Low-dose sodium nitroprusside reduces pulmonary reperfusion injury

Background. Reperfusion injury is a significant cause of early allograft dysfunction after lung transplantation. We hypothesized that direct pulmonary arterial infusion of an intravascular nitric oxide donor, sodium nitroprusside (SNP), would ameliorate pulmonary reperfusion injury more effectively than inhaled nitric oxide without causing profound systemic hypotension. Methods. Using an isolated, ventilated, whole-blood-perfused rabbit lung model, we studied the effects of both inhaled and intravascular nitric oxide during lung reperfusion. Group I (control lungs (New Zealand White rabbits, 3 to 3.5 kg) were harvested en bloc, flushed with Euro- Collins solution, and then stored inflated for 18 hours at 4°C. Lungs were then reperfused with whole blood and ventilated with 60% oxygen for 30 minutes. Groups II, III, and IV received pulmonary arterial infusions of SNP at 0.2, 1.0, and 5.0 μg · kg^-1 · min^-1, respectively, whereas group V was ventilated with 60% oxygen and nitric oxide at 80 ppm during reperfusion. Results. Pulmonary arterial infusions of SNP even at 0.2 μg · kg^-1 · min^-1 (group II) showed significant improvements in pulmonary artery pressure (31.35 ± 0.8 versus 40.37 ± 3.3 mm Hg; p < 0.05) and pulmonary vascular resistance (38,946 ± 1,269 versus 52,727 ± 3,421 dynes · s/cm^{- 5}; p < 0.05) when compared with control (group I) lungs after 30 minutes of reperfusion. Infusions of SNP at 1.0 μg · kg^-1 · min^-1 (group III) showed additional significant improvements in dynamic airway compliance (1.98 ± 0.10 versus 1.46 ± 0.02 mL/mm Hg; p < 0.05), venous-arterial oxygenation gradient (116.00 ± 24.4 versus 34.43 ± 2.5 mm Hg; p < 0.05), and wet-to- dry ratio (6.9 ± 0.9 versus 9.1 ± 2.2; p < 0.05) when compared with control (group I) lungs. Lungs that received inhaled nitric oxide at 80 ppm (group V) were significantly more compliant (1.82 ± 0.13 versus 1.46 ± 0.02 mL/mm Hg; p < 0.05) than control (group I) lungs. Conclusions. Pulmonary arterial infusion of low-dose SNP during lung reperfusion significantly improves pulmonary hemodynamics, oxygenation, compliance, and edema formation. These effects were achieved at doses of SNP that did not cause profound systemic hypotension. Direct intravascular infusion of SNP via pulmonary arterial catheters could potentially abate reperfusion injury immediately after allograft implantation.