EFFECT OF INHALED NITRIC-OXIDE ON VENOUS ADMIXTURE DEPENDS ON CARDIAC-OUTPUT IN PATIENTS WITH ACUTE LUNG INJURY AND ACUTE RESPIRATORY-DISTRESS SYNDROME

Background: It has been shown that inhaled nitric oxide (NO) reduces i ntrapulmonary venous admixture (Q(VA)/Q(T)) and improves oxygenation i n patients suffering from acute respiratory distress syndrome (ARDS). The change in Q(VA)/Q(T) during NO inhalation varies individually. Fac tors known to influence the respiratory response to NO are the NO conc eritration and the level of shunt before NO administration. Other fact ors that may modify the effect on gas-exchange during NO breathing are unknown. Methods: We studied the effect of 40 ppm inhaled NO on pulmo nary gas-exchange and haemodynamics in 37 patients with acute lung inj ury (ALI) and ARDS, respectively, and factors that may influence the r espiratory response to NO. Results: Inhalation of 40 ppm NO produced a decrease in mean pulmonary artery pressure (MPAP) from 33.1+/-7.2 to 30.2+/-6.8 (mean+/-SD) mmHg (P<0.0001) while pulmonary artery wedge pr essure (PAWP), cardiac output and mean arterial pressure remained cons tant. Change in Q(VA)/Q(T) during NO inhalation depended on the preinh alation cardiac output and had no association with mixed venous oxygen tension, MPAP-PAWP, and Q(VA)/Q(T) before NO delivery. Q(VA)/Q(T) dec reased in 26 patients (group 1) and increased in 11 patients (group 2) during NO inhalation. In group 1, cardiac output was lower than in gr oup 2 (8.6 vs. 12.2 l . min(-1); P<0.0005). Conclusion: We conclude th at the change in venous admixture during inhalation of SO ppm NO depen ds on cardiac output. If preinhalation cardiac output is high, 40 ppm NO can adversely affect gas exchange in patients with ALI and ARDS.