Inhaled NO (INO) dilates the pulmonary circulation and is used to treat term neonates with pulmonary hypertension. Recently, INO has also been used in the treatment of preterm neonates with severe RDS. (Pediatrics 1993;92:606) Although INO is presumed to effect the pulmonary circulation only, its effects on systemic circulation in the preterm neonate are not known. We investigated the effects of INO in a preterm lamb model of RDS. 11 lambs were delivered at 0.83 of gestation, treated with surfactant (Survanta) and mechanically ventilated. After 1.5 h, 6 lambs were treated with continuous inhalation of 20 ppm of NO (NO group); the other 5 lambs served as controls (C group). Systemic(SAP) and pulmonary arterial (PAP) pressures were monitored continuously; cardiac output (CO) and regional blood flow, includimg cerebral blood flow(CBF) (radiolabelled microspheres technique) were measured at baseline and 1h and 2h after initiation of inhalation in the NO group, and at comparable times after birth in the C group. Table

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There was a significant decline in CBF at 1h in the NO group compared to either the baseline or the C group at 1h (p<0.05). This decline was not associated with a decline in CO, variations in pCO2, a decline in flow to other organs or in flow through the ductus arteriosus. We conclude that INO may have a direct effect on the cerebral circulation in the preterm neonate.(Sponsored by the Univ de Chile, Univ of North Carolina and AGA Chile S.A.)