Purpose: The fate of inhaled nitric oxide (NO) has not been precisely defined in critically ill patients. This study aimed at defining the effects of long-term NO inhalation on circulating NO byproduct levels. Material and Methods: During NO therapy, plasma and urine from 13 critically ill patients were sampled daily for determination of the stable byproducts of NO (nitrite [NO 2 − ] and nitrate [NO 3 − ]. Routine monitoring data included inhaled NO concentration, hemodynamic parameters, arterial blood gases, creatinine clearance, and C-reactive protein. Results: For the first 24 hours of NO inhalation (6.3 ± 1.1 ppm), NO 3 − plasma concentration increased (from 13.3 ± 5.4 to 52.3 ± 17.6 μmol/L), but NO 2 − plasma concentration was not affected. The NO 3 − plasma concentration was correlated with the C-reactive protein level, the inhaled NO concentration. Renal excretion of NO metabolites was unaltered by NO inhalation. The N0 3 concentrations returned to baseline when NO therapy was discontinued. Conclusion: Long-term NO inhalation was associated with a consistent increase in the NO 3 − plasma concentration. NO byproducts may be implicated in the systemic effects associated with this treatment.
