Higher Urine Nitric Oxide Is Associated with Improved Outcomes in Patients with Acute Lung Injury

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Abstract
Rationale: Nitrogen oxide (NO) species are markers for oxidative stress that may be pathogenic in acute lung injury (ALI). Objectives: We tested two hypotheses in patients with ALI: (1) higher levels of urine NO would be associated with worse clinical outcomes, and (2) ventilation with lower Vt would reduce urine NO as a result of less stretch injury. Methods: Urine NO levels were measured by chemiluminescence in 566 patients enrolled in the National Heart Lung and Blood Institute Acute Respiratory Distress Syndrome Network trial of 6 ml/kg versus 12 ml/kg Vt ventilation. The data were expressed corrected and uncorrected for urine creatinine (Cr). Results: Higher baseline levels of urine NO to Cr were associated with lower mortality (odds ratio, 0.43 per log(10) increase in the ratio), more ventilator-free days (mean increase, 1.9 d), and more organ-failure–free days (mean increase, 2.3 d) on multivariate analysis (p < 0.05 for all analyses). Similar results were obtained using urine NO alone. NO to Cr levels were higher on Day 3 in the 6 ml/kg than in the 12 ml/kg Vt group (p = 0.04). Conclusions: Contrary to our hypothesis, higher urine NO was associated with improved outcomes in ALI at baseline and after treatment with the 6 ml/kg Vt strategy. Higher endogenous NO may reflect less severe lung injury and better preservation of the pulmonary and systemic endothelium or may serve a protective function in patients with ALI.

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