With the aim to evaluate the response to treatment with iNO in neonates with hypoxic respiratory failure, we started a terapeutic, open and descriptive trial. Since September 1° 1996 to July 30, 1997, ten neonates with severe hypoxemia refractory to conventional treatment defined by an oxygenation index (OI) >20 or acute clinical deterioration with PaO2<50Hmmg, were enrolled in the study. INO was administered at starting doses of 20 ppm and increased up to 80 ppm. The response to treatment was defined as an increase in PaO2 of 20 mmHg or greater from baseline.

We evaluated: 1) PaO2 and OI pretreatment and 30'6, 12, 24 and 48 hs during iNO administration. 2) Mean duration of treatment. 3) Maximum effective dose in responders. 4) Sistemic arterial pressure. 5) Metahemoglobin levels. 6) Environmental levels of NO and NO2. Results: Mean age X: 39hs, BW X: 3,350gr, Sex Male: 7. Female: 3. Associated diagnosis included: Persistent pulmonary hypertension of the neonate (PPHN): 5, Meconium Aspiration Syndrome (MAS): 1, Congenital Diaphragmatic Hernia (CDH) : 3, Pneumonia: 1. Eight of the patients responded to treatment with iNO, PPHN: 5, MAS : 1, CDH: 2. Table

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Mean duration of treatment in responders: 114+/- 73 hrs. Maximum effective dose in responders: 31.25+/-12ppm Mean Systemic Arterial Pressure; Basal X: 55+/- 6mmHg, 6hrs post-: 52+/-4mmHg. Only one infant reached metahemoglobin levels above 3%.

Conclusions: 1) Treatment with iNO improved oxygenation in all patients with PPHN. 2) When PH was associated with other pathologies the response to treatment was varied. 3) All neonates showed stable arterial systemic pressure values during iNO treatment. 4) In the majority of patients who responded the maximum effective dose was 20ppm. 5) At the evaluated doses only one patient reached metahemoglobin levels above 3%. 6) There was no environmental toxic levels of NO and NO2.