Mixed exhaled nitric oxide and plasma nitrites and nitrates ire newborn infants

Plasma nitrite (NO2-) and nitrate (NO3-) are the stable end-products of end ogenous nitric oxide (NO) metabolism. NO is present in the exhaled air of h umans, but it is not clear if exhaled NO may be an indicator of the systemi c endogenous NO production. The aims of the study were to determine the lev els of exhaled NO and plasma NO2-/NO3- in healthy term and preterm newborns , and to assess if exhaled NO correlates with plasma NO2-/NO3- at birth. Af ter the stabilization of the newborn, we measured by chemiluminescence the concentration of NO in the mixed expired breath of 133 healthy newborns. Me asurement of exhaled NO was repeated after 24 and 48 hours. Plasma NO2-/NO3 - levels at birth were measured by the Griess reaction. NO concentrations w ere 8.9 (Cl 8.1-9.8) parts per billion (ppb), 7.7 (Cl 7.2-8.3) ppb and 9.0 (Cl 8.4-9.6) ppb at birth, 24 and 48 hours, respectively. At birth, exhaled NO was inversely correlated with gestational age (p=0.008) and birth weigh t (p <0.001). Plasma NO2-/NO3- level was 27.30 (Cl 24.26-30.34) mu mol/L. T here was no correlation between exhaled NO and plasma NO2-/NO3- levels at b irth (p=0.88). We speculate that the inverse correlation between exhaled NO and gestational age and birth weight may reflect a role of NO in the postn atal adaptation of pulmonary circulation. At birth, exhaled NO does not cor relate with plasma NO2-/NO3- and does not seem to be an index of the system ic endogenous NO production. (C) 2001 Elsevier Science Inc. All rights rese rved.