EFFECTS OF INHALED NITRIC OXIDE (NO) IN PREMATURE LAMBS WITH MODERATE HYALINE MEMBRANE DISEASE (HMD). † 1467

Gas exchange improvment by low dose NO inhalation without increase of vascular permeability was reported by Kinsella et al. in experimental severe HMD (Pediatr Res 1995; 38: 337A). Our hypothesis was that inhaled NO could be deleterious in less severe respiratory failure by increasing pulmonary blood flow and/or altering vascular permeability. The effects of inhaled NO on gas exchange and lung vascular permeability in moderate HMD were studied. Eighteen moderatly premature lambs (130 days gestation, term=147 days) were randomly assigned to treatment with 20 ppm inhaled NO from the onset of ventilation(HO) or control. After porcine surfactant administration (Curosurf® 100 mg/kg), ventilator was set to maintain PaCO2 values between 40 and 50 mmHg and SpO2 values between 90 and 95%. After 4 hours,125 I-labeled albumine and 51Cr-tagged red blood cells were injected. One hour later, gamma-counting was performed on lung tissue and blood. Wet and dry weights of blood and lung were measured. Pulmonary edema was assessed by measurement of extravascular lung water content (Qwl) normalized for bloodless dry lung weight. Vascular permeability was evaluated by the Lung Leak Index (LLl) measurement (Am Rev Respir Dis. 1993; 148: 1194-203). Oxygenation (OI = Mean Airway Pressure*FiO2/PaO2) and ventilatory index (VI = Mean Airway Pressure*Respiratory Rate) were calculated at 1 and 5 hours. OI was significantly lower after 1 hour of ventilation in the NO vs. control group. However, OI and ventilatory requirement were not significantly different after 5 hours of ventilation. In spite of similar extravascular lung water content in both groups, vascular protein leak was increased in NO group. In conclusion, no benefit of short term NO inhalation (5 hours) could be demontrated for gas exchange in premature lambs with moderate HMD. Moreoever increased lung vascular protein leak in the NO group suggests an alteration of vascular permeability. Benefits of long term NO inhalation should be demonstrated before its clinical use in moderate HMD.Table