Transient response to inhaled nitric oxide in meconium aspiration in newborn lambs

To compare the effects of the sustained exposure to inhaled nitric oxide (NO) on pulmonary gas exchange, cardiovascular function and lung mechanics in newborn lambs with pulmonary hypertension induced by tracheal instillation of meconium. Fifteen newborn lambs (<6 d old) were studied in three groups (n = 5): control, and pulmonary hypertension (5 mL.kg(-1) of a 20% meconium solution) with or without inhaled NO (20 ppm) exposure. Heart rate, systemic and pulmonary arterial pressures, arterial pH and blood gases, cardiac output, and pulmonary mechanics were measured. The exposure to inhaled NO in lambs with pulmonary hypertension, induced by experimental meconium aspiration, produced a transient response. There were a transient improvement in gas exchange, a decrease in pulmonary arterial pressure and airway resistance, without changes in cardiovascular profile. The transient and incomplete response to inhaled NO in experimental MAS might be related to the fact that hypoxemia is not only due to pulmonary vasoconstriction but also to parenchymal lung disease. We hypothesize that this poor and transient response could probably be avoided if strategies that increase lung recruitment, were applied before inhaled NO exposure.